Sandra Lennox
email: sandralennoxj@gmail.com

Lucinda Backwell

Francesco D'errico

Lyn Wadley

A vegetation record based on charcoal analysis from Border Cave, KwaZulu-Natal, South Africa, ~ 227 000 to ~ 44 000 years ago

Keywords: Anthracology, Environment, Late Pleistocene, Quaternary, Vegetation communities, human exploitation of plants 1. Introduction

Border Cave is a key Middle Stone Age (MSA) site in southern Africa, with a 4 m-deep sedimentary sequence that dates from more than 227,000 (227 ka) to 44 ka ago. Lithic assemblages vary considerably during this period and artefacts made from organic materials become common at the end of the MSA sequence. Here we describe charcoal from the 10 members that comprise the stratigraphic sequence. Anatomical features of charcoal were studied by means of reflected light microscopy, the use of the International Association of Wood Anatomists code and modern wood charcoal reference collections. Most woody plants represented by charcoal at the site are evergreen trees. Indicator plants from bushveld and open woodland taxa were most common in Member 6 BS (>227 ka) and Member 5 WA (~227 ka). Moist forest was most common in Members 5 BS (~161-144 ka) and 4 WA (~168-113 ka), while Member 1 RGBS (~74 ka) had a combination of bushveld and moist forest. At about 64 ka, dry bushveld predominated, while in Members 3 BS (72-56 ka) and 2 WA (~60 ka) moist forest was the predominant vegetation type. Member 2 BS.UP (49-44 ka) mostly included bushveld and moist forest patches, while Member 1 WA (~43 ka) was predominantly dry bushveld. The Border Cave occupations seem to have taken place in drier conditions than those at present. The driest members were 5 BS, 4 WA, 1 RGBS and 3 WA, followed by Members 2 BS and 1 WA. Member 3 BS was only slightly drier than present, while Member 2 WA was moderately drier than present. The past vegetation is similar to the modern vegetation profile and there appears to have been remarkable stability through time, suggesting that cultural changes in the sequence may not be linked to environmental change.

The last two decades have witnessed a flourishing of hypotheses, often contradictory, trying to link climate change with the emergence of our species in Africa, its dispersal within and out of this continent, and its biological and cultural evolution. It has been proposed for example that a population bottleneck would have been produced c. 71 ka ago by the climatic deterioration triggered by the Toba eruption [START_REF] Ambrose | Late Pleistocene human population bottlenecks, volcanic winter, and differentiation of modern humans[END_REF], but see Torosin et al., 2020). Ziegler and colleagues (2013) have argued that cultural innovations during the MSA in southern Africa were triggered by periods of humidity that produced higher levels of biomass and consequent increases in human population density. Other authors have proposed that Heinrich events, entailing strong reduction in the North Atlantic sea temperature following the break off from North America and European glaciers, may have rendered large regions of North, East, and West Africa unsuitable for hominin occupation, thus compelling Homo sapiens to migrate out of Africa [START_REF] Carto | Out of Africa and into an ice age: on the role of global climate change in the late Pleistocene migration of early modern humans out of Africa[END_REF]. Low-latitude insolation has been posited as a prominent driver governing the evolution of vegetation and mammal communities in eastern and western Africa by increasing stable ecotonal settings, which would have in turn played a role in early modern human adaptation [START_REF] Kaboth-Bahr | Paleo-ENSO influence on African environments and early modern humans[END_REF]. Humid intervals in the Levant have been proposed as a potential trigger of modern human dispersal out of Africa [START_REF] Langgut | Evidence for a humid interval at ∼ 56-44 ka in the Levant and its potential link to modern humans dispersal out of Africa[END_REF]. Rapid climatic variability has been modelled as a possible cause for the loss of complex cultural innovations [START_REF] Kolodny | Evolution in leaps: the punctuated accumulation and loss of cultural innovations[END_REF]. A varied climate towards the end of the penultimate glacial, followed by an abrupt change to relatively stable moist climate during the last interglacial would have favoured selection for behavioural versatility, population growth, and range expansion, supporting scenarios of early, multiple dispersals of modern humans from Africa [START_REF] Lamb | 150,000-year palaeoclimate record from northern Ethiopia supports early, multiple dispersals of modern humans from Africa[END_REF]. By applying ecological niche agues (2018) have identified a niche shift characterized by a significant expansion in the breadth of the Howiesons Poort ecocultural niche compared with the preceding Still Bay. This expansion is coincident with aridification occurring across Marine Isotope Stage 4 (c. 72-60 ka) and especially pronounced at 60 ka.

Climate change would have acted during the last 300 ka as a factor favouring in some instances, and preventing in others, biological and cultural contact across African regions, thus supporting a multiregional and long term scenario for the emergence of our species in Africa (Scerri et al., 2018;[START_REF] Bergström | Origins of modern human ancestry[END_REF]. In a recent study, more weight is given instead to the impact of astronomically forced changes in temperature, rainfall and terrestrial net primary production on the distribution and evolution of Homo populations, as well as the emergence of the first members of our species [START_REF] Timmermann | Climate effects on archaic human habitats and species successions[END_REF]. Global climate change producing contrasting vegetation changes in the two hemispheres may have caused regional niche contractions or expansions affecting movements of hominin populations and therefore human evolution [START_REF] Sánchez Goñi | Regional impacts of climate change and its relevance to human evolution[END_REF]. The precocious appearance 92-80 ka ago, following the disappearance, of cultural innovations at a site located in s Succulent Karoo Biome, has recently been explained by suggesting that climate change modified cultural connectivity between regions during the southern African MSA [START_REF] Mackay | Environmental influences on human innovation and behavioural diversity in southern Africa 92-80 thousand years ago[END_REF].

Most of the above propositions, however, lack the means, apart from contemporaneity and recurrence, by which to verify hypotheses that climate may have influenced cultural shifts, to identify the suite of environmental parameters within which each archaeological culture operated, or to evaluate how these relationships varied through space and time ( , 2013). The emergence of key cultural innovations in our lineage may reflect changes in the nature of such relationships. The more robust connections between cultural and biological evolution on the one hand, and climate on the other, arguably come from approaches that create means for quantification and verification of their findings. Eriksson and colleagues (2012) have for example combined patterns of genetic variation in modern human populations and climatic reconstructions to create a model accounting for human demography and expansion over the past 120 ka. They show that the model is fully consistent with known trends in modern human expansion, which support a clear effect of climate on past population densities and dispersal [START_REF] Eriksson | Late Pleistocene climate change and the global expansion of anatomically modern humans[END_REF]. In most regions, however, the evidence needed to test these hypotheses rigorously is scant, and simply lacking in others. Existing regional palaeoenvironmental records remain spatially and chronologically disconnected from the archaeological record. Very few continuous terrestrial climate archives exist that would permit an integration of climate and behavioural variability, and even when they exist, chronological uncertainties do not allow clear correlations between the two records. High-resolution regional palaeoclimate simulations can only partially overcome the problem and they only provide a rough representation of past climate and vegetation. They need data-model comparisons to be accepted as real. Despite its recognized importance for the biological and cultural evolution of Middle and Later Stone Age populations, southern Africa records only a few continuous climatic sequences covering the large span of the last climatic cycles (Dupont, 2011;Daniau et al., 2013;[START_REF] Urrego | Increased aridity in southwestern Africa during the warmest periods of the last interglacial[END_REF][START_REF] Ziegler | Development of Middle Stone Age innovation linked to rapid climate change[END_REF]Dupont et al., 2019Dupont et al., , 2022;;[START_REF] Chevalier | Temperature change in subtropical southeastern Africa during the past 790,000 yr[END_REF][START_REF] Strobel | Reconstructing Late Quaternary precipitation and its source on the southern Cape coast of South Africa: A multi-proxy paleoenvironmental record from Vankervelsvlei[END_REF]. Most of these records are not high resolution, and rarer are those allowing reconstruction of the evolution of the climate and vegetation of the eastern side of this vast region.

Pollen, in combination with sediment chemistry and carbon isotope analysis from Core Cave, South Africa, where stratigraphic members have been dated between ~227 ka and ~24 ka (Table 1).

Site location and modern vegetation

Border Cave is a large, West-facing shelter located about 82 km West of the Indian Ocean, in the Lebombo Mountains on the border between KwaZulu-Natal in South Africa, and eSwatini, formerly known as Swaziland (Fig. 1). The cave is just below the rim of an escarpment at approximately 600 m above mean sea level (a.m.s.l.) [START_REF] Backwell | New Excavations at Border Cave, KwaZulu-Natal, South Africa[END_REF]. It overlooks eSwatini, and is 2 km North of the Ngwavuma River where the altitude is about 100 m a.m.s.l. and riverine vegetation occurs. The modern Lebombo vegetation around

Border Cave provides the vegetation baseline for the anthracology. A mosaic of vegetation communities exists within a 5 km radius of the cave and the variability of vegetation in this part of the Lebombo is linked to the elevation, moisture availability and soil type. We make use of several commonly-used names to describe the local vegetation communities, for example, bushveld, sourveld, woodland, and forest. Bushveld is defined as sub-tropical woodland [START_REF] Mucina | The Vegetation of South Africa, Lesotho and Swaziland[END_REF]; sourveld is grassland which occurs in cool, moist areas [START_REF] Ellery | Classification of Vegetation of the South African Grassland Biome[END_REF][START_REF] Cowling | Vegetation of Southern Africa[END_REF]; woodland consists of trees and shrubs with an open canopy [START_REF] Coates-Palgrave | Palgrave Trees of Southern Africa, 3rd edn[END_REF][START_REF] Scholes | Savanna[END_REF], while forest consists of closed stands of trees where the crowns of the trees are continuous and some trees are taller than 10 m [START_REF] Scholes | An African Savanna[END_REF]Midgley et al., 2004: 278;[START_REF] Mucina | The Vegetation of South Africa, Lesotho and Swaziland[END_REF]. All of these plant communities, as well as the riverine vegetation near the Ngwavuma River, could have been exploited by inhabitants of Border Cave. [START_REF] Mucina | The Vegetation of South Africa, Lesotho and Swaziland[END_REF] have classified the Lebombo vegetation zones more precisely as Lebombo Summit Sourveld (SVI 17) and Northern (SVI 15) and Southern (SVI 16) Lebombo Bushveld (Mucina and Rutherford, 2006: 500-502). All these vegetation zones occur near Border Cave (Fig. 1). (Mucina and Rutherford, 2006: 502). Lebombo Summit Sourveld (sour grassland) includes some woody plants that also occur in other vegetation zones: Diospyros dichrophylla, Grewia monticola and Acacia caffra (Senegalia caffra) (Mucina and Rutherford, 2006: 502). This grassland vegetation type is not further described in our study, which relies on woody plants.

A recent vegetation survey near the cave (see [START_REF] Backwell | New Excavations at Border Cave, KwaZulu-Natal, South Africa[END_REF] In the broader context, Border Cave is within an area of high biodiversity. The Maputaland centre of endemism is not far from the cave, and nor is the Gwalaweni Forest, which may once have encompassed a greater area of the Lebombo, though at present only about 500 hectares survive. Gwalaweni is a scarp forest (with several endemics) that borders the Lebombo Summit Sourveld [START_REF] Mucina | The Vegetation of South Africa, Lesotho and Swaziland[END_REF] [START_REF] Moll | A Plea for the Gwalaweni Forest[END_REF][START_REF] Midgley | Forest[END_REF] on the plateau (Mucina and Rutherford, 2006: 790). This type of variability may have once occurred in the Border Cave area.

The complexity of the modern environment has made it necessary for us to simplify the vegetation types used for our analysis at Border Cave, so we have concentrated on four types based on plant habitat. Habitat is defined by shrub or tree height and plant community [START_REF] Hammer | PAST: Palaeontological Statistics Software package for education and data analysis[END_REF]Hammer, 2019). We have chosen forest and closed woodland as two types that will be used in our interpretations, and of course there is some overlap between the genera found in each. Bushveld and open woodland are the other two vegetation types, and once again, there is overlap between the genera found in each of these vegetation types. [START_REF] Beaumont | Border Cave[END_REF][START_REF] Beaumont | Contemplating old clues to the impact of future greenhouse climates in South Africa[END_REF].

Excavations at Border Cave

These early excavations demonstrated that the site contains a wealth of organic material, but archaeological charcoal was not studied prior to the Backwell-led excavations between 2015 and 2019. The new campaign aims primarily to produce a high-resolution multi-proxy record of climate change and contemporaneous human behaviour that extends from MIS 7 to MIS 2;

contribute to an understanding of the impact of climate change on subsistence strategies in this region through time; gain insight into site formation processes; identify cultural trends within a secure chronological framework; document the emergence of cultural innovations, and collect and study all organic remains, including grass bedding, seeds, leaves, wood, rhizomes and charcoal [START_REF] Backwell | New Excavations at Border Cave, KwaZulu-Natal, South Africa[END_REF]this volume).

Border Cave chronostratigraphic sequence

The 4 m-deep sedimentary sequence comprises six alternating brown sand (BS) and white ash (WA) members. [START_REF] Beaumont | Border Cave -A Progress Report[END_REF][START_REF] Beaumont | Border Cave[END_REF] and [START_REF] Butzer | Lithostratigraphy of Border Cave, KwaZulu, South Africa: a Middle Stone Age Sequence Beginning c. 195,000 B[END_REF] named the Border Cave members based on whether the layers were predominantly white from accumulated ash (WA members) or whether they were brown sandy layers (BS members). 1 WA and 1 BS Lower dated to between 43 ka and 24 ka and they are said to belong to the Early Later Stone Age (ELSA) [START_REF] Beaumont | Contemplating old clues to the impact of future greenhouse climates in South Africa[END_REF] ; 1 ; V 1 ;

, 2016). Directly above the ELSA deposits is Member 1 BS Upper (Iron Age). In order to avoid the possibility of Iron Age intrusions in our sample, we chose not to analyse charcoal from Member 1 BS Lower in this study. In the new excavations, small layers separated at the centimetre scale have been recognized within each member, and anthropogenic features such as hearths and bedding layers (Fig. 3) have been carefully

mapped [START_REF] Backwell | New Excavations at Border Cave, KwaZulu-Natal, South Africa[END_REF][START_REF] Wadley | Fire and grass bedding construction 200 thousand years ago at Border Cave, South Africa[END_REF]. The Border Cave sequence has been dated by electron spin resonance (ESR) [START_REF] Grün | Border Cave revisited: a revised ESR chronology[END_REF][START_REF] Grün | On the age of Border Cave 5 human mandible[END_REF][START_REF] Millard | Bayesian analysis of ESR dates, with application to Border Cave[END_REF], amino acid racemisation [START_REF] Miller | Dating in the Middle Stone Age at Border Cave, South Africa, by the epimerization of isoleucine in ostrich eggshell[END_REF][START_REF] Miller | Earliest modern humans in Southern Africa dated by isoleucine epimerization in ostrich eggshell[END_REF], and radiocarbon methods [START_REF] Vogel | Revised radiocarbon chronology for the Stone Age in South Africa[END_REF][START_REF] Beaumont | Modern man in sub-Saharan Africa prior to 49 000 years BP: a review and evaluation with particular reference to Border Cave[END_REF][START_REF] Beaumont | On the age of Border Cave hominids 1-5[END_REF][START_REF] Vogel | Pretoria radiocarbon dates III[END_REF][START_REF] Beaumont | Contemplating old clues to the impact of future greenhouse climates in South Africa[END_REF]Bird et 3;[START_REF] Insidewood | InsideWood database[END_REF][START_REF] V P H R J J Beaumont | Border Cave and the beginning of the Later Stone Age in South Africa[END_REF][START_REF] Backwell | New Excavations at Border Cave, KwaZulu-Natal, South Africa[END_REF], see Table 1. Lithic assemblages at the site were divided by [START_REF] Beaumont | Border Cave[END_REF] BS.LR) date to between 44 ka and 24 ka. The new dating results (Tribolo et al., this volume) generally support the earlier chronologies.

Research hypothesis

Here, the hypothesis is that global climate changes caused similar vegetation change at Border Cave to that demonstrated at the mouth of the Limpopo River by Dupont and colleagues (2019). The hypothesis for change through time was also informed by a micromammalian study suggesting that miombo woodland occurred before ~150 ka at Border

Cave and that miombo was later replaced by vegetation similar to mopane woodland [START_REF] Avery | The environment of early modern humans at Border Cave, S.A.: micromammalian evidence[END_REF]. Colophospermum mopane charcoal was indeed found in layer Faan (Member 1 RGBS) (Zwane and Bamford, 2021b), but has not previously sequence, and the tree does not grow near the cave nowadays. Miombo woodland also does not occur near Border Cave today, but a small relic miombo woodland survives in northern South Africa, in the Soutpansberg mountains [START_REF] Pienaar | The biogeography of Brachystegia woodland relicts in southern Africa[END_REF]. The southern range of miombo is in Zimbabwe, though it extends through Mozambique and into Zambia [START_REF] Smith | Field Guide to Trees and Shrubs of Miombo Woodland[END_REF]. Miombo taxa are described by [START_REF] Smith | Field Guide to Trees and Shrubs of Miombo Woodland[END_REF] and den Outer and van Veenendaal (1996). What is clear from vegetation community descriptions is that Brachystegia spp. and Julbernadia spp. (Fabaceae Caesalpinioideae) are characteristic miombo woodland genera, and they would be expected in the Border Cave charcoal assemblage if miombo woodland was represented there in the past.

We aim to depict shifts in the Lebombo woodland vegetation through time by carrying out anthracological analysis on the well-preserved assemblage retrieved from the Border Cave sequence. Identified woody taxa in the various archaeological members will be used to reconstruct vegetation communities through time. Border Cave charcoal is better preserved than that from Sibudu, a site about 300 km South of Border Cave, where the charcoal was fragmented into tiny pieces [START_REF] Allott | Archaeological charcoal as a window on palaeovegetation and wood use during the Middle Stone Age at Sibudu Cave[END_REF]Lennox et al., 2015;Lennox, 2016;Lennox et al., 2017;[START_REF] Lennox | A charcoal study from the Middle Stone Age, 77,000 to 65,000 years ago, at Sibudu, KwaZulu-Natal[END_REF][START_REF] Bamford | Pollen, charcoal and phytolith records from the Late Quaternary of southern Africa: vegetation and climate interpretations[END_REF]Zwane and Bamford, 2021a). We recognise, however, that anthropogenic choice is an important factor to consider when interpreting the presence of taxa collected for firewood.

Materials and methods

During recent excavations between 2015 and 2018, all charcoal, whether recovered from combustion features (hearths and burned bedding layers) or scattered in sediments, was collected from all members. All pieces 20 mm or larger were point-plotted by means of a total station, and were curated individually. Smaller pieces were collected after dry sieving the sediment through 2 mm and 1 mm mesh, and they were curated according to standard procedures for archaeobotany [START_REF] Popper | Selecting quantitative measures in palaeoethnobotany[END_REF][START_REF] Pearsall | Paleoethnobotany: A Handbook of Procedures[END_REF]. Flotation was not used because the site preserves some delicate unburnt plant material that would be destroyed by water.

Approximately 80 specimens of charcoal [START_REF] Stewart | Follow the Senqu: Maloti-Drakensberg paleoenvironments and implications for early human dispersals into mountain systems[END_REF] were analysed from two layers from each member, except from Members 5 BS and 4 WA where more layers were examined (Table 1). Standard anthracological methods were applied to identify the charcoal (see for example Figueiral and Mosbrugger, 2000;[START_REF] Allott | Archaeological charcoal as a window on palaeovegetation and wood use during the Middle Stone Age at Sibudu Cave[END_REF][START_REF] Théry-Parisot | Anthracology and taphonomy, from wood gathering to charcoal analysis: A review of the taphonomic processes modifying charcoal assemblages, in archaeological contexts[END_REF][START_REF] Cartwright | Identifying the woody resources of Diepkloof Rock Shelter (South Africa) using scanning electron microscopy of the MSA wood charcoal assemblages[END_REF][START_REF] Backwell | Multiproxy record of late Quaternary climate change and Middle Stone Age human occupation at Wonderkrater, South Africa[END_REF]Bamford, 2015a, b;[START_REF] Stewart | Follow the Senqu: Maloti-Drakensberg paleoenvironments and implications for early human dispersals into mountain systems[END_REF][START_REF] King | Wood charcoal analysis in tropical rainforest: a pilot study identifying firewood used at toxic nut processing sites in northeast Queensland, Australia[END_REF][START_REF] Bodin | Unraveling pre-Columbian occupation patterns in the tropical forests of French Guiana using an anthracological approach[END_REF][START_REF] Henry | Old taphonomy issues, new charcoal data for Mesolithic contexts: Impact of fragment size and sampling context on the assemblages of Escabasses cave (SW France)[END_REF]. Border Cave specimens were selected for identification by means of random sampling within each sample using random number tables (Drennan, 2009). Consequently, specimen sizes vary between members. This is important because a study of the taphonomy in Escabasses Cave (southwestern France) showed that size class does not affect interpretations of floristic diversity [START_REF] Henry | Old taphonomy issues, new charcoal data for Mesolithic contexts: Impact of fragment size and sampling context on the assemblages of Escabasses cave (SW France)[END_REF]. However, earlier studies by [START_REF] Chabal | L'Homme et l'évolution de la végétation méditerranéenne des âges des métaux à la période romaine; recherches anthracologiques théoriques, appliquées principalement à des sites du Bas-Languedoc[END_REF][START_REF] Chabal | La représentativité paléo-écologique des charbons de bois archéologiques issus du bois de feu[END_REF][START_REF] Chabal | Forêts et sociétés en Languedoc (Néolithique final, Antiquité tardive): l'anthracologie, méthode et paléoécologie[END_REF] 4. [START_REF] Grün | On the age of Border Cave 5 human mandible[END_REF].

By way of reference, a list was compiled of several species occurring near Border

Cave between 2016 and 2019, and the anatomical characteristics were recorded according to the IAWA (International Association of Wood Anatomists) code from the InsideWood database [START_REF] Wheeler | IAWA list of microscopic features for hardwood identification[END_REF][START_REF] Wheeler | InsideWood -a web resource for hardwood anatomy[END_REF] and from published references [START_REF] Kromhout | Sleutel vir die Mikroskopiese Uitkenning van die Vernaamste Inheemse Houtsoorte van Suid-Afrika[END_REF][START_REF] Ilic | CSIRO Atlas of Hardwoods[END_REF][START_REF] Neumann | Woods of the Sahara and the Sahel[END_REF][START_REF] Jansen | A survey of the systematic wood anatomy of the Rubiaceae[END_REF][START_REF] Ruffinato | Atlas of Macroscopic Wood Identification: With a Special Focus on Timbers Used in Europe and Cites-Listed Species[END_REF].

In addition, charcoal reference collections are held at the Evolutionary Studies Institute, University of the Witwatersrand [START_REF] Allott | Palaeoenvironments of the Middle Stone Age at Sibudu Cave, KwaZulu-Natal, South Africa: An Analysis of Archaeological Charcoal[END_REF][START_REF] Chikumbirike | Archaeological and Palaeoecological Implications of Charcoal Assemblages Dated to the Holocene from Great Zimbabwe and its Hinterland[END_REF]Lennox, 2016;[START_REF] Scheel-Ybert | Charcoal collections of the world[END_REF].

Each charcoal specimen was pressure-fractured in order to obtain the three anatomical planes for observation: transverse, radial longitudinal and tangential longitudinal. The anatomical characteristics were compared with those of reference charcoal [START_REF] Allott | Palaeoenvironments of the Middle Stone Age at Sibudu Cave, KwaZulu-Natal, South Africa: An Analysis of Archaeological Charcoal[END_REF][START_REF] Höhn | Settling the rain forestthe environment of farming communities in southern Cameroon during the first millennium BC[END_REF][START_REF] Bamford | Late Pliocene woody vegetation of Area 41, Koobi Fora, East Turkana Basin, Kenya[END_REF][START_REF] Hubau | Charcoal identification in species-rich biomes: A protocol for Central Africa optimised for the Mayumbe forest[END_REF][START_REF] Hubau | Complementary imaging techniques for charcoal examination and identification[END_REF][START_REF] Nelle | Pedoanthracology: analysing soil charcoal to study Holocene palaeoenvironments[END_REF][START_REF] Asouti | Holocene semi-arid oak woodlands in the Irano-Anatolian region of southwest Asia: natural or anthropogenic?[END_REF][START_REF] Chikumbirike | Archaeological and Palaeoecological Implications of Charcoal Assemblages Dated to the Holocene from Great Zimbabwe and its Hinterland[END_REF]Dotte-Sarout et al., 2014;[START_REF] Hubau | Archaeological charcoals as archives for firewood preferences and vegetation composition during the late Holocene in the southern Mayumbe, Democratic Republic of the Congo (DRC)[END_REF][START_REF] Scheel-Ybert | The forest people: landscape and firewood use in the Araruama region, southeastern Brazil, during the late Holocene[END_REF]Bamford, 2015a, b;Lennox and Bamford, 2015;Lennox, 2016, Lennox andBamford, 2017;[START_REF] Lennox | The identification of Cryptocarya spp., Lauraceae in archaeological charcoal[END_REF]. The archaeological charcoal is identified by comparing the IAWA characters of reference material. Most anatomical characteristics are visible using reflective microscopy to 600x magnification. For example, pitting and perforation plates of Curtisia dentata (Fig. 4), and fibre thickness in Brachylaena and Tarchonanthus spp. (Lennox and Bamford, 2017) are observable, while crystals and silica bodies can be detected in Euphorbiaceae such as Spirostachys africana and Sclerocroton spp. (Lennox and Bamford, 2015), and radial canals can be seen in Commiphora spp., in addition to ray width in Cryptocarya spp. [START_REF] Lennox | The identification of Cryptocarya spp., Lauraceae in archaeological charcoal[END_REF]. Nonetheless, IAWA characteristics are sometimes not visible because of post-depositional damage to charcoal, such as cracks caused by diagenesis, and fusion due to vitrification. Carbonisation fuses the structure of cell walls and middle lamellae, which may destroy the pits in vessels and fibres, thus it is not possible to use all IAWA features in anthracology [START_REF] Kwon | An investigation on the transition characteristics of the wood cell walls during carbonization[END_REF][START_REF] Scheel-Ybert | First anthracological atlas of Brazilian species[END_REF].

While it is often not possible for anthracologists to distinguish the species within a woody genus, some African genera, such as Curtisia dentata, have only one species. In such cases we make use of the genus and species attribution. Where several species occur within a genus, we do not attempt to distinguish them, but list them as, for example, Tarchonanthus spp.

Since the micromammalian study mentioned earlier [START_REF] Avery | The environment of early modern humans at Border Cave, S.A.: micromammalian evidence[END_REF] implied that miombo woodland may once have occurred near Border Cave, particular attention was given to the anatomy of the Fabaceae found in the charcoal assemblage because their wood anatomy is highly variable, and often does not permit specific identifications. [START_REF] White | The Vegetation of Africa[END_REF] lists 19 species of Brachystegia, two of Julbernardia, and Isoberlinia angolensis, which occur in miombo as dominant taxa. No miombo species presently grow near Border Cave, but may have been present in the past. Thus particular attention was given to the anatomy of Brachystegia and Julbernadia spp. (as listed in den Outer and van Veenendaal, 1996). The published anatomical features were compared with those of the Border Cave archaeological legumes, and with legumes that occur in the modern Lebombo environment. The anatomical features of the charred reference material were thus grouped according to the distinguishing characteristics, particularly ray width and parenchyma arrangement (abundant or sparse).

Quantitative analysis methods

Detrended correspondence analysis (DCA) was used to compare the woody taxa identifications from charcoal in the ten Border Cave members using Palaeontological Statistics, PAST 3.23 software [START_REF] Hammer | PAST: Palaeontological Statistics Software package for education and data analysis[END_REF]Hammer, 2019). The PAST module uses the same algorithm as the Decorana software [START_REF] Hill | Detrended correspondence analysis: An improved ordination technique[END_REF]. DCA is commonly used in paleoecology. In studies of plant ecology it can suggest the progression of plant communities over time. Correspondence analysis and principal coordinate analysis are particularly useful for dealing with large quantities of data, especially in cases of presenceabsence data, for example plant species, or semi-quantitative data, such as rare, moderately present or abundant specimens. Such analyses allow for ordination of both fixed points like stratigraphic layers, and variables, for example plant taxa. The taxa are grouped into the four broad types of vegetation based on plant habitat that have previously been discussed, that is, groups of woody taxa) and members [START_REF] Hill | Detrended correspondence analysis: An improved ordination technique[END_REF][START_REF] Bloem | Grassland communities of the Verlorenvalei Nature Reserve in the North Eastern Sandy Highveld, North Eastern Transvaal[END_REF][START_REF] Hammer | PAST: Palaeontological Statistics Software package for education and data analysis[END_REF][START_REF] Cruikshank | Developing Biodiversity Indicators and Economic Valuations for Created Grasslands in the U[END_REF]Hammer, 2019).

In the case of Border Cave where continuity and overlap in plant taxa are likely through time, the Decorana module in PAST offers potential to identify trends, for example recurrent ecological associations not detectable through a simple analysis of the data.

Naturally, interpretations suggested by the Decorana need to be assessed using ecological insights and local knowledge about a particular environment.

Results

In the charcoal analysis, 1441 of the 1581 charcoal specimens were identified: 22 families and 28 genera were identified, 25 charcoal specimens remain unidentified and 115 were unidentifiable. Unidentified charcoal did not have enough IAWA features for identification.

Unidentifiable charcoal was in some instances knotted (branched), or damaged beyond recognition by carbonisation, for example it was vitrified. A variety of woody taxa occur in each member ( [START_REF] White | The Vegetation of Africa[END_REF]Den Outer and Van Veenendaal, 1996;[START_REF] Höhn | Wood anatomy of selected West African species of Caesalpiniodeae and Mimosoideae (Leguminosae): A comparative study[END_REF]InsideWood, 2004-onwards). The presence of Brachystegia and Julbernadia can therefore be ruled out amongst the archaeological charcoal identified at Border Cave.

The genera representing evergreen or deciduous plants (Fig. 5) or forest/closed woodland and bushveld/open woodland habitats (Fig. 6) are expressed as a percentage of the total number of genera identified in each member. Thus, the figure is not a measure of the percentage of fragment counts of identified material, but rather a measure of percentage ubiquity, present across samples [START_REF] Kabukcu | Sampling and quantitative analysis methods in anthracology from archaeological contexts: Achievements and prospects[END_REF].

Discussion

Wood could not have entered the deep cave without being brought there; certainly no plants can grow in the dry sediments and darkness in Border Cave. Humans brought wood to the cave and used it predominantly as fuel in their fireplaces. The practice occurred prior to 227 ka and continued throughout the occupation of the site. Some of the taxa identified are known to be good fuelwoods in the sense that they produce charcoal that retains heat, for example Protea spp., Acacia spp. and Leucosidea sericea [START_REF] Allott | Archaeological charcoal as a window on palaeovegetation and wood use during the Middle Stone Age at Sibudu Cave[END_REF]. Possibly some taxa were also collected for their medicinal properties. Of particular interest in this regard, are Tarchonanthus spp. (from Members 6 BS, 5 WA, 1 RGBS, 2 WA, 2 BS and 1 WA),

Spirostachys africana (from Members 5 WA and 4 WA) and Cryptocarya spp. (from Members 6 BS to 4 WA, and 3 BS to 2 BS) that may have served an insecticidal or medicinal purpose, as seems to have been the case at Sibudu [START_REF] Wadley | Middle Stone Age bedding construction and settlement patterns at Sibudu, South Africa[END_REF]Lennox andBamford, 2015, 2017). Fresh leaves and wood of Tarchonanthus spp. and Cryptocarya spp.

are aromatic, and Spirostachys africana wood creates noxious smoke when burned (Lennox and Bamford, 2015). People select their firewood and tinder deliberately from the best available woody plants, and for this purpose modern gatherers are prepared to collect from about 2 km from their homesteads [START_REF] Archer | Planning with people -ethnobotany and African uses of plants in Namaqualand (South Africa)[END_REF][START_REF] Archer | Ethnobotany of Namaqualand: the Richtersveld[END_REF][START_REF] Cunningham | Earliest evidence of personal ornaments associated with burial: the Conus shells from Border Cave[END_REF]. It is likely that people in the past also had good knowledge of the properties of various woods; thus the list of woody taxa may reflect human choice, and need not fully represent the vegetation profile in the vicinity of the archaeological site. The absence of taxa does not imply that they were not growing in the area. Furthermore, an abundance of charcoal from some species may imply human preference rather than high frequency in the environment [START_REF] Cunningham | Earliest evidence of personal ornaments associated with burial: the Conus shells from Border Cave[END_REF][START_REF] Wadley | Recognising complex cognition through innovative technology in Stone Age and Palaeolithic sites[END_REF][START_REF] Lennox | Charcoal analysis from 49 000-year-old hearths at Sibudu: implications for wood uses and the KwaZulu-Natal environment[END_REF]. Nonetheless, the suites of archaeological charcoal do provide useful clues for the reconstruction of ancient environments.

Through the long sequence of human occupation that began before 227 ka, woody plants representing at least 22 families and 28 genera were brought to the cave. The greatest diversity is recorded in Member 3 BS (n = 18) dated from about 72-56 ka. The least diversity is in 1 RGBS (n = 11) where diagenesis may have played a role in selectively preserving charcoal dated to 74 ± 4 ka. This period is approximately the time of both the Toba eruption and the start of the last glacial episode in the northern hemisphere [START_REF] Svensson | A 60000 year Greenland stratigraphic ice core chronology[END_REF].

While both events potentially affected southern African vegetation, this remains to be clearly demonstrated. Certainly, we find no evidence at Border Cave to support 1998 suggestion that the Toba eruption caused depopulation. Although not present in our charcoal collection, nor present near the cave nowadays, a small amount of Colophospermum mopane charcoal was recently identified in Member 1 RGBS (Zwane and Bamford, 2021b). This tree thrives in hot, dry conditions. Mopane produces excellent firewood that would have been selected when available in the area. Reduced woody plant diversity as a result of anthropogenic impact on the stability of woodland vegetation due to long-term huntergatherer presence in the vicinity of a site [START_REF] Asouti | Holocene semi-arid oak woodlands in the Irano-Anatolian region of southwest Asia: natural or anthropogenic?[END_REF]) is an improbable scenario at Border Cave. Occupation in Member 1 RGBS was sporadic, likely by small groups of people for short periods of time, as evidenced by the low number of archaeological finds per sediment volume (de la Pena et al., this volume). In addition, the site is located in Southern Lebombo Bushveld, a vast sub-tropical woodland (see Fig. 1) that would have been impervious to the wood gathering activities of MSA people, no matter how large the size of the group or the length of their stay.

Details of the habitats and modern environmental requirements of the woody taxa identified at Border Cave are presented in Appendix Table 2. These help to explain conditions that may have existed in the past, when the taxa concerned grew in the Border Cave area. The shrubs and trees identified here from the wood anatomy of Border Cave charcoal include evergreen and deciduous taxa (Fig. 5) from the broadly-defined habitats of forest/closed woodland, and bushveld/open woodland (Fig. 6). In other words, all the vegetation communities that have already been described for the area in modern times seem to have created a mosaic of communities in the past, perhaps within close proximity to each other. Of the taxa listed as important to the modern Southern Lebombo Bushveld by Mucina and Rutherford (2006: 502), several were found in the Border Cave charcoal record, suggesting continuity between past and present. These persistent taxa include Acacia and Combretum sp., Olea sp., Commiphora sp., Diospyros sp. and Vitex sp. Yet, each Border

Cave member has some woody taxa no longer found nearby. This may sometimes be because the modern environment is anthropogenically altered by subsistence farmers. Frequent burning of the area by farmers may have eliminated some taxa, like Protea sp. [START_REF] Poultney | Changes in abundance and distribution of Protea caffra in the central and northern Drakensberg as a consequence of climate and land use change[END_REF], and overexploitation may have played a role in other cases. Among the taxa absent today, but present in the past at Border Cave are: Curtisia dentata that prefers moist forests, and the pioneer Leucosidea sericea that favours scrub thicket near water. Other taxa absent from the modern Lebombo environment, like Commiphora sp., are bushveld taxa. Since there are still many bushveld taxa in the Border Cave region, the absence of those listed above may imply minor recent loss of diversity rather than a change in the vegetation type. The ancient forests, suggested by various taxa at Border Cave, may have been relatively small, and they probably occupied the deep, cool, moist valleys near the site. The forest taxa represented in the charcoal assemblage do not imply that the Gwalaweni Forest was near Border Cave in the past.

Several environmental implications arise from this study of woody plants. The vegetation communities implied by the identified woody plants comprise some shrubs, together with large numbers of small-or medium-sized trees and some large trees.

Many of the taxa are evergreen, particularly in the older members 5 BS and 1 RGBS. While evergreen taxa are often associated with forest, this is not necessarily the case because some evergreens, like Olea spp. and Tarchonanthus spp., can occur in bushveld, while some deciduous taxa, like Celtis sp. and Commiphora sp., also grow in forests. Evergreen and deciduous taxa are almost evenly distributed in the Border Cave members. The woody taxa at Border Cave do, indeed, appear to come from a mosaic of vegetation communities that must have co-existed contemporaneously relatively near to the cave, but the size of the various communities may have altered through time. To some extent this could be described as niche contraction or expansion, to use the Sánchez Goñi (2020) terminology mentioned in the (Wadley, 2004;[START_REF] Allott | Archaeological charcoal as a window on palaeovegetation and wood use during the Middle Stone Age at Sibudu Cave[END_REF]Sievers, 2006;[START_REF] Bamford | Pollen, charcoal and phytolith records from the Late Quaternary of southern Africa: vegetation and climate interpretations[END_REF]Zwane and Bamford, 2021a). The Border Cave record might also be compared to an East African paleoenvironmental simulation using temperature and precipitation coupled with a biome model for the MSA [START_REF] Timbrell | A spatiotemporally explicit paleoenvironmental framework for the Middle Stone Age of eastern Africa[END_REF] Cave and the technological changes that were identified by Beaumont (summarised in Table 1). Our charcoal results do not, on their own, support the idea that climate change caused cultural change. We acknowledge, however, that our anthracology results must be taken as distant proxies in archaeological debates, and that time lag is an important consideration.

Conclusion

The 10 archaeological members at Border Cave studied here are dated between ~227 and 43 ka, and all have evidence of human occupation and combustion features in the form of fireplaces and burned grass bedding. Charcoal analysed from the 10 members resulted in the identification of woody plants representing 22 families. These comprised a few shrubs, mostly small-or medium-sized trees, and some large trees. The plants represent taxa from forests, forest margins, closed and open woodland and bushveld habitats. The vegetation succession suggests a past environment that supported gradual transitions. Overall, the archaeological charcoal from all members implies that the area contained trees that were mostly evergreen in habit, and that more bushveld and open woodland trees than forest and closed woodland trees were represented.

Notwithstanding the likely presence of mosaic vegetation communities through much of the time that Border Cave was occupied, it is possible to suggest some predominant habitats. In terms of indicator species, for example, in Member 6 BS (>227 ka) bushveld and open woodland taxa were most common, as was also the case in Member 5 WA (~227 ka).

Moist forest was most common in Members 5 BS (~161-144 ka) and 4 WA (~168-113 ka),

while Member 1 RGBS (~74 ka) had a combination of bushveld and moist forest present. In Member 3 WA (~64 ka) dry bushveld predominated, while in Members 3 BS (72-56 ka) and 2 WA (~60 ka) moist forest was the predominant vegetation habitat. Member 2 BS.UP (49-44 ka) mostly included bushveld and moist forest patches, while Member 1 WA (~43 ka) was predominantly dry bushveld. In comparison with modern vegetation, the Border Cave occupations from approximately 227 ka seem to have taken place in a dry environment, beginning with Members 6 BS and 5 WA. The dryness ameliorated in Members 5 BS, 4 WA and 1 RGBS, but recurred in Member 3 WA, then became less dry in 3 BS, moderately dry in 2 WA, and finally it was considerably drier in Members 2 BS and 1 WA. Overall, however, the past vegetation seems similar to the modern vegetation profile and there appears to have been remarkable stability through time.

Plants once represented in the area, but are no longer near the site, include The stable plant habitats present at Border Cave between ~227 ka and ~44 ka ago suggest that the area would have been a suitable refugium for plants during periods of instability elsewhere in the region. This may well explain its repeated occupation during the MSA. There are, of course, observable shifts in the proportions of, for example, bushveld and forest species. While this might imply changing sizes in vegetation communities when effective precipitation increased or decreased, we also acknowledge human agency in the presence of wood in Border Cave. Firewood preferences may have changed through time for reasons that we cannot now decipher, though we can speculate that issues like negotiating a precipitous cliff to collect wood from forest trees when their patch size decreased may have deterred foragers.

Importantly, the emergence of cultural innovations in Border Cave cannot be chronologically linked to the changes that we see in the vegetation record.

MD96- 2048 ,

 2048 retrieved in the middle of the Delagoa Bight and covering the last 2 Ma, provide at present the best record to identify long term trends in the evolution of vegetation in the area during the Quaternary(Dupont et al., 2022). Pollen source areas cover the region north of the Delagoa Bight in southern Mozambique and the region west of the Lebombo Mountains and the Drakensberg escarpment. The pollen record allows for a detailed reconstruction of the biome developments over the last 790 ka(Dupont et al., 2022). This recently extended record and the presence in the region of an archaeological site, Border Cave, preserving a well-dated stratigraphic sequence covering the last seven climatic cycles, and presenting exceptional preservation of organic matter, provides the opportunity to contrast the evolution of vegetation at a regional scale and the choices made by human groups visiting the site when selecting the plant taxa in their immediate environment to burn for heating and pyrotechnology. The identification of archaeological charcoal from abandoned fireplaces and living areas enables the reconstruction of vegetation communities around the site. Anthracology in northern(Thery-Parisot et al., 2010) and southern latitudes (Scheel-Ybert, 2020) has demonstrated that different firewood gathering scenarios result in most local vegetation types being represented in archaeological charcoal assemblages. On the one hand, firewood collection for daily domestic use generally has low species selectivity, with dead wood randomly gathered. On the other hand, multiple fire functions tend to result in the selection of multiple types of wood. In both cases, the charcoal remains of an occupation that lasted for a sufficiently long time would include most of the species in the different vegetation types around the settlement(Thery-Parisot et al., 2010; Scheel-Ybert, 2020). While human selection may account for under-or over-representation of specific taxa in an archaeological charcoal assemblage, it may not be the only explanation. Other factors should also be considered, such as the reliability of the analysed samples in terms of the number of charcoal pieces identified, the duration of site occupation, the context in which the charcoal was found, whether concentrated in combustion features or scattered in sediments, and whether the taxa concerned occur in low or high frequency in the surrounding environment. Here we present results of the study of archaeological charcoal from Border

Fig. 1 .

 1 Fig. 1. Location of Border Cave and the surrounding vegetation types. a. Map of South

  The new excavations directed by Backwell retain the Beaumont nomenclature. At the base of the sequence, Members 6 BS and 5 WA are older than 227 ka. A portion of the older part of the sequence (Members 6 BS-4 BS) is illustrated in Figure 2. Above the long MSA sequence are Members

Fig. 2 .

 2 Fig. 2. Lower part of the Border Cave sequence showing the East profile in squares N108

Fig. 3 .

 3 Fig. 3. Border Cave Member 2 WA combustion features. Stacked combustion features show

  into MSA 1, MSA 2/Howiesons Poort (HP), MSA 3/post-HP and ELSA. The MSA 1 lithic assemblages (Members 5 WA, 5 BS, 4 WA, 4 BS) span 238 ka to 71 ka when minimum and maximum standard deviations M 2/HP assemblages (Members 1 RGBS, 3 WA, 3 BS) range between 82 ka and 54 ka, and the MSA 3/post-HP assemlages (Members 2 WA; 2 BS.LR C, B and A; 2 BS.UP) fall between 63 ka and 42 ka. The ELSA assemblages (Members 1 WA, 1

  The anatomical features were observed by means of light microscopy, utilising an Olympus SZX 16 stereomicroscope magnified up to 110 times, an Olympus USB camera and Soft Imaging Solutions software. Anatomical details were studied in greater detail by means of an Olympus BX51 reflective, polarised light microscope magnified up to 600 times, and Olympus Stream Essentials image analysis software with Extended Focal Image (EFI) capability was used.

  forest, closed woodland, bushveld and open woodland. The horse-shoe curve produced by correspondence analysis is straightened out by Decorana, enabling a comparison between values along a relatively horizontal line. Two of three axes are plotted, increasing from zero along the x and y axes. The scale is even and increases incrementally, not logarithmically or exponentially. The lines link similar values in the four groups. The position of each woody taxon (data row) is plotted once; Eigen values group woody taxa and the Border Cave stratigraphic members. The hulls represent correlations between plant habitat (determined by

Fig. 5 .

 5 Fig. 5. Percentage of evergreen and deciduous woody genera in Members 6 BS to 1 WA at

Fig. 6

 6 Fig. 6 Border Cave percentage of woody genera from forest/closed woodland and

Fig. 7 .

 7 Fig. 7. Detrended correspondence analysis convex hulls of woody taxa habitats represented at

  Commiphora sp. (an open woodland and bushveld taxon), Protea sp. (an open woodland taxon) and Curtisia dentata (an evergreen forest taxon). All these taxa have a wide southern African distribution and their absence today need not imply anything other than a gradual reduction of species in the modern environment. The modern environment appears to be somewhat impoverished compared with that in the past. We suggest this because of the suite of taxa occurring near Border Cave in the past, but absent from the area today. One reason for the difference could be the considerable firewood exploitation by the large, modern rural population.

Table 1 .

 1 demonstrated that the charcoal analyst of larger or better conserved pieces introduced bias and interpretation errors in the analysis, by underestimating sample diversity. It was statistically demonstrated that larger fragment classes contained only the most frequent species, whereas most species, and all rare species, are represented only in the smallest fragments. Material excavated and records kept during the Backwell campaigns at Border Cave are stored at the Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg. Summary of the members and the layers within them that were used in the study of

	Member

Border Cave charcoal. The bucket points are total station identification numbers from Abbreviations: ELSA (Early Later Stone Age) and HP (Howiesons Poort).

Layers in Backwell excavation Munsell colour Sediment description Bucket point (Backwell excavation) Lithic industry (Beaumont's names) Approx. age (ka) Beaumont excavation Dating method (Beaumont excavation)

	2 BS.UP Grass Mat Brown Feba, Greyish	-	organic,	3221	MSA 3/post-	49.0-44.2 227 ± 11	14C 2
		Carly Plan 1 Brown Kay,		pebbly,		HP
		Very Dark Plan 1	-	sandy -	6693
		Grass Mat Brown Feba, Brown Ken,	10YR -	silty, loose -	4641 6150
		Cassidy 1 Plan Base Plan 1	4/3
	2 WA 4 WA 6 BS	Grass Mat Reddish Brown	10YR 5YR 6/4 -	silty, loose, gritty/ashy -	4585 Ian 3 is 6347	MSA 3/post-MSA 1 MSA 1	60 ± 3 115 ± >227	ESR 2,4 ESR 3,4 ESR 3,4
		Dark Brown Ian 3. Larry, Plan 1	6/2 7,5YR	organic loose	3144.	HP	113 ±
		Yellowish Pinkish Grey Brown	7/2 -	cemented -	PG is 396, 6881		168 ±
		Brown 1, 2, 3 Larry, Plan 2			433.
	5 BS	Dossy 2 Very Dark	10YR	silty, loose	Jan 2 is	MSA 1	161 ±	ESR 3,4
	Dark Greyish Dating methods are radiocarbon (14C) for the younger layers and electron spin resonance for 10YR silty, loose, 5188 3/2 silty, loose 3312. 144 ±
		Yellowish Brown Jan	6/2 10YR	organic sandy	Jan 4 is
	the older ones. 1		(2012); 2. Bird et al. (2003); 3. Grün and Beaumont (2001);
		Brown 1, 2, 4.	3/2	ashy,	3694.
		Dossy Very Dark	10YR	cemented	Jantjie is
	3 BS	Grass Mat Grey Brown	-4/3	organic ashy, loose	4401 3108.	MSA 2b/HP,	56 ± 2	ESR 3,4
		Eco 1 Jantjie.	7.5YR	ashy, loose	Jet 1 is	MSA 2a/HP	64 ± 3
		Dark Brown White	7.5YR 8/1	silty, loose ashy,	5318 4199, 4224.		72 ± 4
		Elmo 1 Jet 1 CF 2.	4/3 10YR	cemented	Jez 1 is
		Combustion Very Dark	3/1		4336, 4378,
		Feature Grey Jez 1,	10YR		4616, 4698,
	3 WA	Light 2.	-3/2	-	6173 4805.	MSA 2/HP	64 ± 2	ESR 3,4
		Reddish Brown Jim.	7.5YR		Jim is 5137,
		Brown Faba, Brown John	4/2		5242, 5254,
		Plan 2 1.			5256, 5360,
	1 WA	Very Dark	10YR	fine silt	3126	ELSA	43	14C 1, 2
		Dark	-	-	6231 5365, 5430.
		Brown Barry	2/2
		Reddish			John 1 is
		1
		Brown			5425, 5469.
		Very Dark	10YR	-	3357
		Faddy, Plan
		Greyish	6/2
		1
	1 RGBS 5 WA	Brown Bill Very Dark Dark	--	--	6622 5645	MSA 2/HP MSA 1	74 ± 4 183 ±	ESR 3,4 ESR 3,4

  Table 2). The IAWA features of each are listed in Appendix Table 1. The porous wood with exclusively solitary vessels and diffuse parenchyma. The vessel diameters average ~50 µm, and frequencies range from 40-100 vessels/mm². Axial parenchyma is diffuse. b. Ray width is 1-3 cells and frequency is 12 rays/mm. c. Perforation plates are scalariform. Vessel-ray pit arrangement is opposite and the mean diameter is ~7 µm. d. Rays are heterocellular and composed of procumbent and marginal upright body cells.

	Scale bars of 50 µm represent 200x (a, b and d) and 20 µm represents 500x (c)
	magnification. pp = perforation plate; p = vessel-ray pit; r = ray; v = vessel.
	Several woody taxa from charcoal representing Fabaceae from subfamilies
	Caesalpinioideae and Mimosoideae were identified in the Border Cave charcoal assemblage

wood anatomy of some of the taxa identified at Border Cave is illustrated in micrographs

where diagnostic anatomical features are described in the captions. diffuse (Appendix Table

A1

;

[START_REF] Metcalfe | Anatomy of the Dicotyledons. 2 Vols[END_REF] den Outer and Van Veenendal, 1996;[START_REF] Neumann | Woods of the Sahara and the Sahel[END_REF] InsideWood, 2004 onwards)

. Other archaeological charcoal identified as Fabaceae closely matches Acacia sp. and Afzelia quanzenis, Type 6 Caesalpinidoideae, Type 7 Mimosoideae and Type 8 Papilionoideae (see Table 2 and IAWA features in Appendix Table 1). No Fabaceae charcoal in the Border Cave sample matches Brachystegia or Julbernadia spp. (as listed by

Table 2 .

 2 Summary of the woody taxa identified from 10 members (M) in Border Cave from ~227 ka (Member 6 BS) to ~43 ka (Member 1 WA). Totals (T) are the total number of charcoal pieces identified to the listed taxa. Preferred modern habitats for the listed taxa are

	presented as bushveld (B), forest (F), or woodland open (W. Op.) or closed (W. Cl). * = Taxa
	not recently observed in the Border Cave area.
	Scientific	Family	Hab	6	5	5	4	1	3	3	2	2	1	T M
	name		itat	BS	W	B	W	RG	W	BS	W	BS	W
					A	S	A	BS	A		A		A
	Acacia sp.	Fabaceae	B	2	1	5	13	1	9	20 8	6	10	1
		Mimosoideae												0
	Afrocarpus/	Podocarpaceae F					1	1	1				3
	Podocarpus
	sp.
	Afzelia	Fabaceae	B	1			1			1				3
	quanzenis	Caesalpinioide
		ae
	Brachylaena	Asteraceae	W.	30 4	10	22	2	1	26 45 19	30	1
	sp.		Op.			6								5
	Celtis sp.	Celtidaceae	W.				1				1	1	1	4
			Op.
	Combretum	Combretaceae W.	2			3		16		2			4
	sp.		Cl.
	Commiphora	Burseraceae	W.	2	3		4	1	12 4	1	4	4	1
	sp.*		Op.,											4
			B
	Cryptocarya	Lauraceae	W.	4	1	9	16			3	1	13		7
	spp.		Cl.
	Curtisia	Cornaceae	F			6	1			5	8			4
	dentata
	Diospyros sp. Ebenaceae	B.,	5	1	12 4		16 9	6	7	5	9
			W.
			Op.
	Diospyros sp.	Ebenaceae	W.		2	29 1			6	5		2	6
	2		Op.
	Erica* sp.	Ericaceae	W.			5				2				2
			Op.
	Harpephyllu	Anacardiaceae F							4				1
	m caffrum
	Leucosidea	Rosaceae	W.								6		3	2
	sericea *		Op.

Table 3 .

 3 introduction, but in the case of the Border Cave vegetation communities, the changes seem not to have been dramatic. If Curtisia dentata, Cryptocarya sp., Harpephyllum caffrum, and Podocarpus spp. are used as forest/closed woodland indicators and Pappea capensis, is taken as a bushveld/open woodland marker (Table3), it is possible to suggest some broad environmental changes through time, even though we acknowledge that this is an oversimplification of the data, not least because of the anthropogenic influence on archaeologically-retrieved charcoal. Moister conditions than present seem to have existed at Selected bushveld/open woodland and forest/closed woodland indicators present in Border Cave through time. The conclusions in the fifth column are highly simplified, but the vegetation types suggested may represent the important communities in the mosaic of habitats.The woody taxa represented in Border Cave suggest not only that a mosaic of habitats occurred in the area for hundreds of thousands of years, but also that conditions enabled gradual transitions between the habitats. What is clear from this study is that miombo woodland was not represented during the occupations of Border Cave. This inference is significant because it contradicts part of the micromammalian study by[START_REF] Avery | The environment of early modern humans at Border Cave, S.A.: micromammalian evidence[END_REF] that concluded that micromammals in the early part of the Border Cave sequence were proxies for miombo woodland. Nonetheless, there is some overlap between climatic conclusions reached by Avery and ones presented here. The identification of mopane wood in Member 1 RGBS byZwane and Bamford (2021b) supports the Avery interpretation of this woodland type.

	least for part of the occupations in Members 5 BS, 4 WA, 3 BS, and 2 WA, based on the
	presence of Curtisia dentata. In Members 4 WA (168 ± 5-113 ± 5 ka) and 2 BS (60-44 ka)
	the percentage frequencies of forest and bushveld taxa are similar, and in both cases
	evergreen taxa are more common than deciduous ones. More (than 50%) bushveld/open
	woodland than forest/closed woodland trees were represented in all members.
	Member Age (ka) Bushveld/ Open Woodland	Forest/ Closed Woodland	Possible vegetation
			indicator	indicator	type
	6 BS	>227	Pappea capensis		bushveld/
					open woodland
	5 WA	227 ± 11	Pappea capensis		bushveld/
		183 ± 20			open woodland
	5 BS	161 ± 10		Curtisia dentata	forest/
		144 ± 11		Cryptocarya spp.	closed woodland
	4 WA	168 ± 5		Curtisia dentata	forest/
		115 ± 8		Cryptocarya spp.	closed woodland
		113 ± 5
	1 RGBS 74 ± 4	Pappea capensis	Curtisia dentata.	bushveld/
				Podocarpus sp.	open woodland
				Cryptocarya spp.	and forest
	3 WA	64 ± 2	Pappea capensis	Podocarpus sp.	bushveld/
					open woodland and
					forest
	3 BS	72 ± 4		Curtisia dentata	forest
		64 ± 3		Podocarpus sp.
		56 ± 2		Harpephyllum caffrum
	2 WA	60 ± 3		Curtisia dentata	forest
				Cryptocarya spp.
	2 BS.UP 49-44	Pappea capensis	Cryptocarya spp.	bushveld and
					closed woodland
	1 WA	43	Pappea capensis		bushveld/
					open woodland

Table 4 .

 4 Border Cave forest/closed woodland and bushveld/open woodland taxa in Members 6 BS to 1 WA. Celtis sp., Leucosidea sericea, Protea sp. In the Decorana, Afrocarpus/Podocarpus spp. are forest indicators, Cryptocarya spp. is a closed woodland indicator; Celtis sp. is an open woodland indicator and Pappea capensis and Spirotachys africana are bushveld indicators (for further examples, see Table 4; Fig. 7). Acacia sp., and Members 6 BS and 2 BS. Member 6 BS has a strong positive correlation with Olea sp. from open woodland, as well as with bushveld indicators and closed woodland taxa like Cryptocarya spp. These data support our earlier suggestion that a mosaic of habitats probably occurred near Border Cave during the occupation of Member 6 BS as well as during other periods. Thus, the results of the detrended correspondence analysis support the intuitive observation that mosaic vegetation communities had a long-standing existence in the area. Overall the vegetation record at Border Cave appears to have been stable through time. Notwithstanding this, forest and closed woodland patches may occasionally have occurred as part of a mosaic alongside bushveld and open vegetation. A varied vegetation mosaic was also suggested from archaeobotanical research at Sibudu

	Plant habitat	Examples of taxa
	Forest/Closed Woodland	Forest: Afrocarpus/Podocarpus, Curtisia dentata

The oldest member, 6 BS, shows a positive correlation (overlap) with woody taxa from three habitats (bushveld, closed and open woodland) that may have occurred as mosaics near the site. Members 5 WA and 2 WA have a strong positive correlation with open woodland and both have charcoal representing Commiphora sp. (Fig.

7

). Member 3 BS correlates positively with closed and open woodland (Fig.

5

). Member 2 BS includes Tarchonanthus sp., a taxon that fits well with other closed woodland taxa. There is a close correlation between Cryptocarya spp., a closed woodland indicator, and Members 6 BS, 5 WA and 2 BS. There is a strong positive correlation between bushveld-indicator,

  . Here, in MIS 5 and MIS 3, people may have inhabited ecotones to take advantage of resources in both open and forested areas.The relative stability found through time in the vegetation record at Border Cave compares favourably with the climate-modeled vegetation stability through time during both glacial and interglacial cycles in East Africa[START_REF] Sánchez Goñi | Regional impacts of climate change and its relevance to human evolution[END_REF]. Nonetheless, a combination of stable isotopes, geochemical proxies and a pollen record from a marine core taken near the mouth of the Limpopo River(Dupont et al., 2019) demonstrates that vegetation did undergo some changes between glacial and interglacial periods in south east Africa. The pollen study yielded four time-related assemblages implying heathland, mountain forest, shrubland and woodland biomes(Dupont et al., 2019). The results from this research suggest that forests grew in moderate glacial conditions and that open ericaceous vegetation only occurred during extremely cold conditions(Dupont et al., 2019). However,Chevalier et al. (2020) used these data to show, further, that the south-eastern part of southern Africa followed global climatic trends at the time, with differences of only ∼4°C between glacial minima and interglacial maxima. The results from Dupont and colleagues (2019) are only partly applicable to the inland Border Cave scenario. The pollen in the marine core is purely an environmental signal, whereas the cave charcoal represents firewood that people deliberately selected from a range of potential taxa. Nonetheless, the suggestion that ericaceous vegetation only occurred during very cold conditions might explain why Erica sp., a popular kindling in mountainous regions even presently, is uncommon in the cave. Indeed, heathland seems not represented in its sequence. The suggestion byChevalier et al. (2020) that only about 4°C separated glacial and interglacial maxima in south east Africa is also helpful to explain the relative stability observable in the Border Cave vegetation record through time. The other noteworthy observation is that we see no correlation between the timing of vegetation changes at Border

  If such relationships do exist, they will need to be demonstrated using other climate proxies from the site. culture represented by organic artifacts from Border Cave, South Africa. P. Natl. Acad. Sci. USA. 109(33), 13214-13219. , F., Banks, W.E., 2013. Identifying mechanisms behind Middle Paleolithic and Middle Stone Age cultural trajectories. Curr. Anthropol. 54(S8), S371-S387. Daniau, A-L., Sánchez Goñi, M.F.S., 2017. Identifying early modern human ecological niche expansions and associated cultural dynamics in the South African Middle Stone Age. P. Natl. Acad. Sci. USA. 114(30), 7869-7876. Daniau, A.L., Sánchez Goñi, M.F.S., Martinez, P., Urrego, D.H., Bout-Roumazeilles, V., Desprat, S., Marlon, J.R., 2013. Orbital-scale climate forcing of grassland burning in southern Africa. P. Natl. Acad. Sci. USA. 110(13), 5069-5073. Lithic technological and spatial analysis of the final Pleistocene at Border Cave, South Africa. Quaternary Sci. Rev. Under review. den Outer, R.W., van Veenendaal, W.L.H., 1996. Wood anatomy of the Aphanocalyx-Monopetalanthus complex (Caesalpiniodeae) Iawa J. 17(2), 205-223. Dotte-Sarout, E., Carah, X., Byrne, C., 2014. Not just carbon: assessment and prospects for the application of anthracology in Oceania. Archaeol. Ocean. 50(1), 1-22. Drennan, R.D., 2009. Statistics for archaeologists. A Common Sense Approach, 2nd edn. Springer Science, London. Dupont, L.M., 2011. Orbital scale vegetation change in Africa, Quaternary Sci. Rev. 30, 3589-3602. Dupont, L.M., Caley, T., Castañeda, I.S., 2019. Effects of atmospheric CO 2 variability of the past 800 kyr on the biomes of southeast Africa. Clim. Past. 15(3), 1083-1097.

	D	G	H
	P ñ P		D	,
	2022.

Acknowledgements

SJL would like to express her gratitude to Prof. Marion Bamford for botanical advice. The Evolutionary Studies Institute (ESI) provided the necessary instruments. The field research

BS, layer Brown Jim), identified from reference specimen LFA 47 (also, Kromhout, 1977;[START_REF] Noshiro | Systematic wood anatomy of Cornaceae and allies[END_REF]InsideWood, 2004 onwards;[START_REF] Allott | Palaeoenvironments of the Middle Stone Age at Sibudu Cave, KwaZulu-Natal, South Africa: An Analysis of Archaeological Charcoal[END_REF]. a.


MD Yves Roquelaure
email: yvroquelaure@chu-angers.fr

MD Catherine Ha

MSc Natacha Fouquet

MD Alexis Descatha

PhD Annette Leclerc

MD Marcel Goldberg

MD Ellen Imbernon

Attributable risk of carpal tunnel syndrome in the general population: implications for intervention programs

Keywords: burden of disease, carpal tunnel syndrome, population attributable risk, prevention, work, work-related Attributable Risk of Carpal Tunnel Syndrome

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Carpal tunnel syndrome (CTS) represents one of the most significant and costly health problems occurring in the working population world-wide [START_REF]Musculoskeletal Disorders and the Workplace: Low back and Upper Extremity musculoskeletal disorders[END_REF]. Epidemiological studies have identified several combinations of personal and work-related risk factors for CTS [START_REF]Musculoskeletal Disorders and the Workplace: Low back and Upper Extremity musculoskeletal disorders[END_REF][START_REF] Palmer | Carpal tunnel syndrome and its relation to occupation: a systematic review[END_REF]. Most of the work-related risk factors for CTS are more modifiable than individual risk factors, and the implementation of intervention programs in the workplace is expected to reduce the burden of CTS in the population [START_REF]Musculoskeletal Disorders and the Workplace: Low back and Upper Extremity musculoskeletal disorders[END_REF]. Using the results of a large survey of musculoskeletal disorders and their risk factors in the working population of the Pays de la Loire region, we recently calculated that up to 31% of cases in manual workers could theoretically be prevented by lowering the levels of physical work exposure in that population [START_REF] Melchior | Why are manual workers at high risk of upper limb disorders? The role of physical work factors in a random sample of workers in France (the Pays de la Loire study)[END_REF]. The proportion of avoidable work-related musculoskeletal disorders (WR-MSDs) is less in the whole working population [START_REF] Palmer | How common is RSI?[END_REF].

In France, as in many countries, information regarding CTS and its risk factors at the population level is still scanty, although more information is available at the workplace level [START_REF] Roquelaure | Epidemiological Surveillance of Upper Extremity Musculoskeletal Disorders in the Working Population: the French Pays de la Loire Study[END_REF]. The French Institute for Public Health Surveillance (InVS) therefore implemented an epidemiological surveillance system for CTS in the general population of the Maine-et-Loire region in West-Central France in 2002 to assess the risk of CTS according to industry and occupation and the proportion of cases attributable to work. Recently reported (6) results showed a higher incidence rate of CTS in employed than in unemployed persons with highest risks for two occupation categories (lower-grade white-collar workers for women and bluecollar workers for both genders) and four major industries (agriculture and service industries for women, manufacturing for both genders, construction for men). Assuming that other risk factors remain unchanged and that there is a causal relationship between work exposure and CTS, the population attributable fractions of CTS to work (PAF) in high risk industries and occupations should reveal the proportion of CTS cases that might be prevented following reduction of the risk of CTS at the workplace level [START_REF] Rockhill | Use and misuse of population attributable fractions[END_REF]. Such information thus provides an estimation of the theoretically maximum potential impact of the prevention programs of CTS in the workplace [START_REF] Punnett | Work-related musculoskeletal disorders: the epidemiologic evidence and the debate[END_REF]. This would be particularly useful for public policy and prevention programs and for selecting which sectors or occupations require intervention. Our aim in this study was therefore to assess the PAFs of CTS according to the main industry sectors and occupation categories characterized by a high risk of CTS in a French general population.

Methods

Protocol

Population: The population included in the CTS surveillance program comprised residents of the Maine-et-Loire region in the 20-59 age group [194,276 women and 193,802 men].

According to the French National Institute of Statistics and Economic Studies (INSEE) census of 1999, the economic structure of the region was diversified and similar overall to that of most French regions, except Paris. The main sectors were distributed as follows: agriculture (women, 6%; men, 11%), construction (women, 1%; men, 10%), manufacturing (women, 18%; men, 27%) and service industries (women, 75%; men, 52%). The employment rate was 66% for women and 81% for men.

Outcome definition: Subjects who had undergone electrodiagnostic studies (EDS) of the upper-limbs by all five physicians working at the only four electrodiagnostic centers of the Maine-et-Loire region were eligible for the study if they were residents of the defined geographic area. Only cases of CTS without prior history of CTS of the same wrist were included prospectively between 2002 and 2004. All incident cases of CTS were defined by both clinical and electrophysiological criteria using the same standardized protocol, which followed published recommendations [START_REF] Rempel | Consensus criteria for the classification of carpal tunnel syndrome in epidemiological studies[END_REF][START_REF] Jablecki | Practice parameter: Electrodiagnostic studies in carpal tunnel syndrome. Report of the American Association of Electrodiagnostic Medicine[END_REF]. To be included, symptoms had to be classified as classic/probable CTS using the Katz hand diagram [START_REF] Rempel | Consensus criteria for the classification of carpal tunnel syndrome in epidemiological studies[END_REF] and at least two of the following EDS criteria were required [START_REF] Jablecki | Practice parameter: Electrodiagnostic studies in carpal tunnel syndrome. Report of the American Association of Electrodiagnostic Medicine[END_REF]: delay in the distal motor latency of the median nerve, decrease in sensory conduction velocity of the median nerve, decrease in amplitude of the sensory potentials or a relative delay in sensory distal latency of the median nerve compared with the ulnar nerve. See Roquelaure et al [START_REF] Roquelaure | Work Increases the Incidence of Carpal Tunnel Syndrome in the General Population[END_REF] for details.

Inclusion and data collection procedure: Each eligible patient was informed of the study by the physician and signed a consent form after the clinical examination and EDS. Medical history, including prior history of CTS, hand symptoms, and the conclusion regarding the EDS of the median nerve(s) were reported to our laboratory. A self-administered questionnaire was then mailed to each subject. Information was collected on medical and surgical history (obesity defined by body mass index (BMI) >30 kg/m², diabetes mellitus, thyroid disorders, gynaecological history, wrist/hand trauma, prior CTS, and upper limb musculoskeletal disorders) and employment (industry, occupation and description of tasks during the preceding 5 years). See Roquelaure et al [START_REF] Roquelaure | Work Increases the Incidence of Carpal Tunnel Syndrome in the General Population[END_REF] for details.

Coding of occupations. Jobs were coded for Economic activity of the employers (NAF) and occupation (PCS), using the one-digit codes of the French version of the European Community Activities Nomenclature (NAF codes, 4 classes) and the French classification of occupations (PCS codes, 8 classes). The lower-grade white-collar category includes employees of trade and commerce (e.g., cashiers) and personal services (e.g., hairdressers and waitresses), and lower-grade government executive officials and public service workers (e.g., school cleaners, nurses' aides and lower-grade public office workers). The blue-collar category includes material handlers, skilled and unskilled industrial workers (e.g., machine operators and food operators), skilled and unskilled craft workers (e.g., plumbers and bricklayers), and unskilled agricultural workers (e.g., horticulture and vineyards workers).

Analysis

The characteristics of the general population of the M&L region were extracted from the 1999 INSEE census, which was the last available census at the time of the study. Incidence rates were estimated per patient and not per wrist, so that any patient with bilateral CTS was regarded as one case. The date of the EDS study was used to define the date of diagnosis of CTS, because the date of onset of symptoms was imprecise or not available for about 30% of cases.

Age-and gender-specific annual incidence rates were computed with the number of persons suffering from CTS newly diagnosed during the year under consideration as numerator.

Assuming that the general population remained stable, the denominator was an estimate of the average number of person-years during the same period based on the 1999 INSEE census data 11 . The age-adjusted relative risks (RR) of CTS according to industry sectors and occupation categories were computed using the Mantel-Haenszel method with the whole sample of subjects included in the study as reference, whether they were employed at the time of diagnosis or not. The non working subjects included both subjects who had never worked, mainly women, pensioners and all unemployed subjects in the year of diagnosis or the year of the census. Subsequently, the population attributable fraction of risk (PAF [%]) to work in the occupation category (or industry sector) under consideration was computed using the following formula [START_REF] Kleinbaum | A pocket guide to epidemiology[END_REF]:

PAF = Pe (RR-1)/[Pe (RR-1)+1] (equation 1)

The PAF takes into consideration the proportion of subjects involved in the general population (Pe [%]) and represents the proportion of cases of CTS in the whole population for each gender which could be avoided if the occupation category under consideration (or industry sector) did not expose to an excess of risk of CTS [START_REF] Kleinbaum | A pocket guide to epidemiology[END_REF].

Results

A total of 1,168 cases (819 women, 349 men; male:female ratio 1:2.3), corresponding to 1,644 wrists affected by CTS, were included during the 3-year period. Medical and surgical history and employment status were available for the 815 women and 320 men who completed the questionnaire. Mean age was 44.9 (SD 9.4) years in women and 43.3 (SD 9.5) years in men. The population-based annual incidence rates of CTS were 1.4 for 1,000 females and 0.6 for 1,000 males, and increased substantially with age for both genders (P < 0.001).

The prevalence of obesity (16 %) and diabetes mellitus (4%) were similar between men and women. The prevalence of thyroid disorders was high only in women (13%). Furthermore, 20% of men and 30% of women had obesity, diabetes mellitus, or thyroid disorders, without significant differences according to industry or occupational categories.

About 79% of women and 89% of men suffering from CTS were working at the time of diagnosis and 90% of women and 97% of men had worked in the 5-year period before the diagnosis. The mean length of employment in the last job was 7 years, without difference between men and women. Most men (71%) and women (62%) had the same job during the last five years. Few men had occupied two (13%) or more (8%) during this period, the corresponding values for women being 16% and 10%. In most of these cases, the changes of occupation in the period preceding the diagnosis did not modify the industry sector and occupation category. The excess risk of CTS was statistically significant for two main occupational categories: blue-collar workers (for both genders) and lower-grade services, sales and clerical white-collar workers (for women) (table 1). Among female blue-collar workers, the excess risk of CTS concerned mainly skilled blue-collar workers (RR = 3. In terms of industry sectors, work in agriculture (for women), manufacturing (for both genders), construction (for men) and service industries (for women) was associated with an excess risk of CTS (table 2). Among women, this latter sector mainly involved blue-collar and lower-grade white-collar workers (84%); among men, service industries involved blue-collar workers (49%) and also a relatively large percentage (29%) of qualified white-collar workers and professionals.

The PAF of CTS for male blue-collar workers reached 50% ( The PAF for women was higher for the service industries sector (16%), which is the largest industry sector in the region, than for the manufacturing (10%) or agriculture (5%) sectors.

For men, the PAF was relatively high for two sectors: construction (13%) and manufacturing (17%) (table 2).

Discussion

The strength of this study is the inclusion of incident cases of CTS in the general population reported by a sentinel surveillance network of physicians covering almost all the inhabitants of the region, irrespective of their employment status. The organization, efficacy and representativeness of the CTS surveillance network are discussed elsewhere [START_REF] Roquelaure | Work Increases the Incidence of Carpal Tunnel Syndrome in the General Population[END_REF].

Schematically, the network suffered from a lack of exhaustiveness because of several factors.

For example, some people living in the Maine-et-Loire area might have undergone electrodiagnostic studies in an area not covered by the network. A few eligible subjects refused to sign the consent form for various reasons, mainly lack of time. The participation of the sentinel physicians over the 3-year period was uneven since one physician notified us of very few cases and another left the network in 2003 for personal reason. In addition, some eligible cases were not included by physicians because of lack of time. However, no significant differences regarding age, gender and last occupation were observed between the patients included in our study and those treated surgically in the same area [START_REF] Roquelaure | Work Increases the Incidence of Carpal Tunnel Syndrome in the General Population[END_REF]. This indicates that there was no systematic inclusion bias of CTS cases in the surveillance program reported here according to age, gender, employment status and last occupation. Consequently, even if the incidence of CTS was underestimated, estimates of RRs of CTS according to industry sector and occupation category should be considered as unbiased, and the estimate of PAF of CTS as accurate. See reference (6) for details.

Work exposure was appraised at the industry and the job title level without in-plant job analysis, and therefore no precise assessment of the actual exposure to biomechanical and psychosocial risk factors of CTS was performed. The collection and coding of occupational and economic activity information relied on detailed information on the jobs and tasks using a methodology comparable to that of the INSEE census. Most patients were professionally active during the five years period before the diagnosis and at the time of the diagnosis.

Length of service was high and most workers had remained in the same occupation during the previous five years. Moreover, when occupational changes occurred, very few shifts from one occupational category (or industry sector) to another one were observed. We checked that the results were similar using three slightly different definitions for occupation: occupation at the time of the surgery, last occupation in the five years before surgery, and longest occupation in the 5-year period. This is consistent with the fact that the latest occupation was also the longest one for most patients. CTS cases in 2002-2004 were compared to the 1999 census and some changes could have occurred in the population between 1999 and 2004. Nevertheless, the length of service in the last job was high and most workers did not shift from one occupational category (or industry sector) to another one between 1999 and 2004.

The reference group was enlarged to the whole sample of subjects. Consequently, the ageadjusted RRs and the PAFs of CTS in specific industries and occupation categories were underestimated because the comparison group included a substantial proportion of industrial and occupational groups at high risk of CTS [START_REF] Rossignol | Carpal tunnel syndrome: what is attributable to work? The Montreal Study[END_REF]. Analyses were controlled for age and gender, but not for other potential confounding factors related to occupational and nonoccupational risk factors of CTS (1) since since only limited information on the medical history was available. Both diabetes mellitus and obesity were twice more frequent among cases than in the general population of the region, which agrees with surveys of CTS in the general population [START_REF]Musculoskeletal Disorders and the Workplace: Low back and Upper Extremity musculoskeletal disorders[END_REF]. Nevertheless, the prevalence of obesity and diabetes among cases did not differ drastically between industries and occupations [START_REF] Roquelaure | Work Increases the Incidence of Carpal Tunnel Syndrome in the General Population[END_REF]. The data available in the general population of this area did not allow more precise analysis of the relative role of obesity and occupation on the risk of CTS. No information was available on non-occupational physical activities, such as housework, leisure and sports activities. Some of them, such as housework among women, may be more prevalent in the lower income categories, and therefore be a confounding factor for the association between CTS and blue-collar occupations. However, except for sex and age, which were taken into account in the analyses, the non-occupational causes of CTS seem unlikely to play a major role as confounding factors [START_REF]Musculoskeletal Disorders and the Workplace: Low back and Upper Extremity musculoskeletal disorders[END_REF][START_REF] Palmer | Carpal tunnel syndrome and its relation to occupation: a systematic review[END_REF][START_REF] Roquelaure | Occupational and personal risk factors for carpal tunnel syndrome in industrial Workers[END_REF].

PAF data reported in the Maine-et-Loire region should be treated with caution since the values could be different in populations with different socio-economic characteristics, depending on the proportions (Pe [%] ) of blue-and white-collar workers and the sizes of the industry sectors, even if the relative risks of CTS were similar [START_REF] Kleinbaum | A pocket guide to epidemiology[END_REF]. Nevertheless, the socioeconomic structure of the Maine-et-Loire region is comparable to those of most French regions, except Paris (1999 INSEE census). At the workplace level, the attributable risk of CTS could be different, since wide variations in exposure to work constraints may exist between companies in the same industry sector [START_REF] Roquelaure | Epidemiological Surveillance of Upper Extremity Musculoskeletal Disorders in the Working Population: the French Pays de la Loire Study[END_REF].

The computation of the potential impact of intervention strategies assumed several hypotheses, namely a causal relationship between the occurrence of CTS and work exposure [START_REF]Musculoskeletal Disorders and the Workplace: Low back and Upper Extremity musculoskeletal disorders[END_REF][START_REF] Palmer | Carpal tunnel syndrome and its relation to occupation: a systematic review[END_REF][START_REF] Kleinbaum | A pocket guide to epidemiology[END_REF][START_REF] Viikari-Juntura | Biomechanical risk factors for carpal tunnel syndrome[END_REF] and a substantial impact of prevention intervention. Although multidimensional ergonomic workplace intervention programs to prevent CTS appear to be effective (1), only limited evidence of their efficacy is available [START_REF] Verhagen | Ergonomic and physiotherapeutic interventions for treating work-related complaints of the arm, neck or shoulders in adults. A Cochrane systematic review[END_REF]. Moreover, insufficient information is available on the temporal and quantitative relationships between the decrease in exposure to repetitive and forceful constraints following large intervention studies and the decrease in the incidence of CTS [START_REF]Musculoskeletal Disorders and the Workplace: Low back and Upper Extremity musculoskeletal disorders[END_REF][START_REF] Punnett | Work-related musculoskeletal disorders: the epidemiologic evidence and the debate[END_REF][START_REF] Lotters | Are changes in mechanical exposure and musculoskeletal health good performance indicators for primary interventions?[END_REF].

Our findings on the industry sectors at high risk of CTS in the region are in line with the epidemiological literature [START_REF]Musculoskeletal Disorders and the Workplace: Low back and Upper Extremity musculoskeletal disorders[END_REF][START_REF] Leclerc | A longitudinal study on upper limb disorders in repetitive work[END_REF]. Work in the service industries was associated with a higher risk of CTS in women and a lower risk in men. This might be explained by the gender division of work in this sector, with most of the women in the two lowest occupational categories (at high risk of CTS), whereas many men belonged to high-grade occupation categories.

The excess risk of CTS was only statistically significant for lower grade occupation categories: blue-collar workers for men and women and lower-grade services, sales and clerical white-collar workers for women. The estimates of RR for blue-collar workers were in the same order of magnitude as those calculated in the only comparable study (the Montreal study) comparing the incidence of surgical release of the median nerve between manual and non-manual workers in 1994-5 [START_REF] Rossignol | Carpal tunnel syndrome: what is attributable to work? The Montreal Study[END_REF].

Despite its value from the public health viewpoint, very little has been published in the literature assessing the PAF of CTS to work [START_REF] Mc Farlane | Identification and prevention of work-related carpal tunnel syndrome[END_REF]. This indicator would be valuable for public policy, because it describes the proportion of cases occurring in the population which could theoretically be avoided if the industries or occupations considered did not result in an excess of risk of CTS. Our study shows that half of male and a fifth of female cases of CTS could theoretically be avoided in the general population if such interventions were implemented for blue-collar workers. For female lower-grade white-collar workers, almost a quarter of cases could be avoided.

For women, the attributable proportion of CTS cases of lower-grade white-collar workers was greater than that of blue-collar workers, despite a lower risk of CTS. Similarly, the impact of the service industries on the burden of female CTS was greater than that of the manufacturing sector. This confirms that intervention programs must be targeted not only in terms of the level of risk but also of the number of workers involved. Our results thus suggest focusing prevention on blue-collar occupations for men, and on blue-collar and overall lower-grade white-collar occupations for women. More precisely, intervention programs should focus on the blue-collar workers of the manufacturing (for both genders) and construction sectors (for men), and on the female lower-grade white-collar workers of the service industries (e.g., cashiers, hairdressers, nurses' aides).

In France, as in several countries, WR-MSDs are a national priority and many preventive intervention programs have been implemented at the company level. Although our study did not attempt to evaluate intervention programs, it suggests that the maximum theoretical impact of programs for prevention of CTS in the whole population might be between 5 and 50% if totally effective intervention programs were to be implemented in specific occupational categories or industry sectors. However, reducing the risk of CTS in manual workers performing repetitive or forceful movements to the mean level of the general population is probably unrealistic, and more realistic objectives should probably be targeted [START_REF] Melchior | Why are manual workers at high risk of upper limb disorders? The role of physical work factors in a random sample of workers in France (the Pays de la Loire study)[END_REF][START_REF] Palmer | How common is RSI?[END_REF].

  2 [2.7-3.8]) and unskilled agricultural workers (RR= 4.2 [3.2-5.7]). Among male blue-collar workers, the excess risk of CTS involve skilled (RR = 1.8 [1.5-2.3]) and unskilled (RR = 3.5 [2.7-4.5]) blue-collar workers and unskilled agricultural workers (RR= 3.5 [2.2-5.5].

  7] -Note. a Persons working during the 5-year period before the diagnosis; ; Pe (%): percentage in the general population of the Maine-et-Loire area; N (%): number and distribution of CTS incident cases by industry sectors; CI 95 % : 95% confidence interval; b Unspecified sector: 1 for women (0.1%) and 3 for men (1.0%); c Non-working persons haven't Nace code (80 women and 10 men); d range computed using the lower and upper limits of the confidence interval of the RR of CTS in equation (1).

7- 8 .

 8 Pensioners and other non-working persons 19.Note. a Persons working during the 5-year period before the diagnosis; Pe (%): percentage in the general population of the Maine-et-Loire area; N (%): number and distribution of CTS incident cases by occupation category; CI 95 % : 95% confidence interval; b Unspecified categories: 6 for women (0.7%) and 4 for men (1.3%); d range computed using the lower and upper limits of the confidence interval of the RR of CTS in equation[START_REF]Musculoskeletal Disorders and the Workplace: Low back and Upper Extremity musculoskeletal disorders[END_REF].

table 1

 1

), suggesting that more than half of CTS cases diagnosed in the population could be avoided if the excess risk of CTS in blue-collar workers could be eliminated. Considering the subcategories of blue-collar workers in men at high risk of CTS, PAFs were 15.7

[8.8-22.1]

in skilled workers, 20.9

[15.3- 26.1]

) in unskilled workers and 6.9

[3.6-10.2

] in agricultural workers. The PAF was lower for female blue-collar workers (19%), but reached a higher value (24%) for female lower-grade services, sales and clerical white-collar workers. Considering the two subcategories of bluecollar workers at high risk of CTS in women, the PAFs were 13.2 [10.2-16.0] in unskilled workers and 5.0

[3.6-6.7

] in agricultural workers.

TABLE 1 -Relative risks and attributable risk fractions in population of CTS according to occupation categories

 1

	OCCUPATION CATEGORY (PCS CODE) a,b	Pe (%) N (%)	RR [CI 95% ] PAF (%)[CI 95% ] d
	WOMEN
	1. Farmers	1.9	19 (2.3)	1.0 [0.6-1.5]	-
	2. Craftswomen, saleswomen and managers	2.3	10 (1.2)	0.5 [0.3-0.9]	-
	3. Professionals	4.3	23 (2.8)	0.7 [0.5-1.0]	-
	4. Technicians, associate professionals	14.2	64 (7.8)	0.6 [0.4-0.7]	-
	5. Lower grade white-collar workers	30.5 384 (46.8) 2.0 [1.8-2.3]	23.8 [18.7-28.5]
	6. Blue-collar workers	12.4 234 (28.5) 2.9 [2.5-3.4]	18.9 [15.3-22.4]
	7-8. Pensioners and other non-working persons 34.4	80 (9.8)	0.2 [0.2-0.3]	-
	MEN
	1. Farmers	4.8	14 (4.4)	1.2 [0.7-2.1]	-
	2. Craftsmen, salesmen and managers	6.3	13 (4.1)	0.6 [0.3-1.0]	-
	3. Professionals	9.1	17 (5.3)	0.7 [0.4-1.2]	-
	4. Technicians, associate professionals	16.7	29 (9.2)	0.5 [0.4-0.8]	-
	5. Lower grade white-collar workers	7.8	24 (7.6)	1.3 [0.8-2.0]	-
	6. Blue-collar workers	35.9 210 (66.7) 3.8 [3.0-4.7]	49.7 [41.3-56.8]
	7-8. Pensioners and other non-working persons 19.4	10 (3.1)	0.2 [0.1-0.4]	-
	Note. a Persons working during the 5-year period before the diagnosis; Pe (%): percentage in the general
	population of the Maine-et-Loire area; N (%): number and distribution of CTS incident cases by occupation
	category; CI 95 % : 95% confidence interval; b Unspecified categories: 6 for women (0.7%) and 4 for men (1.3%); d
	range computed using the lower and upper limits of the confidence interval of the RR of CTS in equation (1).

TABLE 2 -Relative risks and attributable risk fractions in population of CTS according to industry sectors

 2

	INDUSTRY SECTOR (NACE code) a,b,c Pe (%)	N (%)	RR [CI 95% ]	PAF (%)[CI 95% ] d
	WOMEN
	1. Agriculture	4.0	80 (9.8)	2.4 [1.9-3.0]	5.2 [3.1-7.2]
	2. Construction	0.7	6 (0.7)	2.3 [1.0-5.2]	-
	3. Manufacturing	11.5	166 (20.4)	2.0 [1.7-2.4]	10.3 [7.1-13.4]
	4. Service industries	49.5	477 (58.5)	1.4 [1.2-1.6]	16.0 [8.9-22.0]
	MEN
	1. Agriculture	8.7	34 (10.6)	1.3 [0.9-1.9]	-
	2. Construction	8.2	63 (19.7)	2.9 [2.2-3.8]	13.3 [8.4-18.0]
	3. Manufacturing	22.0	115 (35.9)	1.9 [1.5-2.4]	17.0 [10.0-23.5]
	4. Service industries	41.8	93 (29.1)	0.5 [0.4-0.

TABLE 1 -Relative risks and attributable risk fractions in population of CTS according to occupation categories OCCUPATION CATEGORY (PCS CODE) a,b

 1

	Pe (%) N (%)	RR [CI 95% ]	PAF (%)[CI 95% ] d

Acknowledgments

The authors thank Drs Marie-Christine Pelier-Cady, Pierre Lonchampt, Guillaume Nicolas, Guy Raimbeau, Anne Vieillart, and Jacques Klein for their participation in the Sentinel Network.

This research study was supported by the French Institute for Public Health Surveillance (Institut de Veille Sanitaire) without any corporate sponsor.