Marc Testé
email: marc.teste@lgp.cnrs.fr

Aline Garnier

Nicole Limondin-Lozouet

Enecon Oxlaj

Cyril Castanet

Louise Purdue

Eva Lemonnier

Lydie Dussol

Philippe Nondédéo

The phytoliths of Naachtun (Petén, Guatemala): Development of a modern reference for the characterization of plant communities in the Maya Tropical Lowlands

Keywords: Phytoliths assemblages, Naachtun, Maya Lowland, Petén forests, Sival wetland, phytolith indexes

come   L'archive ouverte pluridisciplinaire

Introduction

Today, while more and more studies are focusing on the systemic collapse of our modern civilization [START_REF] Meadows | The limits to growth: the 30-year update[END_REF]Erhlich and Ehrlich, 2013;[START_REF] Servigne | Comment tout peut s'effondrer: petit manuel de collapsologie à l'usage des générations présentes[END_REF], some are interested in ancient societies that have disappeared as a way of addressing modern social or environmental crises [START_REF] Tainter | The collapse of complex societies, New studies in archaeology[END_REF][START_REF] Diamond | Collapse: how societies choose to fail or succeed[END_REF]. The Maya societies of the Yucatán Lowland, well known for their huge architectural remains, are a good example. Studies testify to two major collapse events that occurred in the 2nd century (pre-classical collapse) and the 10th century (classical collapse) CE. While these collapse events are sometimes presented as the result of overly intensive environmental exploitation [START_REF] Abrams | The causes and consequences of deforestation among the prehistoric Maya[END_REF][START_REF] Hansen | Climatic and environmental variability in the rise of Maya civilization: A preliminary perspective from northern Peten[END_REF][START_REF] Lentz | Tikal timbers and temples: ancient Maya agroforestry and the end of time[END_REF][START_REF] Turner | Classic Period collapse of the Central Maya Lowlands: Insights about human-environment relationships for sustainability[END_REF], other authors question this hypothesis by citing the Maya's considered and sustainable management of forest and plant resources [START_REF] Fedick | The Maya Forest: Destroyed or cultivated by the ancient Maya?[END_REF][START_REF] Mcneil | Deforestation, agroforestry, and sustainable land management practices among the Classic period Maya[END_REF][START_REF] Lentz | Agroforestry and Agricultural Practices of the Ancient Maya at Tikal[END_REF][START_REF] Thompson | Connecting Contemporary Ecology and Ethnobotany to Ancient Plant Use Practices of the Maya at Tikal [WWW Document[END_REF].

Located in the extreme north of Guatemala (Fig. 1), four kilometers from the border with Campeche (Mexico), the archaeological site of Naachtun was first surveyed in 1922, by SG.

Morley, and 10 years later by CL. Lundell [START_REF] Lundell | Exploring Nohoxna: A Lost City of the First Maya Empire[END_REF]. Since 2000, Naachtun has been the site of archaeological and palaeoenvironmental studies [START_REF] Reese-Taylor | Proyecto Arqueológico Naachtun: Resultados preliminares de la primera temporada de campo 2004[END_REF][START_REF] Nondédéo | Prosperidad económica en Naachtun: resultados de las dos primeras temporadas de investigación[END_REF]2013) and is also one of the location of the Lidar project, which aims to map the geographical and archaeological characteristics of Maya sites in northern Guatemala [START_REF] Canuto | Ancient lowland Maya complexity as revealed by airborne laser scanning of northern Guatemala[END_REF]. Given its well-preserved monumental remains, the site holds a certain archaeological interest. Indeed, the first archaeological evidence of occupation dates to the 5th century BCE, although the development of the city only began in earnest in the 1st century CE; that is, at around the time of the pre-classical period Maya collapse [START_REF] Hansen | Climatic and environmental variability in the rise of Maya civilization: A preliminary perspective from northern Peten[END_REF]. Located halfway between Tikal and Calakmul, the two great Maya kingdoms of Petén during the classical period, Naachtun played the role of a regional political center and may have counted several thousand inhabitants. The site was eventually abandoned around 950 CE, relatively late period in comparison to the other capitals of the Petén region [START_REF] Nondédéo | Crisis multiples en Naachtún: aprovechadas, superadas e irreversibles[END_REF].

In order to understand the link between past cultural and environmental changes, this study uses both the archaeological context and geomorphological/palaeoenvironmental context. Naachtun is located on a large hilly escarp and is bordered to the north and south by two depressions of the karstic polje type [START_REF] Castanet | Dynamiques croisées des milieux et des sociétés dans les basses terres tropicales mayas : hydrosystème et agrosystème à Naachtun (Guatemala)[END_REF], called bajos, with dispersed perennial wetlands, locally called Sival (Fig. 2). During the wet season, these Sival are fed by water and result in considerable palustrine-alluvial sedimentation. These sedimentary sequences located in the northern bajo cover the periods of occupation of the Naachtun site and create a good trap for the bioindicators (phytoliths, mollusks, etc.) used for palaeoenvironmental reconstructions.

In the Maya Lowlands, most bio-proxies used in palaeoenvironmental studies to reconstruct past vegetation dynamics are either pollen [START_REF] Islebe | A Holocene vegetation history from lowland Guatemala[END_REF][START_REF] Leyden | Pollen evidence for climatic variability and cultural disturbance in the maya lowlands[END_REF][START_REF] Carozza | Landuse and soil degradation in the southern Maya lowlands, from Pre-Classic to Post-Classic times: The case of La Joyanca (Petén, Guatemala)[END_REF][START_REF] Wahl | Holocene vegetation change in the northern Peten and its implications for Maya Prehistory[END_REF]2013) or charcoal (Lentz and Hockabay, 2009;Lentz, 2015;[START_REF] Dussol | Ancient Maya sylviculture of breadnut (Brosimum alicastrum Sw.) and sapodilla (Manilkara zapota (L.) P. Royen) at Naachtun (Guatemala): A reconstruction based on charcoal analysis[END_REF].

However, in Naachtun's bajo records, pollen are poorly preserved, while the identifiable charcoals are too diluted to allow for systematic study. This poor conservation led us to look for new bioindicators of past vegetation changes. Due to their siliceous structure, phytoliths are resistant to oxidation and are well preserved in such tropical environment deposits [START_REF] Alexandre | Phytoliths: indicators of grassland dynamics during the late Holocene in intertropical Africa[END_REF][START_REF] Madella | Taphonomy and phytoliths: A user manual[END_REF]Piperno, 2006;[START_REF] Watling | Differentiation of neotropical ecosystems by modern soil phytolith assemblages and its implications for palaeoenvironmental and archaeological reconstructions II: Southwestern Amazonian forests[END_REF]. They also allow good monitoring of herbaceous environments thanks to the morphotype diversity of Cyperaceae and Poaceae [START_REF] Twiss | Morphological Classification of Grass Phytoliths1[END_REF][START_REF] Fredlund | Modern Phytolith Assemblages from the North American Great Plains[END_REF][START_REF] Lu | Phytoliths of common grasses in the coastal environments of southeastern USA[END_REF]Stromberg, 2004, Iriarte andPaz, 2009;[START_REF] Novello | Phytolith signal of aquatic plants and soils in Chad, Central Africa[END_REF]. Moreover, unlike pollen, phytoliths are a good local bioindicator of plant formations [START_REF] Madella | Taphonomy and phytoliths: A user manual[END_REF]Piperno, 2006). However, in the Maya zone, research involving phytoliths is scarce and has been conducted using only a few particular morphotypes [START_REF] Beach | A review of human and natural changes in Maya Lowland wetlands over the Holocene[END_REF], or in specific archaeological contexts (Bozart and Guderjan, 2004;[START_REF] Abramiuk | Linking Past and Present: A preliminary paleoethnobotanical study of Maya nutritional and medicinal plant use and sustainable cultivation in the Southern Maya Mountains[END_REF].

Given the lack of phytolith studies in this forest region, it is difficult to interpret fossil assemblages in the sedimentary archives. The main problem in forest environments is that phytoliths do not allow for taxonomic discrimination between woody dicotyledons [START_REF] Alexandre | Phytoliths: indicators of grassland dynamics during the late Holocene in intertropical Africa[END_REF]Piperno, 2006;[START_REF] Mercader | Phytoliths in woody plants from the Miombo woodlands of Mozambique[END_REF][START_REF] Collura | Wood and bark phytoliths of West African woody plants[END_REF]. However, in similar environments of tropical lowland forests, like the Amazon rainforest, recent studies have pointed to the possibility of characterizing the different forest ecosystems by studying phytolith assemblages [START_REF] Dickau | Differentiation of neotropical ecosystems by modern soil phytolith assemblages and its implications for palaeoenvironmental and archaeological reconstructions[END_REF][START_REF] Watling | Differentiation of neotropical ecosystems by modern soil phytolith assemblages and its implications for palaeoenvironmental and archaeological reconstructions II: Southwestern Amazonian forests[END_REF].

The aim of this study is, therefore, to assess the potential of phytoliths in the Maya Lowlands to serve as a good proxy of plant formations. To achieve this purpose, a botanical study has been carried out on 43 ecological quadrats located along four transects crossing the different ecosystems of the Naachtun site. For each quadrat, surface soils were sampled and phytolith assemblages analyzed using the general counting and index approaches. The link between phytolith assemblages and plant communities was tested using a distribution diagram, and also a statistical study using a component analysis. In this paper, we will compare the different phytolith indexes and propose a new index to better establish the landscape characteristics of these communities.

Study Area

Climate and geology

The department of Petén is located in the southern part of the Petén tropical forest covering the central lowlands of the Yucatán peninsula, also referred as the Maya Lowlands (Fig. 1). The vegetation of Petén is mainly subject to two control factors: precipitations and regional geomorphology [START_REF] Sánchez-Sánchez | Tropical forest communities in southeastern Mexico[END_REF]Carrilo-Bastos et al., 2012). Indeed, seasonal latitudinal migrations of the Inter-Tropical Convergence Zone (ITCZ) and the North Atlantic High cause considerable seasonality of precipitation [START_REF] Hastenrath | Variations in Low-Latitude Circulation and Extreme Climatic Events in the Tropical Americas[END_REF][START_REF] Hastenrath | Interannual Variability and Annual Cycle: Mechanisms of Circulation and Climate in the Tropical Atlantic Sector[END_REF][START_REF] Brenner | Chapter 6 -Abrupt Climate Change and Pre-Columbian Cultural Collapse[END_REF][START_REF] Hodell | Climate change on the Yucatan Peninsula during the Little Ice Age[END_REF][START_REF] Carrillo-Bastos | Geospatial analysis of pollen records from the Yucatán peninsula, Mexico[END_REF]. Thus, most of the rainfall, between 1,000 and 1,500 mm, is concentrated in the period from May to December, while the period from January to April corresponds to a dry season. Due to the intertropical position of the peninsula, temperatures remain relatively stable throughout the year [START_REF] Wilson | Physical geography of the Yucatan Peninsula. Yucatan: A world apart[END_REF]. These umbrothermal conditions correspond to an Am-type climate in the Köppen classification [START_REF] Pennington | Árboles tropicales de México. Manual para la identificación de las principales especies[END_REF]).

The regional geomorphology of Petén is a vast Meso-Cenozoic carbonate platform, composed mainly of limestone, at low altitude (250-300 m). The fractures and heterogeneities of the limestone bedrock have produced karstified landscapes resulting in hills alternating with depressions (bajos) [START_REF] Dunning | Arising from the Bajos: The Evolution of a Neotropical Landscape and the Rise of Maya Civilization[END_REF][START_REF] Beach | Human and natural impacts on fluvial and karst depressions of the Maya Lowlands[END_REF][START_REF] Beach | A review of human and natural changes in Maya Lowland wetlands over the Holocene[END_REF]. Consequently, differences in hydrology and soil composition are also observed, with thin layers of well-drained rendosol on hill and slope areas, and seasonally waterlogged vertisol-histosol in bajo areas [START_REF] Beach | Human and natural impacts on fluvial and karst depressions of the Maya Lowlands[END_REF].

The plant formations of Petén

The Petén forest was first described in the 1930s by [START_REF] Lundell | Plants probably utilized by the old empire Maya of Petén and adjacent lowlands[END_REF] and was defined as a semi-sempervirent tropical forest. However, this ecological classification does not reflect the true diversity of forest ecosystems found in the different geomorphological contexts of Petén. The hill zones are covered by high semi-evergreen forests (30-40 m) with calcareous plant associations. The wide trees, characteristic of these forests, belong mostly to the Burseraceae, Fabaceae, Meliaceae, Moraceae, Sapindaceae, and Sapotaceae. The relatively sparse undergrowth is occupied by Arecaceae and Piperaceae shrubs, and a small number of grassy plants. The bajo areas are covered by a low forest (5-8 m), where plant associations are adapted to clayey soils and the seasonal submersions and drying periods. These are mainly composed of species belonging to the Anacardiaceae, Euphorbiaceae, Fabaceae and Myrtaceae families. The bajo forest undergrowth is relatively bare, with very few grasses. In addition to these two main forest ecosystems, it is possible to find other vegetation types, such as palm forests, pine forests, or humid or dry savannahs, adapted to local geomorphological conditions [START_REF] Lundell | Plants probably utilized by the old empire Maya of Petén and adjacent lowlands[END_REF]Martínez and Galindo-Leal, 2002;Schulze and Whitacre, 1999). Currently, the Petén forests are less populated than during the Maya period [START_REF] Canuto | Ancient lowland Maya complexity as revealed by airborne laser scanning of northern Guatemala[END_REF].

Methodology

Vegetation study and soil sampling

The vegetation study was conducted during two fieldwork sessions at the end of the dry season in March 2016 and April 2017. We have conducted ecological transects crossing all altitude and humidity domains. Thus, we defined three north-south oriented transects in the north bajo area (T1, T2, and T3), and one north-south/west oriented transect (T4), over distances of about one kilometer. These transects therefore covered different plant formations of forests and herbaceous areas from hills and bajo (Fig. 2). Along these transects, we identified areas where plant communities were changing. Depending on the extent of a plant community, one to two blocks, each of about 100m², have been positioned in the middle of it. On each quadrat, we recorded the plant species presences based on local common names and annotated their relative quantity.

Vegetation cover values were estimated from colorimetric processing (light rate [light-white pixels] relative to vegetation coverage rate [dark pixels]) of forest cover photographs taken vertically and to up. Finally, for the phytolith analysis, only a few grams of the surface portion of the A1 horizon (the A0 litter having been removed from the sample) were taken from several locations in each of the quadrat. All samples were mixed to create a single sample of approximately 100 g by quadrat. It allowed us to prevent our sampling producing ultra-local biases in phytolith assemblages.

The ecological survey was carried out with the help of a local forester able to identify the plants by their vernacular names in Spanish and/or Mayan. The vernacular names were then translated into scientific names using the available literature and databases [START_REF] Lundell | Plants probably utilized by the old empire Maya of Petén and adjacent lowlands[END_REF][START_REF] Standley | Flora of Guatemala[END_REF]Schulze and Whitacre, 1999;Martínez and Galindo-Leal, 2002;[START_REF] Atran | Plants of the Petén Itza' Maya: Plantas de los maya itza' del Petén, Memoirs[END_REF], while some plant specimens were compared with taxonomic types from the Paris Herbarium in France's National Museum of Natural History (MNHN). However, the local nomenclature of Naachtun plants contains many synonymies (one local name = different taxa) or polynomials (several local names = one taxon). To resolve this issue, we chose to apply taxonomic corrections, such as the following:

-Multiplication of nomen: zakate is used to designate both Kyllinga pumila, a Cyperaceae, and Olyra latifolia, a Poaceae. In these cases, the vernacular name, nomen, was used several times, to allow for better taxonomic and ecological representativeness.

-Construction of species complex: Manilkara chicle, Pouteria glomerata, Pouteria reticulata, Sideroxylon tepicense, trees belonging to the Sapotaceae family, are all named zapote or zapotillo. In such cases, we decided to group all these scientific names under the nomen zapote.

Phytoliths do not allow for differentiation between woody dicotyledon species. We, therefore, chose to create species complexes for trees (62 nomens associated with woody dicotyledons). Phytoliths are, however, a good tool for characterizing monocotyledon families, such as Arecaceae, Cyperaceae, Commelinaceae, Musaceae, and Poaceae (Piperno, 2006;[START_REF] Honaine | Phytolith analysis of Cyperaceae from the Pampean region, Argentina[END_REF][START_REF] Eichhorn | Seed phytoliths in West African Commelinaceae and their potential for palaeoecological studies[END_REF][START_REF] Novello | Phytolith signal of aquatic plants and soils in Chad, Central Africa[END_REF][START_REF] Chen | Phytolith variability in Zingiberales: A tool for the reconstruction of past tropical vegetation[END_REF]. With some families, it is sometimes possible to determine the genus or species. Thus, for herbaceous plants, we multiplied the nomens to allow for better ecological monitoring using phytoliths (18 nomens). Finally, from the 157 initial occurrences, 75 nomens were assigned to a genus and five nomens to a family (See Table 3 in appendix). It should be noted that these sampling and identification methods were designed to be used primarily on ecological rather than taxonomic assemblages.

Plant associations were studied by quadrat using a statistical study of nomen occurrences.

Each nomen class selected was classified for each of the quadrats based on the following criteria: Absent (0 occurrences), Present (1 to 8 occurrences) or Abundant (> 8 occurrences) (Table 3).

These occurrence data (coded 0, 1 and 2 respectively) were studied using a hierarchical bottom-up classification coupled with a factor analysis of the correspondences. This statistical methodology aimed to verify the representativeness of the assemblages across the site and compare them with the literature [START_REF] Lundell | Plants probably utilized by the old empire Maya of Petén and adjacent lowlands[END_REF]Schulze and Whitacre, 1999;Martínez and Galindo-Leal, 2002).

Preparation and counting of phytolithes

The procedure for phytolith extraction was adapted from Piperno (2006). For approximately 20 g of soil: (1) Organic Matter was destroyed using hydrogen peroxide (H 2 O 2 ), (2) clays were deflocculated using sodium hexametaphosphate (SHMP; 40 g/L), (3) sand and gravel were removed by sieving at 250 µm, (4) clays were eliminated by draining, and (5) amorphous siliceous matter was concentrated and extracted by densimetric sorting using sodium polytungstate diluted to a density of 2.30-2.35.

The dried residue was mounted on microscope slides in immersion oil to allow rotation and 3-D analysis. Observations, identifications, and counts were performed under a microscope at magnifications between x450 and x630. As counting methods influence the ecological interpretation of phytolith assemblages, we followed recommendations in counting at least 200 diagnostic phytolith morphotypes for each sample (Stomberg, 2009;Zurro, 2017). In addition to these diagnostic phytoliths, we also counted non-diagnostic phytolith morphotypes, sponge spicules, and diatoms. The results are presented in a diagram of the relative abundances of diagnostic morphotypes. The diagram also includes the relative abundances of non-diagnostic shapes and bioindicators, calculated as the total sum of all particles counted.

Classification of phytolithes

Although phytolith assemblages in the forests of Petén have not yet been studied, other forests in intertropical zones have been the subject of studies, such as those from Amazonia [START_REF] Piperno | Phytolith analysis: an archaeological and geological perspective[END_REF][START_REF] Dickau | Differentiation of neotropical ecosystems by modern soil phytolith assemblages and its implications for palaeoenvironmental and archaeological reconstructions[END_REF][START_REF] Watling | Differentiation of neotropical ecosystems by modern soil phytolith assemblages and its implications for palaeoenvironmental and archaeological reconstructions II: Southwestern Amazonian forests[END_REF], Africa [START_REF] Alexandre | Phytoliths: indicators of grassland dynamics during the late Holocene in intertropical Africa[END_REF][START_REF] Barboni | Phytoliths as paleoenvironmental indicators, West Side Middle Awash Valley, Ethiopia[END_REF][START_REF] Runge | The opal phytolith inventory of soils in central Africa -quantities, shapes, classification, and spectra[END_REF][START_REF] Aleman | Reconstructing savanna tree cover from pollen, phytoliths and stable carbon isotopes[END_REF], Indonesia [START_REF] Chabot | Phytolith analysis from the archaeological site of Kota Cina (North Sumatra, Indonesia)[END_REF] and New Guinea [START_REF] Boyd | Phytolith analysis for a wet tropics environment: Methodological issues and implications for the archaeology of Garua island, West New Britain, Papua New Guinea[END_REF]. Others researches conducted on current Central and South American plant phytoliths complete this first overview [START_REF] Piperno | The silica bodies of tropical American grasses: morphology, taxonomy, and implications for grass systematics and fossil phytolith identification[END_REF][START_REF] Iriarte | Assessing the feasibility of identifying maize through the analysis of cross-shaped size and three-dimensional morphology of phytoliths in the grasslands of southeastern South America[END_REF][START_REF] Iriarte | Phytolith analysis of selected native plants and modern soils from southeastern Uruguay and its implications for paleoenvironmental and archeological reconstruction[END_REF][START_REF] Watling | Phytoliths from the coastal savannas of French Guiana[END_REF]. Our phytolith classification (Table 1) is based on these regional studies and other work [START_REF] Iriarte | Assessing the feasibility of identifying maize through the analysis of cross-shaped size and three-dimensional morphology of phytoliths in the grasslands of southeastern South America[END_REF][START_REF] Eichhorn | Seed phytoliths in West African Commelinaceae and their potential for palaeoecological studies[END_REF][START_REF] Fenwick | Palm reading: a pilot study to discriminate phytoliths of four Arecaceae (Palmae) taxa[END_REF][START_REF] Collura | Wood and bark phytoliths of West African woody plants[END_REF][START_REF] Neumann | Taxonomic, ecological and palaeoecological significance of leaf phytoliths in West African grasses[END_REF], as well as the nomenclature of the ICPN working group [START_REF] Madella | International Code for Phytolith Nomenclature 1.0[END_REF].

Sclereid shapes (Plate I, a-c)

The sclereids represent a particular group associated with the sclerenchyma of woody dicotyledons (Piperno, 2006) and for which the nomenclature is not well established. Many morphotypes have been described in the literature; the majority exceed 50 µm and can reach up to 200 µm. Some are elongated [START_REF] Postek | The Occurrence of Silica in the Leaves of Magnolia grandiflora L[END_REF][START_REF] Runge | The opal phytolith inventory of soils in central Africa -quantities, shapes, classification, and spectra[END_REF]Piperno, 2006;[START_REF] Garnier | Phytolith taphonomy in the middle-to late-Holocene fluvial sediments of Ounjougou (Mali, West Africa)[END_REF] or polyhedral with a smooth, faceted surface and relatively thick edges (Kealhofer and Piperno, 1998;[START_REF] Runge | The opal phytolith inventory of soils in central Africa -quantities, shapes, classification, and spectra[END_REF][START_REF] Neumann | [END_REF][START_REF] Garnier | Phytolith taphonomy in the middle-to late-Holocene fluvial sediments of Ounjougou (Mali, West Africa)[END_REF]. Other morphotypes are larger, threedimensional and irregular in shape, with a smooth surface [START_REF] Runge | The opal phytolith inventory of soils in central Africa -quantities, shapes, classification, and spectra[END_REF][START_REF] Stromberg | [END_REF][START_REF] Garnier | Phytolith taphonomy in the middle-to late-Holocene fluvial sediments of Ounjougou (Mali, West Africa)[END_REF]. It is also possible to find variants of this more regular morphotype in the form of large, smooth polyhedral with well-defined faces [START_REF] Mercader | Phytoliths in woody plants from the Miombo woodlands of Mozambique[END_REF][START_REF] Garnier | Phytolith taphonomy in the middle-to late-Holocene fluvial sediments of Ounjougou (Mali, West Africa)[END_REF]. Finally, smaller, undefined shapes, between 20 and 60 µm, may show protuberances or growths on their surface [START_REF] Garnier | Phytolith taphonomy in the middle-to late-Holocene fluvial sediments of Ounjougou (Mali, West Africa)[END_REF][START_REF] Collura | Wood and bark phytoliths of West African woody plants[END_REF]. All of these morphotypes, belonging to the large sclereid class, have been identified in the leaves, wood, and bark of many woody plants [START_REF] Runge | The opal phytolith inventory of soils in central Africa -quantities, shapes, classification, and spectra[END_REF]Piperno, 2006;[START_REF] Collura | Wood and bark phytoliths of West African woody plants[END_REF].

Globular shapes (Plate I, d-k)

Spherical to ellipsoid shapes can be differentiated from their ornamentation. Globular shapes with a smooth surface have been identified many times in the tissues of woody dicotyledons [START_REF] Wilding | Scanning Electron Microscopy of Opaque Opaline Forms Isolated from Forest Soils in Ohio1[END_REF][START_REF] Piperno | Phytolith analysis: an archaeological and geological perspective[END_REF][START_REF] Iriarte | Phytolith analysis of selected native plants and modern soils from southeastern Uruguay and its implications for paleoenvironmental and archeological reconstruction[END_REF][START_REF] Watling | Phytoliths from the coastal savannas of French Guiana[END_REF], as well as in some monocotyledons [START_REF] Runge | The opal phytolith inventory of soils in central Africa -quantities, shapes, classification, and spectra[END_REF][START_REF] Bremond | Advantages and disadvantages of phytolith analysis for the reconstruction of Mediterranean vegetation: an assessment based on modern phytolith, pollen and botanical data (Luberon, France)[END_REF]. The globular decorated shapes (warty, rough, crenellated, aggregate, etc.; Plate I, f-g) described in the literature [START_REF] Piperno | Phytolith analysis: an archaeological and geological perspective[END_REF][START_REF] Alexandre | Phytoliths: indicators of grassland dynamics during the late Holocene in intertropical Africa[END_REF]Kealhofer and Piperno, 1998;[START_REF] Barboni | Phytoliths as paleoenvironmental indicators, West Side Middle Awash Valley, Ethiopia[END_REF][START_REF] Iriarte | Phytolith analysis of selected native plants and modern soils from southeastern Uruguay and its implications for paleoenvironmental and archeological reconstruction[END_REF][START_REF] Garnier | Phytolith taphonomy in the middle-to late-Holocene fluvial sediments of Ounjougou (Mali, West Africa)[END_REF] are produced in the fruits, leaves and wood of woody dicotyledonous.

Sometimes the globular morphotypes are formed of aggregate particles, named globular compound [START_REF] Garnier | Phytolith taphonomy in the middle-to late-Holocene fluvial sediments of Ounjougou (Mali, West Africa)[END_REF][START_REF] Collura | Wood and bark phytoliths of West African woody plants[END_REF], or angular particles, named globular nodular [START_REF] Neumann | The Early Holocene palaeoenvironment of Ounjougou (Mali): Phytoliths in a multiproxy context[END_REF][START_REF] Collura | Wood and bark phytoliths of West African woody plants[END_REF]. In our study, all these shapes are classified under the "globular mixed" category.

We chose to create a separate category for globular faceted morphotypes (Plate I, d), as they are characteristic of the Cucurbitaceae family [START_REF] Piperno | Phytoliths in Cucurbita and other Neotropical Cucurbitaceae and their Occurrence in Early Archaeological Sites from the Lowland American Tropics[END_REF]Piperno, 2006), one of the key crops of Maya societies.

The last globular morphotype is the globular echinate (Plate I, i-k). It is a spheroid shape covered with tips. This morphotype, widely observed in the literature, is generally associated with Arecaceae [START_REF] Tomlinson | Anatomy of the monocotyledons[END_REF][START_REF] Piperno | Phytolith analysis: an archaeological and geological perspective[END_REF]Kealhofer and Piperno, 1998;[START_REF] Runge | The opal phytolith inventory of soils in central Africa -quantities, shapes, classification, and spectra[END_REF][START_REF] Dickau | [END_REF][START_REF] Watling | Differentiation of neotropical ecosystems by modern soil phytolith assemblages and its implications for palaeoenvironmental and archaeological reconstructions II: Southwestern Amazonian forests[END_REF]. However, the production of this morphotype depends on the subfamily [START_REF] Thomas | Anatomie comparée des palmiers: Identification-assistée par ordinateur[END_REF].

Hat-shapes

This hat-shape morphotype (Plate I, l) is a semi-spherical shape crowned by one and several thorns. It is relatively small in size: less than 25 µm [START_REF] Piperno | Phytolith analysis: an archaeological and geological perspective[END_REF](Piperno, , 2006;;Kealhofer and Piperno, 1998;[START_REF] Dickau | [END_REF][START_REF] Watling | Phytoliths from the coastal savannas of French Guiana[END_REF][START_REF] Watling | Differentiation of neotropical ecosystems by modern soil phytolith assemblages and its implications for palaeoenvironmental and archaeological reconstructions II: Southwestern Amazonian forests[END_REF]. It is generally associated with Arecaceae but is more representative of certain subfamilies, such as Arecoideae (Thomas, 2011). 3.3.4. Grass short-cell phytolith (GSCP) shapes (Plate I, m-aa)

The grass short-cell phytoliths (GSCPs) are divided into three main morphotypes: the lobate, saddle and rondel shapes. These three classes of phytoliths represent a great diversity of shapes and can be divided into numerous sub-variants (Mulholand, 1989;[START_REF] Piperno | The silica bodies of tropical American grasses: morphology, taxonomy, and implications for grass systematics and fossil phytolith identification[END_REF][START_REF] Barboni | Phytoliths of East African grasses: An assessment of their environmental and taxonomic significance based on floristic data[END_REF][START_REF] Novello | Phytolith signal of aquatic plants and soils in Chad, Central Africa[END_REF][START_REF] Neumann | Taxonomic, ecological and palaeoecological significance of leaf phytoliths in West African grasses[END_REF]. [START_REF] Barboni | Phytoliths of East African grasses: An assessment of their environmental and taxonomic significance based on floristic data[END_REF] suggest that the multiplication of sub-variants reduces the effects of taxonomic redundancy within the subfamilies of Poaceae. However, other researchers claim that the development of a complex classification system, with characters that are not objective and therefore difficult to reproduce from one author to another, has led to an increase in the various forms and thus to errors in the interpretation of assemblages [START_REF] Rovner | Potential of Opal Phytoliths for use in Paleoecological Reconstruction[END_REF][START_REF] Neumann | Taxonomic, ecological and palaeoecological significance of leaf phytoliths in West African grasses[END_REF]. In our study, we chose to use this last approach to GSCP classification to build our base [START_REF] Barboni | Phytoliths of East African grasses: An assessment of their environmental and taxonomic significance based on floristic data[END_REF][START_REF] Neumann | Taxonomic, ecological and palaeoecological significance of leaf phytoliths in West African grasses[END_REF].

Lobate shapes are mainly produced by Panicoideae [START_REF] Twiss | Predicted World Distribution of C3 and C4 Grass Phytoliths[END_REF][START_REF] Piperno | The silica bodies of tropical American grasses: morphology, taxonomy, and implications for grass systematics and fossil phytolith identification[END_REF]Piperno, 2006). There are three main variants: bilobate (Plate I, m-p), cross (Plate I, q-s) and polylobate (Plate I, u-v) shapes. The classification proposed by [START_REF] Neumann | Taxonomic, ecological and palaeoecological significance of leaf phytoliths in West African grasses[END_REF] classifies bilobate and cross shapes according to particle size and shank length. This is particularly important in our study, as it has been shown that the size of crosses could be an indicator of domesticated Zea mays [START_REF] Prat | General Features of the Epidermis in Zea Mays[END_REF][START_REF] Pearsall | Antiquity of Maize Cultivation in Ecuador: Summary and Reevaluation of the Evidence[END_REF][START_REF] Iriarte | Assessing the feasibility of identifying maize through the analysis of cross-shaped size and three-dimensional morphology of phytoliths in the grasslands of southeastern South America[END_REF]. Polylobate shapes (Plate I, u-v) and other rare shapes of lobate (e.g. triangle cross, Plate I, t) are not subdivided into variants.

Saddle-shaped GSCPs are produced by Chloridoideae [START_REF] Barboni | Phytoliths of East African grasses: An assessment of their environmental and taxonomic significance based on floristic data[END_REF][START_REF] Garnier | Phytolith taphonomy in the middle-to late-Holocene fluvial sediments of Ounjougou (Mali, West Africa)[END_REF]. Because Neumann et al. (2017) point out that the different shapes of saddles can't be assigned to taxonomic classification, we chose to view saddles (Plate I, w-x) as a single class of GSCP.

The rondel morphotypes (Plate I, y-aa) show relatively large morphological variation (Mulholand, 1989;[START_REF] Novello | Phytolith signal of aquatic plants and soils in Chad, Central Africa[END_REF], but are not characteristic of a Poaceae subfamily [START_REF] Barboni | Phytoliths of East African grasses: An assessment of their environmental and taxonomic significance based on floristic data[END_REF][START_REF] Neumann | Taxonomic, ecological and palaeoecological significance of leaf phytoliths in West African grasses[END_REF]. Thus, in our classification, rondel shapes are classified into one morphotype, except for two particular shapes (Plate I, y-z). [START_REF] Pearsall | Identifying maize in neotropical sediments and soilsusing cob phytoliths[END_REF] identified a rondel shape recognizable by a top with three spaced ridges (Plate I, aa) that is both corn and teosinte specific in the Maya zone. Given the importance of maize to Maya societies, we decided to keep apart this morphotype.

Papillae shapes (Plate I, ab-ag)

Papillae phytolith morphotypes are associated with Cyperaceae [START_REF] Ollendorf | Toward a Classification Scheme of Sedge (Cyperaceae) Phytoliths[END_REF][START_REF] Runge | The opal phytolith inventory of soils in central Africa -quantities, shapes, classification, and spectra[END_REF][START_REF] Thorn | Phytolith evidence for C4-dominated grassland since the early Holocene at Long Pocket, northeast Queensland[END_REF][START_REF] Lu | Phytoliths as quantitative indicators for the reconstruction of past environmental conditions in China I: phytolith-based transfer functions[END_REF][START_REF] Honaine | Phytolith analysis of Cyperaceae from the Pampean region, Argentina[END_REF][START_REF] Neumann | The Early Holocene palaeoenvironment of Ounjougou (Mali): Phytoliths in a multiproxy context[END_REF][START_REF] Garnier | [END_REF][START_REF] Novello | Phytoliths in modern plants and soils from Klasies River, Cape Region (South Africa)[END_REF]. From our observations, most papillae morphotypes have a swelling that is angular or rounded, relatively large, and generally in the center of the shape. This lump appeared hollow on all morphotypes observed. Studies have shown that, currently, it is not possible to discuss its taxonomic assignment more precisely [START_REF] Ollendorf | Toward a Classification Scheme of Sedge (Cyperaceae) Phytoliths[END_REF][START_REF] Honaine | Phytolith analysis of Cyperaceae from the Pampean region, Argentina[END_REF].

Nevertheless, each variant of papillae morphotype has been retained in our classification. The distinctive characteristics of these variants are the general shape of the plate, its texture, the ornamentation of the margins, and finally the size and structure of the luminous core.

3.3.6. Non-diagnostic shapes and other bioindicators (Plate II) Some phytolith morphotypes are considered not diagnostic such as bulliform cells and elongate shapes. Bulliform cells are produced in the epidermis of plant leaves, from both monocots and dicots (Piperno, 2006). They are rather large morphotypes, generally > 20 µm, with various morphologies. In our study, we identified three bulliform shapes: cuneiform (Plate II, a-b), smooth parallelepiped (Plate II, c-d) and ornamented parallelepiped (Plate II, e-f). Although they do not have a taxonomic role, these shapes can nevertheless provide information on the ecological parameters of the deposition site, and the availability of water for certain plants in particular [START_REF] Bremond | Advantages and disadvantages of phytolith analysis for the reconstruction of Mediterranean vegetation: an assessment based on modern phytolith, pollen and botanical data (Luberon, France)[END_REF]. The second non-diagnostic phytolith family is that of the elongate morphotypes (Plate II, g-k). They are produced both in the tissues of herbaceous plants [START_REF] Twiss | Morphological Classification of Grass Phytoliths1[END_REF][START_REF] Lu | Phytoliths of common grasses in the coastal environments of southeastern USA[END_REF] and dicotyledons [START_REF] Piperno | Phytolith analysis: an archaeological and geological perspective[END_REF][START_REF] Runge | The opal phytolith inventory of soils in central Africa -quantities, shapes, classification, and spectra[END_REF]. Two subtypes can be discerned: elongate smooth shapes and elongate decorated shapes.

Finally, in our non-diagnostic counts, we included sponge spicules and diatoms (Plate II, ls). These non-phytoliths siliceous forms are associated with water environments and can provide information about wetlands.

Use of phytolithic indices

The D/P index was developed to describe the density of tree cover [START_REF] Alexandre | Phytoliths: indicators of grassland dynamics during the late Holocene in intertropical Africa[END_REF].

It is calculated as a ratio of globular shapes associated with dicotyledons to GSCPs [START_REF] Alexandre | Phytoliths: indicators of grassland dynamics during the late Holocene in intertropical Africa[END_REF][START_REF] Barboni | Phytoliths as paleoenvironmental indicators, West Side Middle Awash Valley, Ethiopia[END_REF][START_REF] Bremond | Advantages and disadvantages of phytolith analysis for the reconstruction of Mediterranean vegetation: an assessment based on modern phytolith, pollen and botanical data (Luberon, France)[END_REF]. Until now, this index has been little used in American tropical environments [START_REF] Dickau | Differentiation of neotropical ecosystems by modern soil phytolith assemblages and its implications for palaeoenvironmental and archaeological reconstructions[END_REF]. In this study, we tested its effectiveness in neotropical zones.

Statistical analysis

The statistical analysis in this study aims to attest our observations in the field, as well as the results from counting the phytolith assemblages. The statistical analysis of the quadrats, which had been grouped according to the main types of plant community, was carried out in two stages. The vegetation quadrat groupings were tested by a dissimilarity analysis using HAC (Hierarchical Agglomerative Clustering) clusters. It allows verifying whether quadrat groupings in ecosystems are represented by at least one similarity index, to identify poorly defined quadrats and ultimately to justify our groupings in the following factor analysis. The second step in the statistical analysis of modern vegetation environments is a component analysis. This method allowed to assign groups based on the data matrix and identify the main characteristics that contribute to this graphical morphology: namely, plant taxa. A component analysis was performed on the quadrat/phytolith data matrices. By using the plant groups identified by the HAC the scatter plot obtained by analyzing the phytoliths was compared with the analysis of the current plant communities, and at the same time, the coherence between modern plant communities and phytolith assemblages was tested.

Results

Botanical study: Plant communities at the Naachtun site

The study of plant communities along the four transects from the bajos at low altitudes to the hills identified six major types of plant communities (Fig. 2 and3). These field observations were tested by the use of a correspondence analysis. The Sival areas are bordered by a low forest dominated almost entirely by the tinto (Haematoxylum campechianum), a small knotty tree, cracked bark, with thorny branches and small leaves. These anatomical characteristics correspond to the usual adaptations of xerophytic vegetation in areas with high desiccation and strong sunlight. The name of this area, Tintal, can be explained by the predominance of this tree species. There is also a small Tintal zone in the southern bajo (quadrat S35, transect T4, Fig. 3). This type of environment has been recorded throughout northern Petén and appears characteristic of bajo areas bordering aguadas (wetland) [START_REF] Lundell | Plants probably utilized by the old empire Maya of Petén and adjacent lowlands[END_REF]Schulze and Whitacre, 1999;Martinez and Galindo-Leal, 2002).

The Chechemal zone (Plate III, d)

Further away from the Sival zone, the concentration of tinto decreases and is replaced by associations of shrubs belonging to the Anacardiaceae, Euphorbiaceae, Fabaceae and Myrtaceae families, such as chechem negro (Metopium brownei), subin, katsin and jiesmo (Acacia sp.), cascarillo (Croton sp) and guayavillo (Eugenia sp.). The Chechemal zones, being those furthest from the water areas, contain some palm species, such as cambray (Chamaedorea seifrizii) and escobo (Cryosophila stauracantha). The herbaceous stratum is poorly represented, with some sparse zakate I (Olyra latifolia), zakate II (Kyllinga pumila), zakate III (Cyperus ochraceus) and zakate de huecht (Rhynchospora cephalotes). Plant species are widely dispersed in Chechemal environments, and their relative proportions may vary depending on the geographical area studied. [START_REF] Lundell | Plants probably utilized by the old empire Maya of Petén and adjacent lowlands[END_REF] does not seem to consider this plant community to be a bajo environment, but rather an area of secondary regrowth. Martinez and Gallindo-Leal (2002) found the same association in the Calakmul region and named it bajo mixto. Tikal, Schulze and Whitacre (1999) considered these species associations to be a swamp forest environment distinct from the Tintal forest. We chose to name this environment Chechemal due to the presence of a particular tree, the chechem negro (Metopium Brownei).

The Escobal zone (Plate III, c)

The northern slopes of the bajo and the eastern slopes of the southern bajo are covered by dense forest, higher than the bajo forests, and dominated by palm trees of the escobo (Cryosophila stauracantha) variety. Those are secondary species habitually growing in the higher areas of the site as well as Chechemal zones. Herbaceous plants are rare: zakate (Olyra latifolia) was observed only rarely. These dense palm forests are interpreted as the transition forests in the literature and referred to Escobal by [START_REF] Lundell | Plants probably utilized by the old empire Maya of Petén and adjacent lowlands[END_REF]. They are found on the non-flooded slopes of transects T1, T3, and T4, and on the margins of the bajo zone along T2 (Fig. 2 and Fig. 3). zone can be considered one of its typical plant associations. Carrizal areas do not appear to be particularly associated with topographical or edaphic conditions, or archaeological structures.

Statistical tests of plant communities

We first used hierarchical cluster analysis to assess the validity of grouping the environments into six ecosystems (Fig. 4). The HAC checks, in the form of a cluster, whether a hierarchy index finds initial groupings. In our case, the Euclidean hierarchy index was the most consistent. Nonetheless, five samples (S01, S02, S16, S22, and S24) do not correspond to our initial classification. With this HAC, S22 was interpreted as Escobal vegetation, while S24 was interpreted by the analysis as Chechemal vegetation. The three other quadrats clearly contained transitional vegetation and are defined as such in our statistical analysis.

The first two axes of the component analysis (CA) of all quadrats explain 25.0% of the total variance (Fig. 5a). The contribution tables of Fig. 5 show the species that contributed most to the morphology of the scatter plot and that are considered as ecological indicators. Axis 1 (14.6% of the variance) distinguishes open habitat quadrats with Sival species, located at the positive end, from forest quadrats, located at the negative end. Axis 2 (10.4% of the variance) distinguishes plant communities according to the main altitude ranges. Samples and species typical of bajo forests are located at the positive end, while forest samples from the archaeological site, more upper, are grouped at the negative end. Two irregularities were identified within this first CA. Quadrat S24 is interpreted to be a relatively open zone in the bajo, whereas it is a forest zone disturbed by a compacted path at the edge of a Sival zone. This observation leads us to conclude that this sample is problematic. The second problem is that the scatter plot corresponding to the hill vegetation environments is too condensed to discriminate the quadrats. Thus, to refine our classification, we chose to perform a second CA on these samples (Fig. 5b).

For the second CA, the first three axes explain 35% of the variance. The CA conducted on the first two axes (Fig. 5b) shows that Axis 2, which explains 11.1%, is not decisive in the distribution of samples and species. Axis 1 (15.3% of the variance) distinguishes the quadrats associated with the bajo areas located at its negative end from the hill and site quadrats at its positive end. Axis 3 (9.4% of the variance; Fig. 5c) distinguishes the forest areas of hills with samples of the Ramonal/Zapotal zones at its negative end, and samples of Carrizal environments at its positive end These conclusive statistical analyses demonstrate that our sampling and botanical survey method is statistically reliable, except for the identified plant transition zones. Thus, this classification of plant communities can be used to characterize modern phytolith assemblages. 4.3. Modern phytolith assemblages (Fig. 6 and Fig. 7)

The phytoliths counts from each quadrat have been summarized in Fig. 6 and Fig. 7. The distribution diagram (Fig. 6) shows the relative abundances of phytolith morphotypes by quadrat, grouped into plant communities. The first part of the diagram concerns the relative abundances of diagnostic morphotypes. They are expressed as a percentage of the total number of diagnostic morphotypes. The second part of the diagram concerns the abundance of non-diagnostic phytoliths and bioindicators. They are expressed as a percentage of the total number of counted particles. The diagram of the descriptive statistics for the morphotypes (Fig. 7) shows the amplitude of the distribution of morphotype classes across the six types of plant communities. This second diagram completes the relative abundances diagram. On these diagrams, quadrats that were not discriminated by the HAC (Fig. 4; S1, S2, and S16) were not included in the calculations in Fig. 7.

Sival: Six samples are assigned to this environment (S10, S11, S12, S25, S26, and S27). The phytolith assemblages are dominated by globular mixed, GSCP (especially saddle and rondel) and papillae morphotypes. On average, papillae morphotypes represent 35% of Sival assemblages, reaching up to 85% in S10. Globular mixed, saddle and rondel phytoliths represent on average 15% of Sival assemblages but could account for over 30% (Fig. 6). The D/P index accounts systematically less than 1. For bioindicators, Sival environments record the highest average proportion of sponge spicules (30%) and diatoms (6%) of all assemblages. Analysis of the relative abundance diagram points to differences between the assemblages in forest environments (Ramonal, Carrizal, Escobal, Chechemal, and Tintal) and wet/open environments (Sival; Fig. 6).

Tintal: Four samples are assigned to this environment (S9, S13, S28, and S35). The phytolith assemblages are dominated by globular mixed, GSCP (lobate) and papillae morphotypes.

On average, globular mixed morphotypes represent 37% of Sival assemblages, reaching up to 50% in S9 and S28 (Fig. 6 and Fig. 7). Lobate and papillae morphotypes each account for on average 21% of Tintal assemblages (Fig. 7). The D/P index oscillates between values close to 1. The proportions of bioindicators are close to those observed in the Sival, with an average of 28% for sponge spicules and 3% for diatoms.

Chechemal: Seven samples are assigned to this environment (S15, S24, S31, S32, S33, S34, and S36). The main feature is the high percentage of globular mixed shapes, accounting for on average 80% of assemblages but reaching up to 87% (S31 and S36; Fig. 6 and Fig. 7). Accordingly, the D/P index values are high (15)[START_REF] Novelo | Classification work of phytolith forms in modern and ancient soils and sediments: 1[END_REF](17)(18)(19)(20). As regards bioindicators, diatoms are absent, while sponge spicules account for on average 8%.

Escobal: Eight samples are assigned to this environment (S9, S17, S18, S19, S20, S22, S23, and S37). Globular mixed (50%) and globular echinate (40%) phytoliths are predominant (Fig. 7).

The D/P values are also very high, at 27 on average. The proportions of sponge spicules and diatoms in these assemblages are very low (less than 1% in average).

Carrizal: Four samples are assigned to this environment (S04, S07, S41, and S42). The phytolith assemblages are dominated by globular mixed morphotypes, exceeding 60%. The most conspicuous feature is the high percentage of rondel GSCPs, accounting for 26%, and the rondel crested morphotype, reaching values around 20% (Fig. 7). The non-diagnostic phytoliths, bulliform parallelepiped and elongate psilate morphotypes are particularly well represented in these samples (Fig. 6). The D/P values are low for a forest environment, recording 3 on average. Sponge spicules and diatoms are absent.

Ramonal/Zapotal: Eight samples are assigned to this environment (S3, S5, S6, S21, S38, S39, S40, and S43). Globular mixed and hat-shape morphotypes dominate these assemblages, representing 65% and 18% respectively. The D/P index is extremely high, with 38 on average. Sponge spicules and diatoms are absent.

Statistical tests of phytolith assemblages

The assembly groups defined based on the distribution diagram and ecosystems were tested by a component analysis. The variables were the phytolith morphotypes and quadrat samples. The contribution table of Fig. 8 indicates the morphotypes that contribute most to the morphology of the scatter plot. Axis 1 and Axis 2 explain 52.7% of the variance (Fig. 8a). Axis 1, which explains 36.3% of the total variance, distinguishes between the openness and/or humidity of the environments: the Sival and Tintal environments are located at the positive end and are mainly influenced by sponge spicules, diatoms, and papillae morphotypes. GSCPs are also present at the positive end. The negative side includes the samples taken from forest areas and morphotypes such as globular mixed and globular echinate.

Axis 2 of our analysis explains 16.43% of the total variance and differentiates grassy undergrowth forests from forest areas with trees only. The variables on the positive side of this axis that contribute most to the morphology of the scatter plot are the rondel crested GSCP, bulliform cells and elongate morphotypes. However, the samples from Ramonal, Escobal and Chechemal forest areas form a group of samples that are difficult to analyze. This highlights the necessity of isolating the Carrizal areas from the other forest areas on the site and in the bajo.

A second CA (Fig. 8b-c) was needed to distinguish the different Naachtun forest samples (Chechemal, Ramonal/Zapotal, Escobal). The first three axes explained 73.5% of the total variance.

In the second graph (Fig. 8b), Axis 1 (29.2% of the variance) and Axis 2 (23.4% of the variance) help to distinguish between the site's different forest ecosystems. The sponge spicules variable contributes considerably to the morphology of the scatter plot for these two axes, and the Chechemal samples are therefore located in the upper right corner of the graph and isolated from the other samples. The second contributing variable for both axes is the globular echinate morphotype, which is located on the negative part of Axis 1 and the positive part of Axis 2. This morphotype allows to differentiate between the different Escobal-type forests (Fig. 8b). Axis 3 in the second CA suggests that hat-shape morphotypes help to distinguish between the Ramonal/Zapotal samples (Fig. 8c). Finally, the vegetation samples interpreted as "undefined areas" by the HAC (S1, S2, and S16; Fig. 4), were not characterized by our component analysis either (Fig. 8).

Discussion

Definition and identification of Naachtun plant communities

The study and interpretation of phytolith assemblages show significant differences between plant formations. They point to the necessity of applying the general approach, as well as taking into account not only non-diagnostic phytoliths but also other bioindicators during the interpretation process.

The phytolith assemblages in Sival zones can be explained by their plant associations.

Papillae morphotypes are produced by Cyperaceae, the family to which tul (Cyperus articulatus) belongs [START_REF] Novello | Phytolith signal of aquatic plants and soils in Chad, Central Africa[END_REF][START_REF] Watling | Phytoliths from the coastal savannas of French Guiana[END_REF], while saddle and rondel morphotypes are produced by certain subfamilies of Poaceae, such as Arundinoideae, to which zakaton (Phragmites australis) belongs [START_REF] Ollendorf | Phytolith Analysis as a Means of Plant Identification: Arundo donax and Phragmites communis[END_REF][START_REF] Piperno | The silica bodies of tropical American grasses: morphology, taxonomy, and implications for grass systematics and fossil phytolith identification[END_REF][START_REF] Liu | Response of phytoliths in Phragmites communis to humidity in NE China[END_REF]. The high proportions of diatoms could indicate the presence of perennial water.

The Tintal zones' assemblages were interpreted as assemblages of a transitional plant community between open and forest areas. The globular mixed phytoliths were most likely produced by tinto (Haematoxylum campechianum), which is the only woody dicotyledon in this plant community. The high proportions of papillae and bilobate morphotypes and other bioindicators can be explained by various processes. The Sival areas contained a much higher percentage of papillae morphotypes than in other studies [START_REF] Barboni | Comparative study of modern phytolith assemblages from inter-tropical Africa[END_REF][START_REF] Novello | Phytolith signal of aquatic plants and soils in Chad, Central Africa[END_REF].

The seasonal flooding of Sival areas may allow for the registration of Cyperaceae tissues and phytoliths, as well as diatoms and sponge spicules, in Tintal soils. Finally, the significant presence of bilobate morphotypes could be explained by the irregular presence of seasonal grassy undergrowth, consisting of Cyperaceae and Panicoideae, as was observed in 2017.

Chechemal forest assemblages can be partly explained by the rare occurrences of herbaceous species (Poaceae, Cyperaceae, etc.) or monocot trees, and by a predominance of the woody dicotyledons that produce globular mixed morphotypes. It is principally the presence of sponge spicules, due to seasonal flooding in these forest areas that permit these environments to be characterized.

The palm groves of the Escobal environments are characterized by a predominance of both globular echinate and globular mixed which morphotypes originating from the ligneous trees of the forest. The globular echinate morphotypes are produced by certain subfamilies of Arecaceae, such as Coryphoideae (Thomas, 2015), which escobo (Cryosophila stauracantha), the dominant species in this palm grove community, belongs to. The presence of sponge spicules indicates that these areas are subjected to a seasonal flood.

The Ramonal/Zapotal high forests are defined by a phytolith association composed of globular mixed and hat-shape morphotypes. Globular mixed morphotypes are produced by the woody dicotyledons of the forest, while hat-shape morphotypes may have originated from xate (Chamaedorea sp.), the dominant species in this plant community. Indeed, Thomas (2015) indicates that this morphotype is overrepresented in Arecoideae species, including the Chamaedorea genus.

However, some samples (S6, S39, S40, and S43) contained lower proportions of hat-shape morphotypes (Fig. 6). This can be explained by the fact that the Zapotal plant association, described by [START_REF] Lundell | Plants probably utilized by the old empire Maya of Petén and adjacent lowlands[END_REF] and Schulze and Whitacre (1999), have undergrowth with lower xate content. This type of assemblage could, therefore, be confused with those in the upper areas of a bajo that do not contain sponge spicules (S01). Within the high forest vegetation, areas with bamboo thickets (Carrizal) were identified by an association of globular mixed, rondel crested, bulliform decorate and elongate smooth morphotypes. The fact that the undergrowth is dominated by Rhipidocladum bartleddii suggests that this bamboo species produce some of the morphotypes in this association.

The discovery of similar rondel morphotypes in other bamboos (rondel three-pikes, [START_REF] Pearsall | Identifying maize in neotropical sediments and soilsusing cob phytoliths[END_REF] may confirm this hypothesis.

To conclude, three levels of interpretation of the assemblages can be highlighted. (1) The first level concerns the differentiation between forest and open areas. High proportions of GSCPs and papillae shapes indicate open environments, while high proportions of globular mixed morphotypes, which may or may not be accompanied by palm tree morphotypes (globular echinate and hat-shape), are representative of forest environments. Forest zones with grassy undergrowth or "savannahs" are characterized by high proportions of globular mixed morphotypes and one or more morphotypes of GSCP or papillae, as in the case of the Carrizal and Tintal environments. (2) The second level of identification concerns the wet character of the vegetation. The presence of high proportions of papillae shapes (> 15%) in the assemblages indicates wet plant associations. As regards bioindicators, the presence of diatoms is associated with perennial water bodies, while sponge spicules suggest the presence of occasional or seasonal water bodies in the bajo zone. This is useful to identify the forest areas located in the bajo's influence zone during the wet season. (3) The last level of interpretation of the diagrams concerns the identification of forest areas at the edges of hills, slopes, and bajos. At Naachtun, the proportion of phytoliths produced by the Arecaceae seems to be useful in distinguishing the palm transition forests and the Ramonal forest from the hills of the site.

Discussion of the use of indices

Identify the cover layer

The first studies conducted using the D/P index represented the tree cover as a ratio of globular decorated, produced by woody dicotyledons, to GSCPs and morphotypes associated by some authors with Poaceae [START_REF] Alexandre | Phytoliths: indicators of grassland dynamics during the late Holocene in intertropical Africa[END_REF][START_REF] Alexandre | Late Holocene Phytolith and Carbon-Isotope Record from a Latosol at Salitre, South-Central Brazil[END_REF][START_REF] Bremond | Advantages and disadvantages of phytolith analysis for the reconstruction of Mediterranean vegetation: an assessment based on modern phytolith, pollen and botanical data (Luberon, France)[END_REF][START_REF] Bremond | Phytolith indices as proxies of grass subfamilies on East African tropical mountains[END_REF]. Changes in the classification of phytoliths prompted the authors to adapt this formula to the morphotypes and environments studied [START_REF] Stromberg | [END_REF][START_REF] Bremond | Advantages and disadvantages of phytolith analysis for the reconstruction of Mediterranean vegetation: an assessment based on modern phytolith, pollen and botanical data (Luberon, France)[END_REF][START_REF] Barboni | Comparative study of modern phytolith assemblages from inter-tropical Africa[END_REF][START_REF] Neumann | The Early Holocene palaeoenvironment of Ounjougou (Mali): Phytoliths in a multiproxy context[END_REF][START_REF] Garnier | Phytolith taphonomy in the middle-to late-Holocene fluvial sediments of Ounjougou (Mali, West Africa)[END_REF][START_REF] Dickau | Differentiation of neotropical ecosystems by modern soil phytolith assemblages and its implications for palaeoenvironmental and archaeological reconstructions[END_REF]. According to [START_REF] Alexandre | Phytoliths: indicators of grassland dynamics during the late Holocene in intertropical Africa[END_REF], a D/P index > 1 is representative of open environments, while D/P values < 1 indicate forest areas.

Thus, for Naachtun plant environments, our results indicate that forest areas have high D/P values recording an average of 38 for Ramonal/Zapotal samples, 27 for Escobal samples and 16 for Chechemal samples. These values, higher than 1, are associated to dense vegetation areas, which is consistent with these forest environments. In the Sival samples without tree strata, the D/P index average was around 0.53, suggesting that the D/P index can be used to identify open environments.

However, Carrizal areas, with grassy undergrowth, and Tintal areas, with seasonally grassy undergrowth, have D/P values higher than 1 but much lower than for forested areas. The average D/P index for Carrizal areas was 2.84, but varied between 1.1 and 6, while the index values for Tintal zones varied between 0.36 and 2.1 (Fig. 6, Fig. 9 and Fig. 10).

The D/P index does not seem suitable for identifying certain plant formations whose values overlap, such as those in the Carrizal, Tintal and Sival zones. This is particularly true of the Tintal and Sival environments, which contain similar phytolith assemblages dominating by Cyperaceae and GSCPs. To overcome this obstacle to interpretation, we decided to adjust the D/P formula to our study by including certain useful morphotypes (Cyperaceae, sclereid, globular echinate and hatshape). Fig. 9 shows the variation in the D/P values for each quadrat studied and compares them with the vegetation cover values for seven different D/P index formulae. The seven formulae correspond to a variation in the sum and type of morphotypes applied to the numerator, denominator, or both simultaneously (Table 2).

The first observation leads to the conclusion that including globular echinate and hat-shape morphotypes in the formula maximizes D/P values, especially for Sival zones where the D/P average was 0.9. Thus, the use of these morphotypes in the D/P formula does not seem justified.

Including sclereid morphotypes in the index calculation does not have a significant effect on D/P values. This can be explained by the low proportions of this morphotype in the assemblages.

Including papillae morphotypes in the denominator of the index significantly reduces the index values for Sival (0.24 on average) and Tintal (0.98 on average) zones. If including papillae shapes minimize the values for Tintal zones, this highlights the opening of the Sival zones and therefore it seems necessary in our D/P index calculations. However, the simultaneous addition of sclereid morphotypes to the numerator and papillae morphotypes to the denominator increases the D/P values for Tintal zones (1.11 on average) while maintaining the best numerical representation of the Sival zones (0.29 on average). Thus, for the purposes of our study, and for geographical areas where papillae morphotypes make up a significant percentage of phytolith assemblages, we recommend to adjust the D/P index using the following formula: Globular mixed + Sclereid / GSCP + Papillae

Identify the mixed zones

Even after adapting the D/P index to suit the particularities of our plant zones, it still does not seem possible to use the D/P index to identify mixed zones with grassy and woody layers. Indeed, our study shows that the D/P index for Carrizal and Tintal zones sometimes have the same values for Sival zone. It seems, therefore, necessary to develop a new index that allows these mixed zones, misinterpreted by the D/P index, to be clearly identified.

In this study, we propose a new index that defines a mixed zone characterized by a combination of woody trees and herbaceous plants as an addition D+P. This D+P assemblage must be matched with a tree D assembly and a grassy P assembly. We propose the following formula: The calculation of this formula implies that the predominance of any one part of the assembly (D or P) over the other parts will tend to minimize the denominator and thus produce high values indicating strictly forest or strictly savannah areas. Whereas a mixed assembly (D = P) will produce D/P index values of around 1, but this new index will allow the presence of both a herbaceous zone and tree stratum to be confirmed. Indeed, in such a case, the average values of D and P will increase the denominator, which will cause the index values to fall to a minimum value. This new index, named LU (limits/undergrowth) index, was developed for our samples and has good potential for ecological recovery in our environmental contexts (Fig. 10). The lowest values were obtained for environments containing both a herbaceous stratum and tree cover, such as the Carrizal and Tintal environments. These LU values put into perspective the average D/P index values of these environments and confirm their mixed nature. The Sival zones generated different LU index values depending on the sampling zone. The values for quadrats S12, S25 and S27 were low and comparable to those of the Carrizal zones, which could be explained by the fact that the edges of the Tintal and Ramonal zones are located nearby. Conversely, the LU index values for the samples from the center of the Sival zone (S10, S11, and S26) were higher due to the distance from the wooded areas. The new index values calculated for the Escobal and Ramonal environments were relatively high and would indicate a sparse herbaceous stratum. This is in agreement with the high D/P index values. Finally, the Chechemal environment quadrats had relatively low values compared to other forest areas. Some of the low values from the new index (for quadrats S33 and S34) could correspond to forest areas where the herbaceous stratum is only seasonally present, as observed in other bajo areas at Naachtun. Based on the quadrats and vegetation parameters (tree cover, herbaceous undergrowth), we can define 0.25 as the maximum LU index value identifying mixed and transitional vegetation areas.

Development of a paleoenvironmental tool for Maya archaeology

One main objective of this study was to test the potential of phytolith assemblages in Petén for characterizing past landscapes and past ecosystems. The main hurdles to the development of a bioindicator tool are the different post-deposition taphonomic processes that can modify thanatocoenosis and thus the interpretation of assemblages [START_REF] Madella | Taphonomy and phytoliths: A user manual[END_REF]. These disturbance factors include the differential diagenetic recording of morphotypes [START_REF] Piperno | Phytolith analysis: an archaeological and geological perspective[END_REF][START_REF] Alexandre | Phytoliths: indicators of grassland dynamics during the late Holocene in intertropical Africa[END_REF], the vertical translocation of assemblages [START_REF] Runge | The opal phytolith inventory of soils in central Africa -quantities, shapes, classification, and spectra[END_REF][START_REF] Fishkis | Phytolith transport in soil: A field study using fluorescent labelling[END_REF] and lateral transport [START_REF] Fredlund | Modern Phytolith Assemblages from the North American Great Plains[END_REF][START_REF] Osterrieth | Taphonomical aspects of silica phytoliths in the loess sediments of the Argentinean Pampas[END_REF]Madella and Lanceloti, 2012;[START_REF] Watling | Differentiation of neotropical ecosystems by modern soil phytolith assemblages and its implications for palaeoenvironmental and archaeological reconstructions II: Southwestern Amazonian forests[END_REF]. Finally, factors making interpretation more difficult may also occur during the production and deposition of phytoliths, depending on the composition of plant communities and sediment types.

Initially, the analysis of fossil samples, and their palaeoenvironmental interpretation must be carried out with the awareness that "time averaging" in Holocene sediment can easily represent from several years to tens or hundreds of years [START_REF] Fredlund | Modern Phytolith Assemblages from the North American Great Plains[END_REF][START_REF] Albert | Taphonomy of phytoliths and macroplants in different soils from Olduvai Gorge (Tanzania) and the application to Plio-Pleistocene palaeoanthropological samples[END_REF].

For phytoliths records in fossil samples, it is difficult to know the period of the deposit. Thus, a phytolith record contains a mixture of consecutive plant associations at a location over an unknown number of years. However, this problem also exists for modern samples. The first centimeters of the A horizon sampled are not representative of the current vegetation, but rather of the vegetation from a recent period which is not precisely known and could cover several months to a few decades. The part of transect T3 from the Sival zone to the southeast of the northern bajo (S24 to S27) is a good example. The vegetation within the Sival zone is organized into specific vegetation rings linked to the expansion of perennial water in spring: first the tul/zakaton association, then a halo of tul only, then a tul/yerba buena/zarza association. As observed during field missions, every spring, water availability is different, and this affects the plant composition of quadrats S24 to S28. It can link with the spatial mobility of the Sival zone's plant rings depending on water precipitation. Because it is a continuous phenomenon continues, 2017 samplings in the eastern Sival zone may correspond to an average of phytolith records from the vegetation at different seasons. Thus, in Sival assemblages, the high proportions of papillae morphotypes represent the rings of tul (Cyperaceae), while high proportions of saddle shapes represent the rings of zakaton (Arundinoideae), and globular mixed and sclereid morphotypes indicate the rings of zarza (Fabaceae).

Phytolith assemblages can be affected by lateral transport effects, caused by wind, water, gravity or bioturbation [START_REF] Fredlund | Modern Phytolith Assemblages from the North American Great Plains[END_REF][START_REF] Alexandre | Phytoliths: indicators of grassland dynamics during the late Holocene in intertropical Africa[END_REF][START_REF] Barboni | Phytoliths as paleoenvironmental indicators, West Side Middle Awash Valley, Ethiopia[END_REF]Piperno, 2006). The systematic approach of ecological transect sampling allows to test the estimation of morphotype transport from one quadrat to another one. [START_REF] Alexandre | Phytoliths: indicators of grassland dynamics during the late Holocene in intertropical Africa[END_REF] point out that high tropical forests' canopies limit wind transport. However, transport by water should be accounted for interpreting assemblages. At Naachtun, phytolith transport by water may be facilitated by the substantial drainage system from the high areas to the bajo, as well as the flooding period of the bajo during the wet season. Our results show that phytolith assemblages are not affected by transport and are most representative of the local vegetation. The vegetation of the seasonally flooded lowlands (Sival, Tintal) is dominated by papillae polygonal and diatoms, while globular mixed morphotypes are relatively few and mainly restricted to upper woody dicot areas.

The same observation can be made for the slope area samples. The drainage of high zones does not result in the mixing of phytolith associations. For example, phytolith assemblages in the transition area from S7 to S8 on transect T1 are not subject to contamination from rondel crested morphotypes. Moreover, looking at the sloped area running along transect T3 (S22-S26), the upper samples, which are rich in globular mixed morphotypes, have little influence on the D/P index value for the bajo samples. Thus, for the current Naachtun site, phytolith transport plays a minor role in the alteration of phytolith assemblages.

Transport does not affect the identification of plant landscapes. However, the transport of phytoliths may play a role in the taxonomic representativeness of the quadrats studied. In all the plant communities studied, palm phytoliths were observed in an average of around 5-10% of the phytolith associations. In environments such as Tintal or Sival zones where Arecaceae are absent, these high proportions of palm phytoliths raise questions over their transport. The high numbers of phytoliths produced by the Arecaceae and their greater resistance to erosion [START_REF] Chabot | Phytolith analysis from the archaeological site of Kota Cina (North Sumatra, Indonesia)[END_REF] could mean that they have a ubiquitous record. We surmise that comparable proportions (5-10%) of Arecaceae phytoliths in fossil samples can be interpreted as the result of contamination caused by transport, rather than as an identifying ecological signal.

Conclusion and Future Researches

This work has allowed for the development of a tool to study paleoenvironments in the Maya zone. Phytoliths are particularly useful in tropical forest areas where other types of fossil conservation can be lacking. The analysis of modern soil samples from Naachtun has shown the potential of phytolith assemblages as bioindicators of plant landscapes in the Maya zone. A robust interpretation of phytolith assemblages has been enabled both by sampling the modern soil and studying the modern plant communities' distribution. We used a general approach to interpret phytolith assemblages diagrams and multivariate statistical analyses, as well as an index approach.

These results testify of the possibility to distinguish wet and open Sival areas from bajo, Tintal and Chechemal forest areas. The use of both phytoliths assemblages and phytolith indices seems to be particularly appropriate to differentiate opened, closed, and transitional plant environments. The consistency of the results between modern plant communities and phytolith assemblages demonstrates the validity of our methodology.

However, the environments of this study are only part of Petén environments. "Natural" and "anthropic" environments were certainly much more diversified in Maya times, and are still today.

Thus, the realization of a current reference collection of phytoliths in anthropized areas is necessary to define more precisely the interpretation of the fossil phytolith assemblages from the occupation period of the Naachtun site. Some other environments, such as the savannahs of central Petén [START_REF] Lundell | Plants probably utilized by the old empire Maya of Petén and adjacent lowlands[END_REF] or the drier forests of northern Yucatán could have reached the Naachtun region during drier climatic periods. More humid environments of the lake or lagoon variety (Yaxha, Dos Lagunas, etc.) could also have been present during wet phases. Modern soil sampling of these environments also seems necessary to construct a complete and current phytolith reference system for Maya environments on the Petén level.

Finally, the characterization of plant communities could be improved in taxonomic terms.

As we have seen, the Naachtun ecosystems are mostly dominated by woody dicotyledons. A general study on the sclereids in such closed environments is needed to refine the taxonomic precision. More precise taxonomy could also be achieved by combining phytolith data with the data on other local bioindicators which are sensitive to variations in climatic parameters and ecological plant niches.

Morphological description

Plate of 1 to 3 papillae with luminous nucleus (LC) Smooth irregular shape with short margins and a LC Smooth irregular shape with elongated LC Rugulate irregular hexagonal shape with LC Rugulate irregular shape with collumelated margins with LC Smooth iiregular shape with wavy marges 3D flattened shape, with two lobes connected by a central shank Special form of bilobate with the outside of the hollowed lobes 3D flattened shape, with 4 lobes connected in a central point A special cross shape with only 3 lobes Lengthened lobate shape with at least 3 lobes Extended saddle shape with elongated convex sides Saddle shape where convex sides are shorter than concave sides Roughly parallelepiped shape with very high convex margins Non-symmetrical saddle shape with a collapsed plane Cylindrical shape with opposite bases symmetrical or not Rondel shape with a head covered by ridges or thorns in 2D Elongated shape, linear or twisted, with facets Irregular shape covered by branches in relief Irregular shape covered with pointed ornamentation Large irregular shape with smooth size Smooth polyhedral shape, often in parallelepiped block Spherical to sub-spherical shape with no visible ornamentation Sub-spherical shape with a rough, warty, or coarse surface Spherical to subspherical shapes grouped in the form of a complex Big shape with an ornamented surface by large polygonal faces Sub-spherical shape with a surface covered by thorns Hemispherical shape covered with thorns pani.

1 ,4,6,8,13,14,1,4,5,6,7 1,4,6,13,14,1,4,5,7 8,4,5 1,7,8,13,14,5,6,7 1,4 1,4,8 13 chlo. 1,4,8,1,4 1,4,8,1 8 1,4,8,13,1,6,7 4,5 4,6,7,14,4

  4.1.1. The Sival zone (Plate III, f) Today, almost the entire Naachtun site is covered by forest. The only exception is the Sival zone, located in the northern bajo, which is characteristic of a wet savannah composed of zakaton (Phragmites australis) and tul (Cyperus articulates). The wet nature of the Sival is supported by the presence of lechuga (Pistia stratiotes). On the edge of the water area, an association of yerba buena (Mentha x piperita) and zarza (Mimosa pigra) was observed. Wild squash, calabaza de raccoon (Cucurbita radicans), was also observed at the edge of the Sival zone along transect T3. This association on the edge of a Sival zone had already been observed in Naachtun's northern bajo by Lundell in 1937 and was also reported by Martinez and Galindo-Leal in the Calakmul area in 2002 under the name savana humeda. 4.1.2. The Tintal zone (Plate III, e)

  4.1.5. The Ramonal/Zapotal zone (Plate III, a)The main vegetation on the archaeological site and hilly areas is a high forest dominated by trees up to 40 meters high belonging to the Sapotaceae, Sapindaceae, Myrtacae, and Moraceae. The most representative trees of this forest are the ramon (Brosimum alicastrum) and the chicozapote (Manilkara zapota). It can explain why two types of high forests were identified by[START_REF] Lundell | Plants probably utilized by the old empire Maya of Petén and adjacent lowlands[END_REF] and Schulze and Whitacre (1999): the Ramonal and Zapotal high forests. The Ramonal areas are characterized by a large population of ramon and an undergrowth rich in populations of xate (Chamaedorea sp.) and cordoncillo (Piper sp.). The forests of Zapotal are rich in Sapotaceae species and have relatively low palm undergrowth. In 1938, Lundell proposed that the domination of these resource-producing trees over the site areas should be inherited from old maintained gardens. In this study, we consider these forest communities as a single forest named here Ramonal/Zapotal area. In these forest environments, herbaceous plants are rare: only zakate (Olyra latifolia) is occasionally found. 4.1.6. The Carrizal zone (Plate III, b) Locally, we observed some open patches in the Ramonal/Zapotal zone (T1 and T4) characterized by dense herbaceous thickets, which we refer to as Carrizal zones. Observed by Lundell in Naachtun in 1937, they consist of juvenile bamboos called carrizo (Rhipidocladum bartlettii). Concentrations of grass are relatively rare at the Naachtun site, meaning that the Carrizal

  [((D+P)/P + (D+P)/D)/(D+P)]x10 which can be reduced to the form [(D+P)/(D*P)]x10

Fig. 1 .Fig. 2 .Fig. 3 .Fig. 4 .Fig. 6 .Fig. 7 .Fig. 8 .Fig. 9 .

 12346789 Fig. 1. Map of main archaeological sites of the Mayan lowlands and the semi-evergreen tropical

  .3 (appendix): Table of correspondence between nomens and scientific names of plant species, relative richness of nomens by plant environments: O : Dominant or typical species of an ecosystem ; +++ : Species observed in at least 75% of the sampling points of an ecosystem ; ++ : Species observed in at least 50% of the sampling points of an ecosystem ; + : Species observed in at least 25% of the sampling points of an ecosystem ; -: Species observed in at least one time of the sampling points of an ecosystem Eugenia capuli (Schltdl. & Cham.) Hook. & Arn.

	Herbs	arun. pooï. ehrh. bamb. Poac. Cordoncillo Chaya Chechem blanco Guayavillo Jiesmo Katsin Laurel Majagua Manzanita Mora Nanze Cype. Cascarillo Palo de Hormigas	1,4,1 1,4 8 4,8,13,1 3 Croton guatemalensis Lotsy 4,1 1,4 8,10,14,4,6,7 4,8,1 3 6 Croton reflexifolius Kunth Cnidoscolus aconitifolius (Mill.) I.M.Johnst. 1,8 1,4,4 1,4,8 1,5 8 7,8 4,6 10 Cameraria latifolia L. Piper amalago L. Piper psilorhachis C.DC. Eugenia axillaris (Sw.) Willd. Eugenia ibarrae Lundell Eugenia tikalana Lundell Acacia angustissima (Mill.) Kuntze Acacia dolichostachya S.F.Blake Lysiloma acapulcense (Kunth) Benth. Acacia gaumeri S.F.Blake Acacia riparia Kunth Nectandra coriacea (Sw.) Griseb. Nectandra sanguinea Rol. ex Rottb. Hampea tomentosa (C.Presl) Standl. Hampea trilobata Standl. Mortoniodendron guatemalense Standl. & Steyerm. Malpighia glabra L. Malpighia lundellii C.V. Morton Maclura tinctoria (L.) D.Don ex Steud. Byrsonima bucidifolia Standl. Byrsonima crassifolia (L.) Kunth Alvaradoa amorphoides Liebm.	,5	14 4	6,5 ++ O ---+ --	1,4,8 1,4,8 1,4,8,3,4,5 4,3 4,5,6,7	13 5,6 6 6,7 + ++ ----	5	-++ -++ ----	O -+ -+++ ++ + -++ -++ + -	-+
			Piñón	Jatropha curcas L.			-					-
			Quiebrahacha	Wimmeria bartlettii Lundell Wimmeria concolor Cham. & Schltdl.			-
			Subin	Acacia collinsii Saff. Acacia cornigera (L.) Willd.					-		+	+++
			Zarza	Mimosa pigra L.									O
	m.	)	Zikiya	Chrysophyllum mexicanum Brandegee Chrysophyllum oliviforme L.							+	-
			Bayal	Desmoncus chinantlensis Liebm. ex Mart.			-		-		+
			Cambray	Chamaedorea seifrizii Burret			++				++	++
			Escobo	Cryosophila stauracantha (Heynh.) R.J.Evans			++				O	+
	PALMS		Guano / Botan Xate	Sabal mauritiiformis (H.Karst.) Griseb. & H.Wendl. Sabal mexicana Mart. Chamaedorea elegans Mart. Chamaedorea oblongata Mart.			+ O		+ ++		O +	+ +
			Bejuco de aro	Bignonia aequinoctialis L.			-
			Calabaza de raton	Cucurbita radicans Naudin									++
			Carrizo	Rhipidocladum bartlettii (McClure) McClure					O
			Lechuga	Pistia stratiotes L.									O
			Mozote ambra	Teucrium vesicarium Mill.									++
	HERBS		Mozote macho Navajuella Tres marias	Triumfetta semitriloba Jacq. Cyperaceae ind. Forchhammeria trifoliata Radlk. ex Millsp.			-					--	++	++ +
			Tul'	Cyperus articulatus L.									O
			Yerba buena	Mentha × piperita L.									O
			Zakate ambra	Panicum trichanthum Nees									++

Tab

Acknowledgements

This research is supported by the Projet Naachtun 2010-2018 (Dir. Ph. Nondédéo), the Project HydroAgro (coord. E. Lemonnier et C. Castanet), The Project PAYAMA (coord. A. Garnier and E. Lemonnier), the LabEx DynamiTe (ComUE heSam), the Ministère des Affaires Etrangères (France), the Pacunam foundation, the Perenco company (Guatemala), the CNRS (France) and the Université de Paris 1 Panthéon Sorbonne. This research benefits from the institutional support of the Centro de Estudios Mexicanos y Centroamericanos (Guatemala).