Amalia Spina
email: amalia.spina@unipg.it

Marco Vecoli

Armelle Riboulleau

Geoff Clayton

Simonetta Cirilli

Alessandro Di Michele

Annunziato Marcogiuseppe

Roberto Rettori

Paola Sassi

Thomas Servais

Laurent Riquier

Application of Palynomorph Darkness Index (PDI) to assess the thermal maturity of palynomorphs: A case study from North Africa

Keywords: Colour Index, TAI: Thermal Alteration Index and PDI: Palynomorph Organic matter, thermal maturity, Silurian, Devonian, Palynomorph Darkness Index, North Africa

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

1.

Introduction

It is well known that palynomorphs can be used successfully for a wide range of geological investigations other than biostratigraphy, including sediment provenance analysis (e.g., [START_REF] Vecoli | Quantitative evaluation of microplankton palaeobiogeography in the Ordovician-Early Silurian of the northern Trans European Suture Zone: implications for the timing of the Avalonia-Baltica collision[END_REF], structural geology (e.g. [START_REF] Delcaillau | Morphotectonic evidence from lateral propagation of an active frontal fold; Pakuashan anticline, foothills of Taiwan[END_REF][START_REF] Dorning | Organic microfossil geothermal alteration and interpretation of regional tectonic provinces[END_REF], geo-thermometry (e.g. [START_REF] Pross | Thermal alteration of terrestrial palynomorphs in mid-Cretaceous organic-rich mudstones intruded by an igneous sill (Newfoundland Margin, ODP Hole 1276A)[END_REF] and hydrocarbon source rock potential (e.g. [START_REF] Jiang | Spore/Pollen Fossil Colouration and Petroleum Source Rock Quality[END_REF]. Sedimentary organic matter (OM) is known for its high sensitivity to thermal evolution. Palynomorphs (e.g. sporomorphs and acritarchs) are composed of resistant organic polymers, the exact molecular structure of which remains the subject of debate; an important characteristic of these polymers is the internal re-ordering of their molecular structure resulting from processes acting during burial (depth and duration, geothermal flux, fluid geochemistry). In many palynomorphs, these processes result in colour alteration that is directly related to the maximum temperature attained. Nonetheless, post-depositional oxidation due to weathering can not only corrode or even destroy palynomorphs but can also lighten their colour (e.g. Traverse, 2008 and references therein). The characteristic of palynomorphs to change colour with increasing temperature has enabled the development of powerful tools for identifying the thermal history of sedimentary basins (e.g., [START_REF] Batten | Palynofacies and petroleum potential[END_REF][START_REF] Marshall | Quantitative spore colour[END_REF][START_REF] Smith | Spectral correlation of spore coloration standards[END_REF]Gray and Boucout, 1975). In order to evaluate the thermal maturity of sedimentary OM, several optical, physical and chemical maturity methods have been developed (Hartkopf-Fröder et al., 2015 and references therein). Thermal maturity is generally estimated using organic geochemistry (e.g. Rock-Eval pyrolysis; etc.) and optical methods (e.g. Thermal Alteration Index, Spore Colour Index, Acritarch Alteration Index, Palynomorph Darkness Index, Vitrinite and Chitinozoan Reflectances, etc.). Rock-Eval pyrolysis provides different information on the organic content, such as the petroleum potential of a rock, the nature of the kerogen and T max , which is defined as the pyrolysis temperature at which the maximum amount of hydrocarbon is released by kerogen [START_REF] Espitalié | La pyrolyse Rock-Eval et ses applications[END_REF]. As a general rule, T max increases linearly with increasing maturity of the OM.

Organic optical methods such as the Thermal Alteration Index (TAI; [START_REF] Staplin | Sedimentary organic matter, organic metamorphism and oil and gas occurrence[END_REF], Spore Color Index (SCI; [START_REF] Smith | Spectral correlation of spore coloration standards[END_REF], Acritarch Alteration Index (AAI; [START_REF] Williams | Thermal maturity and burial history of Paleozoic rocks in western Newfoundland[END_REF][START_REF] Legall | Thermal maturation, burial history and hotspot development, Paleozoic strata of southern Ontario-Quebec, from conodont and acritarch colour alteration studies[END_REF] are based on the sensitivity of palynomorph colour to evolve progressively in response to increasing temperature in the lower range of thermal maturity [START_REF] Marshall | Quantitative spore colour[END_REF]. These approaches are based on the visual inspection of a selected class of palynomorphs to determine their alteration index that can then be correlated with other indicators such as vitrinite reflectance. The estimation of thermal maturity based on optical investigation of microfossils is also relatively inexpensive. Geochemical methods have the main advantage of being independent from the operator's colour perception in contrast to the qualitative TAI, SCI and similar methods. That said, some organic geochemical methods are less reliable in rocks with scarce OM and need specialized and relatively expensive analytical equipment. Recently, [START_REF] Goodhue | Palynomorph Darkness Index (PDI)a new technique for assessing thermal maturity[END_REF] proposed a new quantitative method to establish the thermal maturity of OM: the Palynomorph Darkness Index (PDI). This is a relatively simple method that utilizes a transmitted light microscope with digital imaging capacity and software capable of simple image analysis. In this study, we applied this method to samples from two subsurface sections in the Ghadamis Basin in southern Tunisia and western Libya of Silurian and Devonian age respectively. PDI values were calibrated against a variety of other thermal maturity indicators in order to evaluate the PDI as a method that can provide a rapid and inexpensive means of estimating thermal maturity and can be deployed during routine palynostratigraphic investigations in thermal history studies of sedimentary basins.

Geological setting

The studied subsurface material was obtained from two boreholes, one in southern Tunisia (Tt-1 borehole), and one in western Libya (D1-26 borehole). During Silurian-Devonian time, the study area occupied the depocentre of the Ghadamis Basin, covering an area of about 200,000 km 2 (Fig. 1). This is now an intracratonic depression containing important hydrocarbon plays. To the north and east, the Ghadamis Basin is bounded by the Talemzane Arch (Dahar-Naffusah High) and the Qarqaf Uplift, respectively. The western margin of the basin is marked by the prominent Amguid-El Biod High, a highly faulted uplift trend. To the south, the Ghadamis Basin is separated from the neighbouring Illizi Basin by a series of highs of lower relief. All of these structural features have complex histories, originating during the late Precambrian Pan African orogeny and undergoing repeated reactivation during the Phanerozoic. The sedimentary succession of the Ghadamis Basin ranges in age from Palaeozoic to Cenozoic. It attains a maximum thickness of 3600 m and consists of alternating transgressive and regressive marine sandstone, shales, siltstones and locally limestones, and is represented by the Mamuniyat, Tanezzuft, Acacus, Tadrart, Ouan Kasa, Awaynat

Wanin, Tahara and Mrar formations [START_REF] Acheche | Ghadames Basin, southern Tunisia: a reappraisal of Triassic reservoirs and future prospectivity[END_REF].

Lithostratigraphy

Tt-1 borehole

The studied stratigraphic interval from -1286.9m to -1240.5m, belongs to the "Argiles Principales" Formation, attributed to the Rhuddanian-Ludfordian time interval (Fig. 2; [START_REF] Vecoli | Palynology, organic geochemistry, and carbon isotope analysis of a latest Ordovician through Silurian clastic succession from borehole Tt-1, Ghadamis Basin, southern Tunisia, North Africa: palaeoenvironmental interpretation[END_REF][START_REF] Jaeger | Le Silurien enTunisie; ses relations avec le Silurien de Libye nord-occidentale[END_REF] [START_REF] Jaeger | Le Silurien enTunisie; ses relations avec le Silurien de Libye nord-occidentale[END_REF]. The uppermost interval (from -1247.9m), yielded miospores and chitinozoans of late Ludfordian age [START_REF] Vecoli | Palynology, organic geochemistry, and carbon isotope analysis of a latest Ordovician through Silurian clastic succession from borehole Tt-1, Ghadamis Basin, southern Tunisia, North Africa: palaeoenvironmental interpretation[END_REF]. The Silurian sequence ends at a major erosional surface, above which Lopingian deposits were documented [START_REF] Jaeger | Le Silurien enTunisie; ses relations avec le Silurien de Libye nord-occidentale[END_REF].

D1-26 borehole

The D1-26 borehole penetrated the Acacus Fm. (Silurian) to Garian Fm. (Turonian). In the present study, core samples from the Devonian Awaynat Wanin Group were analysed (Fig. 2). In its Awaynat Wanin type area, this group is subdivided into four formations, the Awaynat Wanin I to IV [START_REF] Ben Rahuma | The Stratigraphic Evolution of the Devonian Sequences, Awaynat Wanin area, Southern Ghadamis Basin: a Fieldguide Book[END_REF][START_REF] Mergl | A palaeontological review of the Devonian and Carboniferous succession of the Murzuq Basin and the Djado Sub-basin[END_REF]. The same formations were also reported by [START_REF] Massa | Paléozoïque de Libye Occidentale. Stratigraphie et Paléogéographie[END_REF] [START_REF] Vos | Sedimentology of an Ordovician fan delta complex, western Libya[END_REF]. [START_REF] Massa | Paléozoïque de Libye Occidentale. Stratigraphie et Paléogéographie[END_REF] indicated that the radioactive shale is located at the transition between the Awaynat Wanin III and IV formations. Samples from core 7 are within the radioactive shales but samples from core 8 are outside this unit. The resistivity curve shows a marked increase from -2353m to ~-2362.2m (Fig. 2) corresponding to the organic-rich clays. From these observations, the boundary between the Awaynat Wanin III and IV formations is placed at -2353m.

The macrofauna and microfauna are impoverished due to restricted facies or even euxinic conditions. Small bivalves, tentaculites, foraminifera and ostracods are recognized and the Awaynat Wanin IV Fm. was tentatively attributed to the Famennian [START_REF] Massa | Paléozoïque de Libye Occidentale. Stratigraphie et Paléogéographie[END_REF].

Material and methods

Twenty-six samples (8 from Tt-1 borehole and 18 from D1-26 borehole) were processed for palynological and geochemical study, including PDI, and Rock-Eval analyses as follows:

Palynological analysis:

Twenty grams of sediments from each sample were dissolved in HCl and HF to isolate the organic fraction. No oxidation was performed on the organic residue which was sieved at 10 μm in order to eliminate the finer fraction of the amorphous OM and facilitate optical microscopy. Three to nine palynological slides for each sample were studied in order to reach a 250 palynomorph count for each sample. The stratigraphical occurrence of miospore taxa in borehole D1-26 is shown in Table 1. Palynological slides are stored in the collection of the UMR 8198 Evo-Eco-Paleo, Université de Lille, Villeneuve d'Ascq (France).

Thermal Alteration Index (TAI) and Spore Colour Index (SCI):

Optical microscopy was used to establish the thermal maturity of the OM in this study. TAI [START_REF] Staplin | Sedimentary organic matter, organic metamorphism and oil and gas occurrence[END_REF] and SCI [START_REF] Marshall | Spore colour measurement[END_REF][START_REF] Hillier | Organic maturation, thermal history and hydrocarbon generation in the Orcadian Basin, Scotland[END_REF][START_REF] Collins | The 1-10 Spore Colour Index (SCI) scale: a universally applicable colour maturation scale, based on graded, picked palynomorphs[END_REF][START_REF] Fisher | Organic maturation and hydrocarbon generation in the Mesozoic sediments of the Sverdrup Basin, Arctic Canada[END_REF][START_REF] Haseldonckx | Relation of palynomorph colour and sedimentary organic matter to thermal maturation and hydrocarbon generating potential[END_REF]Fig. 3) were assessed from the colour of smooth, unfolded and unornamented miospore specimens in unoxidised residues based on a visual comparison to Munsell colour standards as suggested by [START_REF] Pearson | Pollen/spore colour "standard[END_REF] in [START_REF] Traverse | Paleopalynology[END_REF]. TAI uses a five-point scale.

Transparent to pale yellow colour indicates TAI 1, medium orange TAI 2, dark brown TAI 3, black TAI 4, and vitreous black with breakage indicates TAI 5 [START_REF] Staplin | Sedimentary organic matter, organic metamorphism and oil and gas occurrence[END_REF]. SCI ranges from 1 to 10 and reflects a colour gradation from colourless or pale yellow to black (Fig. 3). Approximately 50 miospores per sample were examined in order to estimate TAI and SCI.

Acritarch Alteration Index (AAI):

In the present study, AAI was established for leiospheres as suggested by [START_REF] Legall | Thermal maturation, burial history and hotspot development, Paleozoic strata of southern Ontario-Quebec, from conodont and acritarch colour alteration studies[END_REF] and for acritarchs as indicated by [START_REF] Williams | Thermal maturity and burial history of Paleozoic rocks in western Newfoundland[END_REF]Fig. 3). [START_REF] Legall | Thermal maturation, burial history and hotspot development, Paleozoic strata of southern Ontario-Quebec, from conodont and acritarch colour alteration studies[END_REF] studied the change in leiosphere colour and proposed a 5-point scale, the Acritarch Colour Alteration Index (AAI), originally based on leiosphere and acritarch colour. Leiospheres and acritarchs change progressively in colour from light yellow and translucent, through pale yellow, yellow orange, orange, brown, to black. However, more recent studies reveal that leiospheres may follow a different colour maturity path to that of acritarchs [START_REF] Hartkopf-Fröder | Optical thermal maturity parameters and organic geochemical alteration at low grade diagenesis to anchimetamorphism: a review[END_REF][START_REF] Williams | Thermal maturity and burial history of Paleozoic rocks in western Newfoundland[END_REF] with leiosphere colour changing more rapidly at lower temperatures than that of acritarchs [START_REF] Duggan | Colour change in the acritarch Veryhachium as an indicator of thermal maturity[END_REF][START_REF] Dorning | Organic microfossil geothermal alteration and interpretation of regional tectonic provinces[END_REF], probably due to differences in wall chemistry. The scale of [START_REF] Legall | Thermal maturation, burial history and hotspot development, Paleozoic strata of southern Ontario-Quebec, from conodont and acritarch colour alteration studies[END_REF] may therefore be more applicable to prasinophycean algae than to acritarchs. In the scale of Legall et al. Acritarchs considered in this study are thin, smooth-walled forms without an inner body. About 50 acritarchs and prasinophycean algae (i.e. Tasmanites) per sample were selected in order to estimate AAI.

Palynomorph Darkness Index (PDI):

PDI is determined from measurement of the red, green and blue (RGB) intensities of light transmitted through palynomorphs to produce a single greyscale value. In the present study, palynomorphs were digitally imaged using a Leica DM1000 microscope, with a LeicaICC50 ® with Tasmanites) per sample were selected. Ten measurements of circa 16 µm 2 areas were performed for each palynomorph. Unornamented, unfolded, smooth and unalterated acritarchs, Tasmanites and miospores as Retusotriletes spp. and Ambitisporites sp. were chosen for PDI studies (Table 2).

Images were collected at a constant illumination setting using 40× magnification. These images were analysed using ImageJ, an open source Java image processing program (http://imagej.net/ImageJ) and the following procedure. The palynomorph interior was selected manually using the Lasso Selection Tool of ImageJ. The palynomorph image was acquired and processed to obtain a PDI value for each sample analysed (Plate 1), following the suggestions of [START_REF] Goodhue | Palynomorph Darkness Index (PDI)a new technique for assessing thermal maturity[END_REF]. PDI (i.e. PDImiospore, PDIacritarch, PDITasmanites) values obtained from the Tt-1 and D1-26 boreholes, respectively, are shown in Table 2.

Rock-Eval Pyrolysis:

The two main aims of Rock-Eval pyrolysis analysis were to characterize the type and maturity of the OM present and to determine the petroleum potential of the rocks sampled.

The total organic carbon content (TOC in weight %) from Tt-1 core samples was determined on 100 mg of ground sediment sample with a Rock-Eval instrument, an Oil Show Analyser device (OSA or RE2, [START_REF] Espitalié | La pyrolyse Rock-Eval et ses applications[END_REF] at the Université Paris 6, France. The D1-26 core samples were analyzed on a Rock-Eval 6 instrument (RE6) at the Institut Français du Pétrole. Other parameters given by the Rock-Eval are the petroleum potential (S 2 in mg HC/ g of rock), the hydrogen index (HI in mg HC/g TOC) depending to the origin and state of preservation of the OM, and the T max (°C), an indicator of thermal maturity of the OM [START_REF] Espitalié | La pyrolyse Rock-Eval et ses applications[END_REF].

Palynostratigraphy of D1-26 borehole

Detailed taxonomic evaluation of the various groups of palynomorphs is beyond the scope of the present paper. Here, only the major features of the assemblages and their chronostratigraphic significance are discussed in order to assess the age determination. [START_REF] Moreau-Benoit | Palynological study of the Devonian in the Illizi Basin (East Algerian Sahara) biostratigraphical approach[END_REF]Boumendjel et al., 1988), Saudi Arabia and Tunisia [START_REF] Breuer | Devonian spore assemblages from northwestern Gondwana: taxonomy and biostratigraphy[END_REF] and Libya [START_REF] Moreau-Benoit | Les spores du Dévonien moyen et supérieur de Libye occidentale: compléments, systématique, répartition stratigraphique[END_REF]. Other forms such as C. cyathus and G. lemurata have a worldwide distribution, extending through the Givetian and

Frasnian (Breuer and Steemans, 2013 with references). [START_REF] Loboziak | Middle-Upper Devonian miospores from the Ghadamis Basin (Tunisia-Libya): Systematics and stratigraphy[END_REF] brasiliensis. Evittia spp., Duvernaysphaera spp. and Gorgonisphaeridium spp. were also recorded.

Overall, the above assemblage is consistent with a Late Devonian (Frasnian-Famennian) age, in agreement with the age indications from the miospore assemblage.

Thermal maturation of sedimentary organic matter

TAI and SCI

As shown in Fig. 4A, in Tt-1 borehole, TAI and SCI were established from five core-samples, all of which fall within the oil window with the exception of one sample (-1240.5m). A slight trend of decreasing TAI and SCI values upwards is observed. On the other hand, in D1-26 borehole, 4 of 15 core-samples fall within the oil window with the other 11 core-samples indicate an immature stage, though most of these fall close to the oil window (Fig. 4E). TAI and SCI values are more variable in D1-26 than in Tt-1, and no clear trend upwards is observed.

AAI

In the present study, the AAI of [START_REF] Williams | Thermal maturity and burial history of Paleozoic rocks in western Newfoundland[END_REF]Fig. 4B, F) and [START_REF] Legall | Thermal maturation, burial history and hotspot development, Paleozoic strata of southern Ontario-Quebec, from conodont and acritarch colour alteration studies[END_REF]Fig. 4C, G) were established for acritarchs and prasinophycaeans, respectively, from both the Tt-1 and D1-26 boreholes. Four samples from the Tt-1 borehole fall in the oil window on the basis of acritarch colour, the other samples showed AAI values less than 1.8, suggesting a position in the biogenic gas window (immature zone). A slight decreasing trend of AAI values upwards is noted (Fig. 4B).

Different results were obtained in the same borehole from determinations of the AAI of [START_REF] Legall | Thermal maturation, burial history and hotspot development, Paleozoic strata of southern Ontario-Quebec, from conodont and acritarch colour alteration studies[END_REF] on the basis of Tasmanites colour. In this case, all the samples fall within the oil window (Fig. 4C), without any trend upward. The AAI values of acritarchs from the D1-26 borehole indicate that only seven samples fall within the biogenic gas window and all the others lie within the oil window (Fig. 4F). Similar results were obtained from the AAI of Tasmanites (Fig. 4G). No clear trend of AAI values based on acritarchs and Tasmanites is observed.

PDI

In borehole Tt1, average PDI values for each group of palynomorphs show little variation: almost constant values are noted for Tasmanites and miospores, while a slight decreasing trend upward is noted for acritarchs (Fig. 4D). Acritarchs systematically show lower PDI values than Tasmanites and miospores, reflecting their overall lighter colour. In borehole D1-26, PDI values show more variability (Fig. 4D) with no vertical trend in PDI observed. As in the Tt-1 samples, acritarchs generally show lower PDI values, though the difference to the other palynomorphs is smaller than in Tt-1. It can be observed that some samples (-2350.6m, -2377.4m, -2380.2m) systematically show lower PDI values for the three palynomorphs groups compared to the other samples (Fig. 4H).

Rock-Eval Pyrolysis

Rock-Eval pyrolysis results from borehole Tt-1 previously published by [START_REF] Vecoli | Palynology, organic geochemistry, and carbon isotope analysis of a latest Ordovician through Silurian clastic succession from borehole Tt-1, Ghadamis Basin, southern Tunisia, North Africa: palaeoenvironmental interpretation[END_REF] are summarized in Table 2 andFig slightly less mature than the samples from the lower interval (core 8).

PDI and SCI-AAI

A correlation between PDI and SCI-AAI values from both boreholes (Fig. 6) shows that:

-when PDI and the other colour indicator based on the same palynomorph are compared (Fig. 6A), they generally appear positively well correlated, with exception of PDI Tasmanites vs. AAI Tasmanites in borehole Tt-1 (R 2 =0.17);

-when different thermal maturity indicators from different palynomorphs are considered (e.g. PDI miospore vs. PDI acritarch ; PDI miospore vs. AAI; SCI vs. AAI; etc.), as a rule a positive correlation is generally observed, but of poorer quality (Fig. 6A). This may be related to the fact that colour changes in the different palynomorphs (i.e. miospore, acritarch, Tasmanites) do not occur at the same maturity level. This has been previously described in the literature (e.g. Hartkopf-Fröder et al., 2015 and references therein) and can be related to the different chemical composition of the tissues of these different palynomorphs.

(Fig. 6B, C, D), their correlation is positive although the value of R 2 is only around 0.6. This weak positive correlation might be related to the discrepancy observed between the two datasets from Tt-1-and D1-26 boreholes, when the PDI-T max data are plotted together (see the discussion below).

Rock-Eval Pyrolysis and PDI

PDI values were calibrated with Rock-Eval Pyrolysis data from Tt-1 and D1-26 boreholes (Fig. 7;

Table 2). When all the data from borehole D1-26 are plotted, PDI shows a generally positive linear correlation with T max , consistent with the increased value of PDI with maturity observed by [START_REF] Goodhue | Palynomorph Darkness Index (PDI)a new technique for assessing thermal maturity[END_REF]. Nevertheless, a few data points fall out of the correlation (Fig. 7B). This is the case for the PDI data of miospores and Tasmanites in sample -2158.3m, which appear abnormally high compared to the T max value. Because the number of data points from borehole Tt-1 is smaller, correlations of PDI data with T max values are less solid than in borehole D1-26. However, a positive correlation is observed between T max and PDI data of miospores and Tasmanites. No clear correlation between T max and PDI values from acritarchs is observed (Fig. 7A). Several samples in this borehole were very poor in acritarchs and large standard deviations on the data are observed, which might explain the absence of correlation.

The absence of a correlation between PDI and T max values in some samples could result from a bleaching or a darkening of palynomorphs, leading to lower or higher PDI values, respectively. The modification of palynomorphs colour can be related to oxidation within soils, in the case of sporomorphs, during transport, or during periods of enhanced oxygenation of the sediment [START_REF] Tyson | Palynological kerogen classification[END_REF]. For this reason, these outlying samples were removed from further consideration, and only samples showing a strong linear PDI -T max relationship were plotted in the other PDI vs. Rock-Eval parameter diagrams (Hydrogen Index, S2 and Production Index; Fig. 7C-H).

In both boreholes, PDI is negatively and poorly correlated with PI (R 2 < 0.05), although, in Tt-1, the negative correlation of PDI miospore is clear (R 2 value ~0.67; Fig. 7G). The poor correlation between PDI and PI values is surprising, since both parameters should increase with maturity. However, PI values also depend on petroleum migration: expulsion of petroleum from the rock leads to a decrease of the S 1 and PI, while these parameters increase in the case of oil accumulation in a rock [START_REF] Espitalié | La pyrolyse Rock-Eval et ses applications[END_REF]. A negative or very low correlation between PDI and PI values can therefore be expected for rocks where petroleum migration has occurred as is likely to be the case in both studied boreholes.

In borehole Tt-1 and D1-26, for all three palynomorph groups the PDI is generally weakly correlated with HI (Fig. 7C,D). Correlation between PDI and S 2 is also poor (Fig. 7E,F).

Very low positive correlations are recognized in the borehole D1-26 comparing PDI with HI, mostly due to one sample with a high S 2 value (-2371.3m). Hydrogen index values decrease when the maturity of the OM increases [START_REF] Espitalié | La pyrolyse Rock-Eval et ses applications[END_REF]. For this reason, one might expect to observe a good negative correlation between HI and PDI values. Nevertheless, HI values also strongly depend on the origin of the organic matter and its degree of (bio)degradation [START_REF] Espitalié | La pyrolyse Rock-Eval et ses applications[END_REF]. As previously discussed, the Rock-Eval parameters indicate that in both boreholes, the organic matter belongs to the types II and III (Fig. 5), indicating that the source and/or degree of degradation of the OM is variable. In addition, S 2 and HI values also depend on oil migration, which likely occurred in these boreholes. Bearing in mind that mature algo-bacterial (type II) OM can have a higher HI value than immature OM of terrestrial origin (type III), the variable origin of the OM in both boreholes Tt-1 and D1-26, added to possible oil migration, probably explains the poor correlations observed between PDI and HI.

As shown in Fig. 8 (A,C,E), for each category of palynomorphs, the correlation between PDI and T max values is different in the two studied cores. As a result, poor correlations between PDImiospore and PDITasmanites values and Rock-Eval data are obtained when data from the two boreholes are combined (Fig. 8A,E). The discrepancy between these two datasets could be of geological origin and either related to different sedimentological context for the two studied intervals [START_REF] Massa | Paléozoïque de Libye Occidentale. Stratigraphie et Paléogéographie[END_REF][START_REF] Vecoli | Palynology, organic geochemistry, and carbon isotope analysis of a latest Ordovician through Silurian clastic succession from borehole Tt-1, Ghadamis Basin, southern Tunisia, North Africa: palaeoenvironmental interpretation[END_REF], or to different source organisms for the OM. The similar discrepancy observed between the two boreholes in the SCI or AAI vs. PDI data (Fig. 6) gives support to such explanation. Nevertheless, we explored the possibility that it could be due to the different origins of Rock-Eval data. Indeed, these came from two different machines: RE2 for Tt-1 borehole and RE6

for D1-26 borehole. [START_REF] Behar | Rock-Eval 6 technology: performances and developments[END_REF] showed there was a small difference in S 2 values and consequently in T max values generated by these different generations of Rock-Eval machines: RE6

gives slightly higher T max values than RE2. We converted T maxRE6 values from D1-26 to T maxRE2 values following the equation T maxRE2 = 0.895(T maxRE6 ) + 41.870 proposed by [START_REF] Behar | Rock-Eval 6 technology: performances and developments[END_REF] Table 2). After conversion of T max values, while the PDI-T max correlation for the total dataset is little modified for acritarchs (Fig. 8D), this correlation improves for miospores and Tasmanites (Fig. 8B,F).

Rock-Eval Pyrolysis and SCI-AAI

SCI and AAI values were also compared with Rock-Eval Pyrolysis data by plotting the same samples considered for PDI calibration vs. T max (Fig. 9).

In borehole Tt-1 both SCI and AAI (calculated on acritarchs) are not well correlated with T max showing R 2 ~0.2 and 0.5, respectively (Fig. 9A,C) and AAI (calculated on Tasmanites) and T max

shows very poor correlation (Fig. 9E). These poor correlations can be related to the very small number of data in this borehole. Better results were obtained from correlation of optical and Rock-Eval parameters in D1-26 borehole. Here, AAI (calculated on acritarchs) and T max show a strong positive correlation (R 2 ~0.8; Fig. 9D), while positive correlations were obtained for SCI (Fig. 9B)

and AAI (calculated on Tasmanites: Fig. 9F).

6.8 Vitrinite reflectance and PDI in D1-26 borehole.

Recently, [START_REF] Clayton | Correlation of Palynomorph Darkness Index and vitrinite reflectance in a submature Carboniferous well section in northern Saudi Arabia[END_REF] tentatively established the relationship between PDI determined on spores and Ro (i.e. vitrinite reflectance, the industry standard for determination of maturity) to be: PDI=65.01Ro+11.587. In D1-26 borehole, this relationship was used to calculate the vitrinite reflectance values from PDI miospore (Table 2). The vitrinite reflectance for the interval from -2164m to -2158.3m calculated ranges from 0.47 to 0.65% with an average of 0.52%. This value supports the vitrinite reflectance measurements of 0.41 to 0.45% published by [START_REF] Underdown | The importance of constraining regional exhumation in basin modelling: a hydrocarbon maturation history of the Ghadames Basin, North Africa[END_REF] from the considered depth interval. Encouraging results were also obtained for the other depth interval of D1-26 considered in this work, ranging from -2381.4m to -2346.9m where the vitrinite reflectance rangess from 0.51 to 0.59% and the vitrinite values calculated from PDI miospore are of 0.56%.

Conclusions

In the present study, we have analysed the organic matter content from two stratigraphic intervals of different ages: the first one belongs to the "Argiles Principales" in Tt-1 borehole, attributed to Wenlock-Ludlow time interval by [START_REF] Jaeger | Le Silurien enTunisie; ses relations avec le Silurien de Libye nord-occidentale[END_REF] and [START_REF] Vecoli | Palynology, organic geochemistry, and carbon isotope analysis of a latest Ordovician through Silurian clastic succession from borehole Tt-1, Ghadamis Basin, southern Tunisia, North Africa: palaeoenvironmental interpretation[END_REF]; the second one is characterized by the Awaynat Wanin III and IV formations in borehole D1-26, attributed on the basis of palynomorphs content, to the Frasnian -latest Famennian.

Thermal maturity of the OM was estimated using Rock-Eval Pyrolysis and optical methods (TAI, SCI, AAI and PDI). Rock-Eval pyrolysis indicates that in both boreholes the OM is at the beginning of the oil window. The organic matter is mainly of marine origin (Type II) in Tt-1 borehole, while in borehole D1-26, some samples belong to Type III, indicating altered OM of marine origin, and/or terrestrial OM.

We are fully aware that, although our dataset is quite small and that the range of maturity of the samples studied here is not large, comparison of different thermal maturity indices revealed that the qualitative methods, TAI and SCI do not always yield reliable results. Conversely, our data confirm the validity of the quantitative PDI method as a thermal indicator. We here show that, in addition to sporomorphs, the PDI approach can be applied to marine palynomorphs (acritarchs and Tasmanites). As for the other optical methods, PDI values in a sample vary according to the palynomorph considered, so that only PDI values from the same type of palynomorph must be compared. Though more studies are needed before establishing a reliable calibration of PDI values against Rock-Eval, our data suggest that, like T max , PDI could have a general applicability, as long as it is applied only to the same type of palynomorph. The direct correlation of sporomorph PDI to vitrinite reflectance recently proposed by [START_REF] Clayton | Correlation of Palynomorph Darkness Index and vitrinite reflectance in a submature Carboniferous well section in northern Saudi Arabia[END_REF] is also validated here.

(

  1981), translucent to light yellow (AAI = 1) and light yellow to pale yellow (AAI = 2) indicate the immature hydrocarbon zone (temperatures less than 70 °C). Pale yellow to orange leiospheres (AAI = 3) indicate the upper part of the oil and wet gas window, and orange to dark brown leiospheres (AAI = 4) indicate the peak of the oil and wet gas window. Black leiospheres (AAI = 5) are indicative of the lower oil and wet gas window and the upper part of the dry gas window. A different, 4-point AAI scale for acritarchs colour change was proposed by Williams et al. (1998).

  . 5A. These values indicate that generally the OM dominantly belongs to Type II, and is of marine origin. The average T max value of 436°C indicates that, overall, the OM is at the beginning of the oil window in the interval investigated. Pyrolysis results from borehole D1-26 are presented in Table2 and Fig. 5B. Although they include the radioactive shales that are rich in OM of marine origin, the samples investigated are only moderately to poorly enriched in OM with a mean TOC of 1.6%. The samples studied are mostly characterized by Type III OM corresponding to altered OM of marine origin, and/or to terrestrial OM, although the other OM corresponds to Type II. The average T max value of 437°C indicates that the OM has reached the beginning of the oil window. Nevertheless, samples from the upper interval (cores 6 and 7) are

Figure captions : Fig. 1 :

 :1 Figure captions:

Fig. 2 :

 2 Fig.2: Stratigraphic log and sonic and resistivity curve (the scale is unknown) of investigated tract of borehole D1-26 (modified from Oasis Oils Company, 1961). Black rectangles with numbers correspond to cored sections. Stratigraphic log of investigated tract of borehole Tt-1 (for more detailed information on the lithostratigraphy please refer to[START_REF] Vecoli | Palynology, organic geochemistry, and carbon isotope analysis of a latest Ordovician through Silurian clastic succession from borehole Tt-1, Ghadamis Basin, southern Tunisia, North Africa: palaeoenvironmental interpretation[END_REF].

Fig. 3 :

 3 Fig. 3: Phases of oil and gas generation and correlation between optical thermal maturity parameters (from Hartkopf-Fröder et al., 2015 and references therein).

Fig. 4 :

 4 Fig. 4: Organic matter alteration index from Tt-1 and D1-26 boreholes. Tt-1 borehole: A: Thermal Alteration Index (TAI) and Spore Colour Index of miospores; B: Acritarch Alteration Index (AAI) of acritarchs; C: Acritarch Alteration Index (AAI) of Tasmanites; D: PDI of miospores, acritarchs and Tasmanites. D1-26 borehole: E: Thermal Alteration Index (TAI) and Spore Colour Index of miospores; F: Acritarch Alteration Index (AAI) of acritarchs; G: Acritarch Alteration Index (AAI) of Tasmanites; H: PDI of miospores, acritarchs and Tasmanites.

Fig. 5 :

 5 Fig.5: Diagram of[START_REF] Espitalié | La pyrolyse Rock-Eval et ses applications[END_REF] showing the relationship between HI and T max in the borehole Tt-1 (A) and in the borehole D1-26 (B).

Fig. 6 :Fig. 7 :

 67 Fig. 6: Correlation of PDI and SCI-AAI values from Tt-1 and D1-26 boreholes. R 2 value in the yellow cell indicates a negative correlation between the values of thermal maturity parameters.

Fig. 8 :

 8 Fig. 8: PDI-T max correlation for the total dataset. A: T max values from two different machines: RE2 for Tt-1 borehole and RE6 for D1-26 borehole. B: T maxRE6 values from D1-26 borehole converted in T maxRE2 applying the formula of Behar et al. (2001).

Fig. 9 :

 9 Fig. 9: Correlation of SCI-AAI and T max values in Tt-1 and D1-26 boreholes. PDImiospore: orange dots and line; PDIacritarch: blue dots and line; PDITasmanites: green dots and line.

Fig. 2

 2 Fig. 2

Fig. 3

 3 Fig. 3

Fig. 4

 4 Fig. 4

Fig. 5

 5 Fig. 5

Fig. 6 A

 6 Fig. 6

Fig. 7

 7 Fig. 7

Fig. 8

 8 Fig. 8

  Fig. 9

  ). The basal part of the formation consists of sandstones and quartzites with interbedded shale layers passing to dark grey to black shales and marls, with rare limestone/dolostone intercalations. The upper part is characterized by a monotonous succession of dark grey silty shales. From bottom to top, graptolites of the vesiculosus and of the murchisoni and rigidus zones indicate a Rhuddanian and Sheinwoodian age, respectively. The lundgreni graptolite Zone of Homerian age, lies near -1273m to -1270.5m. The overlaying interval includes the vulgaris graptolite Zone of late Wenlock to ?lower Ludlow age

  from subsurface data. Rocks with the highest hydrocarbon source rock potential are developed in the Awaymat Wanin III and IV formations, where this palynological study was yielded. The Awaynat Wanin III Fm. is characterized by an abundance of shales. The Awaynat

	Wanin IV Fm. is mainly characterized by calcilutites with shaly intercalations in the lower part. The
	upper part consists of shales with scattered sandstone intercalations. The sediments of the Awaynat
	Wanin Group were deposited in a shallow marine deltaic environment within the storm wave base,
	with prodelta silty clay/claystone beds passing upward into distributary channel sandstones. Fluvial
	intervals are minor but present

  3.1 mpx resolution digital camera, and LAS EZ ® image acquisition software. The palynomorph content of twenty-six samples (eight from Tt-1 borehole and eighteen from D1-26 borehole) was suitable for PDI analysis. Approximately thirty palynomorphs(10 miospores, 10 acritarchs, 10

  The investigated sequence comprises the top of the Awaynat Wanin III Fm. and the overlying Awaynat Wanin IV Fm. From bottom to top, the palynological assemblage varies in terms of preservation, diversity and palynomorph content (Plate 2, Table1). Permanent tetrads such as Tetrahedraletes medinensis and dyads such as Dyadospora murusattenuata in assemblage with smooth trilete spores as well as Ambitisporites sp. and Retusotriletes spp. occurred scarcely in the Awaynat Wanin III Fm. (-2381.4m to -2375.9m). Near to the top of the Awaynat Wanin III Fm. (-2372.2m), trilete spores such as Cymbosporites senex, C. cyathus, Grandispora inculta and Verrucosisporites polygonalis occurred. Only a few specimens of Retusotriletes spp. were recognized from the lowest sample of the Awaynat IV Fm. The remaining basal part (-2348.1m to -2346.9m) was barren in terms of miospore content. The upper levels of the Awaynat Wanin IV Fm. (-2164.0m to -2158.3m) yielded a very well preserved and diversified microflora. The assemblage is characterized by an abundance

of Retispora lepidophyta and less R. macroreticulata in assemblage with Knoxisporites literatus, Verrucosisporites nitidus and other miospore taxa.

The microflora recorded shows close similarities with Mid-Late Devonian assemblages from Gondwana and other palaeogeographic areas. Almost all the miospores from the top of the Awaynat Wanin III Fm. are Frasnian or older. Grandispora inculta has been recorded previously from the Givetian to Frasnian of Algeria (Moreau

  attributed core sample -2440.0m, from near the base of the Awaynat Wanin III Fm. to the Frasnian. Accordingly, on the basis of the stratigraphic range of miospores recorded and the age attribution of the sample from -2440.0m, we assigned a Frasnian age to the Awaynat Wanin III Fm.Spores such as R. lepidophyta, from the topmost Awaynat Wanin IV Fm., show a widespread and global distribution and are stratigraphically confined to the latest Devonian (late Famennian), as reported by numerous authors. In the palynological literature, R. lepidophyta is considered to be a late Famennian palynostratigraphic index species, making its latest occurrence in close proximity to Acritarch assemblages are well-preserved, relatively abundant and well diversified in the analysed samples, indicating fully marine, shelf depositional conditions, throughout the study section.

	Biostratigraphically important species were recognized, such as Umbellasphaeridium deflandrei,
	Unellium winslowiae, Polyedryxium pharaone, P. decorum, Stellinium octoaster, Maranhites cf.

the Devonian-Carboniferous boundary

(Wicander and Playford, 2013 and references therein)

. The co-occurrence of V. nitidus further restricts the age of this assemblage to the LN (lepidophytanitidus) biozone of

[START_REF] Streel | Spore stratigraphy and correlation with faunas and floras in the type marine Devonian of the Ardenne-Rhenish regions[END_REF]

. Accordingly, the uppermost Awaynat Wanin IV Fm. (-2164.0m to -2158.3m), is here attributed to the latest Famennian time interval.

1,38 159 0,73 2,2 0,06 0,25 436 NO DATA

Acknowledgements

This study could not have been possible without the support of the late Dominique Massa, who provided core material and other precious information on Tt-1 and D1-26 boreholes, including petrophysical logs. Editor Shifeng Dai, Professor Jen O'Keefe and two anonymous reviewers are thanked for their constructive criticisms that highly improved the original version of this paper. This research did not receive any specific grant from funding agencies in the public, commercial, or notfor-profit sectors.

ACCEPTED MANUSCRIPT

DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA 2348.1 NO DATA "47" "51" NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA 2350.6 34 "14" DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA 0,56 2375.9 "46" "51" "49" NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA 0,53 2377.4 28 20

Amb itisporites sp.

Archaeozonotriletes variabilis

Cymb osporites cyathus

Cymb osporites senex Cymb osporites sp.

Geminospora lemurata

Grandispora incognita

Grandispora inculta

Grandispora rarispinosa

Verrucosisporites polygonalis

Verrucosisporites premnus

Verrucosisporites scurrus Verrucosisporites spp.

Knoxisporites literatus

Knoxisporites sp.

Retispora lepidophyta

Retispora macroreticulata

Verrucosisporites nitidus


Anastasia Wolff
email: anastasia.wolff@developpement-durable.gouv.fr

Natacha Gondran

Christian Brodhag

Integrating corporate social responsibility into conservation policy. The example of business commitments to contribute to the French National Biodiversity Strategy

Keywords: conservation policy, corporate social responsibility, business practices, mitigation hierarchy, stakeholders, NBSAP

Integrating corporate social responsibility into conservation policy. The example of business commitments to contribute to the French National

Biodiversity Strategy

Introduction

Halting biodiversity erosion is a tremendous challenge, as human-induced biodiversity loss has reached exceptionally high rates [START_REF] Ceballos | Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines[END_REF]. It has been argued that the governance of biodiversity cannot rely solely on a law-based approach, but that a multiplicity of other sources of normative rules, integrating the potential role of all groups with relevant interests, are necessary to design an effective policy portfolio [START_REF] Doremus | A policy portfolio approach to biodiversity protection on private lands[END_REF][START_REF] Sampford | Environmental governance for biodiversity[END_REF]. Given the role companies play in biodiversity alteration and their financial and political power, expectations regarding business contribution to biodiversity conservation are growing [START_REF] Robinson | Common and Conflicting Interests in the Engagements between Conservation Organizations and Corporations[END_REF]. In 2010, the Conference of the Parties (COP) of the Convention for biological diversity (CBD), the main international governance body for biodiversity conservation, adopted a Decision entitled "Business engagement" that "[recognizes] the importance of drawing on the capacities of business and private enterprise" and invited the parties "to promote a public policy environment that enables private sector engagement and the mainstreaming of biodiversity into corporate strategies and decision-making" (COP10 CBD, 2010). Such an engagement of companies in biodiversity conservation can be considered as part of their corporate social responsibility (CSR), as CSR "concerns actions by companies over and above their legal obligations towards society and the environment" (European Commission, 2011). Mobilizing CSR in conservation policy thus rely on non-coercive, voluntary approaches [START_REF] Börkey | Voluntary Approaches for Environmental Policy. An assessment[END_REF].

While biodiversity issues had been poorly integrated in CSR compared to other environmental challenges [START_REF] Ernst | La responsabilité sociétale des entreprises : une démarche déjà répandue[END_REF], this political momentum seems to have participated to bring biodiversity issues to economic actors' attention. In a survey comprising more than 1,500 business executives, 64% answered that biodiversity was important to some level to their companies [START_REF] Bonini | The next environmental issue for business: McKinsey Global Survey results[END_REF]. Disclosure on biodiversity issues in CSR reporting has also significantly increased these last years [START_REF] Adler | United Nations Decade on Biodiversity: A study of the reporting practices of the Australian mining industry[END_REF]. A multiplicity of international standard-settings and monitoring mechanisms have been developed in line with the framework provided by the CBD [START_REF] Morgera | From Corporate Social Responsibility to Accountability Mechanisms: The Role of the Convention on Biological Diversity[END_REF], along with new assessment tools (Wolff et al., 2017a). While this gain of visibility may have led firms to put biodiversity higher on their political agenda, whether this translates into concrete efforts to reduce biodiversity loss still needs to be investigated. This materialization is not obvious as the implementation of practical measures has been found to be challenging for companies [START_REF] Overbeek | Biodiversity and the Corporate Social Responsibility Agenda[END_REF][START_REF] Robinson | Common and Conflicting Interests in the Engagements between Conservation Organizations and Corporations[END_REF]. Criticisms have raised regarding the effectiveness and the legitimacy of mobilizing the private sector [START_REF] Macdonald | The Devil is in the (Bio)diversity: Private Sector "Engagement" and the Restructuring of Biodiversity Conservation[END_REF][START_REF] Robinson | Common and Conflicting Interests in the Engagements between Conservation Organizations and Corporations[END_REF][START_REF] Rose | Green Corporate partnerships -are they an essential tool in achieving the conservationist mission, or just a ruse for covering up ecological crimes[END_REF]. Understanding what are (or could be) the effective conservation impacts of biodiversity-oriented CSR has thus become critical for conservationists and policy makers [START_REF] Sutherland | One Hundred Questions of Importance to the Conservation of Global Biological Diversity[END_REF]: What kind of concrete practices do companies put in place as part of their CSR? Who is involved in their implementation? How to integrate CSR in the policy portfolio so that it effectively contributes to the achievement of conservation objectives? Biodiversity-oriented CSR approaches have been somewhat overlooked in the scientific literature. A few studies looked more closely at the corporate practices of specific sectors, such as farming [START_REF] De Snoo | Toward effective nature conservation on farmland: making farmers matter[END_REF][START_REF] Santangeli | Voluntary non-monetary approaches for implementing conservation[END_REF], fish processing [START_REF] Wolff | In hunt for sustainable seafood: sustainaibility effects of CSR in three fish processing companies[END_REF], forestry and mining (Boiral and Heras-Saizarbitoria, 2017a) but this literature is still fragmented. There is thus a need to undertake a trans-sectoral review of business initiatives and to develop a comprehensive framework to classify and interpret them in a consistent manner [START_REF] Winn | Business, Ecosystems, and Biodiversity New Horizons for Management Research[END_REF]. Several studies have pointed out that stakeholders involvement was crucial in the implementation of corporate practices related to biodiversity conservation, notably because of their complexity and the need for business to comfort the legitimacy of such measures (Boiral and Heras-Saizarbitoria, 2017b;[START_REF] Overbeek | From sponsor to partner: NGO-business alliances that support nature conservation in the Netherlands[END_REF][START_REF] Reade | CSR, Biodiversity and Japan's Stakeholder Approach to the Global Bumble Bee Trade[END_REF]. The collective nature of biodiversity-oriented CSR practices thus seems to be an important parameter to take into account if contribution of businesses to biodiversity conservation is to be fostered.

The French National Biodiversity Strategy and Action Plan (NBSAP) 2011-2020 includes a public voluntary program [START_REF] Börkey | Voluntary Approaches for Environmental Policy. An assessment[END_REF]. This policy instrument is used to officially endorse commitment plans of organizations that contribute to the achievement of biodiversity conservation objectives. These commitment plans provide a quite detailed description of the actions that companies have put in place or plan to undertake. Building on the case study of the NBSAP corporate commitment plans, the objectives of this article are to propose a classification of biodiversity-oriented CSR practices, to provide some insights regarding the roles played by stakeholders in their implementation and based on this analysis to draw some lessons on how to better integrate CSR in the policy portfolio for biodiversity conservation.

The paper is organized as follows. Section 2 provides a literature review on biodiversityoriented CSR. Then, Section 3 describes the case study and the methodology used to analyze the corporate commitment plans. The results are subsequently presented in Section 4 in line with the research questions. Finally, Section 5 discusses the study's implications for policy makers and business managers as well as avenues for future research.

Biodiversity-oriented CSR

Positioning CSR in the policy portfolio for biodiversity conservation

There is a spectrum of policy options to engage businesses in biodiversity conservation: coercive approaches based on 'command and control' regulation (e.g. fishing quotas), marketbased mechanisms (e.g. payment for ecosystem services and certification schemes) [START_REF] Lambooy | Opportunities and challenges for private sector entrepreneurship and investment in biodiversity, ecosystem services and nature conservation[END_REF][START_REF] Pirard | Market-based instruments for biodiversity and ecosystem services: A lexicon[END_REF] and voluntary approaches (with or without financial compensation) [START_REF] Santangeli | Voluntary non-monetary approaches for implementing conservation[END_REF]. Voluntary approaches are schemes whereby firms make commitments to improve their environmental performance [START_REF] Börkey | Voluntary Approaches for Environmental Policy. An assessment[END_REF]. Thus, CSR relates primarily to voluntary approaches, although market-based options can also be framed to fit within CSR definition. Three main types of voluntary approaches can be distinguished: unilateral commitments made by companies, environmental negotiated agreements between industry and public authorities and public voluntary programs [START_REF] Börkey | Voluntary Approaches for Environmental Policy. An assessment[END_REF]. The French NBSAP instrument on which is based this article is an example of public voluntary program for biodiversity conservation. Public authorities may develop other more indirect technics to influence CSR [START_REF] Steurer | The role of governments in corporate social responsibility: characterising public policies on CSR in Europe[END_REF].

Compared to regulatory and market-based mechanisms, the rationalities that shape the adoption of CSR practices are less explicit, and so are the political levers. Three forces may contribute to institutionalize CSR practices [START_REF] Dimaggio | The Iron Cage Revisited: Institutional Isomorphism and Collective Rationality in Organizational Fields[END_REF][START_REF] King | Industry Self-Regulation Without Sanctions: The Chemical Industry's Responsible Care Program[END_REF]:

-coercive forces relate to the pressures institutional stakeholders can exert even in the absence of explicit penalties. Companies failing to respond to such external pressures are exposed to potential impacts on their political influence and legitimacy. Drivers of business engagement in ecological issues thus typically encompass improved regulatory compliance, social license to operate, reduced risk of conflict as well as access to capital (a growing number of investors and financing agencies impose ecological standards, such as the International Finance Corporation performance standard on biodiversity conservation and sustainable management of living natural resources (IFC, 2012)) [START_REF] Barkemeyer | Corporate reporting on solutions to wicked problems: Sustainable land management in the mining sector[END_REF].

-normative forces relate to the professionalization of firms notably through the development of sectoral standards. Certification systems and norms, whether they are public (the European organic certification) or private (e.g. the Forest Stewardship Council (FSC), the Global reporting initiative (GRI)) contribute to make more operational and concrete the issues of biodiversity for the company, acting as vectors of appropriation of these issues.

-mimetic forces contribute to the development of environmental CSR through the dissemination of information on best practices, private benefits and competitors' performances.

Thus CSR is not a policy tool for biodiversity conservation by itself but rather a corporate contribution that can be influenced and fostered by a spectrum of policy instruments.

Business-biodiversity interactions and CSR practices

Business engagement in biodiversity conservation can encompass a large variety of practices (CBD, online; [START_REF] Schaltegger | Corporate Biodiversity Management Handbook[END_REF]. How corporate activities interact with biodiversity and ecosystem services orientates the strategy and types of measures that may be adopted by a company [START_REF] Houdet | Understanding changes in business strategies regarding biodiversity and ecosystem services[END_REF]. Three types of business-biodiversity interplay can be distinguished [START_REF] Feger | Nouvelles comptabilités au service des écosystèmes. Une recherche engagée auprès d'une entreprise du secteur de l'environnement[END_REF][START_REF] Overbeek | Biodiversity and the Corporate Social Responsibility Agenda[END_REF]:

1. business activities negatively affect biodiversity. Five types of anthropic pressures are responsible for biodiversity loss: habitat change, overexploitation of wild populations, invasive species, pollutions and climate change (Millennium Ecosystem Assessment, 2005;[START_REF] Scbd | Global Biodiversity Outlook 3. Secretariat of the Convention on Biological Diversity (SCBD)[END_REF]. Companies may exert such ecological pressures not only on their own industrial sites, but also beyond their land and premises, at multiple stages of their value chain through their operations, supply chains and the products and services they deliver (Wolff et al., 2017b). 2. business activities are dependent on services provided by ecosystems, such as natural water purification (e.g. water industry), soil erosion regulation (e.g. agriculture), material and food provision (e.g. forestry and fishery), aesthetic quality (e.g. tourism). 3. business activities contribute to strengthen biodiversity resilience through the provision of services to ecosystems (ecological engineering, depollution activities…).

In the first case, companies are expected to mitigate their impacts on biodiversity. Stakeholders, and notably NGOs, may pressure companies to go beyond regulatory compliance if they consider that ecosystems are threatened by corporate activities. Stakeholders can then either take an adversarial approach (i.e. expert coercive forces such as shame campaigns) or a cooperative approach by offering technical support to the firm or reward for compliance [START_REF] Lyon | Corporate Social Responsibility and the Environment: A Theoretical Perspective[END_REF]. In the second case, a company has a direct incentive (its economic viability) to secure the quality and quantity of ecosystem services on which it relies by ensuring the maintenance of ecosystems' functioning [START_REF] Teeb | The Economics of Ecosystems and Biodiversity in Business and Enterprise[END_REF]. Finally, companies whose core activities aim at improving ecosystems health may seek to develop innovative services and business models to support clients liable for ecosystem management (e.g. municipalities, private landowners) [START_REF] Feger | Nouvelles comptabilités au service des écosystèmes. Une recherche engagée auprès d'une entreprise du secteur de l'environnement[END_REF].

The implementation of CSR practices in action arenas

From an organizational point of view, corporate biodiversity practices can be classified based on who is in charge of, or involved in, their implementation. Boiral and Heras-Saizarbitoria proposed a framework that differentiates corporate biodiversity practices based on two main axes (Boiral and Heras-Saizarbitoria, 2017a):

-practices that are under the responsibility of managers (e.g. implementation of management systems) vs. under the responsibility of experts and specialists (e.g. fauna and flora inventories);

-internal practices that are implemented by the firm itself (e.g. monitoring of performance indicators) vs. external practices implemented in association with various stakeholders (e.g. research programs in partnership with academic institutions).

Such an involvement of external stakeholders in the implementation of corporate biodiversity can be understood both because of the collective nature of biodiversity issues (what Elinor Ostrom calls the "Commons") and because of CSR norms (ISO, 2010; OECD, 2011) that require companies not only to imbed CSR within their organizations but also to practice it throughout their spheres of influence, defined as the "range/extent of political, contractual, economic or other relationships through which an organization has the ability to affect the decisions or activities of individuals or organization" (ISO, 2010, p. 4).

Corporate biodiversity practices can thus be implemented in different 'action arenas' [START_REF] Ostrom | Institutional Analysis and Development: Elements of The Framework in Historical Perspective[END_REF] in which stakeholders are associated at different degrees from simple informative up to decisional positions [START_REF] Green | A typology of stakeholder participation for company environmental decision-making[END_REF]. The most frequently cited stakeholder categories in the ecological management literature are environmental NGOs, experts and academics, public authorities and industry coalitions [START_REF] Barkemeyer | Corporate reporting on solutions to wicked problems: Sustainable land management in the mining sector[END_REF]Boiral and Heras-Saizarbitoria, 2017b;[START_REF] Overbeek | Biodiversity and the Corporate Social Responsibility Agenda[END_REF]. The concept of action arena is used in this study to identify patterns of stakeholders' involvement in the implementation of biodiversityoriented CSR practices.

Research design

The French National Biodiversity Strategy and Action Plan

In order to translate the international conservation framework of the CBD at the national level, France updated its National Biodiversity Strategy and Action Plan (NBSAP) in 2011 with the ambition to "preserve, restore, strengthen and value biodiversity and ensure its fair and sustainable use; to involve everyone and every sector of activity, in order to succeed" (Prime [START_REF] Minister | National Biodiversity Strategy[END_REF]. This NBSAP includes an original instrument whose objective is to broaden actors' contribution. Organizations (companies, but also associations, local councils and public agencies) can engage on a voluntary basis in two steps: adherence to NBSAP principles and commitment to contribute to the NBSAP concretized by a commitment plan.

This instrument gives a large flexibility to project leaders to define the strategy and actions that will be part of their commitment plans. Commitment plans are evaluated based on a framework setting quality criteria (Box 1) through a peer-review process involving colleges representing different categories of stakeholders (state, local elected representatives, professional associations, workers unions, NGOs, public agencies as well as qualified individuals).

Commitments that pass the review process are recognized as contributions to the French NBSAP for a three-year period (exceptionally for one-year only). The organization is then allowed to advertise the actions undertaken as contributions to the NBSAP.

Box 1-Criteria used by the NBSAP committee to evaluate the commitment plans.

consistency with NBSAP targets consistency of the action plan (projects organization and phasing) level of involvement of the top management and stakeholders connection with core business activities and feasibility, significance of the ecological potential and scalability additionality relatively to regulatory obligations measurability adaptive management continual improvement perspective commensurability with the capacities of the organization

Business commitment plans collection

Between 2012 and 2016, 49 commitment plans submitted by private and public companies were recognized as contributing to the NBSAP (Ministère de la transition écologique et solidaire, 2017).Erreur ! Source du renvoi introuvable. "Energy", "mining and carrying", as well as "water, waste and environment" sectors are the most represented sectors in the program and large companies dominate (Figure 1).

All private and public companies whose commitment plans were endorsed between 2012 and 2016 were contacted by email to get an access to their commitment plans. 31 companies (70%) responded positively. Although most commitment plans have a confidential status, a few are in open-access [START_REF] Eiffage | Programme d'actions d'Eiffage 2015-2018 au titre du renouvellement de son engagement dans la Stratégie Nationale pour la Biodiversité[END_REF][START_REF] Grtgaz | Engagement volontaire de GRTgaz en faveur de la Biodiversité[END_REF]STB Matériaux, 2013;[START_REF] Tigf | Dossier d'engagement de TIGF à la Stratégie nationale pour la biodiversité 2011-2020[END_REF][START_REF] Vertdéco | Notre engagement volontaire pour la stratégie nationale pour la biodiversité[END_REF]. Figure 1 describes the composition of the studied sample compared to the profile of total business participants. It can be noticed that large companies are slightly under-represented compared to small and medium-size (SME) and intermediate-size enterprises, and that less than 50% of the actors from the waste-water-environment and finance sectors were included in the study.

Content analysis

CSR practices and stakeholders' involvement were scrutinized following a content analysis approach:

1. The individual actions that the companies committed to undertake 1 were identified and extracted from the NBSAP plans. 2. A categorization framework was inductively develop to classify and characterize these actions regarding the types of practices undertaken and the stakeholders involved. 3. Actions were systematically described according to this categorization scheme based on a binary coding. Depending on its complexity and range, a given action could encompass several practices and stakeholders simultaneously. 4. Categories of CSR practices and of stakeholders were interpreted and grouped by themes and action arenas respectively, and the coded data was quantitatively analyzed with the open-source software R studio.

The categorization framework was improved through iterations between steps two to four as new trends emerged from the analysis.

1 Actions were used as unit of analysis to fit the way companies organized their commitment plans. This division showed some limits. Indeed from a company to another, or even in a single plan, scopes of actions showed great variation regarding the financial and human resources needed. We recognize that individual action is an imperfect unit of analysis but it was consistent with how business segmented their initiatives and monitored them. It thus reflects the relative emphasis the companies gave to their initiatives.

Results

The commitment plans endorsed as contributions to the French NBSAP offered a quite detailed and consistent description of business practices and of the roles played by stakeholders in their implementation. We first present subsequently the typology of CSR practices and the structure of action arenas that emerged from the analysis, and then present findings regarding how these actions arenas are mobilized in the implementation of CSR practices.

Corporate practices

In total, 496 actions that companies committed to undertake were identified. Biodiversityoriented CSR practices were quite heterogeneous across the companies, as they deal differently with biodiversity depending on their sectors, locations, sizes and maturity for instance. Figure 2 displays the typology of practices that emerged from the analysis of these commitment plans.

It also provides an overview of the proportion of companies that committed to develop such practices.

Figure 2 -Typology of CSR practices presented in the commitment plans and percentages of companies that committed to undertake them. Activities in bold were presented by more than two-third of the companies.

This typology makes a dichotomy between, on one hand, practices that directly mitigate biodiversity loss in an operational way, and on the other hand, procedural activities that support the integration and management of biodiversity issues.

Direct mitigation practices

Direct mitigation practices were classified under: impact avoidance, impact minimization, compensation and care provided to ecosystems. The three first categories are consistent with the three steps of the mitigation hierarchy framework (Cf. Box 2). Avoidance activities, based on the evolution of consumption patterns and of the business portfolio composition, had a preventive character. Minimization practices had a more curative dimension and compensation can be regarded as an end-of-pipe approach. Care activities had an adaptive character as they aimed at increasing the long-term resilience of ecosystems and thus their capacities to support future stresses.

Box 2 -The mitigation hierarchy.

The mitigation hierarchy is a stepwise framework widely used in conservation policy and management. It usually follows three steps: avoid negative impacts whenever possible, then minimize them and eventually compensate/offset the residual impacts in order to achieve no net loss or net positive impact (EU NNL WG, 2013). In France, the mitigation hierarchy was first introduced in the environmental law in 1976, further specified through guidance documents (MEDDE, 2012) and strengthen in 2016 by the law n° 2016-1087 related to biodiversity. It has been so far mainly applied to projects with substantial land footprint (e.g. mining, infrastructure projects).

It appears that mitigation practices were more or less specifically targeting anthropic pressures. Table 1 summarizes which processes altering biodiversity were addressed in the commitment plans by the active mitigation measures. Habitat loss was addressed by all types of activities while other anthropic pressures were found to be targeted only by avoidance and/or minimization activities.

X X X Offer evolution X X X Impact minimization Eco-efficient production X X X X X Responsible purchasing X X Land management X X X Compensation On-site restoration X Offset X Care provision to ecosystems X
The most recurrent mitigation initiatives were two minimization measures: eco-efficient production and land management (Figure 2). Land management measures aimed generally at moving from 'conventional' green space management to more ecologically sound practices.

For instance, one company proposed "to phase out pesticides, to ban invasive plants, to substitute horticultural varieties by local plants, to delay and limit the number of mowing" (Eiffage, 2015, p. 30). The area effectively covered by such land management practices and their consistency at a landscape scale were found to greatly differ among companies. Eco-efficient production initiatives were more closely related to core business activities. Some practices aimed for instance at limiting invasive species diffusion by improving excavated soil management, at reducing dams' fragmentation of freshwater habitats or at decreasing light pollution of industrial sites overnight. Eco-efficient production practices encompassed thus a variety of technical measures reducing the industrial impacts on biodiversity. They addressed in various ways the all range of anthropic pressures (Table 1).

4.1.2. Support activities A relatively strong emphasis was put in the commitment plans on support activities (Figure 2). These were classified into categories related to knowledge development and knowledge diffusion, development of managerial capacities, governance and funding of biodiversity conservation.

Among support activities, the most frequent practices (implemented by more than two thirds of the companies) were related to: ecological data collection, tools development, raising awareness, providing training and sharing feedbacks. Data collectionsometimes part of larger programs led by an NGO or a scientific institutionincluded fauna and flora inventories, but also ecosystems mapping, geochemical soil analyses, monitoring of invasive species… Contribution to voluntary fauna and flora inventories was especially developed in sectors that are subject to environmental impact assessments on a regulatory basis (e.g. mining and quarrying). To track the improvement of their ecological performance, companies put also efforts in tools development, enabling the integration of biodiversity components in their internal environmental management system, or producing metrics and indicators for assessing business impacts.

A gradient of technicity was observed among the knowledge transfer practices. Awareness raising had the broader scope and targeted a non-specialist audience (public, employees, clients, partners…). While campaigns often addressed biodiversity issues in general (e.g. the importance of biodiversity and its decline), they were sometimes tailored more specifically to the company (e.g. business-biodiversity interactions, species present onsite). The distinction between awareness and communication practices was thin, as the media used to increase awareness about biodiversity were usually simultaneously used to promote the company's good practices. Training activities were more centered on the issues encountered by the company itself and were dedicated both to the operational staff (how to implement recommendations in day-to-day practices) and to managers (how to integrate biodiversity issues into decisionmaking processes). Finally, feedbacks aimed at disseminating results of experimental approaches and at upscaling best practices through internal or sectoral publications and working groups. For instance, several committed companies contributed as members of the 'Linear infrastructure and Biodiversity Club' to the publication of a report providing recommendations for "optimising the connection between ecological networks and infrastructure networks" (e.g. roads, gas pipelines, electric power lines) (IUCN France and CILB, 2015, p. 14).

While not tackling directly the processes responsible for biodiversity loss, support activities contributed to institutionalize biodiversity issues in companies at different levels.

Action arenas

The implementation of these biodiversity-oriented CSR practices relied on multiple stakeholders. These stakeholders were grouped into four action arenas (Figure 3):

-within companies, where environment managers played a central role to coordinate and structure the actions. This action arena also included the top management and staff members ranging from operators to R&D and marketing managers;

-territorial systems where the company operates. The territorial stakeholders were local communities, councils with political influence on the territory (e.g. municipalities, local officials) and experts with specific naturalist knowledge on the local ecosystems;

-the value chain of the company, encompassing suppliers, clients and project-specific economic partners;

-and finally, the institutional system that set the regulations, taxes, norms and biodiversity policies. The stakeholders grouped in this action arena had influence capacities at a national level or broader: public institutions playing an administrative or political role, large environmental NGOs, academic institutions and professional organizations. Although classified under a unique action arena, some stakeholders could be regarded as acting at the interface. This was notably the case of local councils that made the connection between the institutional and the territorial systems, as well as industrial organizations that made the link between value chains and the institutional system. In some cases, the company's value chain was embedded into the territorial system. This situation was notably encountered within small companies with local suppliers and clients. Thus, the apparent overlap between these four action arenas in the commitment plans was highly dependent on the companies' characteristics: business size, sector, number of industrial sites… External stakeholders were found to be involved in 70% of the actions presented in the commitment plans, suggesting they played key roles in the implementation of biodiversityoriented CSR. Globally, each company apparently interacted with a diversity of external stakeholders. Most systematically involved stakeholders were large NGOs and local councils (both cited in 77% of the commitment plans) as well as naturalist experts with local knowledge (cited in 74% of the commitment plans). The analysis suggested some sectoral differences. The companies belonging to the energy, mining & quarrying and waste-water-environment sectors seemed to have quite intense interactions with territorial stakeholders. For instance, the quarry company STB Matériaux emphasized its interactions with local land-management agencies to optimize post-exploitation restoration projects. GRTgaz, that manages pipeline networks, stated that its collaborations "with local actors has helped define pipeline delineation respectful of the territory" and that "the informed advice of local partners contributed to propose avoidance and compensation measures going often beyond regulatory requirements" (GRTgaz, 2013, p. 13).

In contrast, construction & infrastructure companies appeared to be more largely involved with institutional stakeholders. Eiffage for example made a specific focus on its participation to diverse working groups and colleges led by public institutions, foundations, associations and industrial coalitions.

Stakeholders' roles in biodiversity-oriented CSR activities

Stakeholders were involved either as executors, supporters or targets of the biodiversityoriented measures. Stakeholders belonging to the value chain, the territorial system and the institutional system were respectively involved in 25%, 34% and 38% of the actions presented in the commitment plans. The analysis of their involvement in the different kind of activities suggests that these three action arenas played distinct roles (Table 1).

The value chain appeared to be quite frequently mobilized in the implementation of direct mitigation practices. The roles of the value chain stakeholders were polarized by their upstream (suppliers) or downstream (clients) positions in the value chain. Actions involving the downstream side of the value chain had been primarily qualified as avoidance measures. To address clients, companies adopted two complementary approaches:

a demand-side approach, to influence clients' expectations and needs toward more ecologically sound consumption patterns,

and an offer-side approach by developing new low-impact portfolios of products and services.

In contrast, CSR practices mobilizing the upstream side of the value chain were mainly minimization measures. Suppliers acted as both targets and executors of minimization activities, as some companies encouraged or requested them to comply with specific guidelines and ecological standards.

Stakeholders from the territorial system were apparently mobilized by companies in heterogeneous ways. Territorial councils were found to be involved in almost all kind of probiodiversity activities. Naturalist experts were more specialized in data collection (e.g. fauna and flora inventories) and improvement of land management as they notably provided recommendations to companies to better integrate their activities in the local ecosystems. The general public and local communities were essentially the targets of events and communication program aiming at raising awareness and promoting the actions taken by the companies.

Finally, the stakeholders from the institutional system, which were the most represented categories of actors in the NBSAP evaluation committee (Cf. Section 3.1), were also the most frequently cited in the commitment plans. The institutional stakeholders were essentially mobilized in support activities. The primary role of professional organizations was related to disseminating feedbacks. Environmental NGOs were the principal beneficiaries of business sponsorship, but also played a supporting role in raising awareness, developing trainings and sharing experiences and best practices among actors. Academics were found to be specifically involved in ecological knowledge development as well as in knowledge transfer through the development of databases and were also substantial beneficiaries of sponsorship. The administration was the less cited stakeholder category in activities implementation, with no clear pattern of involvement.

Discussion and conclusions

This research provides a detailed and trans-industry typology of biodiversity-oriented CSR practices that were implemented by companies as contributions to the French NBSAP. We suggest that this structured classification could be used to design research protocols on corporate biodiversity management in a consistent manner and facilitate inter-sectoral comparisons. It complements the framework proposed by Boiral and Heras-Saizarbitoria that classified biodiversity management practices based on their technical vs. managerial character and on their internal vs. external implementation (Boiral and Heras-Saizarbitoria, 2017a). While the framework of Boiral and Heras-Saizarbitoria focuses on organizational aspects, the typology proposed in this paper takes a more biodiversity-centered view as it discriminates on one hand activities that directly mitigate biodiversity loss (impact avoidance, minimization and compensation, as well as care provision) and on the other hand, procedural activities that provide support for a better integration of biodiversity issues (through knowledge generation and diffusion, development of management capacities, governance and funding). This diversity of actions should be fully exploited and synergies explored by researchers and practitioners. This typology could be an operational benchmark tool for managers to identify the strengths and weaknesses of the biodiversity action plans of their own organizations. Two types of imbalance between business practices were observed in the present study. First, support activities dominated in the commitment plans. A strong focus on support activities at the expense of direct mitigation practices poses the risk to undermine the actual contribution of businesses to biodiversity conservation. Second, direct mitigation practices were primarily minimization of impacts. This finding is consistent with the results of other studies that show that the mitigation hierarchy is often biased by economic actors who tend in practice to downplay the first avoidance step and focus primarily on impacts minimization [START_REF] Bigard | The inclusion of biodiversity in environmental impact assessment: Policy-related progress limited by gaps and semantic confusion[END_REF][START_REF] Phalan | Avoiding impacts on biodiversity through strengthening the first stage of the mitigation hierarchy[END_REF]. It thus seems critical to reduce such imbalances to enhance the effective contribution of CSR to biodiversity conservation.

This case study also gives insights regarding the action arenas that support the implementation of such activities through the involvement of different stakeholder groups. Companies were found to extensively interact with stakeholders, highlighting the collaborative nature of biodiversity-oriented CSR practices. Our results thus comfort the idea that stakeholders are used as a positive lever by companies to manage biodiversity issues (Boiral and Heras-Saizarbitoria, 2017b;[START_REF] Overbeek | Biodiversity and the Corporate Social Responsibility Agenda[END_REF]. Furthermore, the analysis suggests that stakeholders from the territorial system, the value chain and the institutional system are involved at various degrees in the different categories of CSR practices. So business strategies should be designed by taking into account stakeholders' complementarities. More specifically, our results suggest that value chains play a central role in the implementation practices that directly mitigate biodiversity loss. Previous studies have pointed out that companies encounter inherent management difficulties in this action arena whose scope can be very broad [START_REF] Fritz | A supply chain perspective of stakeholder identification as a tool for responsible policy and decision-making[END_REF][START_REF] Kogg | Environmental and social responsibility in supply chains: The practise of choice and inter-organisational management[END_REF]. We thus suggest that future research could help identify more precisely how a company may interact with the various stakeholders along its supply chain and the impacts of such interactions on environmental pressures mitigation.

Although the scope of the corporate commitments to the French NBSAP is quite specific, the lessons from this case study may be relevant at a broader scale, notably for other companies and in other countries. The companies whose commitment plans have been analyzed represent a large variety of sectors and business sizes. They cannot be considered as representative of the private sector as a whole as they clearly displayed proactive behavior in biodiversity conservation through their engagement in the NBSAP mechanism. Somehow, with the exception of a few small companies, it can be noticed that most of these companies have primarily 'conventional' business models (in contrast with 'niche' sustainable companies, whose business models would be imbedded in ecological entrepreneurship). They exhibited a global dynamic that could be characterized as continuous improvement, a frequent approach in companies that are concerned by CSR and environmental management. Furthermore, while our research is based on a French case study, some of our results may also be relevant in other places, notably in developed countries with a comparable level of environmental regulation, for instance other European Union member states. We found for instance a significant overlap between the typology of CSR practices that came out of this analysis and categories of business practices identified in Netherlands [START_REF] Overbeek | Biodiversity and the Corporate Social Responsibility Agenda[END_REF] and Germany [START_REF] Schaltegger | Corporate Biodiversity Management Handbook[END_REF]. The applicability of these findings in other contexts is less obvious as the institutional and political environment greatly influence CSR and interactions with stakeholders [START_REF] Doh | Corporate Social Responsibility, Public Policy, and NGO Activism in Europe and the United States: An Institutional-Stakeholder Perspective[END_REF]. We thus suggest that the robustness and possible extrapolations of these results should be further explored through case study research notably by (i) testing the relevance of the CSR practices typology for specific industries, (ii) examining if action arenas are mobilized in a similar way by companies operating in developing countries, and (iii) analyzing the outcomes of other voluntary approaches (e.g. voluntary industry initiatives) compared to programs driven by public authorities.

While recognizing that further research is needed to comfort the representativeness of our findings, we draw some recommendations for future policy developments on how to integrate CSR activities within conservation policies. More precisely, we discuss here how CSR could be better connected to two important policy tools: the mitigation hierarchy and NBSAPs.

The mitigation hierarchy has been primarily developed for projects with a substantial land footprinte.g. infrastructure construction projects, carriesto achieve no net loss of natural habitat. This study highlights that CSR activities that fit into the structure of the mitigation hierarchy are already implemented by a larger diversity of sectors, though not always conceptualized this way, and that they can address not only habitat degradation but also other anthropic pressures. We thus argue for an extension of this framework to systematically address the ecological pressures exerted across sectors. Such extensions have already been partially explored for instance for the commercial agriculture and forestry sectors [START_REF] Aiama | No Net Loss and Net Positive Impact Approaches for Biodiversity -Exploring the potential application of these approaches in the commercial agriculture and forestry sectors[END_REF] and to integrate climate change issues in forests compensation [START_REF] Sansilvestri | Intégrer le facteur climatique dans la compensation écologique. L'exemple des écosystèmes forestiers[END_REF]. Furthermore, adding a 'care' step would make this framework practicable for the companies working in ecological engineering.

NBSAPs, which are the main instruments to implement the CBD at a national level, will be renewed in about two years. Sarkki et al. foresaw that "there is space in the national policy systems for NBSAP processes especially to facilitate iterative multi-sector dialogue, to support innovations for combining business and biodiversity and to develop institutional responsibilities, as well as a sense of commitment towards biodiversity" (Sarkki et al., 2016, p. 17). To adopt a more strategic approach in mobilizing business in NBSAPs, policy makers may translate national targets into explicit sectoral objectives in order to set expectations regarding business contributions [START_REF] Wolff | Responsabilité sociétale : quelles contributions des entreprises à la conservation de la biodiversité ?[END_REF]. The typology developed in this paper may provide policymakers with a support to consistently review business commitments, and identify potential gaps and imbalances. Finally, given the role stakeholders appear to play, it may be relevant to design policy tools that address companies not as individual actors but rather as organizations that can extend their scope of action beyond their own perimeter through their value chains, their geographic locations and their institutional networks.

Figure 1 -

 1 Figure 1 -Companies characteristics. Black marks indicates the number of companies included in the study relatively to the number of companies with NBSAP commitments (grey bars) by (a) sectors and (b) business size.

Figure 3 -

 3 Figure 3 -Action arenas and stakeholders involved.

Table 1 -

 1 Anthropic pressures driving biodiversity loss tackled by direct mitigation practices. Pressures explicitly addressed in commitment plans are designated with crosses.

	Category	Activities	Pressures responsible for biodiversity loss
		Habitat	Pollu-	Invasive	Climate	Over-
		loss		tions	species	change	exploitation
	Impact	Influence on
	avoidance	consumption

Table 1 -

 1 Action arenas mobilized for the activities: percentage of actions for which stakeholders belonging to the value chain, the territorial system or the institutional system are involved (most solicited action arena is highlighted in grey).

	Categories	Activities (n=action count)	Value chain	Territorial system	Institutional system
		Impact avoidance	Influence on consumption (n=2)	100%	50%	50%
	Direct mitigation	Impact minimization Compensation	Offer evolution (n=27) Eco-efficient production (n=69) Responsible purchasing (n=18) Land management (n=123) On-site restoration (n=24) Offset (n=11)	89% 45% 89% 31% 25% 82%	22% 30% 6% 37% 75% 45%	37% 28% 11% 29% 46% 45%
		Care provision to ecosystems	Care (n=9)	56%	56%	44%
		Knowledge development	Data collection (n=74) Research (n=29) Development (n=53)	23% 10% 40%	58% 28% 28%	57% 93% 53%
			Awareness (n=138)	30%	42%	33%
		Knowledge transfer	Communication (n=45) Training (n=46) Feedbacks (n=67)	22% 33% 30%	47% 35% 34%	31% 48% 45%
	Support activities	Management	Databases (n=28) Tools (n=48) Human resources (n=9) Contracts & conventions (n=32) Standards (n=12)	14% 25% 44% 44% 25%	50% 21% 22% 50% 25%	75% 40% 22% 38% 42%
			Pooling & up-scaling (n=16)	63%	31%	44%
			Environmental policy (n=21)	43%	33%	24%
		Governance	Involvement in institutional processes (n=22)	18%	59%	68%
			Accountability (n=15)	47%	33%	33%
		Funds	Sponsorship (n=39) Funding mechanisms (n=8)	8% 88%	46% 38%	79% 25%

Acknowledgments

The authors would like to thank the companies that accepted to give them access to their commitment plans.

Funding: This work was supported by AgroParistech and Mines Saint-Etienne.

Vitae

Anastasia Wolff has a PhD degree in environmental sciences. She studies the potential of corporate social responsibility (CSR) to contribute to biodiversity conservation.

Natacha Gondran is associate professor in environmental assessment at Mines Saint-Etienne and affiliated to the interdisciplinary laboratory 'Environment, city and society' (UMR 5600).

Christian Brodhag is Professor at Mines Saint-Etienne. He works on sustainable development, social responsibility and innovation. He had also administrative and political experience in sustainable development.