Devineau Jl

Savanna fire regimes assessment with MODIS fire data: their relationship to land cover and plant species distribution in western Burkina Faso (West Africa)

The West African savannas are subject to changes in fire regimes related to land use intensification, which may infer significant biological modifications. We investigated the efficiency of MODIS fire products to account for the variability of fire regimes in relation to changes in land cover and savanna vegetation. The specificity and complementarities of both MODIS active fire (MOD14A2 and MYD14A2) and burned area (MCD45A1) products were assessed in order to characterize fire regimes and to relate them with land cover. In addition the distribution of plant species between landscape units characterized by specific fire regimes was assessed. The calculation of the mutual information made it possible to set apart species more frequent in landscapes little or not at all subject to fires and species more frequent in burnt areas. The first group is the expression of the nature of the unburnt land-cover units, mainly constituted by the agricultural areas dominated by fields and fallows. It consists of more potential threats (weeds, encroachers, invasive species etc.) than the second group, which is more typical of sudanian savannas. It thus appears that unburnt landscape units are currently more sensitive and vulnerable to some biological threats than the burned savannas, where fire provides the long-term stability needed to preserve the ecosystem.

Introduction

Fire is a main determinant of the West African savannas, thus changes in fire regimes, i.e. the intensity and frequency of fire, may infer significant biological modifications [START_REF] Menaut | The structure and dynamics of a West African savanna in Huntley B and Walker B eds Ecology of tropical savannas Springer[END_REF][START_REF] Gillon | The fire problem in tropical savannas[END_REF][START_REF] Frost | The ecological effects of fire in savannas[END_REF], Louppe et al. 1995a& b, Getzin 2002[START_REF] Govender | -The effect of fire season, fire frequency, rainfall and management on fire intensity in savanna vegetation in South Africa[END_REF][START_REF] Nielsen | The fire regime of Senegal and its determinants Danish[END_REF]. Severe changes in vegetation types and in floristic composition can indeed be expected, as demonstrated by various investigations made in different fire-prone vegetation worldwide [START_REF] Aubréville | Les expériences de reconstitution de la savane boisée en Côte d'Ivoire[END_REF][START_REF] Goldammer | Potential Impacts of Climate Change on Fire[END_REF], Hoffman 1999[START_REF] Moreira | Effects of fire protection on savanna structure in Central Brazil[END_REF][START_REF] Wheaton | Changing Fire Risk in a Changing Climate: A Literature Review and Assessment SRC Publication[END_REF][START_REF] Williams | Fire regime, fire intensity and tree survival in a tropical savanna in northern Australia[END_REF][START_REF] Whitlock | The Role of Climate and Vegetation Change in Shaping Past and Future Fire Regimes in the Northwestern U.S. and the Implications for Ecosystem[END_REF][START_REF] Backer | Impacts of Fire-Suppression Activities on Natural Communities[END_REF][START_REF] Dellasala | Beyond Smoke and Mirrors: a Synthesis of Fire Policy and Science[END_REF][START_REF] Mckenzie | Climatic Change, Wildfire, and Conservation[END_REF][START_REF] Bond | The global distribution of ecosystems in a world without fire[END_REF][START_REF] Doe | Fire management policy and environmental NGO movement: critical contemporary perspectives, indicators and prospects in savannas[END_REF][START_REF] Moretti | Determinants for the conservation of a vulnerable firedependent species at its marginal range[END_REF][START_REF] Pausas | Are wildfires a disaster in the Mediterranean basin? A review[END_REF][START_REF] Roitman | Tree dynamics of a fire-protected cerrado sensu stricto[END_REF]. Such changes can have social and economic consequences, notably because of the importance of pastoral and wild resources for the sudanian rural societies. Fire regimes may therefore reveal land cover patterns and related land uses [START_REF] Dolidon | L'espace des feux en Afrique de l'ouest[END_REF][START_REF] Dolidon | The multiplicity of scales in the analysis of a phenomenon at the nature/society interface. The example of bushfires in West Africa[END_REF]; detecting spatial or temporal changes in fire regimes can then help to detect underlying environmental changes [START_REF] Morgan | Mapping fire regimes across time and space: understanding coarse and fine-scale fire patterns[END_REF][START_REF] Kasischke | Recent changes in the fire regime across the North American boreal region-Spatial and temporal patterns of burning across Canada and Alaska[END_REF].

The assessment of fire regimes across broad territories is carried out efficiently by means of data obtained by remote sensing [START_REF] Kerr | From space to species: ecological applications for remote sensing[END_REF][START_REF] Mayaux | Introduction : apport des techniques satellitales pour la gestion des aires protégées en Afrique sub-saharienne[END_REF][START_REF] Lentile | Remote sensing techniques to assess active fire characteristics and post-fire effects[END_REF][START_REF] Chuvieco | Global characterization of fire activity: toward defining fire regimes from Earth observation data[END_REF]) such as MODIS fire data, that are specifically designed for this purpose [START_REF] Justice | [END_REF]. The MODIS products are currently downloadable free of charge and can thus be very generally used. Many studies highlighted potentialities and limitations of the MODIS active fire product [START_REF] De Klerk | A pragmatic assessment of the usefulness of the MODIS (Terra and Aqua) 1-km active fire (MOD14A2 and MYD14A2) products for mapping fires in the fynbos biome[END_REF], which maps fires detected four times a day when the satellites pass overhead [START_REF] Justice | The MODIS fire products[END_REF]. For MODIS burnt area products (which maps the spatial extent of recent fires), of which only a provisional version is available up to now for evaluation purposes, such studies are however few [START_REF] Giglio | MODIS Collection 4 Active Fire Product User's Guide on line visited 07[END_REF], Giglio et al. 2005[START_REF] Roy | Southern Africa Fire Network (SAFNet) regional burned-area product-validation protocol[END_REF][START_REF] Roy | MODIS Collection 5 Burned Area Product MCD45 User[END_REF]. The results provided by the two products may diverge for some areas, but they also may be complementary [START_REF] Roy | MODIS Collection 5 Burned Area Product MCD45 User[END_REF]. Therefore, ascertaining the accuracy of MODIS fire data in relation to various local conditions is currently required [START_REF] Giglio | An active-fire based burned area mapping algorithm for the MODIS sensor[END_REF]).

In the savanna biome, fire regimes are closely related to the amount of standing herbaceous phytomass that varies in quantity and composition over space and time according to topography, land use, herbivores pressure and climatic variability [START_REF] Mbow | Savannah fires in east-central Senegal: distribution patterns, resource management and perceptions[END_REF], Mbow et al. 2003[START_REF] Van Langevelde | -Effects of fire and herbivory on the stability of savanna ecosystems[END_REF][START_REF] Hennenberg | Phytomass and fire occurrence along forestsavanna transects in the Comoé National Park, Ivory Coast[END_REF]. Changes in land use and climatic variability are likely to change the fire regimes that modify the effects of fire on ecosystems; in particular this may alter the balance among taxa according to their fire tolerance. In fire-adapted ecosystems plant life histories appear fine-tuned to particular fire regimes linked to specific sites [START_REF] Glover | The role of fire and other influences on the savannah habitat, with suggestions for further research African[END_REF][START_REF] Moreira | Effects of fire protection on savanna structure in Central Brazil[END_REF][START_REF] Bond | The global distribution of ecosystems in a world without fire[END_REF][START_REF] Bond | On Incorporating Fire into Our Thinking about Natural Ecosystems: A Response to Saha and Howe The[END_REF]).

In the West African sudanian zone, the contrast between the pyrophytic flora of savannas and a former endemic flora of dry forests, still persisting in some place free of fire, was often reported [START_REF] Aubréville | The Disappearance of the Tropical Forests of Africa (La mort des forêts de l'Afrique tropicale) Unasylva[END_REF][START_REF] Aubréville | Climat, forêt et désertification de l'Afrique tropicale[END_REF][START_REF] Devineau | Structure et dynamique de quelques forêts tropophiles de l'Ouest africain[END_REF], 2001[START_REF] Swaine | Characteristics of dry forest in West Africa and the influence of fire[END_REF][START_REF] Neumann | Forêts sèches au sud-ouest du Burkina Faso: Végétationsols-action de l'homme[END_REF]. The capacity of some of these so-called dry forest species to colonize unburnt areas had also been demonstrated, so that some wooded areas may be recent [START_REF] Larrue | Le Parc National du Niokolo-Koba : un exemple de rupture entre le milieu et la société mandingue (Sénégal Oriental)[END_REF]. In addition the removal or alleviation of fire may favour the establishment of exogenic and wideranging species (D 'Antonio & Vitousek 1992). For example, in the zone studied these latter species are more abundant in the agricultural areas, which can result from, among other possible causes, a reduction in the activity of fires [START_REF] Devineau | Ordinary biodiversity" in western Burkina Faso (West Africa): what vegetation do the state forests conserve[END_REF]. Up to what point such a disappearance of fire or such a reduction of the associated constraints can allow this dry forest (endemic) flora or, on the contrary, an exogenic flora of wide-ranging species to substitute for the savanna flora can therefore be questioned. The interrelations between savanna fire regimes and vegetation dynamics are indeed complex; they are constrained by various climatic, biotic and anthropogenic factors involving various feedbacks [START_REF] Scholes | Tree-Grass Interactions in Savannas[END_REF][START_REF] Hoffmann | Positive feedbacks of fire, climate, and vegetation and the conversion of tropical savanna[END_REF][START_REF] Van Langevelde | -Effects of fire and herbivory on the stability of savanna ecosystems[END_REF][START_REF] Beerling | The origin of the savanna biome[END_REF] and they are still not well understood either in their ecological or in their human aspects [START_REF] Laris | Burning the Seasonal Mosaic: Preventative Burning Strategies in the Wooded Savanna of Southern Mali[END_REF][START_REF] Wiegand | A patch-dynamics approach to savanna dynamics and woody plant encroachment -Insights from an arid savanna[END_REF]).

This study aims at evaluating how fire regimes -characterized from the MODIS fire dataare related to land-cover variability and which differences in floristic composition can be connected to these regimes. Taking into account what is known about the ecology of plants of West African savannas, the assessment of the mutual information between the fire regimes and the presence of the species within the landscapes affected by given fire regimes will help to specify both the accuracy of the MODIS data and the impact of fire regimes on phytodiversity.

Study area

The zone studied extends from 11° to 12° 2' latitude North in western Burkina Faso (in the provinces of Houet, Tuy, Balé, Mouhoun and Sanguié). The climatic and ecological conditions range from South sudanian with 900 to 1 100 mm annual rainfall and 5 to 6 dry months (with under 50 mm rainfall) to North sudanian with 800 to 900 mm annual rainfall and 6 to 7 dry months (about November and October to April) [START_REF] Fontès | Carte de la végétation et de l'occupation du sol (Burkina Faso). Note explicative. Laboratoire d'Ecologie Terrestre[END_REF] (figure 1). The whole zone is part of the "cotton area", with agriculture based mainly on sorghum, millet, groundnuts and some legumes; but the agricultural production in the South sudanian zone is more intensive and more varied, especially as a result of the cultivation of yams and of perennial crops (mangos, citrus fruits, cashew nuts, etc.). The region studied includes many protected areas that succeed one another along the Mouhoun river and a South-North climatic gradient from the "Mare aux Hippopotames" Biosphere Reserve to the Tiogo "Forêt Classée".

Fire-prone savannas cover the whole zone, but due to increasing climatic dryness various floristic and physiognomic changes are observed: patch forests or gallery forests become scarce northward, while deciduous trees become more abundant, e.g. the higher frequency of Acacia species [START_REF] Wittig | L'importance du genre Acacia L. (Mimosaceae) pour la végétation du secteur soudanien du Burkina Faso[END_REF]).

Strict laws provide for the regulation and management of fire in the rural areas and watchwords against the abusive cutting of wood, the divagation of animals and the bush fires were even given during the "three fights" period (1985) in Burkina Faso. In spite of that, fire indeed remains a fundamental characteristic of the savanna ecosystem in the West of Burkina Faso, as more generally in African savannas (Ampadu-Agyei 1998). More pragmatic legal approaches were subsequently adopted by distinguishing management and customary ritual fires from bush fires (Government of Burkina Faso 1998, [START_REF] Grégoire | Caractérisation de la dynamique des feux et de l'évolution du couvert végétal dans le Parc du W : Burkina Faso[END_REF][START_REF] Laris | -Good, bad or 'necessary evil'? Reinterpreting the colonial burning experiments in the savanna landscapes of West Africa[END_REF]. Nowadays bush fires, defined as uncontrolled, are prohibited; the other types are tolerated, but in a precise framework. The management fires must be under the control of their perpetrators;, they are typically clearing fires and "early" fires lit in order to settle or clean cultivation fields. They also include technical management fires such as for the maintenance of pastoral areas and for the conservation of protected areas (national parks, game reserve, state forests). Ritual fires, which may be lit in different places as part of customary ceremonies, must be supervised both by the State and the traditional authorities and, most of all, controlled. This new realistic legislation is more consistent with everyday practices in most countries in West Africa, since rural populations use fires as a working tool for agricultural purposes, for pasture management and for hunting [START_REF] Bruzon | Les pratiques du feu en Afrique subhumide, exemple des milieux savanicoles de la Centrafrique et de la Côte d'Ivoire[END_REF]). In addition, ritual fire is a still deeply rooted practice, as shown by [START_REF] St | Des sites sacrés à incendier. Feux rituels et bosquets sacrés chez les Bwaba du Burkina Faso et les Bassar du Togo[END_REF][START_REF] St | Incendies rituels et bois sacrés en Afrique de l'Ouest : une complémentarité méconnue[END_REF] who put in light the social and symbolic character of the yearly ritual burning of holy sites among Bwaba (Burkina Faso) and Bassar (Togo) societies.

Materials and methods

Acquisition and calculation of MODIS data

We used the 1 km resolution 8-day summaries of the MODIS active fire data (MOD14A2 and MYD14A2). Products were downloaded thanks to the NASA Land Processes Distributed Active Archive Center (LP-DAAC) anonymous FTP server (ftp://e4ftl01u.ecs.nasa.gov/ ).

The period studied goes from 2000.03.05 to 2008.06.30 and the zone studied was extracted from the tile h17v07.

We also downloaded the Monthly Tiled 500 m Burned Area Product (MCD45A1) from the ftp server ftp://ba1.geog.umd.edu/ . Data acquired (the last on 2008.06.27) goes from 2000.09 to 2008.04, but 2004.09 to 2004.12 were missing.

Thanks to the MODIS Reprojection Tool (MRT v4.0), the MODIS "hdf" files were transformed into a GEOTIFF format to be worked with the MAPINFO software.

For MOD14 and MYD14, we considered pixel class higher than or equal to 7 as fire pixel.

For MCD45A1 data, we considered pixel with a value of approximately Julian day of burning as burnt and all others as not burnt.

We compiled data according to four periods during the dry season: very early (Julian days (JD) 249-304), early , late (JD 001-064) and very late fires (JD 065-151).

These limits are generally accepted for the area studied (Bationo et al. 2001a et b, Laris, 2005[START_REF] Moumouni | L'impact des feux sur les strates herbacée et ligneuse[END_REF], they take into account the shortening of the dry season from the South to the North of the area [START_REF] Nielsen | Nielsen_&_Rasmussen_2001 Utilization of NOAA AVHRR for assessing the the determinants of savanna fire distribution[END_REF], 2001) and are in accordance with the climatic seasonality and the phenological rhythms of the vegetation [START_REF] Fournier | Phénologie, croissance et production végétales dans quelques savanes d'Afrique de l'Ouest. Variations selon un gradient climatique[END_REF], 1994[START_REF] Devineau | Évolution saisonnière et taux d'accroissement des surfaces terrières des ligneux dans quelques peuplements savanicoles soudaniens de l'0uest burkinabé[END_REF], 1999). In addition we compiled data on an annual basis.

We calculated 1) fire density as the number of pixels that got fire within given areas (the entire zone studied, specific areas such as protected areas, and the various land-cover and landform units) and 2) fire frequency as the return interval of fire (i.e. the number of years a pixel got fire relatively to the number of observed years). The fire return frequency per year was calculated considering together active fire and burnt area data.

Establishing relationships between surface variables and MODIS data

Crossing MODIS fire data with land cover units previously established from ETM+ satellite data

The zone studied is exactly delimited by the 196-052 ETM + satellite scene of which three images on June 3, 2001, June 22, 2002and December 28, 2001 were previously analysed. This former study defined eleven land-cover units according to vegetation cover and soils, both assessed by way of ETM+ remote sensing satellite data [START_REF] Devineau | Changes in the availability and uses of wild yams according to climatic dryness and land-cover in Western Burkina Faso (West Africa): a joint ecological and ethno-botanical approach using GIS and remote sensing[END_REF]. The land cover characteristics of each MODIS fire pixel can therefore be assessed as the proportion of ETM pixels (28,5 meters) classified in the eleven land cover units. The relationships between occurrences and frequencies of fire and land cover units can then be summarised in term of contingency tables (i. e. frequencies of ETM land cover classes belonging to MODIS fire classes) whose statistical significance can be evaluated by Chi² tests and then factorized by correspondence analyses.

Linking MODIS fire data to terrain surveys

Terrain data are 635 vegetation relevés of a georeferenced database established for the area [START_REF] Vidal | Un exemple d'interaction entre le substratum géologique et les écosystèmes : la cartographie du risque de ravinement par l'exploitation de la base/SIG " ECOSAV " pour les aires protégées de l'Ouest du Burkina-Faso[END_REF] and 50 supplementary observations ascertaining pre-and post-fire conditions in September and December 2008 for some precise MODIS fire classes. The vegetation relevés were founded on the classic phyto-sociological method of the homogeneous area. The sample-plot size (generally 40*40m plots) was in practice a compromise that guaranteed a valid representation of the woody species diversity and made it possible to ensure the physiognomic homogeneity of the stand with regards to the physiognomy of the woody species community and dominant herbaceous species [START_REF] Devineau | Generalist versus specialist: a contrasted sociology of woody and herbaceous species in a fallow-land rotation system in the West African savanna (Bondoukuy, Western Burkina Faso)[END_REF]. The vegetation plots were investigated in every vegetation type along tracks distributed in the whole of the area studied, inside and outside protected areas. Each plot was geo-referenced and could be associated with a MODIS fire class and with an ETM+ landcover class as well. Because of the small size of the ETM pixel, the correspondence of the latter with terrain observations was always carefully verified.

The Mutual Information (MI) [START_REF] Godron | Quelques applications de la notion de fréquence en écologie végétale (recouvrement, information mutuelle entre espèces et facteurs écologiques, échantillonnage)[END_REF][START_REF] Daget | Analyse fréquentielle de l'écologie des espèces dans les communautés[END_REF][START_REF] Steuer | The mutual information: Detecting and evaluating dependencies between variables[END_REF] and also a Chi² test were calculated between species frequencies (considering presence data) and MODIS fire classes with the ADE4 software [START_REF] Thioulouse | ADE-4: a multivariate analysis and graphical display software[END_REF]. As MI and Chi² don't give fully corresponding results as to the significance of co-occurence, we considered that a link between a species and a fire regime could be established only when the MI of the species was equal at least to the lowest MI value corresponding with a significant Chi² test (0.05). As both tests strongly differ in their discriminating efficiency they appear to be complementary.

As a normalized value, the Chi² is not reliable for low-frequency species, while the MI measures the connection between two variables whatever the number of individuals of the population, but doing so, the assessment may be biased towards rare species.

In order to know something of the opinion of villagers about fire change, questions were asked of 15 persons (croppers and herders) in ten localities between Bondoukuy and Dédougou (80 km apart) in September 2008. This informal enquiry aimed only at giving some clues for interpreting remote-sensing data.

Results

Correspondence of fire regimes assessed by MODIS data with land-cover units

Differences between active fires and burned areas data

The ability of active-fire-data and of burnt-area-data to account for areas affected by fire is somewhat different. During the whole period of observation, 42 % of the area were indeed detected by both MODIS products as having been affected by fire and 26 % as not having been burnt; but 24 % of the areas affected by fire were detected only by active-fire-data and 8 % only by burnt-area-data. These differences can however be related to land cover characteristics. The crossing between ETM land cover units and MODIS either burnt or active-fire-data shows that both are dependent (Chi² test was significantly different from random distribution beyond the 99.9% level; this is also the case for all the following relationships among land cover, fire frequencies and seasonality and that will not be repeated). Unburnt areas correspond to the agricultural domain (fields, fallows of slopes and bottom-slopes) and to bare soils, in contrast active fire and burnt areas were detected together mainly on bushy savannas on gravelly soils and hardpan (figure 2). Areas only detected as burnt were mainly tree or open savannas, particularly on upperslopes that usually have a continuous herbaceous stratum but a low phytomass. Areas only detected as active fire places were mainly savanna woodlands of wet places, usually with high herbaceous phytomass, but typically fragmented. fallows. Fires are however not always absent from such areas, where they can affect sparse patches of not very dense vegetation, but they are neither strong enough to be detected as active fire nor large enough to be detected as burnt areas. As an example, no fire was detected on a wide part of the South-West of the Sorobouly state forest, that corresponds to the illicit or tolerated establishment of fields; but between these fields, many small burnt areas were observed, which correspond to small places with a herbaceous cover of low biomass (e.g.

patches of Loudetia togoensis, Elionurus elegans in scattered clumps and Michrocloa indica forming a low continuous cover) or to the burning of the leaf-litter of woody species under shrubby thickets.

Land cover and fire seasonality

In order to study the variability of the seasonal density of fires according to landcover, we took into account the four seasonal periods (very early, early, late, and very late fires) and some of their combinations (these last ones taking into account the return of fire in several seasons on the same pixel). The great majority of the surface of the area studied was burnt between November and February, early fires (November-December) being obviously more dense and frequent (figure 3).

Figure 3 -Seasonal distribution of fires on the studied area in Western Burkina Faso (proportion of MODIS pixels that got fire during each season; data compiled from 2000 to 2008).

The seasonality of fires varied markedly however according to land cover. Agricultural zones on slopes and bare soils on bottom slopes appeared again as not burnt areas. Very early fires affected mainly open or herbaceous savannas on gravelly soils and hardpan. Seasonal fires return on the same pixels were observed mainly for tree and bushy savannas on complexes of gravelly soils and hardpan, whereas late and very late fires featured wet places (dense savannas and savanna woodlands on downslopes, wet grasslands etc.) and also some cultivated areas (e. g. fields and fallows on downslopes) as shown by the median position of the modalities "late" and "very late" relative to the positive part of axis 1 and to the negative part of axis 2 (figure 4). In addition fires occurred earlier in the drier parts of the area studied, in relation with the beginning of the dry season, but the pattern of fire seasonality according to land cover was nevertheless similar over the whole area.

Figure 4 -Correspondence analysis between land cover units and seasonal occurrence of fires 1 (Western Burkina Faso) 2

Variability of fire frequency according to land cover and land use

The most frequent fires (yearly or biennal) were observed mainly on hardpan and gravelly soils. Fairly frequent fires were observed in all savanna formations, but fires were infrequent or missing on agricultural lands, in particular on lowlands, where cultivation is more intensive and fallows are sparser and shorter (figure 5). As a rule, yearly or biennial fires predominated in protected areas (table 1) but fires were however scarcer in those including wide areas poorly covered, in particular in the northern part of the zone studied (figure 6).

Plant species distributions according to the fire regimes

The assessment of mutual information showed up as statistically significant and ecologically meaningful links between the distribution of species and the fire regime units could be established by means of MODIS data. Fifty-one out of the 204 species studied were thus statistically significantly linked with fire units (see electronic supplementary data). The correspondence analysis of the frequency distribution profiles for these 51 species enables the characterisation of the species distributions according to fire regimes. It clearly appears that species distributions are organized according to two main groups, the first related to annual, biennal and fairly frequent fires, the second related with infrequent fires and the absence of detected fires (figure 7). With the exception of Vetiveria nigritana (a species of stream-sides and swampy areas), the second group consists of species with not very specific habitats or related mainly to open savannas and fallows in agricultural zones (table 2).

Infrequent fires or no fire

Pandiaka involucrata Pain

Woody

Schwenckia americana Scam

Azadirachta indica

Azin Spermacoce chaetocephala Spch

Diospyros mespiliformis

Dime Spermacoce radiata Spra

Gardenia erubescens

Gaer Spermacoce stachydea Spst

Grewia barteri

Grba Tephrosia pedicellata Tepe

Guiera senegalensis Guse Waltheria indica Wain

Ozoroa insignis

Ozin Climbers

Terminalia avicennioides Teav Cissus diffusiflora Cidi

Cissus lelyi Cile

The first group contains relatively more trees, perennial herbaceous species and endemic species (soudano-zambesian) than the second group where shrubs, herbaceous annuals, widespread species, weeds and potential invaders are more numerous (figure 8).

Figure 7 -Correspondence analysis between species and fire frequency (species significantly linked to fire's regime) (between brackets: absolute contribution of fire frequency regimes to respectively the first and second axis)

Figure 8 -Life traits of species significantly linked to fire's regime units.

Discussion and conclusion

The current study shows how joining MODIS active fires and MODIS burnt areas data can be helpful to understanding the link between fire and landscape type in sudanian savannas.

Active fire data successfully detects some sparsely patched flammable environments too small to be identified by burnt area data. On the other hand, burnt area data reveals not very productive environments, barely visible for the active fire sensors. Both types of data are thus needed as complementary tools to characterise the savanna fire regimes.

On the basis of fire seasonality and frequency, we established landscape fire units and assessed then their dependence on land cover and land use. As quoted by Nielsen & Rasmussen (2001) the higher the land use intensity, the lower the fire frequency: indeed our results attest the high frequency of fire inside protected areas and on gravelly soils and hardpan complexes unsuitable for agriculture. They also confirm that the majority of fires take place in savanna-woodlands as shown by previous studies (Nielsen & Rasmussen 2001[START_REF] Clerici | Monitoring and assessing fire impacts and land-cover change in tropical and subtropical ecosystems using satellite remote sensing and GIS techniques[END_REF][START_REF] Grégoire | Dynamique des brûlis dans le Parc Régional du W,le Parc National de La Boucle de la Pendjari et la Réserve d'Arly Implications pour la gestion de ces aires protégées[END_REF]. Overall, our results confirm that fire occurrence is influenced primarily by land use practice [START_REF] Hudak | Trends in fire patterns in a southern African savanna under alternative land use practices Agriculture[END_REF]). Conversely the decrease in the herbaceous standing crop, due to the shortening of the fallow period [START_REF] Fournier | Phénologie, croissance et production végétales dans quelques savanes d'Afrique de l'Ouest. Variations selon un gradient climatique[END_REF][START_REF] Fournier | Cycle saisonnier et production nette de la matière végétale herbacée en savanes soudaniennes pâturées : les jachères de la région de Bondoukuy (Burkina Faso) Ecologie[END_REF][START_REF] Fournier | Quand les annuelles bloquent la succession post culturale. Expérimentation sur Andropogon gayanus en savane soudanienne (Bondoukuy, Burkina Faso)[END_REF][START_REF] Fournier | ): La jachère en Afrique tropicale. De la jachère naturelle à la jachère améliorée[END_REF], the extension of cultivated and cleared fields, and more generally the increment in landscape discontinuities limit the spread of fire and the size of burnt areas [START_REF] Devineau | Impact écologique de la recolonisation des zones libérées de l'Onchocercose dans les vallées Burkinabé (Nazinon, Nakambé, Mouhoun, Bougouriba)[END_REF][START_REF] Clerici | Monitoring and assessing fire impacts and land-cover change in tropical and subtropical ecosystems using satellite remote sensing and GIS techniques[END_REF][START_REF] Dolidon | The multiplicity of scales in the analysis of a phenomenon at the nature/society interface. The example of bushfires in West Africa[END_REF]). Because of the high impact of agriculture in the area studied (cotton zone) the area burnt annually is relatively limited outside protected areas (21 %) whereas 29 % appeared as not burnt. Conversely 47 % of the protected areas are burnt and only 8 % unburnt. These values are similar to those of [START_REF] Menaut | Biomass burning in west African savannas[END_REF] who found that 25-50 % of the sudanian savanna in West Africa was burnt annually or with those of Eva and Lambin (1998b) who found that 28 % of the sudanian savanna of Central Africa had been affected by fires during a year.

The comparison of active fire and burnt area data indicates that fire frequency and intensity are thus related mainly to the herbaceous layer continuity and phytomass. Fire density peaks in November-December; however fire seasonality depends on vegetation hygrophily, very early fires mainly affect savannas on gravelly soils and hardpan whereas late and very late fires are observed in wetlands, but also on agricultural lands in accordance with previous observations by [START_REF] Bruzon | Les savanes du Nord de la Côte d'Ivoire. Mésologie et dynamique : l'herbe, le feu et le pâturage[END_REF] or Nielsen & Rasmussen (2001). Moreover fire begins all the more early as the climate is dry. Field enquiries revealed a tendency towards fires later and later in agricultural areas because of a growing difficulty in controlling people In such increasingly crowded landscapes; the need for limiting fires was also reported several times (mainly by herders). With physical and biological changes in environment, this feeling could explain the observed patterns of fire distribution. Fire rarefaction in degraded savanna could indeed be due to changes in land management, in particular for pastoral activities for which burning annual grasses is rather prejudicial, contrary to the burning of the perennial grasses of the former "true" savanna [START_REF] Fournier | Dans quelle mesure la production nette de matière végétale herbacée dans les jachères en savane soudanienne est-elle utilisable pour le pâturage? Actes atelier : « La jachère, lieu de production[END_REF]September 2008 enquiries).

Furthermore, species frequency relationships with landscape fire regimes were established.

Due to the initial pixel size (1 km²) the fire's type units however relate to savanna landscape fragments that juxtapose various biotopes or plant species habitats. Although the probability of exposure to fire for a species can be assumed to be a function of the density and the intensity of fires in the landscape matrix, the difference in scales in our studies does not make possible a direct approach of the sensitivity of the species to fire. The surfaces used for the observation of presence of a species in a habitat, and those used to characterise the type of fire in the landscape matrix in which this habitat is included are too different. Moreover the reasons for the more frequent presence of species in landscape fire units are indeed varied; they may express fire-regime preferences, but also situations of refuge.

In the cotton zone of western Burkina Faso, the influence of fire on the environment is more marked within than without protected areas. These state forests, parks etc. are protective of the sudanian savannas biotopes and hence undergo frequent fires (generally annual) that are one of their distinctive features. As expected, plant species statistically linked with frequent fire landscape units are typical of sudanian savanna: many are endemic to the sudanian area, many are perennial grasses -the constituent life form of sudanian savannas (Fournier 1991 p. 11 et 248), some are woody species typical of sudanian woodlands e. g. Prosopis africana, Afzelia africana [START_REF] Stark | Relationship between fire and basal scarring on Afzelia africana in Benoue National Park[END_REF][START_REF] De Wolf | Species composition and structure of the woody vegetation of the Middle Casamance region (Senegal)[END_REF], Bationo et al. 2001[START_REF] Onana | Afzelia africana Smith ex Persoon dans le Nord-Cameroun. Etat actuel des peuplements et utilisation pastorale[END_REF].

However some species regarded as rather fire sensitive e.g. Anogeissus leiocarpus, Tamarindus indica do not appear to be linked to any fire landscape units, because they are frequently hosted in refuge habitats (thickets, groves, termite mounds etc.) in fire-prone landscapes (Traoré et al. 2008[START_REF] Liberski-Bagnoud | Les « bois sacrés[END_REF]), which counterbalances their presence in rarely burnt or not burnt areas. Furthermore the preference of A. leiocarpus for the best lands (chemically rich) [START_REF] Aubréville | Flore forestière soudano-guinéenne[END_REF][START_REF] Maydell | Arbres et arbustes du Sahel[END_REF], would explain its rarefaction in certain strongly exploited agricultural lands : in such conditions it occupies mainly gravelly soils and hardpan complexes [START_REF] Devineau | Les espèces ligneuses indicatrices des sols dans des savanes et jachères de l'Ouest du Burkina Faso[END_REF][START_REF] Liberski-Bagnoud | Les « bois sacrés[END_REF]. A seeming lack of specialization of a species can thus result from its elimination from its preferential habitats by a harmful disturbance. Two grass species give another example of a certain discrepancy or lack of precision in the links detected between species requirements and fire landscape units.

Andropogon chinensis and Schizachyrium sanguineum are two perennial grass species typical of fire-proclimax tree savanna. S. sanguineum appears significantly linked to frequently burnt landscape units (table 2) but not A. chinensis. Certain features of these polymorphic species which have a wide distribution in the tropics can explain this. In sudanian environments they usually grow together as dominant species on sandy or gravelly soil in uncultivated areas, but their maximum abundance is on slightly to rather gravelly soils on plateaus for A. chinensis and on sandy and plainly gravelly soils on midslopes of hills for S. sanguineum. Both can also be found on old (over 20 year-) fallow land, where S. sanguineum comes somewhat later than A. chinensis in the succession. All in all the ecological range of A. chinensis is a little wider than that of S. sanguineum and is linked to soils more suitable for agriculture [START_REF] Mamadou | écologie comparée de deux espèces de graminées pérennes : Andropogon ascinodis C.B. Cl. et Schizachyrium sanguneum (Retz) Alston dans la région de Bondoukuy[END_REF]. A. chinensis is thus more likely to be found in landscape units including cultivated (and hence not burnt) lands, although its preference is clearly for savannas or very old fallow lands.

The flora of lands slightly or not affected by fires thus reflects the chiefly agricultural nature of these areas: wide-ranging species and weeds are the main constituents of their flora, whereas the fire-sensitive species of the "dry forest" -such as Diospyros mespiliformis -are currently poorly represented there. Previous work in the region studied indeed showed that agricultural intensification leads to the establishment of wide-ranging species, particularly weeds and that, in addition to the dominance of some shrubby species were noteworthy characteristics of such lands, where they often became encroaching plants [START_REF] Devineau | Ordinary biodiversity" in western Burkina Faso (West Africa): what vegetation do the state forests conserve[END_REF]). The groups of species significantly related to fire regimes actually include many weeds and potentially invasive species linked to unburnt units, as was observed in some other semiarid ecosystems [START_REF] Macdonald | The invasion of introduced species into nature reserves in tropical savannas and dry woodlands[END_REF], Puyravaud et al. 1995). Moreover some exotic species such as Azadirachta indica -the Neem tree, a native from tropical South East Asiatypically linked to highly anthropized and fire-released lands can be locally naturalised or invasive. Similar observations were made in Guinean and Soudano-Guinean savannas where suppression or alleviation of fire favours exotic or invasive species such as the invasion of a fire protected savanana by Chromolaena odorata (Gautier 1996) or the establishment of Gmelina arborea and Tectona grandis on plots totally protected or managed with early fires (Louppe et al. 1995a & b). It thus appears that unburnt landscape units are currently more sensitive and vulnerable to some biological threats than the burnt savannas. Although disturbances are often thought to favour invaders, in the present case it is the suppression of the disturbance which seems to support threatening processes [START_REF] Buckley | Disturbance, invasion and re-invasion: managing the weed-shaped hole in disturbed ecosystems[END_REF]). As quoted by [START_REF] Wright | Landscape development, forest fires, and wilderness management[END_REF], fire may indeed provide the long-term stability needed to preserve the ecosystem; it can be seen as an incorporated disturbance that enables the savanna resilience and pseudo-stability, but whose disappearance is destabilizing [START_REF] Holling | Resilience and stability of ecological systems[END_REF][START_REF] Allen | Hierarchy perspectives for ecological complexity[END_REF][START_REF] Bergkamp | A hierarchical approach for desertification assessment[END_REF][START_REF] Ingegnoli | The impact of the widened landscape ecology on vegetation science: towards the new paradigm[END_REF]. Therefore the absence or the rarefaction of fires indicates land use intensification, but also ecosystems whose dynamics deviate from those of sudanian savannas.

Species name Fire regime

No fire

Figure 1 -

 1 Figure 1 -Localisation of the area studied (Landsat ETM+ 196_052 scene)

Figure 2 -

 2 Figure 2 -Correspondence analysis between land cover units and type of fire detection: active fire or burnt areas (Western Burkina Faso). (Between brackets: absolute contribution of fire type to respectively the first and second axis)

Figure 5 -

 5 Figure5-Correspondence analysis between land cover units and fire frequencies (Western Burkina Faso

Table 1 -

 1 Fire's regimes occurrence within and without protected areas (West Burkina Faso, 1 area delimited by the 196-052 ETM + scene) 2

		inside	outside
		protected	protected
		areas	areas
	No Fire	8.2%	29.4%
	Infrequent fires	13.1%	22.4%
	Fairly frequent fires	31.3%	27.2%
	Yearly or biennal fires	47.4%	21.0%

Table 2 .

 2 Species significantly linked with landscape fire's regimes in Western Burkina Faso (highest mutual information and H0 probability <= 0.05)

	Frequent , yearly,

biennal fires Infrequent fires or no fire Woody Grasses and sedges

	Afzelia africana	Afaf Aristida sieberana	Arsi
	Bombax costatum	Boco Bulbostylis abortiva	Buab
	Burkea africana	Buaf Ctenium newtonii	Ctne
	Entada africana	Enaf Cyperus rotundus	Cyro
	Prosopis africana	Praf Cymbopogon schoenanthus Cysc
	Pterocarpus erinaceus	Pter Digitaria debilis	Dide
	Grasses	Euclasta condylotricha	Euco
	Andropogon tectorum	Ante Microchloa indica	Miin
	Diheteropogon hagerupii	Diha Paspalum scrobiculatum	Pasc
	Hyparrhenia smithiana	Hysm Vetiveria nigritana	Veni
	Loudetiopsis kerstingii	Loke Forbs
	Schizachyrium sanguineum	Scsa Amorphophallus aphyllus	Amap
	Forbs	Cochlospermum tinctorium	Coti
	Raphionacme daronii	Rada Crotalaria retusa	Crre
	Sub-shrubs	Curculigo pilosa	Cupi
	Cochlospermum planchoni	Copl Evolvulus alsinoides	Eval
	Climbers	Fadogia agrestis	Faag
	Asparagus africanus	Asaf Gladiolus gregarius	Glgr
	Cissus populnea	Cipo Indigofera stenophylla	Inst
	Baissea multiflora	Bamu Lantana rhodesiensis	Larh

Species not statistically significantly linked with fire units

		Species name Species name Species name Species name Species name	Fire regime Fire regime Fire regime Fire regime Fire regime
		No fire No fire No fire No fire No fire	Infrequen fires Infrequen fires Infrequen fires Infrequen fires Infrequen fires	Fairly frequent fires Fairly frequent fires Fairly frequent fires Fairly frequent fires Fairly fires frequent	Yearly or biennal fires Yearly or biennal fires Yearly or biennal fires Yearly or biennal fires Yearly or fires biennal	Total Freq. Entropy Total Freq. Entropy Total Freq. Entropy Total Freq. Entropy Total Freq. Entropy	MI MI MI MI MI	Khi² Proba Khi² Proba Khi² Proba Khi² Proba Khi² Proba
	1	Species statistically significantly linked with fire units Guiera senegalensis J.F Gmelin Cochlospermum planchonii Hook. f. Andropogon tectorum Schumach. & Thonn. Waltheria indica L. Burkea africana Hook. F. Grewia barteri Burret Hyparrhenia smithiana (Hook. F.) Stapf Amorphophallus aphyllus (Hook.) Hutch. Terminalia avicennioides G. & Perr. 42 56 22 1 54 12 26 3 32 Pterocarpus erinaceus Poir. 34 Entada africana Guill. & Perr. 25 Fadogia agrestis Schweinf ex Hiern 26 Pandiaka involucrata (Moq.) B.D. Jacks. 15 Afzelia africana Smith ex Pers. 1 Prosopis africana (Guill. & Perr.) Taub. 19 Bombax costatum Pellegr. & Vuillet 10 Indigofera stenophylla Guill & Perr 19 Gardenia erubescens Stapf & Hutch. 46 Gladiolus gregarius Welw. ex Baker 12 Diospyros mespiliformis Hochst. ex A. Rich. 52 Bulbostylis abortiva (Steud.) C.B. Clarke 27 Cymbopogon schoenanthus (L.) 33 Spreng. subsp. schoenanthus Ctenium newtonii Hack 15 Spermacoce chaetocephala DC. 6 Vetiveria nigritana (Benth.) Stapf 7 Cyperus rotundus L. 13 Loudetiopsis kerstingii (Pilger) Conert 2 Cochlospermum tinctorium A. Rich. 29 Ozoroa insignis Del. 24 Cissus diffusiflora (Baker) Planch. 17 Schizachyrium sanguineum (Retz) Alston 17 Aristida sieberana Trin. 23 Curculigo pilosa (Schum & Thonn) Engl 31 Crotalaria retusa L. 6 Cissus lelyi Hutch. 9 Diheteropogon hagerupii Hitchc. 23 Digitaria debilis (Desf.) Willd. 35 Spermacoce radiata (DC.) Hiern. 49 Lantana rhodesiensis Moldenke 15 Tephrosia pedicellata Bak 39 Azadirachta indica A. Juss. 10 Asparagus africanus Lam. 3 Evolvulus alsinoides (L.) L. 24 Spermacoce stachydea DC. 64 Paspalum scrobiculatum L. 26 Euclasta condylotricha (Steud.) Stapf. 22 Baissea multiflora A. DC. 6 Microchloa indica (L.f.) P. Beauv. 59 Cissus populnea Guill. & Perr. 28 Raphionacme daronii Berhaut 1 Schwenckia americana L. 7 Stylosanthes fruticosa (Retz.) Alston 14 Tamarindus indica L. 18 Eriospermum abyssinicum Baker 16 Hoslundia opposita Vahl. 5 Sporobolus festivus Hochst. ex A. Rich. 46 Acacia dudgeoni Craib ex Hall 27 Strychnos spinosa Lam. 18 Pandiaka angustifolia (Vahl) Hepper 36 Holarrhena floribunda (G. Don) Dur. & Schinz 9 Exell. 45 Cymbopogon giganteus Chiov. var giganteus 7 Ampelocissus grantii (Baker) Planch. 18 Hymenocardia acida Tul. 22 Brachiaria jubata (Fig. & De Not) Stapf 4 Biophytum petersianum Klotzsch. 7 Dioscorea bulbifera L. 10 Loudetia simplex (Nees) C.E. Hubbard 7 Dioscorea abyssinica Hochst. ex Terminalia laxiflora Engl. 58 Schizachyrium rupestre (K. Schizachyrium exile (Hochst.) 28 Schoenefeldia gracilis Kunth 6 Schum.) Stapf 4 Descoings 3 Cyphostemma waterlotii (A. Chev.) Cassia tora L. 6 Kunth 20 Balanites aegyptiaca (L.) Del. 14 Maytenus senegalensis (Lam.) Brachiaria lata (Schumach.) C.E. Hubbard 3 Indigofera trichopoda Lepr. ex Guill. & Perr. 20 Benth. 18 Tephrosia linearis Pers. 6 Fimbristylis ovata (Burm. f.) Kern 2 Boswellia dalzielii Hutch. 2 Capparis sepiaria L. 8 Gardenia sokotensis Hutch. 5 Dichrostachys cinerea (L.) Wight & Arn. 44 Engl. & Diels 8 Hexalobus monopetalus (A. Rich.) Sporobolus pyramidalis P. Beauv 18 Excoecaria grahamii Stapf 22 Fimbristylis ferruginea (L.) Vahl 3 Krause 39 Lepidagathis anobrya Nees 24 Lannea microcarpa Engl. & K. Grewia venusta Fresen. 11 Striga hermonthica Benth. 6 Voigt 48 Flueggea virosa (Roxb. Ex Willd.) Parinari curatellifolia Planch. ex Elionurus elegans Kunth 36 Sida rhombifolia L. 8 DC. 37 Trichilia emetica Vahl 7 Combretum glutinosum Perr. ex Fimbristylis hispidula (Vahl) Kunth. 37 & Perr. 41 Anogeissus leiocarpus (DC.) Guill. Kyllinga erecta Schumach. 7 Grewia bicolor Juss. 9 Albizia chevalieri Harms 10 Vitex simplicifolia Oliv. 20 Polygala arenaria Willd. 5 Euphorbia convolvuloides Hochst ex Benth 4 Vicoa leptoclada (Webb) Dandy 4 Khaya senegalensis (Desr.) A. Juss. 14 Isoberlinia doka Craib & Stapf 10 Sterculia setigera Del. 14 Hibiscus asper Hook. f. 20 Diheteropogon amplectens (Nees) W. D. Clayton 7 Acacia sieberiana DC. 11 Brachiaria xantholeuca (Hack. ex Mitracarpus scaber Zucc 3 Andropogon fastigiatus Sw 46 Cyanotis longifolia Benth. 11 Lannea velutina A. Rich. 35 Pennisetum pedicellatum Trin. 69 Feretia apodanthera Del. 34 Andropogon chinensis Merr. 53 Benth. 7 Cissus gracilis Guill. & Perr. 12 Perr. 51 Andropogon gayanus Kunth 52 Detarium microcarpum Guill. & Acacia ataxacantha DC. 11 Siphonochilus (Schweinf.) B.L.Burtt 38 aethiopicus Vitex chrysocarpa Planch. ex Guill. & Perr. 35 Combretum nigricans Lepr. ex (Nees) Stylochiton warneckei Engl. 32 Triumfetta pentandra A. Rich. 9 Ctenium elegans Kunth 4 Ximenia americana L. 21 Bridelia ferruginea Benth. 21 Melochia corchorifolia L. 3 Cassia nigricans Vahl 7 Schinz) Stapf 5 Crinum zeylanicum auct. 6 Monocymbium ceresiiforme (Nees) Stapf 4 DC 44 Acacia macrostachya Reichenb. ex Brachiaria distichophylla (Trin.) 45 Vitellaria paradoxa C.F. Gaernt. 95 Pilger Combretum micranthum G. Don 15 Stapf. Indigofera dendroides Jacq 28 Hackelochloa granularis (L.) O Ktze 29 Sclerocarya birrea (A. Rich.) Hochst. 37 Xeroderris stühlmannii (Taub.) Mendonça & E.P. Sousa 10 Annona senegalensis Pers. 71 Pteleopsis suberosa Engl. & Diels. 43 Tacca leontopetaloides (L.) O Ktze 30 Crotalaria cephalotes Steud ex A Rich 12 Senna singueana (Del.) Lock 19 Cyperus esculentus L. 7 Dioscorea dumetorum (Kunth) Pax 22 Wissadula amplissima (L.) R.E. Fries 22 Pericopsis laxiflora (Benth.) Meeuwen 19 Andropogon pseudapricus Stapf. 42 Sida alba L. 25 Crotalaria senegalensis (Pers) Bacle ex DC 10 Dioscorea togoensis Knuth 12 Acacia seyal Del. 7 Leptadenia hastata (Pers) Decne 4 Zornia glochidiata Reichb ex DC 9 G. Don.) Benth. 41 Crossopteryx febrifuga (Afzel. ex Milne-Redhead. 74 Piliostigma thonningii (Schumm.) Gardenia ternifolia Schumach. & Thonn. 40 Combretum fragrans F. Hoffm. 20 Combretum molle R. Br. ex G. Don 17 Strychnos innocua Del. 5 Lannea acida A. Rich. 58 Saba senegalensis (A. DC.) 23 Cassia sieberiana DC. 34 Hyptis spicigera Lam. 11 Lepidagathis collina (Endl.) Milne-10 Redhead Ipomoea eriocarpa R. Br. 7 Swartzia madagascariensis Desv. 9 Tephrosia bracteolata Guill. & Perr. 24 Cyanotis lanata Benth. 14 Melliniella micrantha Harms 11 Mollugo nudicaulis Lam. 4 Hyparrhenia subplumosa Stapf 7 Dactyloctenium aegyptium (L.) 7 Combretum collinum Fresen 41 Willd. Pichon. Aspilia kotschyi (Sch. Bip.) Oliv. 20 Sarcocephalus latifolius (Smith) 8 Piliostigma reticulatum (DC.) 15 Terminalia macroptera G. & Perr. 14 Hochst. Grewia lasiodiscus K. Schum. 31 Alysicarpus ovalifolius (Schum. & 9 Thonn.) Léonard Bruce Loudetia togoensis (Pilger) C.E. 63 Setaria pallide-fusca (Schumach.) Stapf & C.E. Hubbard 38 Stereospermum kunthianum 22 Cham. Hubbard Leucas martinicensis (Jacq.) R. Br. 7 Digitaria horizontalis Willd. 4 Chasmopodium caudatum (Hack) Stapf 5 Euphorbia hirta L 3 Securidaca longepedunculata Fres. 15 Loudetia hordeiformis (Stapf) 5 C.E.Hubbard Parkia biglobosa (Jacq.) Benth. 39 Total number of relevés 160 Schizachyrium (Franch.) Stapf 8 Cassia mimosoides L. 46 Mitragyna inermis (Wild) Kuntze 15 A. Cheval. 6 Digitaria gayana (Kunth.) Stapf ex Hochst. ex Steud. 20 Tripogon minimus (A. Rich.) platyphyllum Daniellia oliveri (R.) Hutch. & Dalz. 35	Infrequen fires 51 51 9 53 41 24 4 25 42 40 42 33 8 9 27 22 29 49 9 37 23 33 7 10 12 10 4 38 21 18 36 26 33 9 10 39 47 65 16 39 3 6 17 84 20 12 5 73 17 5 6 10 8 12 1 55 42 32 51 2 41 9 10 19 9 16 5 7 70 39 10 7 5 9 20 22 11 34 19 12 9 8 4 6 42 11 13 25 7 40 25 10 11 51 48 5 49 9 44 55 2 4 10 14 7 8 8 13 14 16 34 7 22 8 67 12 29 78 41 71 3 14 75 69 11 37 37 34 7 8 29 19 7 11 8 6 10 57 63 113 13 51 53 38 12 81 58 27 12 22 5 12 31 18 61 24 13 6 16 11 8 55 88 39 15 24 12 77 15 34 10 13 8 13 34 18 7 4 6 14 43 15 13 18 19 35 12 67 42 24 4 4 14 3 20 8 38 188 10 53 17 8 30 40	Fairly frequent fires 33 70 16 38 49 12 18 12 36 76 66 17 9 13 21 35 18 53 5 41 16 19 18 1 4 8 10 27 15 9 47 17 32 2 4 50 35 48 6 47 3 11 13 66 16 21 17 57 38 10 2 8 20 12 10 43 58 32 62 6 43 2 11 15 7 9 6 14 76 37 11 9 7 12 20 22 9 32 13 11 7 9 11 5 44 14 16 23 8 55 32 12 10 55 41 5 63 6 42 55 8 13 16 14 5 6 6 8 18 30 24 17 28 5 61 10 37 84 37 82 8 10 77 69 12 41 38 38 9 9 30 20 8 10 11 5 13 64 51 111 17 53 45 31 25 76 53 24 8 18 5 20 20 33 78 18 8 14 16 12 7 65 87 35 22 25 7 69 23 35 10 14 8 11 35 23 13 5 7 15 51 29 8 13 22 49 14 75 44 28 6 5 12 7 17 8 42 209 5 47 11 8 30 42	Yearly or biennal fires 8 32 13 7 20 1 10 6 5 26 21 5 0 7 21 14 2 8 0 14 4 10 1 1 0 0 7 5 3 2 17 3 4 0 0 24 8 16 3 7 1 8 5 24 5 3 7 21 14 5 0 1 9 1 2 14 22 19 30 4 11 3 4 4 6 5 4 7 22 19 3 1 2 4 5 8 2 17 5 1 2 4 5 0 18 6 7 6 1 15 9 3 3 19 15 2 20 3 15 24 4 5 1 5 6 6 6 7 11 8 9 4 9 4 27 8 12 25 11 34 2 3 29 29 7 17 13 11 5 2 8 9 3 2 1 1 4 19 16 39 6 14 14 10 9 24 13 7 1 3 0 6 7 14 25 12 1 7 4 3 1 24 33 16 12 15 2 33 9 11 7 7 6 4 9 8 4 1 3 4 18 9 7 7 7 15 4 21 13 9 3 2 6 4 3 1 19 78 2 24 5 1 14 12	Total Freq. Entropy 148 0.233 0.783 0.033 27.81 0.00 MI Khi² Proba 175 0.276 0.849 0.031 26.07 0.00 39 0.061 0.333 0.029 24.87 0.00 152 0.239 0.794 0.029 23.72 0.00 122 0.192 0.706 0.026 19.45 0.00 63 0.099 0.466 0.026 19.47 0.00 35 0.055 0.308 0.023 20.06 0.00 75 0.118 0.524 0.022 19.36 0.00 125 0.197 0.716 0.019 14.69 0.00 176 0.277 0.852 0.018 16.26 0.00 154 0.243 0.799 0.015 13.27 0.00 81 0.128 0.551 0.015 12.48 0.01 32 0.05 0.288 0.015 10.9 0.01 30 0.047 0.275 0.015 10.14 0.02 88 0.139 0.581 0.014 14.26 0.00 81 0.128 0.551 0.014 11.15 0.01 68 0.107 0.491 0.014 10.97 0.01 156 0.246 0.804 0.014 10.43 0.02 26 0.041 0.247 0.014 9.83 0.02 144 0.227 0.772 0.013 11.88 0.01 70 0.11 0.501 0.013 11.05 0.01 95 0.15 0.609 0.013 10.97 0.01 41 0.065 0.345 0.013 9.65 0.02 18 0.028 0.186 0.013 9.6 0.02 23 0.036 0.225 0.013 9.04 0.03 31 0.049 0.281 0.013 8.2 0.04 23 0.036 0.225 0.012 10.99 0.01 99 0.156 0.624 0.012 9.96 0.02 63 0.099 0.466 0.012 9.93 0.02 46 0.072 0.375 0.012 9.47 0.02 117 0.184 0.689 0.012 9.43 0.02 69 0.109 0.496 0.012 9.32 0.03 100 0.157 0.628 0.012 8.71 0.03 17 0.027 0.178 0.012 8.44 0.04 23 0.036 0.225 0.012 8.07 0.04 136 0.214 0.749 0.011 9.6 0.02 125 0.197 0.716 0.011 9.37 0.02 178 0.28 0.856 0.011 9.37 0.03 40 0.063 0.339 0.011 9.08 0.03 132 0.208 0.737 0.011 8.23 0.04 17 0.027 0.178 0.01 10.5 0.02 28 0.044 0.261 0.01 9.79 59 0.093 0.446 0.01 9.31 0.03 238 0.375 0.954 0.01 9.2 0.03 67 0.106 0.486 0.01 8.78 0.03 58 0.091 0.441 0.01 8.66 0.03 35 0.055 0.308 0.01 8.45 0.04 210 0.331 0.916 0.01 8.37 0.04 97 0.153 0.617 0.01 8.05 0.04 21 0.033 0.21 0.01 7.62 0.05 15 0.024 0.161 0.01 7.05 0.07 33 0.052 0.295 0.009 7.33 0.06 55 0.087 0.425 0.009 7 41 0.065 0.345 0.009 6.96 0.07 18 0.028 0.186 0.009 6.57 0.09 158 0.249 0.809 0.008 7.29 0.06 149 0.235 0.786 0.008 7.12 0.07 101 0.159 0.632 0.008 6.99 0.07 179 0.282 0.858 0.008 6.95 0.07 21 0.033 0.21 0.008 6.58 0.09 140 0.22 0.761 0.008 6.57 0.09 21 0.033 0.21 0.008 5.54 0.13 43 0.068 0.357 0.007 6.8 0.08 60 0.094 0.451 0.007 6.52 0.09 26 0.041 0.247 0.004 4.13 0.25 37 0.058 0.321 0.004 4.01 0.26 25 0.039 0.239 0.004 4 0.26 35 0.055 0.308 0.004 3.91 0.27 226 0.356 0.939 0.003 2.16 123 0.194 0.709 0.002 2.2 0.54 30 0.047 0.275 0.001 0.75 0.86 21 0.033 0.21 0.003 2.08 0.56 17 0.027 0.178 0.001 0.76 0.86 0.54 31 0.049 0.281 0.001 0.79 0.85 65 0.102 0.476 0.003 2.27 0.52 66 0.104 0.481 0.001 0.82 0.85 25 0.039 0.239 0.005 4.08 0.25 103 0.162 0.64 0.005 4.02 0.26 55 0.087 0.425 0.005 3.93 0.27 30 0.047 0.275 0.005 3.67 0.30 20 0.031 0.202 0.005 3.66 0.30 23 0.036 0.225 0.005 3.58 0.31 28 0.044 0.261 0.005 3.56 16 0.025 0.17 0.005 2.61 0.46 148 0.233 0.783 0.003 2.27 0.52 39 0.061 0.333 0.001 0.83 0.84 0.31 54 0.085 0.42 0.003 2.38 0.50 76 0.12 0.528 0.003 2.34 19 0.03 0.194 0.003 2.32 149 0.235 0.786 0.003 2.3 90 0.142 0.589 0.001 0.88 0.83 0.52 36 0.057 0.314 0.001 0.96 0.81 0.51 30 0.047 0.275 0.001 1 0.80 0.51 173 0.272 0.845 0.001 1.03 0.80 140 0.22 0.761 0.003 2.43 0.49 20 0.031 0.202 0.003 2.42 169 0.266 0.836 0.003 2.4 25 0.039 0.239 0.001 1.07 0.79 0.50 138 0.217 0.496 0.002 0.95 0.78 0.49 175 0.276 0.849 0.001 1.14 0.77 0.07 21 0.033 0.21 0.006 4.52 0.21 31 0.049 0.281 0.006 4.46 37 0.058 0.321 0.006 4.35 0.23 53 0.083 0.414 0.005 4.93 0.18 23 0.036 0.225 0.005 4.73 0.19 24 0.038 0.232 0.005 4.6 0.20 24 0.038 0.232 0.005 4.6 0.20 42 0.066 0.351 0.005 4.54 0.21 53 0.083 0.414 0.005 4.52 0.21 68 0.107 0.491 0.005 4.51 0.21 87 0.137 0.576 0.005 4.43 0.22 35 0.055 0.308 0.005 4.33 0.23 70 0.11 0.501 0.005 4.12 0.25 20 0.031 0.202 0.003 3 201 0.317 0.901 0.003 2.91 41 0.065 0.345 0.003 2.88 113 0.178 0.676 0.003 2.85 256 0.403 0.973 0.003 2.85 123 0.194 0.709 0.003 2.84 240 0.378 0.957 0.003 2.78 0.43 20 0.031 0.202 0.003 2.68 0.45 39 0.061 0.333 0.003 2.45 232 0.365 0.947 0.003 2.44 219 0.345 0.929 0.001 1.14 0.77 0.49 41 0.065 0.345 0.001 1.16 0.77 0.49 133 0.209 0.74 0.001 1.2 0.76 123 0.194 0.709 0.001 1.21 0.75 115 0.181 0.682 0.001 1.23 0.75 0.42 30 0.047 0.275 0.001 1.28 0.74 0.42 23 0.036 0.225 0.002 1.32 0.73 0.42 88 0.139 0.581 0.002 1.35 0.72 0.41 69 0.109 0.496 0.002 1.35 0.72 0.41 21 0.033 0.21 0.002 1.38 0.72 0.39 30 0.047 0.275 0.002 1.38 0.71 25 0.039 0.239 0.004 2.75 0.43 18 0.028 0.186 0.002 1.4 0.71 0.21 31 0.049 0.281 0.004 2.85 0.42 184 0.29 0.868 0.002 1.42 0.71 0.02 175 0.276 0.849 0.007 6.34 358 0.564 0.988 0.004 3.84 0.28 51 0.08 0.403 0.001 0.72 0.87 0.09 146 0.23 0.778 0.007 6.32 0.10 141 0.222 0.764 0.007 6.32 0.10 116 0.183 0.686 0.007 6.21 0.10 56 0.088 0.43 0.007 5.99 0.11 252 0.397 0.969 0.007 5.93 0.11 167 0.263 0.831 0.007 5.87 0.12 88 0.139 0.581 0.007 5.79 0.12 33 0.052 0.295 0.007 5.48 0.14 62 0.098 0.461 0.007 5.03 0.17 17 0.027 0.178 0.007 3.98 0.26 60 0.094 0.451 0.006 5.81 0.12 80 0.126 0.546 0.006 5.45 0.14 84 0.132 0.564 0.006 5.15 0.16 206 0.324 0.909 0.006 5.07 0.17 79 0.124 0.542 0.006 4.94 32 0.05 0.288 0.006 4.81 0.18 39 0.061 0.333 0.006 4.55 0.21 43 0.068 0.357 0.004 2.95 0.40 30 0.047 0.275 0.004 2.9 25 0.039 0.239 0.004 2.9 0.41 185 0.291 0.87 0.002 1.45 0.70 0.41 282 0.444 0.991 0.002 1.45 0.70 0.17 130 0.205 0.731 0.004 3.81 0.28 69 0.109 0.496 0.004 3.73 0.29 81 0.128 0.551 0.004 3.71 0.29 26 0.041 0.247 0.004 3.65 0.30 237 0.373 0.953 0.004 3.63 0.30 70 0.11 0.501 0.004 3.63 0.30 114 0.18 0.679 0.002 2.17 0.54 38 0.06 0.327 0.002 2.15 44 0.069 0.363 0.001 0.64 0.89 0.55 29 0.046 0.268 0.002 2.07 37 0.058 0.321 0.001 0.61 0.89 0.56 102 0.161 0.636 0.002 1.96 63 0.099 0.466 0.001 0.56 0.91 0.58 35 0.055 0.308 0.002 1.95 14 0.022 0.153 0.001 0.41 0.93 0.59 23 0.036 0.225 0 0.42 0.93 40 0.063 0.339 0.002 1.88 0.60 153 0.241 0.797 0 0.41 0.93 73 0.115 0.515 0.004 3.61 0.31 36 0.057 0.314 0.004 3.6 0.31 53 0.083 0.414 0.002 1.87 62 0.098 0.461 0 0.4 0.94 0.60 130 0.205 0.731 0.002 1.72 0.64 39 0.061 0.333 0 0.34 0.95 226 0.356 0.939 0.004 3.56 0.31 137 0.216 0.752 0.002 1.66 0.65 83 0.131 0.559 0 0.26 0.96 20 0.031 0.202 0.002 1.61 0.66 15 0.024 0.161 0 0.07 0.99 37 0.058 0.321 0.004 3.53 0.32 17 0.027 0.178 0.004 3.4 0.33 55 0.087 0.425 0.004 3.39 22 0.035 0.217 0.002 1.6 0.66 138 0.217 0.755 0.002 1.56 635 0.67 0.34 25 0.039 0.239 0.004 3.13 0.37 170 0.268 0.838 0.004 3.1 48 0.076 0.386 0.004 3.07 0.38 23 0.036 0.225 0.002 1.47 0.69 0.38 94 0.148 0.605 0.002 1.52 0.68 129 0.203 0.728 0.002 1.53 0.68

APPENDIX

Mutual information between species and fire regimes

Output of the EcoTools program from ADE4 [START_REF] Thioulouse | ADE-4: a multivariate analysis and graphical display software[END_REF] Col 2-5: number of relevés in each fire regime unit where the species is present, Total : total number of presence for the species, Freq.: species frequency, Entropy: descriptor's entropy (Daget & Godron, 1982 p. 54), MI: Mutual information between species and the descriptor [START_REF] Daget | Analyse fréquentielle de l'écologie des espèces dans les communautés[END_REF]