Arne Saatkamp
email: arne.saatkamp@imbe.fr

Laurence Affre

Thierry Dutoit

Peter Poschlod

Plant traits and

Keywords: Plant size, Seed banks, Local extinction, Seed number, Specific leaf area

come

Introduction

Global environmental changes such as climate warming, changing land use and habitat fragmentation are identified as major reasons for the decline of plant diversity [START_REF] Bobbink | The effects of air-borne nitrogen pollutants on species diversity in natural and semi-natural European vegetation[END_REF][START_REF] Rogers | Shifts in southern Wisconsin forest canopy and understorey richness, composition and heterogeneity[END_REF][START_REF] Römermann | Eutrophication and fragmentation are related to species' rate of decline but not to species rarity: results from a functional approach[END_REF][START_REF] Van Calster | Unexpectedly high 20th century floristic losses in a rural landscape in northern France[END_REF][START_REF] Wiegmann | Fifty years of change in northern upland forest understories: identity and traits of "winner" and "loser" plant species[END_REF]. However, plants differ in their specific extinction risks according to their functional traits [START_REF] Farnsworth | Functional groups of rare plants differ in levels of imperilment[END_REF][START_REF] Fréville | Prediction of extinction in plants: interaction of extrinsic threats and life history traits[END_REF][START_REF] Kahmen | Conservation management of calcareous grasslands. Changes in plant species composition and response of functional traits during 25 years[END_REF][START_REF] Lavergne | Fingerprints of environmental change on the rare Mediterranean flora: a 115-year study[END_REF][START_REF] Ozinga | Dispersal failure contributes to plant losses in NW Europe[END_REF][START_REF] Piqueray | Plant species extinction debt in a temperate biodiversity hotspot: community, species and functional traits approaches[END_REF][START_REF] Römermann | Eutrophication and fragmentation are related to species' rate of decline but not to species rarity: results from a functional approach[END_REF]. Moreover, works on plant communities showed how traits interact with environment to trigger different extinction risks among plant species [START_REF] Fréville | Prediction of extinction in plants: interaction of extrinsic threats and life history traits[END_REF][START_REF] Kahmen | Conservation management of calcareous grasslands. Changes in plant species composition and response of functional traits during 25 years[END_REF][START_REF] Römermann | Substitutes for grazing in seminatural grasslands-do mowing or mulching represent valuable alternatives to maintain vegetation structure?[END_REF]. Traits identified to trigger major population biological functions include specific leaf area (SLA), plant height, seed size and flowering date, interacting with management, habitat size and nutrient level [START_REF] Fréville | Prediction of extinction in plants: interaction of extrinsic threats and life history traits[END_REF][START_REF] Kahmen | Conservation management of calcareous grasslands. Changes in plant species composition and response of functional traits during 25 years[END_REF][START_REF] Römermann | Substitutes for grazing in seminatural grasslands-do mowing or mulching represent valuable alternatives to maintain vegetation structure?[END_REF]). Works on regional scales suggest that relevant traits to explain interspecific differences in extinction risk depend on specific environmental conditions [START_REF] Fréville | Prediction of extinction in plants: interaction of extrinsic threats and life history traits[END_REF][START_REF] Lavergne | Fingerprints of environmental change on the rare Mediterranean flora: a 115-year study[END_REF][START_REF] Ozinga | Dispersal failure contributes to plant losses in NW Europe[END_REF][START_REF] Rogers | Shifts in southern Wisconsin forest canopy and understorey richness, composition and heterogeneity[END_REF][START_REF] Römermann | Eutrophication and fragmentation are related to species' rate of decline but not to species rarity: results from a functional approach[END_REF][START_REF] Wiegmann | Fifty years of change in northern upland forest understories: identity and traits of "winner" and "loser" plant species[END_REF]. However direction and strength of effects of functional traits on extinction are not well known.

Indeed, relevant effects of traits might be detected when comparing local habitat and population properties, such as population size and mating system, which both have strong effects on population genetic structure [START_REF] Duminil | Can population genetic structure be predicted from life-history traits?[END_REF][START_REF] Ellstrand | Gene flow by pollen: implications for plant conservation genetics[END_REF]. Moreover, the identification of intrinsic risk factors (traits) for extinction in plants also enables to identify the relevant processes that determine local extinction risk. Therefore, one way to generalize results of extinction risks linked to declining populations across sites is to study specifically functional traits together with population sizes and environmental conditions.

Environmental conditions can change in an unidirectional way driving species to extinction, e.g., through changed disturbance regimes in anthropogenic habitats such as arable fields (Fried et al. 2009a). Environment also show temporal variability that may enhance coexistence of populations via storage effect which is linked to specific plant traits [START_REF] Facelli | Differences in seed biology of annual plants in arid lands: a key ingredient of the storage effect[END_REF][START_REF] Levine | Effects of temporal variability on rare plant persistence in annual systems[END_REF]. Both processes can concern the same factor (e.g., soil moisture) and may be on the same temporal scale (years). For example, soil moisture can directly decrease seed populations in the soil via increasing fungal attack [START_REF] Blaney | Effects of fungal pathogens on seeds of native and exotic plants: a test using congeneric pairs[END_REF][START_REF] Saatkamp | The functional role of soil seed banks in natural communities[END_REF][START_REF] Schafer | The influence of soil moisture on losses of buried seeds to fungi[END_REF]. Other factors such as higher nutrient availability and warming of climate have also been shown to change plant community composition and diversity [START_REF] Bobbink | The effects of air-borne nitrogen pollutants on species diversity in natural and semi-natural European vegetation[END_REF]. Thus, directional changes in soil moisture, temperature and nutrient status are interacting with plant traits to influence extinction dynamics of populations for annual plants [START_REF] Fréville | Prediction of extinction in plants: interaction of extrinsic threats and life history traits[END_REF].

Population characteristics known to correlate with extinction risk are population size, genetic structure and diversity. For example, population size influences local extinction, with small populations going extinct faster than large ones [START_REF] Matthies | Population size and the risk of local extinction: empirical evidence from rare plants[END_REF]. Since this makes it difficult to disentangle which factors finally drive a local plant population to extinction, we suggest in this study to use both, plant traits as well as environmental factors and population size in order to go further in the understanding of local plant extinctions. Plant traits can directly modify population dynamics [START_REF] Angert | Linking growth strategies to long-term population dynamics in aguild of desert annuals[END_REF][START_REF] Gardarin | Estimation of key parameters for weed population dynamics models: base temperature and base water potential for germination[END_REF], for example, adaptations at the seed level and soil seed mortality changes population size of annual plants [START_REF] Adams | Importance of the seed bank for population viability and population monitoring in a threatened wetland herb[END_REF][START_REF] Kalisz | Extinction dynamics, population growth and seed banks. An example using an age-structured annual[END_REF][START_REF] Menges | Population viability analyses in plants: challenges and opportunities[END_REF][START_REF] Schmid | Seltenheit und Gefährdung-Populationsbiologische Grundlagen des Artenschutzes[END_REF]. This extinction risk can be related to their short life cycle, differences in survival in the soil seed bank and to anthropogenic disturbances (Saatkamp 1 3 et al. 2011a(Saatkamp 1 3 et al. , 2014)). This also separates seed mortality from seed number, in a trade-off with seed size, and hence separates mortality sources in the seed life stage from those in other life stages (Leishman et al. 2000;[START_REF] Moles | Small-seeded species produce more seeds per square metre of canopy per year, but not per individual per lifetime[END_REF][START_REF] Saatkamp | The seed bank longevity index revisited: limited reliability evident from a burial experiment and database analyses[END_REF]. Finally, the rarity of a plant species at larger spatial scales influences its extinction risk, since colonization events strongly depend on abundance of species in the seed rain arriving from larger distances [START_REF] Hubbell | The unified neutral theory of biodiversity and biogeography[END_REF]. However, until now, soil seed mortality and seed production have not been clearly separated in their effects on local extinction risk in annual plants [START_REF] Saatkamp | The seed bank longevity index revisited: limited reliability evident from a burial experiment and database analyses[END_REF].

Differences in competitive ability among plants as estimated by plant size [START_REF] Fayolle | Differential impacts of plant interactions on herbaceous species recruitment: disentangling factors controlling emergence, survival and growth of seedlings[END_REF] or differences in recovery after disturbances related to relative growth rate tightly linked to specific leaf area [START_REF] Shipley | Net assimilation rate, specific leaf area and leaf mass ratio: which is most closely correlated with relative growth rate? A meta-analysis[END_REF], may help to further understand which processes lead to increased local extinction risk. Finally, also population genetic structure is related to plant traits [START_REF] Duminil | Can population genetic structure be predicted from life-history traits?[END_REF][START_REF] Ellstrand | Gene flow by pollen: implications for plant conservation genetics[END_REF]) and traits might affect extinctions in this way. For instance, the pollen:ovule (P/O) ratio is an indicator trait that relates to gene exchange via breeding system and realized pollination events [START_REF] Cruden | Pollen-ovule ratios-conservative indicator of breeding systems in flowering plants[END_REF][START_REF] Loveless | Ecological determinants of genetic structure in plant populations[END_REF], for which we showed elsewhere a link to other risk factors such as land use changes [START_REF] Lhotte | Are there contrasted impacts of urbanization and land uses on population persistence? The case of Teucrium pseudochamaepitys, an endangered species in Southern France[END_REF]). The P/O ratio also retraces a gradient from low pollen exchanging and inbreeding to high pollen exchanging and obligate outcrossing species [START_REF] Cruden | Pollen-ovule ratios-conservative indicator of breeding systems in flowering plants[END_REF][START_REF] Loveless | Ecological determinants of genetic structure in plant populations[END_REF]. In the context of rapidly changing habitat conditions, pollination can be a key factor for plants to adapt rapidly and hence we hypothesize that the P/O ratio is in this way a factor that influences independently the risk of plant population extinctions.

Annual plants make up one third of plant diversity in the European Mediterranean region and are at comparatively high risks of extinction [START_REF] Médail | Ecological characteristics and rarity of endemic plants from southeast France and Corsica: implications for biodiversity conservation[END_REF]. This extinction risk can be related to their short life cycle, important differences in survival in the soil seed bank and to their habitats typically with strong anthropogenic disturbances (Saatkamp et al. 2011a[START_REF] Saatkamp | The functional role of soil seed banks in natural communities[END_REF]. Despite its importance in species number, we know strikingly little about the specific processes for the decline of annual plants in the Mediterranean region. Works that evaluated the relation between traits and local population dynamics or extinctions, did so for a single species [START_REF] Adams | Importance of the seed bank for population viability and population monitoring in a threatened wetland herb[END_REF][START_REF] Kalisz | Extinction dynamics, population growth and seed banks. An example using an age-structured annual[END_REF]. It is therefore expected that comparative analyses of population dynamics for several species will give new insights [START_REF] Menges | Population viability analyses in plants: challenges and opportunities[END_REF]. For annual plants of cereal fields, population extinctions are due to changing agricultural practices such as herbicide and fertilizer application as well as higher densities of crop plants (Fried et al. 2009b;[START_REF] Schneider | Biologisch-ökologische Grundlagen des Schutzes gefährdeter Segetalpflanzen[END_REF]. Annual plants react faster to environmental changes compared to perennial plants and thus effects are easier to detect. Therefore, annual plants in cereal fields give a good opportunity to test the effects of life history traits and habitat requirements on population dynamics.

In this study, we used data on populations for 24 rare and common arable plants together with novel and detailed experimental data on plant traits and environmental parameters to assess local extinction risk in plants. Our approach was to quantify at the same time influence of environmental factors, such as mean annual temperature, population size at the growing sites and characteristics at the species level such as plant traits and habitat requirements.

More specifically, we wanted to answer (i) how plant traits (especially seed production, survival in soil seed bank, seed mass, plant size, SLA and P/O ratio) and population size influence local extinction risk at the long run; (ii) how site climate influences extinction risks; (iii) how water, nutrient, light and temperature requirements as measured by Ellenberg's indicator values influence extinction and (iv) to finally analyse if plants that are rare on regional scales have a higher local extinction risk.

3

Materials and methods

Study site and species

We gathered data on rare and common cereal weeds in an area of ca. 2500 km 2 around the Luberon ridge in South Eastern France. Traditional agriculture in this area maintained a high diversity of rare arable plants elsewhere extinct in Europe and data have been gathered in the mid-1980s during field surveys [START_REF] Filosa | Les plantes messicoles dans le Parc Naturel Régional du Luberon et contrées limitrophesunpublished report, Conservatoire Botanique National Méditerranéen Filosa D[END_REF]. Based on surveys from 1983 to 1985, we revisited populations for 24 species (Supplementary Fig. 1) of rare arable plants. We also used data on rarity levels from a regional flora [START_REF] Jauzein | Flore des champs cultivés[END_REF] to categorise species into either rare or common (Table 1). Nomenclature followed [START_REF] Jauzein | Flore des champs cultivés[END_REF].

Climatic variables

Since sites were scattered over large areas without nearby weather stations, we used the worldclim data set together with DIVA-GIS software [START_REF] Hijmans | Very high resolution interpolated climate surfaces for global land areas[END_REF] to extract climatic variables for our study sites. Study sites were spaced by more than 1 km in most cases, translating differences in climate into variance in the data-set. Our study region is characterised by Mediterranean climate with mean annual rainfall varying between 596 and 636 mm, with maxima in April and October. We reduced the manifold climatic variables to mean annual temperature (MAT), since this variable reflects the main gradient in a principal component analysis (PCA) using all climatic variables, and which opposed lowland to upland sites. The first axis of the PCA explained 78% of variance, with MAT and all temperature variables being positively correlated to the first axis and annual precipitation and precipitation variables negatively related except precipitation seasonality; MAT and annual precipitation were strongly negatively correlated (R 2 = 0.99, p < 0.001). MAT varied from 8 °C in upland to 13 °C in lowland sites.

Population size and local extinction

We used a census data set on rare cereal weeds dating from 1983 to 1985 to gather population sizes and localisations [START_REF] Filosa | Les plantes messicoles dans le Parc Naturel Régional du Luberon et contrées limitrophesunpublished report, Conservatoire Botanique National Méditerranéen Filosa D[END_REF]). For our analyses we pooled data from 1983 to 1985. In 2005 and 2006 we revisited populations of 24 different plant species. For 290 populations, their size in terms of numbers of individuals has been documented in detail in 1983/1985. These old population sizes enabled us to study its effect on extinction: 192 went extinct and 98 remained stable. The populations were documented by one visit per year at the flowering to fruiting time of the species before wheat harvest. This corresponds to the visits of the initial data collection (D. Filosa, pers. comm.). The census was conducted at the same level of precision as in 1983. For comparison with the 1983 and 1985 data, we also pooled data from 2005 to 2006. In all analyses, we used presence/absence of populations in 2005/2006 as dependent variable. Evidently, the absence of a population in one single year does not equal extinction, since it might be still present in the soil seed bank and this for years [START_REF] Saatkamp | The seed bank longevity index revisited: limited reliability evident from a burial experiment and database analyses[END_REF]). However, we think that pooling the data over two years of inventory limits the amount of unobserved but still present populations, and that absence of populations in two consecutive years is a reasonable indicator of potential local extinction.

Pollen:Ovule ratio

In spring and summer 2006, we collected three stamens per flower bud, and one bud for each of five randomly chosen individuals for all 24 plant species (illustrated in Supplementary Fig. 1). We stored the three stamens for each bud dry together in Eppendorf tubes. The remaining flower was conserved in 70% alcohol in plastic tubes until we counted number of stamens and ovules. Once all species sampled, we dissolved stamen tissue using 550 µl of sulphuric acid per tube for 24-48 h. After that, we crushed the remaining tissues with a small glass pestle, added 1650 µl of water with 2% triton tenside and mixed it. We then centrifuged for 5 min and decanted the superfluous liquid. We added 1000 µl of alcohol (95%) and mixed it again. We centrifuged again for 5 min, removed liquid, and dried to obtain dry pollen samples. We then added 40 µl of a 30% sucrose/20% glycerol solution ('counting solution') and sonicated the solution. We counted pollen grains under a microscope using a 1 µl hematocytometer. We counted ovules under a binocular microscope. We then calculated the number of pollen grains for one stamen as follows: number of pollen grains in 1 µl × 40 µl of counting solution, divided by the three stamens used. We then calculated pollen:ovule ratio (P/O) as the number of pollen grains for one stamen × number of stamens per flower, divided by the total number of ovules [START_REF] Cruden | Pollen-ovule ratios-conservative indicator of breeding systems in flowering plants[END_REF].

Seed production, seed mass and plant size

We counted ripe seeds produced for 10 individual plants per species in the field. For species with multi-seeded fruits or infructescences, we counted the number of fruits or infructescences and sampled two of them per individual to count number of seeds per fruit/infructescence. Seed production per individual was then calculated as mean seed number per fruit/infructescences multiplied by the number of fruits/infructescences counted per individual. In our analyses, we used mean seed production for ten individuals as specific trait value. To measure seed mass for each species, we counted three replicates of 10 seeds and weighed them with an analytical balance (± 0.001 mg). At the time of fruiting, we measured plant size (in mm) in the field for 25 individuals chosen randomly in the population, to calculate mean plant size per species.

Soil seed mortality

We studied soil seed mortality using a burial experiment presented in more detail in [START_REF] Saatkamp | The seed bank longevity index revisited: limited reliability evident from a burial experiment and database analyses[END_REF]. For each species, we collected in the field seed material between June and September 2005. We mixed the ripe seeds from at least 10 individuals and stored them dry in paper bags until burial in October 2005. After burial of seeds in nylon mesh bags in a randomised block design (five block replicates), we retrieved buried seeds after 6, 12, 18, 24 and 30 months of burial from October 2005 to April 2008. We determined the viable fraction for every seed lot including an initial value before burial, by using germination tests in a growth chamber and tetrazolium test for remaining seeds (I.S.T.A 1996). This burial experiment yielded mean mortality percentages for a 2.5 year period.

Specific leaf area (SLA)

Leaf material was collected in field on living individuals at begin of flowering (April to June 2007 and 2008) using only green, intact and undamaged leaves. For each species, five individual plants were chosen at random. Two leaves were collected per plant. Until measurement, we put leaves in sealed plastic bags stored at 4 °C, and processed them within 24 h after collection according to the recommendations in [START_REF] Garnier | A standardized protocol for the determination of specific leaf area and leaf dry matter content[END_REF]. We measured leaf area only on living and fully turgescent leaves. We used scanned images along with reference surfaces of known size to detect leaf area using the lafore-software package [START_REF] Lehsten | Functional analysis and the modelling of vegetation[END_REF]. We then placed leaves in tagged paper bags and dried them at 50 °C for 3 days. We measured dry leaf weight using a fine balance (± 0.001 mg). SLA was calculated for each single leaf as the ratio of fresh leaf area on leaf dry mass. We then used the mean SLA values as plant trait in our analyses. [START_REF] Ellenberg | Zeigerwerte von Pflanzen in Mitteleuropa[END_REF] provided position of a species in gradients of light (L), temperature (T), moisture (F) and nutrients (N) for the central European flora. Indicator values are a very sensible way to characterize habitat conditions for plants [START_REF] Diekmann | Species indicator values as an important tool in applied plant ecology-a review[END_REF]Saatkamp et al. 2011b). We complemented indicator values for Nigella damascena, using information from local floras [START_REF] Jauzein | Flore des champs cultivés[END_REF][START_REF] Molinier | Catalogue des plantes vasculaires des Bouches-du-Rhône. Muséum d'Histoire Naturelle Marseille[END_REF]. All trait data are presented in the Supplementary Table 1.

Ellenberg indicator values

Statistical analyses

Since our data was organized according to three levels of aggregation (populations, sites and species), we run three separate analyses for each level of aggregation i.e.: (1) population size, (2) mean annual temperature aggregated at the site level and (3) plant traits as well as Ellenberg indicator values aggregated at the species level. We first applied a generalized linear regression (GLM) analysis on the three levels of aggregation-populations, sites and species-separately. For the first two levels, we used extinction (1) versus persistence (0) of each population as a binary response variable in a GLM to evaluate effects of population size and site climate and functional traits. All explanatory variables were standardised prior to analyses.

For the species level we used a binomial GLM with logit link (logistic regression) with number of persistence and extinction as success/failure response variable. At the species level we had 24 species and 11 potential explanatory variables, part of which were correlated. We therefore reduced explanatory variables to three use a PCA in the following way. For each of three first PCA-axes with proportions explained variance of 0.25, 0.22 and 0.16, we selected the variable with the highest loading. This retained plant size (PS, loading -0.51 on PCA1), seed number (SN, loading 0.54 on PCA2) and seed bank survival (SB, loading -0.55 on PCA3). Explanatory variables were not correlated according to Pearson's correlation coefficient (r < 0.5). We then fitted GLM using the glm module in R. The use of species as independent data points is controversial since closely related species show similar features because of common ancestry. In our data set, where several major phylogenetic lineages are represented by only a few representatives, and with many closely related species pairs (Table 1) with contrasting traits, we think it is not reasonable to expect phylogenetic 'bias' in the data, which would further be difficult to quantify with such a small set of species. Therefore we did not perform an analysis including species groupings as random effects.

In supplementary document 1, we also present a single analysis, a generalized mixed model (GLMM) with sites and species as random factors and including all levels of aggregation in a single analysis. This file also contains a model selection process. We used GLMM with residual maximum likelihood (REML) in the R package lme4 (Bates and Maechler 2010; R-Core-Team 2014). As outlined above, we were not interested to study explicitly phylogenetic signals in extinction risk and did not include a complete covariance matrix on phylogenetic relations among our species in our GLMM analysis.

Independently from that, we tested whether rarity had an effect on local extinction risk using GLMM with sites and species as random effects.

Results

Effect of population size on extinction

First we analysed the effect of population size on extinction, which showed a highly significant negative effect of population size on extinction in a binomial GLM with a population size effect of -0.4869 (SE = 0.1342, z = -3.630, p < 0.001, AIC = 360.84). This result 1 3

was confirmed in a GLMM with site and species as random factor and population size as fixed factor with a slope of -0.8954 (SE = 0.2305, z = -3.885, p < 0.001, AIC = 329.8). The larger population size the lower was the extinction risk (Fig. 1A).

Effect of mean annual temperature (MAT) on extinction

We then analysed the effect of MAT separately on extinctions in a binomial GLM, which showed a positive effect of temperature on extinction (slope 0.4354, SE = 0.1467, z = 2.968, p = 0.003, AIC 365.6), i.e. more extinctions in warmer sites. We also run a GLMM, including sites and species as random factor, which showed a positive effect of temperature on extinction (slope = 0.5531, SE = 0.2315, z = 2.389, p = 0.017, AIC = 344.3). Overall, high mean annual temperature increased local extinction, with more extinctions being in warmer lowland sites (Fig. 1B).

Effect of traits and Ellenberg values on extinctions

The principal component analysis (PCA) combining all plant traits and Ellenberg indicator values showed that a number of traits and Ellenberg values were correlated across our data-set of 24 species (Fig. 2). The first three axes with a cumulative proportion of variance of 63% identified a set of plant traits explaining variance between species with the first principal component (PC1) being negatively related to plant size (PS, loading -0.51 on PC1) and seed mass (SM, -0.34) and positively to Ellenberg's temperature (T, 0.46) and moisture (F, 0.33) values, the second component being positively related to seed number (SN, loading 0.54 on PC2) and negatively to seed mass (SM, -0.44) and the third to seed bank survival (SB, loading -0.55 on PC3) and negatively to Ellenbergs's nutrient value (N, -0.44).

Based on the PCA we retained the three plant traits that were most related to the first three PCA axes as uncorrelated explanatory variables, which we used in a GLM with a A B Fig. 1 Effect of population size and mean annual temperature on extinctions; note that the dependant variable extinct/persistent was used for grouping and the logarithmic scale for population size 1 3 logit link (logistic regression). We performed this GLM on data aggregated at the species level in order to analyse the persistence/extinction as success/failure presented in Table 2.

This GLM showed a negative effect of seed number on the persistence/extinction ratio with highly productive species beeing less exposed to extinctions compared to species with reduced seed production (Table 2). There were positive effects of plant size on the persistence/extintions ratio, large plants having a higher probability of extinction than small plants (Table 2). The negative effect of survival in the soil seed bank on persistence reflects the fact that species with seed that survived well in our 2.5 year burial experiment had a lower probability of extinction of their populations (Table 2).

The GLMM analysis presented in Fig. 3 revealed that there was a highly significant effect of species' rarity status on extinction events with sites and species as random effects. Species that were rare at a larger scale showed higher proportion of local extinctions than species that were common.

Discussion

Our approach and our data highlighted for the first time that local plant population extinction is related to plant traits, niches and site conditions; with significant effects of population size, position in a climatic gradient, habitat requirements and plant traits.

One of the strongest effects on local population extinction was that smaller populations went extinct more easily than larger ones. This is additional evidence for the higher extinction risk of small populations-a well-known phenomenon but with little empirical evidence-(but see e.g. [START_REF] Fischer | Local extinction of plants in remnants of extensively used calcareous grasslands 1950-1985[END_REF][START_REF] Matthies | Population size and the risk of local extinction: empirical evidence from rare plants[END_REF]). The higher extinction risk of smaller populations has potentially three causes: (i) higher influence of stochastic events in reproduction, growth and mortality, (ii) high impact of stochastic deterioration of the environment [START_REF] Menges | Evaluating extinction risks in plant populations[END_REF]) (iii) consequences of reduced fitness due to limited genetic diversity, caused by inbreeding, accumulation of deleterious mutations and genetic drift [START_REF] Ellstrand | Population genetic consequences of small population size: implications for plant conservation[END_REF].

Additionally, there were more local extinctions of annual plants in warmer sites as indicated by mean annual temperature (MAT) in our analysis. MAT is higher in lowland areas, where summer drought is stronger and vegetation period shorter. However, lowland sites tend also to be subjected to heavier intensification of agriculture, fragmentation and urbanisation since they are close to growing urban areas. Would temperature have increased strongly, species should have disappeared in the warmest sites according to their temperature requirements. These analyses including indicator values [START_REF] Ellenberg | Zeigerwerte von Pflanzen in Mitteleuropa[END_REF]) suggest that changes affect lowland sites which harbour temperature demanding species, but our data did not specifically highlight temperature demanding species to disappear first. The most important variance in plant traits explaining population extinction was related to seed number and seed mass. Populations of species with a high seed production showed decreased probability of extinction compared to plants with low seed production. Seed production was associated with the second principal component in our PCA (Fig. 2), reflecting the well known seed number-size trade-off [START_REF] Moles | Seed size and plant strategy across the whole life cycle[END_REF], and negatively related to seed mass. It has repeatedly been shown that higher seed production is associated with frequent disturbances [START_REF] Pakeman | Impact of abundance weighting on the response of seed traits to climate and land use[END_REF]) and that large seeded plants are particularily endangered by the disappearance of effective dispersers [START_REF] Poschlod | R: A language and environment for statistical computing[END_REF]. Our data suggest that changes in the disturbance regime and habitat of mediterranean cereal fields favour small seeded highly productive plants and that species with large seeds and low seed production are at higher risk of extinction.

Plant size was positively associated with extinction probability on our analysis (Table 2) indicating that large plants are at higher risk of extinction. This can be related to competition between arable weeds and wheat [START_REF] Dutoit | Recherche prospective sur la dualité entre caractéristiques morphologiques et capacités de compétition des végétaux: le cas des espèces adventices et du blé[END_REF] and can be linked to the increasing stem density per square meter of cultivated cereals in our area. This suggests to use a management for less dense stands of extensive cereal fields, a causal relationship and recommendation that has already been elucidated for central Europe [START_REF] Schneider | Biologisch-ökologische Grundlagen des Schutzes gefährdeter Segetalpflanzen[END_REF]. Density increased due to the application of manure, chemicals and herbicides that all increase productivity in cereal stands, which disadvantage plants adapted to low nutrient levels and lower cereal density [START_REF] Storkey | The impact of agricultural intensification and land-use change on the European arable flora[END_REF].

Survival of seeds in the soil seed bank was negatively associated with exctinctions, with plants that had high survival in our 2.5 year seed burial experiment having lower probabilities of extinctions. This is in line with a number of theoretical [START_REF] Cohen | Optimizing reproduction in a randomly varying environment[END_REF][START_REF] Venable | The selective interaction of dispersal, dormancy and seed size as adaptations for reducing risks in variable environments[END_REF] and empirical works [START_REF] Stöcklin | Plants with longer-lived seeds have lower local extinction rates in grassland remnants 1950-1985[END_REF][START_REF] Venable | Bet hedging in a guild of desert annuals[END_REF] showing that soil seed banks play an important role to increase local persistence and decrease probability of extinction. In our data-set, species with low seed survival in the seed bank were at highest risk of extinction in mediterranean cereal fields. Together with data on seed production and seed size, this highlights the need of special attention to short-lived and large seeded plant species such as Agrostemma githago, Asperula arvensis or Vaccaria hispanica, being particularly endangered after current changes in land-use.

Altogether, our data support empirically the importance of interspecific differences in plant traits for extinction risk assessment [START_REF] Menges | Population viability analyses in plants: challenges and opportunities[END_REF][START_REF] Poschlod | Databases on life history traits as a tool for risk assessment in plant species[END_REF] and traces a way how environmental changes and traits can be used to quantify these extinctions and predict future extinctions. We therefore propose to integrate traits e.g. in population viability analyses for plants [START_REF] Brigham | Population viability in plants[END_REF][START_REF] Harrison | Plant population viability and metapopulation-level processes[END_REF][START_REF] Menges | Population viability analyses in plants: challenges and opportunities[END_REF]. However, there are a number of complex interactions between traits, population size and site characteristics which cannot be studied with such a limited set of species in a multi-population survey and which would profit from analyses using larger data-sets on extinctions.

Furthermore, there are more extinction events in rare compared to widespread species. This can be related to dispersal limitation via seeds or pollen and therefore shows the importance of nearby other populations in a metapopulation for local extinctions of plants [START_REF] Harrison | Plant population viability and metapopulation-level processes[END_REF]. Only recently it was shown that specialist arable plants declined stronger than non-specialist ones [START_REF] Meyer | Dramatic losses of specialist arable plants in Central Germany since the 1950s/60s-a cross-regional analysis[END_REF]. However, risks that already drove species to rarity in the past on a regional scale continued to act in the observation period and lead to the observed correlation of recent extinction and regional rarity. The relative rarity of small populations of plants with high soil seed mortality at the beginning of surveys indicates that past risks influenced the relative frequencies of species at the outset. Additionally, this extends previous analyses [START_REF] Fréville | Prediction of extinction in plants: interaction of extrinsic threats and life history traits[END_REF][START_REF] Lavergne | Fingerprints of environmental change on the rare Mediterranean flora: a 115-year study[END_REF]) by 1 3

focusing in a more detailed way on population extinctions and that help to identify underlying processes in order to better inform conservation efforts.

Fig. 2

 2 Fig. 2 Principal Componant Analysis of plant traits and Ellenberg indicator values of the studied species (SB seed bank survival; SN seed number, SM seed mass, PS plant size, SLA specific leaf area, Ellenberg's moisture (F), temperature (T), light (L) and nutrient (N) value, PO pollen:ovule ratio)

Fig. 3

 3 Fig. 3Local extinction risk of populations (n = 290) for 24 species according to their frequency at the regional level (GLMM, Wald's z = 3.358, p < 0.001)

Table 1

 1 Species studied, plant family, rarity class[START_REF] Jauzein | Flore des champs cultivés[END_REF], IUCN red-list classification for South-Eastern France (Noble et al. 2015): LC least concern, VU vulnerable, NT near threatened and number of populations studied

	Species	Family	Rarity	IUCN	Populations
	Adonis annua	Ranunculaceae	R	LC
	Adonis flammea	Ranunculaceae	C	LC
	Agrostemma githago	Caryophyllaceae	R	LC
	Androsace maxima	Primulaceae	R	LC
	Bifora radians	Apiaceae	C	LC
	Bifora testiculata	Apiaceae	R	NT
	Bupleurum rotundifolium	Apiaceae	C	LC
	Camelina microcarpa	Brassicaceae	R	LC
	Centaurea cyanus	Asteraceae	R	LC
	Cnicus benedictus	Asteraceae	R	LC
	Conringia orientalis	Brassicaceae	R	NT
	Consolida regalis	Ranunculaceae	C	LC
	Hypecoum pendulum	Papaveraceae	R	VU
	Legousia hybrida	Campanulaceae	R	LC
	Legousia speculum-veneris	Campanulaceae	C	LC
	Myagrum perfoliatum	Brassicaceae	R	LC
	Neslia apiculata	Brassicaceae	C	LC
	Nigella damascena	Ranunculaceae	C	LC
	Papaver argemone	Papaveraceae	R	LC
	Papaver hybridum	Papaveraceae	R	LC
	Ranunculus falcatus	Ranunculaceae	R	NT
	Roemeria hybrida	Papaveraceae	R	VU
	Turgenia latifolia	Apiaceae	R	NT
	Vaccaria hispanica	Caryophyllaceae	R	NT

Table 2

 2 Effects of plant size, seed number and seed bank survival on extinction in a logistic GLM; variables where standardised prior to analysisThe model was extinctions/persistence ~ PS + SN + SB, where PS plant size, SN seed number, SB seed bank survival

	Explanatory variables	Estimate ± SE	z value	p
	Plant size (PS)	0.2853 ± 0.1442	1.978	0.0479*
	Seed number (SN)	-0.3560 ± 0.1460	-2.438	0.0148*
	Survival in soil seed bank (SB)	-0.2800 ± 0.1420	-1.971	0.0487*

Acknowledgements

We thank all farmers of the Luberon for access to their fields. We are very grateful to Pierre Frapa and Georges Guende (Parc Naturel Régional du Luberon) for funding and documentation and Frauke Behrendt (University of Brighton) for English language revision. AS benefited from the Région Provence Alpes Côte d'Azur grant "Gévoclé" and from funding through the GREAT-med programme under funding by the European Union Neighborhood Partnership Initiative (ENPI CBCMED). We thank two anonymous reviewers for many helpful comments.


Juliane ( Helm
email: juliane.helm@bgc-jena.mpg.de

Thierry Dutoit
email: thierry.dutoit@imbe.fr

Arne Saatkamp
email: arne.saatkamp@imbe.fr

Franziska Solveig
email: solveig.franziska.bucher@uni-jena.de

Matthias Bucher

Christine Leiterer

Römermann

Bucher

Matthias Leiterer
email: matthias.leiterer@tll.thueringen.de

Christine Römermann
email: christine.roemermann@uni-jena.de

S F Bucher

Recovery of Mediterranean steppe vegetation after cultivation: legacy effects on plant composition, soil properties and functional traits

Keywords: Community trait means, Cultivation, Dry Grassland, Grazing, Intraspecific trait variability, Leaf dry matter content, Natural recovery, Restoration, Specific leaf area

published or not. The documents may come   L'archive ouverte pluridisciplinaire

Europe's most species-rich ecosystems [START_REF] Willems | Species composition and above ground phytomass in chalk grassland with different management[END_REF][START_REF] Wallisdevries | Challenges for the conservation of calcareous grasslands in northwestern Europe: integrating the requirements of flora and fauna[END_REF].

Nevertheless, the 20 th century's agricultural intensification caused a dramatic decrease in steppe grasslands worldwide and led to fragmentation as well as eutrophication of these habitats, leading to a decrease in plant diversity [START_REF] Poschlod | Plant species richness in calcareous grasslands as affected by dispersability in space and time[END_REF][START_REF] White | Grassland ecosystems[END_REF][START_REF] Karlik | History or abiotic filter: which is more important in determining the species composition of calcareous grasslands?[END_REF]). To protect the species diversity and to better connect semi-natural grasslands, grassland remnants need to be conserved or, if already altered, restored. For the restoration of these species rich grasslands, several techniques have already been proposed [START_REF] Kiehl | Species introduction in restoration projects-Evaluation of different techniques for the establishment of semi-natural grasslands in Central and Northwestern Europe[END_REF] for review) as the natural colonization of characteristic grassland species into former intensively cultivated areas is usually very slow [START_REF] Römermann | Influence of former cultivation on the unique Mediterranean steppe of France and consequences for conservation management[END_REF], Buisson et al. 2006). It has already been shown that it might take several decades or centuries until the species composition and diversities of grasslands return [START_REF] Forey | Vegetation, soils and seed banks of limestone grasslands are still impacted by former cultivation one century after abandonment[END_REF]; accordingly, active restoration measures are typically needed.

To evaluate restoration success, traditional restoration studies assess the floristic similarity between restored and original (target) vegetation, focussing on species composition as well as diversity [START_REF] Dutoit | The pseudo-steppe of La Crau (South-Eastern France): origin, management and restoration of a Mediterranean rangeland[END_REF]. However, these indicators are highly dependent on site characteristics that determine the local species-pool (Stuble et al. 2017). A complementary way of assessing restoration success is to focus on the restoration of the functional composition [START_REF] Laughlin | Applying trait-based models to achieve functional targets for theory-driven ecological restoration[END_REF][START_REF] Engst | Functional community ecology meets restoration ecology: Assessing the restoration success of alluvial floodplain meadows with functional traits[END_REF], which is especially relevant for those sites where original species are lost from the local species pool. The analyses of plant functional traits can provide insights into how land-use changes affect vegetation dynamics and function (e.g. [START_REF] Römermann | Substitutes for grazing in semi-natural grasslands -do mowing or mulching represent valuable alternatives to maintain vegetation structure?[END_REF][START_REF] Breitschwerdt | Do newcomers stick to the rules of the residents? Designing trait-based community assembly tests[END_REF], but this trait-based approach has rarely been examined in connection with restoration success in Mediterranean dry grasslands. Various habitat filters (e.g., environmental factors such as climate conditions, soil properties, or disturbance) allow only species with certain trait values to establish [START_REF] Keddy | Assembly and response rules: two goals for predictive community ecology[END_REF][START_REF] Weiher | Assembly rules, null models, and trait dispersion: new questions from old patterns[END_REF][START_REF] Diaz | Plant functional traits and environmental filters at a regional scale[END_REF][START_REF] Venn | Using plant functional traits to explain community composition across a strong environmental filter in Australian alpine snowpatches[END_REF]. The species that pass these filters are necessarily similar, which eventually leads to trait convergence [START_REF] Diaz | Plant functional traits and environmental filters at a regional scale[END_REF][START_REF] Wilson | Trait-divergence assembly rules have been demonstrated: Limiting similarity lives! A reply to Grime[END_REF][START_REF] Laughlin | A predictive model of community assembly that incorporates intraspecific trait variation[END_REF]. But, species also need to be dissimilar enough to avoid competition, according to the limiting similarity hypothesis, which eventually leads to trait divergence [START_REF] Macarthur | The limiting similarity, convergence, and divergence of coexisting species[END_REF][START_REF] Wilson | Trait-divergence assembly rules have been demonstrated: Limiting similarity lives! A reply to Grime[END_REF][START_REF] Cornwell | Community assembly and shifts in plant trait distributions across an environmental gradient in coastal California[END_REF][START_REF] Laughlin | A predictive model of community assembly that incorporates intraspecific trait variation[END_REF].

Comparing the functional composition of original vs. changed plant communities and analyzing the trait composition of target species that have already successfully re-established in the restoration sites seem promising as this approach complements the taxonomic evaluation of restoration success, therewith leading to a better undestanding of the factors preventing successful restoration.

The aim of this study was to evaluate whether the taxonomic and functional composition of fallow lands can develop into the direction of original steppe communities without having established active restoration measures such as the addition of propagules.

We performed vegetation relevés to assess whether fallow lands re-developped into the direction of the target steppe vegetation with respect to the species composition and diversity.

To elucidate the potential natural development of fallow land vegetation towards the original steppe vegetation we analyzed temporal trends in vegetation changes by comparing vegetation relevés and soil analyses from 2001 with results for 2015.

We explored the functional composition (community-weighted mean = CWM) of traits related to plant performance and growth rate and as indicators of competitive ability and environmental tolerance of species [START_REF] Garnier | Growth analysis of congeneric annual and perennial grass species[END_REF][START_REF] Reich | From tropics to tundra: global convergence in plant functioning[END_REF][START_REF] Poorter | Causes and consequences of variation in leaf mass per area (LMA): a meta-analysis[END_REF][START_REF] Lauterbach | Factors driving plant rarity in dry grasslands on different spatial scales: a functional trait approach[END_REF][START_REF] Pérez-Harguindeguy | New handbook for standardised measurement of plant functional traits worldwide[END_REF] [START_REF] Chapin | Evolution of suites of traits in response to environmental stress[END_REF][START_REF] Garnier | Growth analysis of congeneric annual and perennial grass species[END_REF][START_REF] Lavorel | Predicting changes in community composition and ecosystem functioning from plant traits: revisiting the Holy Grail[END_REF][START_REF] Pérez-Harguindeguy | New handbook for standardised measurement of plant functional traits worldwide[END_REF][START_REF] Poorter | Ecological significance of inherent variation in relative growth rate and its components[END_REF][START_REF] Poorter | Leaf area ratio and net assimilation rate of 24 wild species differing in relative growth rate[END_REF][START_REF] Römermann | Substitutes for grazing in semi-natural grasslands -do mowing or mulching represent valuable alternatives to maintain vegetation structure?[END_REF][START_REF] Villar | Variation in relative growth rate of 20 Aegilops species (Poaceae) in the field: the importance of net assimilation rate or specific leaf area depends on the time scale[END_REF]. Canopy height reflects the competitive ability of plant communities through better light assessment [START_REF] Gaudet | A comparative approach to predicting competitive ability from plant traits[END_REF][START_REF] Westoby | Plant ecological strategies: some leading dimensions of variation between species[END_REF]), yet the investment in height incurs costs for construction and maintenance of the stem [START_REF] Falster | Plant height and evolutionary games[END_REF]) and thus should be positively related to soil nutrient availability.

Intraspecific variation patterns in plant functional traits are a major determinant of the ability to respond and evolve with climate change and changing environmental conditions [START_REF] Nicotra | Plant phenotypic plasticity in a changing climate[END_REF][START_REF] Laforest-Lapointe | Intraspecific variability in functional traits matters: case study of Scots pine[END_REF][START_REF] Bucher | Stomatal traits relate to habitat preferences of herbaceous species in a temperate climate[END_REF][START_REF] Bucher | Traits and climate are associated with first flowering day in herbaceous species along elevational gradients[END_REF]. In some cases, trait variability can even be more important than particular trait values: species showing high functional variability may successfully re-establish because they manage to adapt to changing environmental conditions [START_REF] Albert | When and how should intraspecific variability be considered in trait-based plant ecology? Perspectives in Plant Ecology[END_REF][START_REF] Jung | Intraspecific variability and trait-based community assembly[END_REF]). In addition to the above mentioned traits we included additional plant width and biomass to test whether high intraspecific trait variability is related to re-establishment success. Both traits reflect competitive strength and should thus relate positively to soil nutrients [START_REF] Pérez-Harguindeguy | New handbook for standardised measurement of plant functional traits worldwide[END_REF].

To summarize, this study combines a taxonomic with a trait-based approach to i) identify the effects of former land uses on present vegetation composition, species diversity and physical-chemical soil parameters, and ii) investigate whether re-development towards the original steppe vegetation can be detected after a further 14 years of recovery under traditional grazing conditions (2001 vs. 2015). Moreover, we iii) investigate whether differences in CWM of plant height, SLA and LDMC between fallow land and original steppe vegetation are still observable and attempt to iv) determine whether the traits of successful colonizers show higher functional variability than those of species that have not re-established on fallow lands yet.

Materials and Methods

Study sites

The plain of La Crau (Fig. 1) is the last remaining xeric steppe [START_REF] Devaux | Notice de la carte phytoécologique de la Crau (Bouches du Rhône)[END_REF] in southeastern France (43°33´N, 4°52´W). The area was formed by ancient river deposits during the Pleistocene period between 2 000 000 BP and 30 000 BP [START_REF] Molliex | Quaternary evolution of a large alluvial fan in a periglacial setting (Crau Plain, SE France) constrained by terrestrial cosmogenic nuclide (10 Be)[END_REF] [START_REF] Colomb | La Crau, données nouvelles et interprétations[END_REF]. Traditionally, the land has been used for itinerant sheep grazing, probably since early Neolithic times (Buisson & Dutoit 2006). Industry, military activities, quarries, highways and intensive agriculture led to fragmentation and reduction of the semi-natural steppe vegetation from approximately 60 000 ha to 11 500 ha in the 20 th century (Buisson & Dutoit 2006;[START_REF] Deverre | La nature mise au propre dans la steppe de Crau et la forêt du Var[END_REF][START_REF] Etienne | Abandoned lands and land use conflicts in southern France. Piloting ecosystem trajectories and redesigning outmoded landscapes in the 21st century[END_REF]. During the period of melon cultivation , intensive fertilization, herbicides and deep ploughing changed the soil structure and degraded the conglomerate [START_REF] Römermann | Histoire culturale de la Crau: potentialités de ré-établissement des espèces caractéristiques du coussous après abandon[END_REF][START_REF] Römermann | Influence of former cultivation on the unique Mediterranean steppe of France and consequences for conservation management[END_REF]. In contrast, cereals (1950)(1951)(1952)(1953)(1954)(1955)(1956)(1957)(1958)(1959)(1960)(1961)(1962)(1963)(1964)(1965)(1966) were cultivated without deep ploughing and using less fertilizer [START_REF] Devaux | Notice de la carte phytoécologique de la Crau (Bouches du Rhône)[END_REF][START_REF] Masip | Le peuplement végétal de la Réserve de Peau de Meau[END_REF]. At the time of abandonment, no active restoration operations were realized. Grazing, representing an important factor for the maintenance of these grasslands, was re-introduced immediately when cultivation ceased [START_REF] Dureau | Etude des pratiques de gestion pastorale des coussouls[END_REF]. The recovery of fallow land in our study area was thus not a strictly passive restoration technique. The flocks of sheep link remaining steppe patches (the target) and fallow lands and potentially facilitate the dispersal and establishment of steppe species into fallow lands [START_REF] Fischer | Experimental studies on the dispersal of plants and animals on sheep in calcareous grasslands[END_REF].

F o r R e v i e w O n l y
their land-use histories were examined (Table 1, Fig. 1). One long-abandoned and one recently abandoned cereal field were included, to represent different time spans.

We conducted vegetation relevés on 20 m x 20 m sites, placing five replicate 2 m × 2 m quadrats at each corner and in the middle (hereafter referred to as 'plots'). Species cover was estimated using the scale of [START_REF] Braun-Blanquet | Pflanzensoziologie : Grundzuge der Vegetationskunde[END_REF]. At each location, at least two sites consisting of one undisturbed steppe plot and one adjacent fallow land plot grazed by the same flock of sheep were studied. The locations Petit Abondoux, Poulagère and Couliès were sampled in May 2014 [START_REF] Tanet | Les fourmis sont-elles de bons indicateurs de la régénération spontanée des pelouses sèches méditerranéennes après dégradation culturale?[END_REF]; Fig. 1), and the locations Peau de Meau, Grand Abondoux and Valigne in April 2015 (Fig. 1).

Percentages of vegetation cover, stone cover and bare ground were estimated on the five plots at the time of vegetation sampling. To estimate the standing crop, we cut the total aboveground biomass on three 0.5 m × 0.5 m randomly chosen quadrat within each site. The leaf area index (LAI), the ratio of foliage area to ground surface area [START_REF] Watson | Comparative physiological studies on the growth of field crops: I. Variation in net assimilation rate and leaf area between species and varieties, and within and between years[END_REF], of each of the five plots was measured using the LAI-2200C Plant Canopy Analyzer. Species richness S representing the total number of species, Shannon diversity index (Hs) and Evenness (E) were calculated for each plot [START_REF] Mühlenberg | Freilandökologie. UTB für Wissenschaft[END_REF].

Soil sampling

To identify the effect of former land use on physical-chemical soil parameters, three replicate mixed soil samples of the upper soil layer (0-10 cm) were collected randomly within each site.

After drying and sieving with a 2 mm mesh sieve, soil samples were analyzed at the INRA soil analysis laboratory (Institut National de la Recherche Agronomique, Arras, France) according to standardized protocols. Organic carbon (C in g kg -1 ) and total nitrogen content (N in g kg -1 ) were analyzed via the dry combustion method using a CHN elemental analyzer (Vario EL Elemental Analyzer, Elementar). Phosphorus content (P in g kg -1 ) was measured by the Olsen method [START_REF] Olsen | Estimation of available phosphorus in soils by extraction with sodium bicarbonate[END_REF]. Calcium (Ca in g kg -1 ), magnesium (Mg in g kg -1 ) and potassium (K in g kg -1 ) were determined by the Metson method [START_REF] Metson | Methods of chemical analysis for soil survey samples[END_REF]. Additionally, soil pH was

F o r R e v i e w O n l y
measured in a 1:1 soil-water solution, after stirring once followed by a 24 h rest period. Carbonnitrogen ratio (C:N) and organic matter (OM in g kg -1 ) were calculated using total C and N results. The amount of clay (> 0.002 mm), fine silt (0.002-0.02 mm), coarse silt (0.02-0.05 mm), fine sand (0.05-0.2 mm) and coarse sand (0.2-2 mm) in g kg -1 were determined according to the Robinson method [START_REF] Robinson | A new method for the mechanical analysis of soils and other dispersions[END_REF] without previous decarbonation [START_REF] Baize | Guide des analyses en pédologie: 2e édition, revue et augmentée[END_REF].

Comparison of vegetation composition between 2001 and 2015

To investigate whether the vegetation composition of the fallow land had re-developed towards the vegetation of unaltered steppes over the previous 14 years, we compared old vegetation relevés from [START_REF] Römermann | Histoire culturale de la Crau: potentialités de ré-établissement des espèces caractéristiques du coussous après abandon[END_REF][START_REF] Römermann | Influence of former cultivation on the unique Mediterranean steppe of France and consequences for conservation management[END_REF] to recent vegetation relevés for the locations Peau de Meau (steppe, cereal fallow, melon fallow; Table 1), Petit Abondoux (steppe, cereal fallow; Table 1) and Valigne (steppe, melon fallow; Table 1). Ten replicate relevés were carried out per site in 2001 and five in 2015.

Trait data and community-weighted means (CWM)

We compiled trait data for SLA (the ratio of fresh leaf area to dry mass in g cm -2 ), LDMC (the ratio of dry mass to fresh mass in mg g -1 ) and canopy height (cm) for all species observed in the vegetation relevés using the trait databases TRY [START_REF] Kattge | TRY-a global database of plant traits[END_REF]) and BROT [START_REF] Paula | BROT: a plant trait database for Mediterranean Basin species[END_REF]. This dataset was then supplemented with our own measurements for species missing from the databases. For our own measurements, five individuals per species were collected at the site where they were most abundant, following the approach described in [START_REF] Rosbakh | Specific leaf area correlates with temperature: new evidence of trait variation at the population, species and community levels[END_REF]. Plants were collected and measured from May to July 2015, following standardized protocols [START_REF] Pérez-Harguindeguy | New handbook for standardised measurement of plant functional traits worldwide[END_REF]. For each species, two healthy sun leaves were collected, wrapped in moist paper and stored in a plastic bag in a cool box until the fresh leaf weight was measured. The fresh leaf area was determined at 300 dpi on a flatbed scanner. Leaf area was measured on scanned fresh leaves with the Leaf Trait package for R Römermann, unpubl.). Then, the leaves were dried at 70° C to constant mass and subsequently weighed. For each vegetation relevé, we then calculated the CWM for SLA, LDMC and canopy height according to: Formula 1:

F o r R e v i e w O n l y (Bernhardt-
𝐶𝑊𝑀 𝑐 = 𝑠 ∑ 𝑖 = 1 𝑝 𝑖𝑐 × 𝑇 𝑖𝑐
where the mean value of trait T for species i in the community c was weighted by species relative abundance p ic in the community, with a total of S species [START_REF] Garnier | Plant functional markers capture ecosystem properties during secondary succession[END_REF][START_REF] Violle | Let the concept of trait be functional![END_REF].

Species selection and trait measurements for intraspecific trait variability (ITV)

Species selection was based on vegetation relevés from 2001 [START_REF] Römermann | Histoire culturale de la Crau: potentialités de ré-établissement des espèces caractéristiques du coussous après abandon[END_REF][START_REF] Römermann | Influence of former cultivation on the unique Mediterranean steppe of France and consequences for conservation management[END_REF] and 2014 [START_REF] Tanet | Les fourmis sont-elles de bons indicateurs de la régénération spontanée des pelouses sèches méditerranéennes après dégradation culturale?[END_REF]). The final selection was based on indicator species analysis conducted with the package 'indicspecies' [START_REF] Cáceres | Associations between species and groups of sites: indices and statistical inference[END_REF] supplemented by expert knowledge.

We identified three successful colonizers as those occurring originally in the steppe but also in the fallow land (Carthamus lanatus L., Lobularia maritima L Desv., Sideritis romana L.). Five unsuccessful colonizers were limited to the steppe (B. retusum, Hypochaeris glabra L., Linum trigynum L., Stipa capillata L., Trifolium campestre Schreb.). Four species whose major distribution was in fallow land were added for comparison (Crepis foetida L., Dactylis glomerata L., Galactites tomentosus Moench., Trifolium subterraneum L.). We sampled a maximum of eight individuals per species and site if abundant: for details, see Table 2 andTable 3. Besides SLA, LDMC and canopy height, we expanded our trait set to include plant width (cm), aboveground biomass (g), seed mass (mg) and leaf carbon (leaf C in mg kg -1 ), nitrogen (leaf N in mg kg -1 ) and phosphorus content (leaf P in mg kg -1 ; Table 3). Plant width was measured with a measuring tape at maximum diameter without extending the plant, biomass was dried at 70° C to constant mass and subsequently weighed. We determined average seed mass by weighing five batches of 20-100 ripe seeds per species, depending on the species. Seed were pooled per site prior to nutrients analyses. Thus, ITV could not be calculated thereof but leaf nutrients could be compared between the different land-use types (see Appendix S3).

To characterize the differences in trait composition between individuals measured in the steppe and the fallow land sites, a principle component analysis (PCA) was conducted (matrix: 854 individuals of 9 species x 9 traits; H. glabra, B. retusum, T. subterraneum were excluded because of data constraints -insufficient biomass and seeds available). Prior to analyses, data was standardized to zero mean and unit variance.

To characterize ITV, the coefficient of variation (CV) was calculated as the standard deviation divided by the mean for all measured traits (Pérez-Harguindeguy et al. 2013) based on the eight individuals per species and site. ITV was calculated for all species occurring in the steppe sites to assess whether species with higher trait variability were more likely to pass through the environmental filter and thus manage to re-establish in fallow land. Therefore, we included four unsuccessful colonizers three successful colonizers and two fallow land species in our CV calculation (Table 2).

Statistical analyses

Vegetation composition and soil properties

To test for the effect of land-use history on vegetation structure (S, H s , E, standing crop, LAI, vegetation cover/stone cover/bare ground) and soil properties (clay, silt, sand, organic matter, total C, total N, C:N, pH, P, Ca, Mg and K), one-way ANOVA followed by a Tukey Honest Significant Difference post-hoc test was performed for normally distributed data with homogeneous variances. Any data not showing normal distribution and homogeneous variances were analyzed by the nonparametric Kruskal-Wallis test followed by the pairwise Wilcoxon test with P-value adjustment according to Holm. To assess associations between differences in vegetation composition and environmental parameters, a detrended correspondence analysis (DCA) was conducted. We used species abundances of the five vegetation relevés per site as the main matrix (a total of 12 species x 16 sites). Then, environmental parameters were correlated with the axes using mean values calculated per site for each parameter. The environmental factors considered were five physical soil variables (clays, fine and coarse silt, fine and coarse sand) and eight chemical soil variables (total C, total N, C:N, pH, P, Ca, Mg and K) as well as percentage cover of vegetation, stones and bare ground and time since abandonment as deduced from the fallow land cultivation period (Table 1). All parameters were standardized to zero mean unit variance prior to analyses.

Comparison of vegetation composition between 2001 and 2015

As the 2001 data were obtained on 2m x 2m plots via the frequency method [START_REF] Pfadenhauer | Überlegungen zu einem Konzept geobotanischer Dauerbeobachtungsflächen für Bayern. Teil 1. Methodik der Anlage und Aufnahme[END_REF]), we harmonized the data for 2001 and 2015 into presence/ absence data to avoid any observer effects in the estimation of the frequencies and for the non-metric multidimensional scaling (NMDS). Species that occurred just once across the overall dataset were removed to avoid discriminating the dataset too strongly by their presence alone instead of discriminating the gradient by their frequencies.

Differences in trait composition: Community-weighted means (CWM) and intraspecific trait variability (ITV)

To analyze differences between CWM of the three land-use types and CVs, a one-way ANOVA followed by a Tukey Honest Significant Difference post-hoc test was performed for normally distributed data with homogeneous variances. Any data not showing normal distribution and homogeneous variances were analyzed by the nonparametric Kruskal-Wallis test followed by the pairwise Wilcoxon test with P-value adjustment according to Holm.

All statistical analyses were carried out in R (version 3.3.1, R Development Core Team 2015, Vienna, AT). Multivariate analyses (DCA, PCA, NMDS) were performed using the R packages 'vegan' (Oksanen et al. 2008) and 'MASS' [START_REF] Venables | Modern Applied Statistics with S. 4 th ed[END_REF].

F o r R e v i e w O n l y

Results

Vegetation and soil attributes

Vegetation structure and soil properties of fallow lands differed from those of adjacent steppe (Table ). The steppe showed highest values in species richness, Shannon diversity and Evenness; cereal fallows typically had intermediate positions (Table 4). Melon fallows had significantly higher values in soil Ca, P and pH. The C/N ration was highest in steppes.

The DCA (Fig. 2) showed a trend towards very homogeneous vegetation composition in the steppe plots at different sites, whereas the fallow lands tended to be more heterogeneous in vegetation composition. The first axis separated steppe from fallow land and was negatively correlated with total soil C, vegetation cover and soil C:N ratio. Percentages of bare ground, clays, pH and P were positively correlated with fallow land.

Comparison of vegetation composition between 2001 and 2015

In 2001, steppe and fallow lands had distinct species composition trends indicated by the separated polygons of the NMDS (Fig. 3). Fourteen years later, the fallow land had developed towards the original steppe vegetation, while there had been little change in steppe vegetation

Differences in trait composition

As shown in Table 4, CWM of SLA was significantly lower in steppe than in fallow-land communities (χ 2 = 54.19, P < 0.001) while CWM of LDMC was significantly higher in steppe communities (F 2,77 = 52.38, P < 0.001). Canopy height differed among all the land-use types.

The highest values were observed in the steppe and the lowest in cereal fallows (F 2,77 = 5.19, P < 0.01). For individual species information see Appendix S1.

The PCA (Appendix S2) partly separated the species according to their trait composition measured in the steppe and the fallow land. C. foetida, D. glomerata, L. trigynum and S. romana showed a tendency towards a distinction between the steppe and fallow lands and thus changes in plant trait values due to land-use change, as indicated by the black arrow.

The CV did not reveal any differences between successful and unsuccessful colonizers (Fig. 4). Overall, significant differences between species were found for SLA (χ 2 = 27.44, P > 0.001), LDMC (χ 2 = 31.75, P > 0.001) and plant width (χ 2 = 36.91, P > 0.001). L. trigynum, as a typical steppe species, varied more in SLA than the fallow land species D. glomerata and the successful colonizer S. romana. Regarding LDMC values, L. trigynum displayed the highest variability, while B. retusum and D. glomerata had significantly lower variability. B. retusum had a significantly lower CV in plant width than L. trigynum and S. romana. S. romana showed significantly higher variation in plant width than C. lanatus (successful colonizer).

Discussion

The recovery of fallow land in our study area implemented grazing and was thus not a strictly passive restoration technique. The fact that more than 35 years after cultivation has ceased the studied vegetation did not fully transform to steppe calls for more active intervention, like seeding and planting. Notwithstanding these results, the comparison of vegetation relevés from 2001 with results for 2015 indicated a (though slow) conversion of fallow land towards steppe vegetation. Furthermore, there was no particular similarity in trait composition between steppe

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species that successfully re-colonized fallow lands and the fallow-land community, and no evidence that intraspecific trait variability is associated with re-colonization success of these species.

Effect of former cultivation on vegetation attributes and soil parameters

Former cultivation practices still influence present vegetation attributes. The species composition of recently abandoned cereal fallows can be distinguished from the species composition of the steppe. However, in the long-abandoned cereal fallow, there is a visible vegetation development towards the original steppe community.

Our results show that the dominant perennial steppe grass B. retusum has so far been unable to re-establish on the fallow land; this is not only directly explained by habitat change due to deep soil ploughing and high fertilization, but also indirectly by competition with the common fallow land species [START_REF] Buisson | Limiting processes for perennial plant reintroduction to restore dry grasslands[END_REF][START_REF] Coiffait | Using a two-phase sowing approach in restoration -sowing foundation species to restore and subordinate species to evaluate restoration success[END_REF]. Moreover, dispersal limitation and the mainly vegetative reproduction of this steppe grass [START_REF] Dureau | Etude des pratiques de gestion pastorale des coussouls[END_REF] have prevented successful re-establishment. The decline of C:N ratios on the fallow land can be explained by organic matter mineralization and the absence of restitution from perennial grass species unable to re-colonize fallow land [START_REF] Römermann | Histoire culturale de la Crau: potentialités de ré-établissement des espèces caractéristiques du coussous après abandon[END_REF][START_REF] Römermann | Influence of former cultivation on the unique Mediterranean steppe of France and consequences for conservation management[END_REF].

The high percentage of bare ground is characteristic of fallow land, where stones were removed for cultivation purposes (Buisson & Dutoit 2006). However, stones create important micro-habitats for the typical steppe vegetation: they preserve humidity, serve as shelter and create safe sites for rhizomes of e.g., B. retusum [START_REF] Bourrelly | Contribution à l'étude écologique de la Crau (Bouches-du-Rhône). Caractéristiques floristiques, dynamique annuelle, production primaire de la Crau steppique[END_REF][START_REF] Caturla | Early post-fire regeneration dynamics of Brachypodium retusum Pers.(Beauv.) in old fields of the Valencia region (eastern Spain)[END_REF][START_REF] Buisson | Limiting processes for perennial plant reintroduction to restore dry grasslands[END_REF].

According to [START_REF] Janssens | Relationship between soil chemical factors and grassland diversity[END_REF], plant diversity is limited by high soil fertility, especially by plant-available phosphorus. The fallow land remains distinguished from the steppe by its elevated phosphorus and potassium content due to former fertilization, as also observed by [START_REF] Gough | A comparison of soil fertility between semi-natural and agricultural plant communities: Implications for the creations of species-rich grassland on abandoned agricultural land[END_REF] on abandoned fields in the UK. Because of different cultivation regime intensities, i.e., deep ploughing, fertilization, the application of pesticides in melon-cultivated

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areas [START_REF] Masip | Le peuplement végétal de la Réserve de Peau de Meau[END_REF] versus less intensive cereal cultivation, phosphorus content was higher in melon fallows than in cereal fallows. Deep ploughing for melon cultivation destroyed the upper part of the geological conglomerate 40 cm deep in the soil, bringing some pieces of the matrix (composed of CaCO 3 ) to the surface. Hence, Ca content increased and higher pH was measured.

The effect of ploughing also appears in the physical soil parameters. As a result of soil disturbance through ploughing, clays from the steppe subsoil layer (20-40 cm) were transported to the topsoil, leading to a higher clay content for the fallow land (10-20 cm; Duclos 1994).

The opposite effect is observed for the coarse silt of the steppe, which was buried in the subsoil as a result of ploughing [START_REF] Bulot | Ecological restoration by soil transfer: impacts on restored soil profiles and topsoil functions[END_REF][START_REF] Chenot | Long-term effects of topsoil transfer assessed thirty years after rehabilitation of dry alluvial quarries in Southeastern France[END_REF]. Öster et al. (2009) found that in semi-natural grassland communities in Sweden, species richness and similarity were still lower in fallow lands more than 50 years after cultivation.

Differences in plant attributes between calcareous grassland and fallow land after 60-100 years were also shown by [START_REF] Fagan | Do restored calcareous grasslands on former arable fields resemble ancient targets? The effect of time, methods and environment on outcomes[END_REF], [START_REF] Karlik | History or abiotic filter: which is more important in determining the species composition of calcareous grasslands?[END_REF] and [START_REF] Forey | Vegetation, soils and seed banks of limestone grasslands are still impacted by former cultivation one century after abandonment[END_REF].

Remnants of fertilization persist in the soil of fallow land for many years and still affect plant communities and the vegetation structure decades after abandonment [START_REF] Willems | Changes in chalk-grassland structure and species richness resulting from selective nutrient additions[END_REF][START_REF] Austrheim | How does continuity in grassland management after ploughing affect plant community patterns?[END_REF][START_REF] Lepš | Nutrient status, disturbance and competition: an experimental test of relationships in a wet meadow[END_REF].

Comparison of vegetation structure between 2001 and 2015

The resurvey of the research site in 2015 shows a trajectory of the former cultivated areas towards the original steppe community, even though differences in vegetation and soil structure still exist. Although common in 2001, ruderal species H. murinum and R. cristata were not recorded on melon fallows in 2015. Similarly, Bromus species-typical species in the first year of abandonment-were less common on fallow land in 2015. In cereal fallows, not only weed species but also some typical steppe species had established by 2015. The steppe vegetation did not change over time because the disturbance regime (i.e., extensive grazing) remained stable between 2001 and 2015 [START_REF] Sauguet | L'élevage ovin en Crau: situation économique, enjeux et perspectives[END_REF]. The more rapid development from cereal fallow vegetation towards steppe vegetation was probably due to the fact that less fertilizer was applied

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during cultivation and that there was no deep ploughing [START_REF] Römermann | Influence of former cultivation on the unique Mediterranean steppe of France and consequences for conservation management[END_REF], Buisson et al. 2006).

Effect of former cultivation on plant functional traits

This study confirms the relevance of the leaf traits SLA and LDMC at community level to explain the response of ecosystems to land-use change, as proposed by previous studies (Díaz et al. 2007;[START_REF] De Bello | Towards an assessment of multiple ecosystem processes and services via functional traits[END_REF][START_REF] Vandewalle | Functional traits as indicators of biodiversity response to land use changes across ecosystems and organisms[END_REF]). The steppe community was characterized by smaller and denser leaves, typical of plants following a conservative strategy [START_REF] Grime | Competitive exclusion in herbaceous vegetation[END_REF][START_REF] Saatkamp | Plant functional traits show non-linear response to grazing[END_REF][START_REF] Pérez-Harguindeguy | New handbook for standardised measurement of plant functional traits worldwide[END_REF]. Our study demonstrates that the fallow land is still a nutrient-rich environment favoring communities with high SLA and low LDMC. This is in line with findings demonstrating the association of low SLA with efficient nutrient conservation strategies, nutrient-poor habitats, slow growth rates and high longevity, as outlined above [START_REF] Poorter | Leaf area ratio and net assimilation rate of 24 wild species differing in relative growth rate[END_REF][START_REF] Garnier | Growth analysis of congeneric annual and perennial grass species[END_REF][START_REF] Chapin | Evolution of suites of traits in response to environmental stress[END_REF][START_REF] Poorter | Ecological significance of inherent variation in relative growth rate and its components[END_REF][START_REF] Lavorel | Predicting changes in community composition and ecosystem functioning from plant traits: revisiting the Holy Grail[END_REF][START_REF] Pérez-Harguindeguy | New handbook for standardised measurement of plant functional traits worldwide[END_REF]. Our analyses showing that the cereal fallows occupy an intermediate position with respect to trait composition also reveal that type of cultivation plays an important role in re-development towards the unaltered steppe vegetation. Plant height was greater in steppe communities than in fallow land, contradicting our initial hypothesis. However, it is in line with findings from Australian ecosystems [START_REF] Falster | Plant height and evolutionary games[END_REF] that showed positive relationships between plant height and LAI. Our finding of higher plants in the steppe may be related to the higher fodder quality in nutrient-rich fallow land, which could lead to preferential grazing by herbivores, reducing plant height [START_REF] Falster | Plant height and evolutionary games[END_REF][START_REF] Saatkamp | Plant functional traits show non-linear response to grazing[END_REF]). This differential selection by herbivores of recently impacted sites due to their higher fodder quality could also have implications for restoration [START_REF] Yates | Grazing effects on plant cover, soil and microclimate in fragmented woodlands in south-western Australia: implications for restoration[END_REF]. Tests of plant and soil mineral content of our data revealed a significantly positive correlation between soil phosphorus and leaf phosphorus content (r = 0.67, P < 0.001), soil nitrogen and leaf nitrogen content (r = 0.35, P < 0.02, analyses not shown). We found no evidence of particular similarity between the trait values of successful colonizers and those of the species typically found in fallow-land communities. We thus have to reject the idea that colonizers simply "fit into" the assembly of recent fallow-land communities with initial assembly conditions of high nutrient levels and recently-moved soil.

Alternatively, the data can be understood as indicating that successful colonizers exploit the diverging conditions created during longer grazing periods with decreased nutrient status, and that these colonizers may be better adapted to grazing than typical fallow-land species [START_REF] Saatkamp | Plant functional traits show non-linear response to grazing[END_REF]). However, our species pool was quite small with differences in sample size, and further studies should consider a more extensive species set covering more families. Furthermore, our data show higher functional variability to be highly species-and traitspecific, with no clear pattern revealed for the trait values of successful or unsuccessful colonizers. This supports the view that plants in fallow lands are assembled according to their adaptability to specific grazed fallow-land conditions, rather than reflecting a wide intraspecific trait variability that ensures their survival in both fallow-land and steppe communities. Hence, our study suggests that plants with specifically high ITV are not favored in the assembly process after abandonment and during grazing.

Conclusions and implications for management

Our study demonstrates that natural recovery of abandoned fallow land, notwithstanding its close proximity to the target vegetation, can take more than 35 years, even when the traditional grazing system is re-introduced just after cultivation abandonment. Regular monitoring of further vegetation development in the abandoned fallow land would enable the potential for natural recovery after a period of cultural land-use to be assessed.

In addition to monitoring natural recovery over the long term, new grazing systems could be introduced to hasten recovery or more active restoration implemented by seeding nurse or structuring species (e.g. B. retusum; Coiffait-Gombault et al., 2012;[START_REF] Buisson | Limiting processes for perennial plant reintroduction to restore dry grasslands[END_REF].

Future analyses could cover an extended set of species and include further traits to better elucidate assembly processes. In particular, they should consider traits closely related to soil water conditions, such as leaf venation traits and water-use efficiency, and traits related to soil stoichiometry, such as root traits, mycorrhizal type [START_REF] Jaunatre | Recovery of arbuscular mycorrhizal fungi root colonization after severe anthropogenic disturbance: four species assessed in old-growth Mediterranean grassland[END_REF]) and seed nutrient content. Future projects need to identify project-specific restoration targets in order to implement a trait-based approach into their restoration protocol. -1974-1977 1969-1970 1965-1968, 1984 Petit Abondoux

F

  grasslands including the steppes of the Mediterranean basin are among

  possible for B. retusum, H. glabra and S. capillata as seed production was not sufficient in 2015. Due to insufficient plant material, leaf samples of the eight individuals

  composition. The steppe communities of both 2001 and 2015 were characterized by perennial species, such as the dominant steppe species B. retusum and S. capillata and the annual species Aira cupaniana Guss. and Linum strictum L.. Cereal fallows in 2001 commonly contained Euphorbia falcata L. and Reseda phyteuma L., whereas Medicago monspeliaca L. and Poa bulbosa L. were identified as late colonizers of these cereal fallows. Melon fallows in 2001 were characterized by Bromus rubens L., Bromus intermedius L., Hordeum murinum L. and Rostraria cristata (L.) Tzvelev. In 2015, these species had declined and Plantago lagopus L. and Catapodium rigidum (L.) C.E.Hubb. had become the typical melon fallow species. For details on species distribution see Fig. 3.

Figure 1 .Figure 2 .

 12 Figure 1. Map of La Crau area in France with the six selected locations. Modified from Sylvain Fadda, IMBE (In light grey, the area of steppe remnants ). At every location, we chose at least two study sites that represented one undisturbed steppe and at least one fallow land.

Figure 3 .Figure 4 .

 34 Figure 3. Results of non-metric multidimensional scaling (NMDS) carried out on the presence/ absence vegetation data for 2001 and 2015. The color of polygons (convex hulls) indicates the land-use types (white: steppe, light grey: cereal fallows, dark grey: melon fallows) while the structure represents the time of assessment (plain: assessed in 2001 with n = 10, dotted: assessed in 2015 with n = 5). Vegetation relevés from Peau de Meau, Valigne and Petit Abondoux were included. Final stress = 0.19. For clarity, only 56 species are displayed (out of 130).

Table 1 .

 1 Overview of the land-use history of the study sites in La Crau studied in 2015. *Comparison between 2001 and 2015.

	o r
	R
	e v
	i
	e
	w
	O n l
	y

Table 2 .

 2 List of the 12 species, classified into unsuccessful colonizers, fallow-land species and successful colonizers, on which trait measurements were performed on the study sites (Table1) in 2015.

	Species group Species	Abbreviation Family	Individuals sampled per species
		Brachypodium retusum (Pers.) P. Beauv.	Bra_ret	Poaceaea
		Hypochaeris glabra L.	Hyp_gla	Asteraceae
	Unsuccessful colonizers	Linum trigynum L.	Lin_tri	Linaceae
		Stipa capillata L.	Sti_cap	Poaceae
		Trifolium campestre Schreb.	Tri_cam	Fabaceae
		Crepis foetida L.	Cre_foe	Asteraceae
	Fallow-land	Dactylis glomerata L.	Dac_glo	Poaceae
	species	Galactites tomentosus Moench.	Gal_tom	Asteraceae
		Trifolium subterraneum L.	Tri_sub	Fabaceae
		Carthamus lanatus L.	Car_lan	Asteraceae
	Successful colonizers	Lobularia maritima L. Desv.	Lob_mar	Brassicaceae
		Sideritis romana L.	Sid_rom	Lamiaceae

Table 3 .

 3 Plant functional traits measured on 12 focal species (Table2). *These plant traits are not part of the main study, but available in Supporting Information (Appendix S2, S3).

	Organ	Plant trait	Abbreviation	Unit	Measurements per site
	Whole plant	Canopy height		cm	8 individuals
		Plant width		cm	8 individuals
		Aboveground biomass		g	8 individuals
	Leaf	Specific leaf area	SLA	g cm -2	8 individuals
		Leaf dry matter content	LDMC	mg g -1	8 individuals
		Leaf carbon content*	Leaf C	mg g -1	pooled
		Leaf nitrogen content*	Leaf N	mg g -1	pooled
		Leaf phosphorus content*	Leaf P	mg g -1	pooled
	Seed	Seed mass*		mg	5 individuals

Table 4 .

 4 Summary of mean ± standard error (SE) of the measured vegetation and soil parameters and community-weighted means (CWM) for the three land-use types. The statistical test values are given. Different letters indicate significant differences between the three land-use types as extracted from pairwise tests. *** P < 0.001; ** P < 0.01; * P < 0.05; n.s. P > 0.05

			Steppe	Cereal	Melon	Statistical
						test values
			Mean ± SE	Mean ± SE	Mean ± SE
		Species richness	35.3±0.1 a	29.0±1.6 b	22.7±1.5 c	χ² = 27.5***
		Shannon diversity index	2.6±0.06 a	2.3±0.1 a	1.9±0.09 b	χ² = 24.7***
	Vegetation	Evenness Standing crop Leaf area index	0.7±0.01 a 42.8±1.2 a 3.0±0.1 a	0.7±0.02 a 17.9±0.7 b 1.3±0.2 b	0.6±0.02 b 18.7±0.8 b 1.0±0.1 b	χ² = 15.9*** F = 289.5*** F = 57.2***
		Vegetation cover	60.3±1.9 a	50.2±3.2 b	43.7±3.4 b	F = 10.2***
		Stone cover	46.5±1.2 a	36.6±2.5 b	45.0±2.0 a	F = 10.7***
		Bare ground	9.9±0.7 b	16.2±1.2 a	18.8±2.5 a	F = 13.6***
		Clays	192.7±2.0 c	202.2±3.4 b	213.4±2.6 a	F = 20.0***
		Fine silt	192.1±1.7	191.4±1.1	194.3±2.3	n.s.
		Coarse silt	161.5±4.0 a	140.1±1.2 b	144.6±2.1 b	F = 12.0***
		Fine sand	210.8±4.8	203.7±3.2	214.4±5.4	n.s.
		Coarse sand	242.9±6.2 b	262.7±4.2 a	233.2±7.8 b	F = 7.2**
		Total Carbon	16.2±0.3	15.6±0.2	15.4±0.6	n.s.
		Total Nitrogen	1.4±0.03	1.5±0.02	1.5±0.05	n.s.
		Carbon-Nitrogen ratio	11.0±0.06 a	10.6±0.04 b	10.5±0.09 b	F = 25.0***
		Organic matter	28.0±0.5	26.9±0.4	26.59±1.1	n.s.

Table 2 .

 2

Acknowledgments

We would like to thank the Conservatoire d'espaces naturels de Provence-Alpes-Côte d'Azur (CEN PACA) and the Réserve Naturelle Nationale des Coussouls de Crau for their support during field work. Thanks to Julie Tanet and Adeline Bulot working at the Mediterranean Institute of Biodiversity and Ecology of Marseille for realizing the botanical relevés in 2014. We acknowledge valuable comments of Karen Russel, Viktoria Wagner, Anna Johnson and an anonymous referee. This study was supported by the TRY initiative on plant traits (http://www.trydb.org) hosted, developed and maintained by J. Kattge and G. Bönisch (Max-Planck-Institute for Biogeochemistry, Jena, Germany). TRY is/was supported by DIVERSITAS, IGBP, the Global Land Project, the UK Natural Environment Research Council (NERC) through its program QUEST (Quantifying and Understanding the Earth System), the French Foundation for Biodiversity Research (FRB), and GIS "Climat, Environnement et Société" France. CR acknowledges financial support by the German Research Foundation (project RO 3842/3-1). The authors declare no conflict of interest.

Supporting Information Appendix S1. Trait values of specific leaf area (SLA), leaf dry matter content (LDMC) and canopy height for all species. Appendix S2. Principal component analysis (PCA) of the species-trait matrix (9 species × 9 traits). Appendix S3. Leaf nutrient content of carbon (C), nitrogen (N) and phosphorus (P) compared between original steppe and fallow lands.

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