Jonathan Jumeau
email: jumeau.jonathan@gmail.com

Julien Lopez

Alain Morand

Lana Petrod

Françoise Burel

Yves Handrich

Cd67

Handrich

Dr J Spi

Factors driving the distribution of an amphibian community in stormwater ponds: a study case in the agricultural

Keywords: refuge habitat, retention ponds, farmlands, semi-natural habitats, modified landscape, pollution abundances, growth rate and distribution, trophic chain length, breeding and dispersal success

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

Introduction

Behind over-exploitation, agriculture is the next-leading cause of current biodiversity decline and 33 affects all taxonomic groups (Butchart et al., 2010;Maxwell et al., 2016). The habitat loss induced by land 34 consolidation leads to a great number of local population extinctions through the modification of the use and 35 layout of land (Fischer and Lindenmayer, 2007). The creation of vast monocultural farmlands causes the 36 fragmentation of residual semi-natural elements and has negative impacts on species richness, population column pollutants can vary through time, an example being the high increase in chloride concentrations in late external and internal abnormalities in amphibians, stunt their growth and increase difficulties during morphological abnormalities on adults was also recorded. To avoid any mistakes due to incorrect identification, 176 edible frogs (Pelophylax kl. esculentus), and pool frogs (Pelophylax lessonae) were gathered in a "green frogs" 177 group. We used the Miaud and Muratet, 2004 identification key. The experimental protocol was authorized by 178 the 5/6/2016 nominative authorisation of the French Environmental Code and followed EU Directive Several factors were also checked and classified in factor groups (Table 1). Environmental factors (e.g.,

182

pH, water and air temperature, visibility, etc) were recorded immediately after samplings for each stormwater 183 pond at every field session. These factors were gathered in the "immediate environmental factors" group.

184

Simultaneously, biological factors were checked (e.g., presence of branches, aquatic plants, fishes, etc.) and 185 gathered in the "biotic factors" group. During the afternoons of the first field session, the stormwater pond 186 characteristics were noted (e.g., nature and state of exclosure measures, nature of substrate, slopes, volume...) 187 and gathered in the "pond design" group. The surface area of landscape elements (e.g., wetlands, crops, forests, 188 etc.) was calculated using GIS with a precision of 1:10 000 (data from CIGAL 2013) in a 500 m-wide buffer 189 ("local-scale group") and 5 km-wide buffer ( "large-scale group") around each stormwater pond (Smith et green

221

The collinear factors were identified and removed with a stepwise procedure based on the Variance Inflation

222

Factor (significance threshold = 3) and associated with ACP and Spearman tests corrected by Holm's method 223 [START_REF] Holm | A simple sequentially rejective multiple test procedure[END_REF]. Factors with insufficient class sample size (<10) were removed from analysis. When possible,

224

different classes were gathered to increase class sample size (Table 1). Boosted regression tree (BRT) models

225

were created [START_REF] Elith | A working guide to boosted regression trees[END_REF] to explain variations in dependent variables (community parameters: global 226 occurrence, global abundance and species richness). These models do not provide p-values but indicate the 227 relative influence of each factor on explained variation. As suggested by [START_REF] Albeare | Comparisons of Boosted Regression Tree, GLM And GAM Performance In The 454 Standardization Of Yellowfin Tuna Catch-Rate Data From The Gulf Of Mexico Lonline Fishery[END_REF], the learning rate Lr was 228 set to obtain at least 1 000 regression trees with a tree complexity of two. To avoid overparameterization, each 229 model created was simplified by using a cross-validation method (dismo package; Elith & Leathwick, 2017) 230 based on deviance reduction. For each dependant variable, a preliminary model was firstly created for each 231 group of factors (e.g., design, pollutants, etc.). A general model was then created using solely the factors 232 remaining after simplification procedures of preliminary models. Only factors with at least 3% of relative influence and 5% of summed relative influences were considered significant and retained for analysis and the 234 discussion. For the three final models (one for each dependant variable), the pseudo-R², called D², was calculated 235 [START_REF] Albeare | Comparisons of Boosted Regression Tree, GLM And GAM Performance In The 454 Standardization Of Yellowfin Tuna Catch-Rate Data From The Gulf Of Mexico Lonline Fishery[END_REF]. To analyse effects per species of these retained factors, a detrented correspondence analysis was 236 performed for each group of factor (vegan and ggord package) using specific abundances. Statistics were 237 performed with R software (v3.3.0) and GIS analysis with QGIS (v2.18.3). The presence of amphibians was observed in 69 (84%) of the 82 stormwater ponds. Fourteen species 241 were found (summarized in Figure 2), representing 78% of the 18 species known in the study area if we 242 consider that the "green frogs" group counted as two species [START_REF] Odonat | Office des données naturalistes du Grand-Est[END_REF]. The four species that were not 243 found were the fire salamander (Salamandra salamandra), the moor frog (Rana arvalis), which has not however 244 been seen in the study area for nine years, the common midwife toad (Alytes obstetricans) and the yellow-bellied 245 toad (Bombina variegata). The species richness of stormwater ponds was 2.44 ± 0.19 species (as a reminder,

246

descriptive statistics are "mean ± standard error of the mean"). We recorded a total of 2 046 adults, with an 247 average of 19.51 (± 3.42) adults per stormwater pond. Abundances differed substantially among species (Figure 248 2).

249

Shannon indices and Equitability index were 0.57 ± 0.06 and 0.71 ± 0.03, respectively.

250

No morphological abnormalities were found on adults. Red fox carcasses were found floating in two stormwater 251 ponds. The first pond had vertical concrete banks and the second had steep banks covered with geomembrane.

252

No service bank or reachable exits were present on the latter, but claw marks were observed on the 253 geomembrane. The month after the study period (August 2016), we observed the death of all the tadpoles in five 254 detention ponds during drought events.

266

Detrented correspondance analysis (results of significant factors per species) show that the age of stormwater 267 ponds was negatively correlated with abundances of the European green toad and green frogs (Figure 6). The 268 presence of many helophytes was negativly correlated with the presence of vegetative fragements in water. The 269 alpine newt abundance was positively correlated with presence of helophytes whereas the agile frog and the 270 marsh frog were negatively correlated with it (Figure 7). The Euopean green toad abundance was positively 271 correlated with pH and possibly with the water temperature too. Similar but less clear correlations were also 272 found for the march frog and for the smooth newt (Figure 8). At local scale (500 m ; Figure 9), green frogs and 273 the European green toad abundances were positively correlated with surface of annual crops (and also at large 274 scale for green frogs ; Figure 10). The surface of deciduous forest was positively correlated with the smooth newt abundance (Figure 9). At large scale (5000 m), the European green toad abundance was positively 276 correlated with surface of road and green frogs abundance was also positively correlated with wetlands surface 277 (Figure 10).

289

which is strongly protected in this study area. The marsh frog (Pelophylax ridibundus) was also frequently found in stormwater ponds. Those two species were both pioneer species [START_REF] Pagano | Distribution and habitat use of water frog hybrid 636 complexes in France[END_REF]Sinsch et al., 2007)

292

tolerates small puddles and gravel pits, the marsh frog needs large ponds, with sufficient depth and high 293 exposure to sunlight (Kuzmin et al., 2009), such as retention stormwater ponds with concrete banks and riprap 294 providing basking sites. The other species, especially newts and those needing more natural conditions, were less 295 abundant. Indeed, even if some stormwater ponds looked like natural ponds with helophytes, clear water,

296

protected species (e.g., odonata, amphibians) and aquatic ecosystems, most (56%) were vegetation-free with 297 cloudy/turbid water. The number of amphibians found in studied ponds was probably underestimated as we did 298 not adjust numbers according to the species detection probability (Schmidt, 2004). However, the global number 299 of individuals per pond was quite high compared to other ponds in the studied area (2.95 time higher for green 300 toad ; Vacher et al., 2015). Stormwater ponds therefore host high number of adults and species with great 301 interspecies variations in population, as found by Scheffers & Paszkowski (2013) and [START_REF] Gallagher | The role of 551 pollutant accumulation in determining the use of stormwater ponds by amphibians[END_REF].

302

Shannon and Equitability values were low, suggesting long-standing populations. This is corroborated by the 303 presence of amphibians in the studied stormwater ponds, whatever the age of the latter. Although our single 304 breeding season observation study leads us to consider stormwater ponds as a real habitat or to have high 305 ecological potentiality in the Bas-Rhin, it is necessary to monitor populations over many years and to do so in 306 other landscapes. Indeed, pollutant-induced genotoxicity could significantly reduce population viability 307 throughout the years [START_REF] Hamer | The importance of habitat design and aquatic connectivity in 564 amphibian use of urban stormwater retention ponds[END_REF]. This would imply that a suitable stormwater pond can at terms 308 increase the extinction probability although it could contain high amphibian abundances and species richness. An 309 approach based on life-history traits is needed in order to conclude about the potential trap effect of stormwater 310 ponds (Sinsch et al., 2007). This approach should compare at least reproductive success between stormwater 311 ponds and controls. In the current study, we initially wanted to include semi-natural ponds as controls but they 312 were located in too different landscapes associated with other communities, or their number were too low to be 313 significant. Therefore, we can't exclude an ecological trap effect and caution is needed. However, the study 314 highlights the relevance of studying the ecological potentiality of stormwater ponds as they can be the last 315 wetlands remaining in highly modified landscapes.

351

Depending on the design of the pond, they can also enter via the outlet. Another hypothesis is that birds could 352 carry eggs of amphibian or fish on their legs, but no publication to date validates this popular thought. However,

366

Few biotic and immediate environmental factors (such as temperature or wind during the field sessions) were 367 retained in the final models. Surprisingly, the presence of fish in the ponds had no effect on community 368 parameters (a similar result to Le Viol et al., 2012), despite evidence that the predation by fish negatively affects 369 the occurrence of amphibians (Brown et al., 2012;McCarthy and Lathrop, 2011). It can indicate that amphibian 370 species had not enough evolutionary time to avoid stormwater ponds with higher densities of predators, or that 371 amphibian had no other ponds to go to. Surprisingly, abundances of odonata larvae were positively associated 372 with those of amphibians despite the fact that they are tadpole predators. However, odonata larvae presence 373 could highlight an overall-high water quality leading to higher number of amphibians (Corbet, 1999 in Kalkman

375

Abundant aquatic vegetation is known to be positively correlated with amphibian occurrence and species 376 richness (McCarthy and Lathrop, 2011;Shulse et al., 2010;Simon et al., 2009). This was partially confirmed in 377 this study, as the presence of helophytes increased global levels of amphibian abundance. However, high 378 quantities of helophytes slightly decreased the amphibian abundance levels. This may be explained by an 379 observational bias, because of the hard detectability of amphibians among dense vegetation rather than because of a real effect of helophytes on the amphibians. A similar effect can probably be observed for algae and vegetative fragments.

382

As commonly found in the literature, the main factors driving the parameters of amphibian communities were explained more than half of the observed variations. Some correlations (for example with wetlands, meadows,

386

surrounding species richness and deciduous forests) were self-explanatory given their accordance with the 387 biology of amphibians [START_REF] Birx-Raybuck | Pond age and riparian zone proximity influence anuran 475 occupancy of urban retention ponds[END_REF][START_REF] Guderyahn | Assessing habitat requirements of pond-breeding 559 amphibians in a highly urbanized landscape: implications for management[END_REF]Le Viol et al., 2012;Simon et al., 388 2009). One of the main discoveries was the unexpected negative correlation between species richness and 389 stormwater ponds located in intermediary zone between cultivated lands and deciduous forest (Grillet et al., 390 2015). A shared hypothesis can be made for intermediate areas of annual crops as the same negative correlation 391 was found. In fact, the landscape dynamic of the studied area could be separated into two types of landscape 392 elements (as ponds were never located in cities): annual crops and semi-natural elements mainly composed of 393 forests and wetlands. When the surface of annual crops decreased, the landscape was mainly composed of more 394 natural elements and potentially suitable habitats for amphibians. Thus, the greater number of amphibians could 395 induce a greater number of amphibians in the stormwater ponds. A similar result was observed in newts by Joly 396 et al., 2001. Fewer semi-natural elements were present in the landscape when the surface area of annual crops 397 increased , so stormwater ponds were probably the only suitable habitats for amphibians and were used as 398 refuges (Le Viol et al., 2012[START_REF] Albeare | Comparisons of Boosted Regression Tree, GLM And GAM Performance In The 454 Standardization Of Yellowfin Tuna Catch-Rate Data From The Gulf Of Mexico Lonline Fishery[END_REF]. Another hypothesis could be simply the change in species composition as 399 the Smooth newt was mainly observed in deciduous forests landscape and as Green frogs and the European 400 green toad were mainly found in farmlands (Fig. 9). In this case, it would suggest that an "intermediate" pond 401 could be less efficient to hold large amphibian diversity than fully located in farmland or in deciduous forest 402 ponds. On the other hand, at a local scale, roads were found to have a strong negative effect on amphibians.

403

Although this effect could be due to road pollutants (light, noises, chemicals), we think the barrier effect of road 404 played the biggest role. Indeed, no amphibians were found when ponds were totally surrounded by roads, as 405 reported by Scheffers and Paszkowski (2013) and [START_REF] Parris | Urban amphibian assemblages as metacommunities[END_REF]. However, at large scale, a positive correlation 406 was found between land covered by roads and abundances of European green toad (Fig. 10), possibly due to an 407 higher amount of stormwater ponds (roads or industrial ones).

As exclosure measures are inefficient in preventing stormwater ponds access to amphibians, the time

419

The design of stormwater ponds should be systematically validated by an herpetologist to avoid creating 420 potentially mortal traps for animals. For example, the unclimbable banks of two stormwater ponds in this study 421 were traps for mammals and possibly for amphibians too (Chang et al., 2011;Zhang et al., 2010). Exit ladders 422 should be systematically installed. As detention pond water is not permanent, all the tadpoles of these sites can 423 die during droughts (Brand and Snodgrass, 2010;[START_REF] Gallagher | The role of 551 pollutant accumulation in determining the use of stormwater ponds by amphibians[END_REF]. Although some amphibian larvae can 424 accelerate their growth and development in harsh ecosystems, they cannot survive these sudden events, which 425 appear to be more frequent with global warming [START_REF] Morand | Phenotypic variation in metamorphosis in five anuran species along a 628 gradient of stream influence[END_REF][START_REF] Newman | Adaptative plasticity in amphibian metamorphosis[END_REF]. We therefore 426 recommend the creation of a permanent minimum water level that can easily be dredged -not only in detention 427 ponds, but also in newly created semi-natural ponds. This extension of the hydroperiod would enhance species 428 occurrences and abundances [START_REF] Guderyahn | Assessing habitat requirements of pond-breeding 559 amphibians in a highly urbanized landscape: implications for management[END_REF].

432

The present study demonstrated a high potential ecological value of stormwater ponds for amphibian 433 communities in the agricultural plain of the Bas-Rhin. Although no pollutant effect was observed on studied 434 community parameters, we cannot unequivocally conclude that pollutants have no effect on the viability of the 435 stormwater ponds amphibian populations and therefore that stormwater ponds are not ecological traps. However,

436

we have demonstrated the ineffectiveness of exclosure measures. In these conditions, we recommend avoiding 437 the installation of costly partitioning measures and reallocating efforts to ecological engineering to create better ecological stormwater ponds and more semi-natural ponds in the study area to limit a possible ecological trap Fischer, J., Lindenmayer, D.B., 2007. Landscape modification and habitat fragmentation: a synthesis. Glob.

  179 2010/63/EU guidelines for animal experiments.

  190 2005). The pollutants of 34 stormwater ponds were quantified between November 2015 and January 2016 in 191 water samples ("water fraction pollutants" group) and sediment ("sediment fraction pollutants" group) collected 192 in the centre of ponds. The entire pollutant sampling protocol was performed by the road maintenance authority 193 as part of its pollutant survey, and was not part of the present study. The set up protocol to collect samples was 194 similar between ponds and pollutants. Samples were always collected after an intense rainy event, with a 10 L 195 flask, and close to the outlet without precise depth. Samples were individually homogenised without creating 196 vortex inside. The SM Table in Supplementary Materials summarizes the list of the measured pollutants, the 197 methods used, the ISO norms, French legal thresholds (Bas-Rhin, 2008; MEEM, 1998) authorized for 198 stormwater pond outlets, and sublethal thresholds, when available. PH was measured twice: once as part of the 199 water fraction pollutants group, and once for the immediate environmental factors group. Finally, the list and200number of species known to be present in the Bas-Rhin and in a 10 km radius around each stormwater pond was 201 evaluated using a local biodiversity atlas[START_REF] Odonat | Office des données naturalistes du Grand-Est[END_REF].

  .1. Objective (1): Qualifying and quantifying amphibian communities thresholds and sublethal/lethal thresholds, when available in the literature.

  Objective (1): Qualifying and quantifying amphibian communities 240

  Objective (2): Identifying factors driving the amphibian community of stormwater ponds 256The proportion of explained deviance D² was high for the three RBT models, one created for each 257 community parameter (global occurrence, global abundance and species richness;

264

  studied community parameters. Fitted functions of each factor with more than 3% relative influence are 265 presented in Figure 3 (occurrence), Figure 4 (abundance) and Figure 5 (species richness).

  The amphibian communities of stormwater ponds 280As hypothesised, most of the stormwater ponds (84%) hosted amphibians. This suggests a high 281 attractiveness of stormwater ponds for amphibians, probably driven by necessity as they cannot find suitable 282 ponds (semi-natural or other). The four species that were never observed on these sites (Salamandra 283 salamandra, Rana arvalis, Alytes obstetricans, Bombina variegata) were not expected to be seen in stormwater 284 ponds as they either avoid large ponds and modified landscapes, or are forest species(Räsänen et al., 2003; Vos 285 and Chardon, 1998). A previous study showed that more than a quarter of the total numbers of individuals of the 286 European green toad (Bufotes viridis) in the study area were located in stormwater ponds (Sané and Didier, 287 2007). Our study shows a similar result, as it was the species with the second highest recorded mean abundances 288 in stormwater ponds. It suggests that stormwater ponds play a crucial role in the conservation of this species,

  316 5.2. Factors driving the amphibian community of stormwater ponds317Despite the known negative impacts of pollutants(Brand et al., 2010;Brand & Snodgrass, 2010; Collins 318 & Russell, 2009;[START_REF] Gallagher | The role of 551 pollutant accumulation in determining the use of stormwater ponds by amphibians[END_REF][START_REF] Karraker | Impacts of Road Deicing Salt on the Demography of Vernal 588 Pool-Breeding Amphibians[END_REF], the concentrations observed in this 319 study were probably too low to have a significant effect. Despite our initial hypothesis, no clear evidence was found of an overall effect of pollutants on amphibian communities at the observed concentrations in stormwater observed concentrations of pollutants on amphibian development and reproduction. pH had the highest relative 325 influence on the studied community parameters (global occurrence, global abundance and species richness), with many ways to enter stormwater ponds. Amphibians can follow street gutters and fall into the drain network.

353

  local fishermen indicated us regular observation of Grey heron (Adrea cinerea) drop off in ponds living 354 amphibians and fishes kept in their beak. Eggs may also be involuntarily carried by humans during maintenance 355 process or fishing activities (some stormwater ponds were even used as stock ponds of Northern pike). Poor 356 vegetation maintenance also allows tall grass to grow against the fences and walls, helping amphibians to reach 357 the top. Access can also be gained through large holes left in small fences after careless maintenance work.358Finally, fence staples can eventually fall out, creating gaps through which amphibians can pass. If the current 359 exclosure measures cannot keep amphibians out of stormwater ponds, the overprotection of stormwater ponds 360 has to be questioned. The cost of creating completely unreachable stormwater ponds is high. It would require 361 high concrete walls, large cattle grids under portal access, bird netting, fine grids over floor drains and outlets, 362 etc., and would require permanent maintenance to avoid the obstruction of hydraulic pipes and the deterioration 363 of netting. Although creating an underground stormwater pond would be far less expensive, the potential 364 ecological value of stormwater ponds is not to be brushed aside in the current context of modified landscape 365 where the number of semi-natural ponds is limited.

410

  and financial means dedicated to them should be reallocated to developing a better sediment cleaning process 411 and creating substitute semi-natural ponds that are not connected to road runoff. Observed pollutant 412 concentrations were observed to have no effect on the studied amphibian community parameters (global 413 occurrence, global abundance and species richness) ; it is therefore futile to overprotect stormwater ponds which 414 have real ecological value, but caution is still required. A sensible approach could be to consider all newly 415 constructed stormwater ponds polluted, and remove the exclosure measures once the low pollutant 416 concentrations have been demonstrated. An easier alternative for road managers would be to install efficient 417 exclosure measures or other compensatory measures only if pollutant concentration reached sub-lethal known 418 thresholds after a five-year survey or before this time if very high pollutants concentrations are measured.

429

  Other recommendations can be found in Clevenot et al. (2018) about other factors not developed in this 430 study, such as dredging and vegetation maintenance.

FiguresFigure 1 :

 1 Figures

Figure 2 :

 2 Figure 2: Specific mean abundances per stormwater pond. Error bars are standard error of the mean. Abundances are the maximal number of adult amphibians observed in a stormwater pond among the three field sessions for each species. Most observed species were Green frogs, European green toad, Smooth newt and Marsh frog.

Figure 3 :

 3 Figure 3: Fitted functions of factors with more than 3% relative influence on the deviance of the global occurrence model. Meaning of factors lettering is in Tab.1. Basic pH, roads at local scale (presumably a barrier effect), and annual crops were the main factors having negative impacts on amphibian presence in stormwater ponds. Wetlands and ponds volume were the main positive ones.

Figure 4 :Figure 5 :

 45 Figure 4: Fitted functions of factors with more than 3% relative influence on the deviance of the global abundance model. Meaning of factors lettering is in Tab.1. Basic pH and surface of deciduous forests at large scale were the main factors having negative impacts on amphibian abundances in stormwater ponds. Road at large scale, meadows, wetlands and ponds volume were the main positive ones.

Figure 6 :

 6 Figure 6: Correlation between species abundances (based on adults) and significant factors of Pond Design group. The abundance of a species whose name is located near the extremity of a factor is positively correlated with the factor. When the name is at the opposite, the correlation is negative. Greens frogs and the European green toad were more abundant in recent stormwater ponds and no clear species correlation was found with the pond volume.

Figure 7 :

 7 Figure 7: Correlation between species abundances (based on adults) and significant factors of Biotic factors group. The abundance of a species whose name is located near the extremity of a factor is positively correlated with the factor. When the name is at the opposite, the correlation is negative. Agile frog was more abundant when no vegetative fragments were present in ponds. Conversely, Alpine newt seemed to prefer ponds with many Helophytes.

Figure 8 :

 8 Figure 8: Correlation between species abundances (based on adults) and significant factors of immediate environmental factors group. The abundance of a species whose name is located near the extremity of a factor is positively correlated with the factor.When the name is at the opposite, the correlation is negative. The European green toad was more abundant in ponds with basic pH (note that pH range of ponds was 5.8-12.35 with a mean value of 9.05).

Figure 9 :

 9 Figure 9: Correlation between species abundances (based on adults) and significant factors of Land use at Local scale group.The abundance of a species whose name is located near the extremity of a factor is positively correlated with the factor. When the name is at the opposite, the correlation is negative. Greens frogs and the European green toad were more abundant in stormwater ponds located in farmland whereas the Smooth newt was mainly present in stormwater ponds located in deciduous forests.

Figure 10 :

 10 Figure10: Correlation between species abundances (based on adults) and significant factors of Land use at Large scale group. The abundance of a species whose name is located near the extremity of a factor is positively correlated with the factor. When the name is at the opposite, the correlation is negative. Greens frogs and the European green toad were more abundant in stormwater ponds located in farmland whereas the Smooth newt was mainly present in stormwater ponds located in deciduous forests.

Table 2). Chlorides were the 258

	262	other sediment pollutants, between 23.08% and 92.31% of stormwater ponds were above known sub-lethal
	263	thresholds. For the water fraction, only Polycyclic Aromatic Hydrocarbons (PAHs) were above known sub-lethal
		thresholds (17.5% of stormwater ponds). No characteristic of exclosures measures was correlated with any of the
	259	only pollutant kept in the statistical BRT model. They had a relative influence of 2.69% on the global amphibian
		abundance alone, with a minor negative correlation. No stormwater pond pollutants were above French legal

  , as 291 observed by Scher and Thièry (2005) in Mediterranean motorway stormwater ponds. If the European green toad

Table 2 :

 2 Relative influences of significant factors on deviance in each model. In line one, the pH explained 16.55% of variations of the global occurrence model, which itself explained 64% of the variation of the global occurrence. Landscape element factors explained 56% of the summed relative influences.

			Relative influence (%)
	Factor	Global Occurrence	Global Abundance	Species richness	Sum of relative
		D²=0.64	D²=0.76	D²=0.54	influence (%)
	pH	16.55	8.05	9.56	34.15
	Volume (m 3 )	4.44	6.53	20.83	31.81
	Roads 500 (m²)	14.81	4.66	4.37	23.84
	Wetlands 5000 (m²)	6.94	10.02	6.24	23.20
	Deciduous forests 500 (m²) (c.t. Mixed and Softwood forest)	4.17	2.64	13.73	20.54
	Roads 5000 (m²)	2.18	14.57	3.30	20.04
	Annual crops 500 (m²) (Meadows, Urban)	i.e. 6.26	4.06	6.05	16.37
	Deciduous forests 5000 (m²) (i.e. Mixed and Softwood forest)	1.87	6.22	6.83	14.92
	Annual crops 5000 (m²) (i.e. vines, copses)	6.96	3.21	3.57	13.73
	Meadows 5000 (m²)	1.08	12.46	0	13.54
	Helophytes (to fix eggs to branches and as shelters)	1.87	5.93	3.54	11.34
	Algae and hydrophytes (to fix eggs to branches and as shelters)	2.85	5.17	0	8.02
	Water temperature (°C) (i.e. Air temperature)	2.87	2.12	2.71	7.70
	Odonata larvae (as predators)	2.65	1.39	3.54	7.58
	Hedgerows 500 (m²)	2.10	1.76	3.52	7.38
	Age (y)	1.45	2.52	2.99	6.95
	Surrounding species richness	3.85	0.62	1.77	6.24
	Vegetative fragments in water (as food)	3.87	0	2.00	5.87
	Hedgerows 500 (m²)	2.10	0	3.52	5.62
	Surrounding species richness	3.85	0	1.77	5.62

Paszkowski, 2013; Scher and Thièry, 2005). With sufficient concentration, pollutants can induce sterility and

Bas-Rhin area, the successive building of dykes along the Rhine having substantially

The sampling protocol was adapted from the "POP Amphibiens communauté"(Barrioz et al., 2016). Sampling

began at dusk. For each pond, sampling began by five minutes of listening to estimate the species richness and

number of adult males. Visual sampling was then performed with headlamps and flashlights. The sampling was

stopped after two patrols around each pond in order to have an equivalent sampling effort between ponds.

Indeed, most of them differed substantially in length but only slightly in width. The number of individuals,

amplexus, eggs and larvae was noted for each species. The number of floating carcasses and any visible

"immediate environmental factors". Measured pollutant concentrations were compared to French legal

ponds in the Bas-Rhin. This result was supported by the absence of morphological abnormalities. However, the

method used in the present study (examination of adult abnormalities) is not as precise as the examination of

tadpoles(Wagner et al., 2014). Further experiments should therefore be performed to examine the effect of the

the most overprotected stormwater ponds equipped with concrete walls hosted amphibians. Indeed, there are

the landscape element factors(Babbitt, Baber, & Brandt, 2006;[START_REF] Birx-Raybuck | Pond age and riparian zone proximity influence anuran 475 occupancy of urban retention ponds[END_REF] Malmgren, 2002;

[START_REF] Pillsbury | Habitat and landscape characteristics underlying anuran community structure 643 along an urban-rural gradient[END_REF] Scheffers & Paszkowski, 2013; Scher & Thièry, 2005; Sinsch et al., 2012). They alone

5.3. Recommendations

effect. Further analysis are needed in other landscapes and over many years to generalise our results.

We thank Margaux Jost, Armando Espinosa and Théo Fort for the help in collecting data. We also thank

Pierre Joly, François Guérold, Pauline Jumeau and Éléonore Drais for their input on the manuscript and Joanna

Lignot for the English editing.

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Barrioz, M., Miaud, C., (coord.), 2016. Protocoles de suivi des populations d'amphibiens de France,

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Brand, A.B., Snodgrass, J.W., Gallagher, M.T., Casey, R.E.,Van Meter, R., 2010. Lethal and sublethal effects of

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Acknowledgements

Author Contributions

445

All authors approve this version of the manuscript. They agree to be accountable for the aspects of the 446 work that they conducted, and will ensure that any questions related to the accuracy or integrity of any part of 447 their work are appropriately investigated and resolved. JJ conceived the idea and design methodology; JJ and JL 448 collected the data; JJ and JL carried out data analysis; JJ, YH, AM, LP and FB organised the writing of the 449 manuscript. All authors played an active part in the drafting of the manuscript. for urban frogs. Ecol. Appl. 28, 1106-1115. https


Françoise Gérard
email: francoise.gerard@cirad.fr

Marie-Gabrielle Piketty
email: piketty@cirad.fr

Impacts of agricultural trade liberalization on poverty: sensitivity of results to factors mobility among sectors

The Purposes of this paper are twofold (i) to evaluate changes in welfare gains and their distribution due to trade liberalization when imperfect labor markets are considered, (ii) to evaluate the impact of the recent reforms of the European agricultural policy on the world welfare. The results of two versions of a dynamic world computable general equilibrium (CGE) model, using the GTAP database version 6 are compared. In the first version, a standard world CGE approach is followed with perfect labor mobility across sectors. In the second version we assume that labor shifts freely within the aggregated sectors -agriculture, manufactures, services-but not across them .After a brief description of the two versions, changes in welfare, represented not only by the world GDP but also by the consumption level of two types of households (middle-low and middle-high) in 7 regions (Brazil, China, India, Least developed countries, European Union, United States, Rest of the World) after partial trade liberalization are presented. Theoretical and political consequences of the results are discussed.

Introduction

Poverty alleviation and food insecurity reduction remain some of the main challenges for economists and policy makers in developing countries. However, despite a plethora of initiatives, very few improvements have been made since the sixties in the least developed countries. After around two decades of failing development projects and interventionist policies, trade liberalization has been presented as a solution in the early eightiees. Agricultural prices are expected to increase with trade liberalization because of the removal of distorting policies in the North, while the release of agricultural domestic and trade policies in the South is expected to allow the production factors to be more efficiently employed. Moreover higher agricultural prices may induce higher investment in agriculture as well as rural income growth, efficiently contributing to economic growth and poverty reduction [START_REF] Timmer | Getting agriculture moving : do markets provide the right signals?[END_REF]. Accompanying trade liberalization negotiations, several studies3 , using partial or general equilibrium approaches address this issue and calculate the welfare gains associated with trade liberalization. However, at the same time, some authors (for example, [START_REF] Stiglitz | Globalization and its discontents[END_REF] underline the importance of government interventions in the presence of markets failures, as well as for the provision of public goods. The net welfare gain of trade liberalization with imperfect markets is a question still debated. Moreover, previous studies show that trade liberalization gains are unevenly distributed among developing countries and households types within country.

The purpose of this study is twofold: (i) providing information on consequences of world partial trade liberalization on poverty, with a special attention to differential impacts among developing countries and to distributional effects within the countries; (ii) contributing in CGE's methodology improvements through the comparison of results obtained with and without labour market imperfections. Results of two versions of a dynamic world CGE model, using GTAP data base version 6, will be analyzed and compared. In one version of the model, perfect labour mobility is assumed ; by contrast the second version includes labour market imperfections allowing only partial shifts of the labour force across sectors.

Several differences hold with previous studies representing labour market imperfections: (i) the model is based on a recursive dynamic approach and includes capital markets imperfection ; (ii) rich and poor household are considered in order to assess distributive impacts within nations; (iii) we suppose endogenous wages but labour markets are segmented between agricultural and other sectors ; (iv) agricultural policies in Europe are explicitly represented, which allows to simulate the impacts on poverty alleviation of the recent European common agricultural policy (CAP) reforms and to compare them with the impacts of possible scenarios of agricultural trade liberalization under negotiation.. In a first section a brief literature review is performed, reminding the main results in term of poverty impacts of agricultural trade liberalization. The main features of the model used are then described with a special attention to its originality (section 2). The third section presents the scenarios analyzed and compares the results. Methodological and political consequences of the results are discussed as concluding remarks.

Poverty impacts of agricultural trade liberalization

Agriculture is an important sector in developing countries, representing still nearly 30 % of the least developed countries GDP and providing the larger part of employment there. It represents a key sector for alleviating poverty since in these countries, even if urban poverty is also important, the poor are mainly living in rural areas with agriculture as a major source of income. Moreover, farm incomes are known to have large spillovers on economic development.

On the international scene, agriculture has remained nearly outside the negotiations until the Doha Round, which did not lead to any agreement except for export subsidies. Thus agricultural markets are still characterized by high level of intervention and tariffs barriers in developed but also in some developing countries. Through trade liberalization, most agricultural commodities prices are expected to increase, leading to increase agricultural production and income in developing countries.

Another benefit is expected through the reduction of agricultural price volatility that could follow trade liberalisation. This price volatility decrease is supposed to come from two main sources. First, through a larger distribution of agriculture production amongst the different countries, the global impact of possible natural events affecting agricultural supply could be lower. Then, through the eviction of the large and unpredictable stocks that are resulting from agricultural policies of major developed countries as Europe, and running out through export subsidies on international markets. As everybody knows, agricultural price volatility is very harmful for producers, particularly of developing countries. What is still a controversial issue is the source of price volatility. Some authors point out that trade liberalization may not reduce agricultural price fluctuations when imperfect information and risks are considered (Boussard and al;[START_REF] Keeney | GTAP-Agr A framework for assessing te implications of multilateral changes in agricultural policies[END_REF].

Of course, as the food share is dominant in poor household expenditures, the situation may not be so beneficial for food net importers since international price increase will increase consumer price and harm poor population. Thus, the impact of agricultural trade liberalization will depend on the position of each poor group net supply of the good to be liberalized country [START_REF] Cirera | Trade liberalization and Poverty : a Handbook[END_REF].

Despite good initial expectations of positive impact of agricultural trade liberalization on poverty, several assessment of world general equilibrium models show less optimistic results. First, in term of US $ / head, very optimistic scenarios, as full trade liberalization, assess that developing countries could expect an income increase of maximum 17 US$/head, which would probably be very insufficient to have large impact on poverty reduction (Table 1). Then most models show that agricultural trade liberalization would rather benefit emerging countries (Argentine, Brazil, India, China) and not least developed countries (see table 2 and3). Finally, inside each country, the estimation of the impact of poverty is not always based on a detailed analysis of distributive impacts but on hypothesis linking economic growth and poverty level (through an elasticity parameter). However, as stated in a recent World Bank report [START_REF] Ferranti | Inequality in Latin America and the Caribbean: Breaking with History ? Washington[END_REF], the capacity of economic growth to reduce poverty can be seriously harmed by the persistence of inequality. Former world general equilibrium models developed to analyze trade liberalization impacts were very optimistic about the capacity of markets, and particularly factors markets, to respond to trade liberalization. As stated by the authors of GTAP themselves, the most common modelling framework used on these issues, a lot of traditional GTAP model applications abstract from structural features that characterized global food and agricultural markets [START_REF] Keeney | GTAP-Agr A framework for assessing te implications of multilateral changes in agricultural policies[END_REF]. In the GTAP AGR model presented above, several new structural features have been introduced such as imperfect mobility of labour and capital between sectors, particularly between agricultural and non agricultural sectors. The factors supply is represented through a Constant Elasticity Transformation Function (CET), whose parameters are based on OECD elasticity estimation of agricultural capital and labour supply elasticity. In the LINKAGE model, rural and urban labour markets are segmented with a migration function between them depending on relative wages. Land and capital supply by sectors are also represented through a CET function.

The Canergie model has included unemployment in urban unskilled labour markets, a structural feature of a lot of developing countries (Polaski 2005). The results show again that modest results must be expected in term of poverty alleviation from agricultural trade liberalization.

It is difficult to compare the results of the different world general equilibrium models because of several assumptions that have to be made at this level of aggregation. Indeed, the predictive capacity of such models is probably low, as large variations of the results are found even from quite similar models as GTAP-Agr or LINKAGE. As also stated by Polaski (2005), the reliability of computable general equilibrium models results is constrained by data limitations and simplification of the economic reality to make the model computable. However, it does not mean that trying to improve these models to better represent the functioning of markets and analyze their impacts, is useless, quite the contrary. Allowing the test of several scenarios and hypothesis, such models can feed important policies debate in front of bilateral or multilateral trade negotiations, as soon as one is aware of the potential impact of key assumptions. They allow to compare policy impacts and to point out what could make the difference. Moreover when similar results are found based on different database or hypothesis, the findings may be more robust.

Whatever, most models finally agree that the negotiations will have very modest consequences on the eradication of poverty in the world, even assuming that markets are perfect4 .

The model

In this section, the main features of the model are exposed, with a specific attention to three original features (i) two versions of the model are considered to allow to evaluate the impact of perfect labour market; (ii) the financial market and investment decisions are detailed (iii) the representation of agricultural policies instead of using OECD subsidy equivalent estimations (PSE), modelling explicitly intervention on prices and public stocks5 .

General features

Let us define the sets I for factors, J for commodities, H for institutions, t for time. Denote by: F j (.) a production function., U ht (.) the utility function of consumer h, and G(.) the investment function which transforms inputs into factors -mainly capital, but manpower as well.

Call z hjt the final consumption of commodity j by consumer h ; x ij the quantity of commodity or factor i used as input for commodity j ; v hjt the demand of commodity j by consumer h for investment, e hi , the quantity of factor I belonging to institution k ; π jt, the profit of industry j ; s ht the savings by institution h, δ hi a depreciation rate. Prices are denoted by p jt for commodity, π it for factors.

The standard recursive6 CGE can be described with the following equations:

(1) F j (... x ijt ..) = z

∑ h hjt + ∑ ∈ J I i , x jit + ∑ h v hjt ,
∑ h ht = p ∑ ∑ j h jt v hjt h∈H (savings) (7) e hit = e hit-1 (1 -δ hi ) + G(..v hjt … ) h∈H, i∈I (recurrence equation)
The model is solved by writing the first-order conditions for producer's and consumer's optima, that are the derivatives with respect to x ijt of equation (2) subject to (3), and the derivatives with respect to z hjt and s ht of equation (4) subject to (5). It is to be noticed that the only intertemporal equation is ( 7), which generalises the basic equation of capital dynamics.

The standard version of the model is derived from these equations. In the imperfect labour market version, equation (3) , which allows complete shift of labour (skilled or unskilled) from one sector to another is replaced by freely shift within 4 subsectors (farm activities, manufacture, services, energy). Labour is immobile between these subgroups except in the last scenario tested where labour is freely mobile between the different sectors (see section 3.1).

As far as growth and accumulation are concerned, equation ( 7) and the function G(..v hjt … ) are of the utmost importance. In some CGE models, capital is easily shifted from one sector to another, so that this is invested in the most productive places. However, such assumptions are not very realistic: they imply that a nuclear power plant can be used to harvest grain It is not very realistic. Many models have been set up with sector-specific capital. The difficulty, in that case, is that neither capital nor labor are obviously stuck with any sector for ever. Some flexibility must be added.

(12) = ) ( ˆjt V π 2 2 1 ) ( - --jt jt π π
In addition, since kjt P ˆ≠ P kjt , some saving may last or be created on time t. It is then credited to or subtracted from saving year t+1. Various expectation and variance functions may be chosen.

The capital available for each branch j is updated in the recursive loop over time:

(13) kj t+1= kj t (1-δ j ) + I jt , where δ j is capital depreciation rate.

Data and Others Setting

The Gtap data base (version 6) has been used to represent the world through 7 regions, 5 production factors and 11 sectors, including 8 for agricultural production (see Table 5).

Two types of households are considered, splitting the population around the income median, and defining middle-low income and middle-high income group, in order to be able to include equity considerations when analyzing the results.

Production is described by embedded CES production functions. At the first level, aggregate added value and aggregate variable inputs are considered. These are disaggregated at the second level, where two other CES are used, one for the five production factor and another for inputs. Parameters are taken from the GTAP data base.

Demand is a linear expenditure system, estimated by using GTAP income elasticities as well as consumption and price levels.

Exchange rates are exogenous. Investment is determined by savings and foreign capital flows, calculated to balance the external trade. Government budget is balanced through public consumption adjustment. The two versions of the model are dynamic, using temporary equilibria. Armington assumption of imperfect substitutes of products from different countries holds. Parameters as well as transport costs are taken from the GTAP data base.

Agricultural Policies

An original feature of the model concerns agricultural policies in the European Union and United States, with a focus on market price support policies which should be dismantled along with trade liberalization and on decoupling, which should replace the old distorting measures. In much of the world CGE models, the true policies had been replaced by Price Support Equivalent (PSE) from OECD, as it is commonly found in the literature. Because a lot of energy has been devoted in Europe, along the last decade, to move from highly distorting price policy to more market friendly domestic support, it can be interesting to represent the real policies and these efforts as well as to evaluate its impacts on developing countries. Equations ( 14) to ( 17) describe mechanisms of public storage or subsidies as included in the model instead of the PSE. One interesting feature is that it allows to evaluate the level of public storage as well as a more precise evaluation of costs.

For guaranteed prices in Europe, the equation for producer supply remains (2) where output price, p jt is now the domestic market price, at least equal to the guaranteed price. In order to achieve that domestic market price be at least equal to the guaranteed price, the government store the excess of supply. A stock, stor jt is thus added to Equation (1 bis):

(14) F j (... x ijt-1 ..) = ∑ h z hjt + ∑ ∈ J I i , x jit-1 + ∑ h v hjt + store jt , j∈J
and an equation is added to determine the stock level, considering pg jt , the corresponding guaranteed price for j product :

(15) p jt ≥ pg jt

We assumed here that public stocks are running out on the international market through export subsidies. The rate of export subsidies is endogenous for these goods. Because of WTO disciplines, the value of export subsidies allowed for each commodity is limited in value. If the limited is reached, the excess stock is destroyed.

The same kind of equations holds for agricultural sector benefiting from quotas (sugar -milk).

The first difference with cereals and livestock is that a quantitative limit is imposed on the production bought at guaranteed price. Moreover, for sugar, over quotas production must be sold on the international markets without export subsidies.

For intervention policy in the United States, the scheme is different since such policy is more similar to a producer subsidy that does not affect domestic consumers, contrary to the European case. Thus (1) stays the same, but equation (2) becomes, with inter jt the level of intervention :

(16)

φ jt = F ) int (p jt jt er + j (... x ij ..) -∑ ∈J i p it x ijt -∑ ∈I i π it x ijt j J ; ∈ ∀i
and another equation is also added to determine the intervention level, considering pinterv jt , the intervention price set each year by the US government : (17) p jt + inter j ≥ pinterv jt

Results and Discussion

Scenarios tested

The results of four scenarios are presented and compared:

-The baseline scenario is the reference and nothing changes between 2001 and 2012 except that new capital is invested from one year through the other between the different sectors (capital sub-model). -In the second scenario (CAP reform), the CAP reform of 2000 and 2003 are introduced. Intervention price decreases are found in Table 6. Factor based payment to land and capital are found in Table 7. They are first increased for cereals and livestock in order to compensate intervention price decrease. Then from 2005, decoupling is considered such that the subsidy rate to land is homogeneous across agricultural sectors (values between -0,68 and -0,70). -In the third scenario (lib-V1), the CAP reforms of 2000 and 2003 are considered as well as agricultural trade liberalization. Export subsidies are progressively decreased from the year 2005 and finally set to zero in 2010. Import tariffs are reduced from the year 2005 and finally set in 2008 to 64 % of the initial tariffs for all developed countries and 76 % for all developing countries. -In the last scenario (lib-V2), the same assumptions are made for CAP reforms and agricultural trade liberalization but unskilled and skilled labour are freely mobile between sectors (no labour markets segmentation).

Some results

Aggregated results give a good idea of the global impact of the four scenarios. Changes in world GDP compared to the baseline are described in Figure 1. The first important feature of the results is the very small impact both of the CAP reforms and of trade liberalization, in relative terms and at the world level. The most significant impact is related to the mobility of labour and, even with perfect labour mobility between sectors, the GDP increase remains under 1.2%. This result underlines the importance of the assumptions, as factors mobility, in evaluations of trade liberalisation gains. It questions also the confidence level to be grant to this kind of results. Shifting to more detailed results allow assessing the heterogeneity of impacts between countries and households groups. For the least developed countries, the impact of perfect labour mobility is favourable for the middle rich households but depressed the middle-poor group purchasing power (figure 2). It is linked to a significant decrease of unskilled labour price which is the dominant source of income of poor households. In the case of Brazil, the perfect mobility assumption has negative impact on consumption level for both "middle-rich" and "middle-poor " households groups, but the impact is deeper for the rich. It is related to the fact that the Brazilian economy, as it is stressed in the GTAP data base, do not suffer from labour rigidity because its agricultural sector is very efficient and exhibits sharp increasing trend. Then, when other countries are not anymore constrained by labour rigidity, they act better and compete with the Brazilian economy, whose gains are thus reduced. For these two sectors the impact of the CAP reform is relatively important because they suffer a sharp drop in guaranteed price as well as a decline in direct support. If the trade liberalization worsens the situation its relative impact is far less important. The impact of labour market imperfection is much more important on the livestock sector than on cereals. In the case of perfect mobility of labour, the livestock production will drop because labour may be employed with better wages in others sector than agriculture. By contrast, other sectors (other crops, other animals) benefit from the reform because the domestic support increases with decoupling and is not affected by the assumption on labour mobility. The cereals production is only affected by the change in labour market imperfection, while the production of other crops is also slightly negatively affected by the CAP reform. Agricultural production will increase in case of perfect labour mobility which is linked to a lack of economic activity outside agriculture in these countries.

Changes in world GDP

Does this drop in

Brazil, China and the rest of the world slightly increase their productions following the CAP reform. Impacts are a bit higher in case of liberalization. India and the least developed countries group do not benefit neither from the CAP reform nor from trade liberalization.

In fact, the principal country benefiting from the CAP reform, particularly when labour is freely mobile across sectors, is the United States (Figure 6 for the case of cereals and livestock 7 ). This is linked to the fact that the scenarios tested do not consider any reforms of the agricultural policies in this country except the elimination of export subsidies and tariffs reduction. Thus all the agricultural sectors still benefit from intervention prices. Moreover, trade liberalization do not harm agricultural sectors because American import tariffs are already very low in the last version of GTAP database (2001), except for the sugar sector, and export subsidies are already null. These large production increases drive market price down and explain why other countries failed to benefit much from European agricultural production decrease and higher market access. 7 Similar results are found for sugar, other-animals and milk.

Concluding remarks

In this paper, we focus on two main issues. The first one is linked to labour market adjustment costs: if labour is allowed to move freely from any sector to the others, does it change significantly the impacts of agricultural trade liberalization? The second one is linked to major agricultural reforms of the Common Agricultural Policy (CAP) in Europe. In effect, European policies are often criticized as they are still largely based on market price support and distorting factor-based payments, both forbidden in a liberal world. Europe has started to implement major reforms with the decoupling of agricultural subsidies and the decrease of intervention price. Will these reforms really affect agricultural trade liberalization impacts?

On the methodological side, we underlined the importance of assumptions on factor markets functioning on results. If it is not important in the trade liberalization impacts in the least developed countries group, it has a significant impact at the world level. That confirms the results of the Canergie model [START_REF] Polaski | Winners and losers : impact of the Doha round on developing countries, Canergie Endowment for International Peace[END_REF] and other simulations including also unemployment will be performed.

On the impacts of recent European agricultural policy reform on the world welfare, the model presented here shows very few impacts. However they are a little higher than with partial trade liberalization. It is interesting to underline that the least developed country group benefits neither from the CAP reform neither from the partial trade liberalization scenario. In the partial rigidity of labour version, gains related to the CAP reforms are evenly distributed among emerging and developed countries. Impacts in these countries are low.

In any case, there is not any significant progress in terms of poverty alleviation in the least developed countries underlining the emergency of other international distribution channels than trade liberalization for these countries.

  Figure1

  Figure 2

  Figure3

  Figure 5The cereals production is only affected by the change in labour market imperfection, while the production of other crops is also slightly negatively affected by the CAP reform. Agricultural production will increase in case of perfect labour mobility which is linked to a lack of economic activity outside agriculture in these countries.

  Figure 6

Table 1 -Level and distribution among nations of full trade liberalization benefits Source base Developing countries Developed countries World Developing countries Developed countries World Billion US $ US $ /head

 1

	GTAP	2001	22	62	84	4,26	64,58	13,70
	LINKAGE	2001	85.7	201.6	287,3	17,41	205,21	46,82
	Sources : GTAP AGR :Hertel et Keeney (2006) ;Linkage : Anderson et al. (2006)

Table 2 -Level and distribution among nations of agricultural trade liberalization

 2

	(Billion US $)
	World High	Income			Developing countries
	countries	Total	Bangladesh Mozambique	Others Sub-Saharan
						African countries
	55.658	41.569	11.930	-0.50	-0.06	-1.67
	Source : Hertel et Keeney(2006)

Table 3 -Level and distribution among nations of full trade liberalization (

 3

	Billion US $)

Table 4 -

 4 Poverty impacts of full trade liberalization (variation of the number of persons living with less than 1$ a day, millions) Developing countries and Sub-Saharan Africa: Anderson et al(2006 b) p518-519 et Anderson et al(2006 a) p382 ; Cameroon and Mozambique : Hertel et Winters (2006) p.27

		Number of poor in the	Full trade liberalization,	Full trade liberalization,	Doha
		reference	dynamic version	comparative static	scenario
	Developing countries	622	-31.9	-23.8	-2.5
	(Linkage)
	Sub-Saharan Africa	340	-21.1	-16	-0.5
	(Linkage)
	Cameroon	6.3		+0.3	-0.02
	(GTAP)
	Mozambique( GTAP)	9		+0.06	+0.03
	Source :

  An original submodel has been developed for capital. The old capital is fixed by sector, just decaying at a constant rate. But the "new" capital owned by each institution is allocated between sectors according to a Markowitz(1970) mean/variance portfolio selection model. Let be :

	k jt : capital of branch j, time t
	S t : total saving period t jt πˆ : expected profitability of capital in branch j
	) V π : expected variance of jt ( ˆjt π
	A k		: risk aversion parameter for institution k
	Pk jt		: price of the capital good for branch j
	P ˆ	k	jt	: expected value of Pk jt
	I jt			: capital good bought for branch j, time t
	Then, I jt is chosen by investors through the maximization of :
	(8)			k A ∑ πˆ) ( jt jt jt I Pk -ˆjt V π	I	jt 2
				j
	subject to :
	(9)			∑	Pk	jt	I	jt	≤	S	t
				j
	with a naïve expectation scheme :
	(10)			jt πˆ=	π	jt	1 -
	(11)			kjt P ˆ= P kjt-1

Table 5 : GTAP database desegregation

 5

	Regions	Sectors	Production factors
	European Union	Wheat	Unskilled labour
	United States	Others cereals	Skilled labour
	China	Livestock	Land
	India	Other animal production	Natural Resources
	Brazil	Milk	Capital
	Least developed countries	Oilseeds
	Rest of the World	Sugar
		Other Crops
		Manufacturing
		Energy
		Services

Table 6 : Intervention price in Europe (% of 2001 initial value

 6

	)

Table 7 Factors based payments -(in % of factor value

 7

	)

See for example the review performed by[START_REF] Van Tongeren | Global models applied to agricultural and trade policies: a review and assessment[END_REF]

The results are more pessimistic when one assumes that agricultural markets are imperfect (see for exampleBoussard and al. 2005).

The explicit modelling of CAP is also made by Gohin in the MEGAAF model (see for example[START_REF] Gohin | Modélisation du complexe agroalimentaire français dans un cadre d'équilibre general[END_REF], a French General Equilibrium model. So far, such attempt has not been made for world general equilibrium models.

"Recursive" here means that plans x tτ made at time t for time τ depend on observed past values x t-1 . However, x tτ may be eventually revised, in such a way that x t+1,1 may be different from x t,2 . Thus, in this framework, a model may be both recursive and multiperiodic, although the planning horizon is only one period ahead in all applications below.