S. Archer, C. Scifres, C. R. Bassham, and R. Maggio, Autogenic Succession in a Subtropical Savanna: Conversion of Grassland to Thorn Woodland, Ecological Monographs, vol.58, issue.2, pp.111-127, 1988.
DOI : 10.2307/1942463

G. Austrheim, E. Gunilla, A. Olsson, and E. Grontvedt, Land-use impact on plant communities in semi-natural sub-alpine grasslands of Budalen, central Norway, Biological Conservation, vol.87, issue.3, pp.369-379, 1999.
DOI : 10.1016/S0006-3207(98)00071-8

G. Balent, Construction of a reference frame for studying the changes in species composition in grassland France geological map 1/50 000: Argeles-Gazost sheet XVI-47. Ministè re de l'Industrie, Options Me´diterraneénnesMe´diterraneénnes, vol.15, pp.73-81, 1980.

N. Barsoum, Relative contributions of sexual and asexual regeneration strategies in Populus nigra and Salix alba during the first years of establishment on a braided gravel bed river, Evolutionary Ecology, vol.57, issue.3, pp.255-279, 2001.
DOI : 10.1023/A:1016028730129

P. J. Bellingham and D. A. Coomes, Grazing and community structure as determinants of invasion success by Scotch broom in a New Zealand montane shrubland, Diversity and Distributions, vol.79, issue.1, pp.19-28, 2003.
DOI : 10.1046/j.1472-4642.2003.00162.x

L. R. Belyea and J. Lancaster, Assembly Rules within a Contingent Ecology, Oikos, vol.86, issue.3, pp.402-416, 1999.
DOI : 10.2307/3546646

J. Bokdam and J. M. Gleichman, Effects of grazing by free-ranging cattle on vegetation dynamics in a continental north-west European heathland, Journal of Applied Ecology, vol.37, issue.3, pp.415-431, 2000.
DOI : 10.1046/j.1365-2664.2000.00507.x

J. M. Briggs, A. K. Knapp, and B. L. Brock, Expansion of Woody Plants in Tallgrass Prairie: A Fifteen-year Study of Fire and Fire-grazing Interactions, The American Midland Naturalist, vol.147, issue.2, pp.287-294, 2002.
DOI : 10.1674/0003-0031(2002)147[0287:EOWPIT]2.0.CO;2

J. R. Brown and S. Archer, Woody plant invasion of grasslands: establishment of honey mesquite (Prosopis glandulosa var.glandulosa) on sites differing in herbaceous biomass and grazing history, Oecologia, vol.29, issue.1, pp.19-26, 1989.
DOI : 10.1007/BF00789926

J. R. Brown, J. C. Scanlan, and J. G. Macivor, Competition by herbs as a limiting factor in shrub invasion in grassland: a test with different growth forms, Journal of Vegetation Science, vol.25, issue.6, pp.829-836, 1998.
DOI : 10.2307/3237048

DOI : 10.2307/3897252

J. Castro, R. Zamora, and J. Hodar, Mechanisms blocking Pinus sylvestris colonization of Mediterranean mountain meadows, Journal of Vegetation Science, vol.87, issue.5, pp.725-731, 2002.
DOI : 10.1658/1100-9233(2002)013[0725:MBPSCO]2.0.CO;2

P. Collin, D. Epron, B. Alaoui-sosse, and P. M. Badot, Growth Responses of Common Ash Seedlings (Fraxinus excelsior L.) to Total and Partial Defoliation, Annals of Botany, vol.85, issue.3, pp.317-323, 2000.
DOI : 10.1006/anbo.1999.1045

A. Cooke, Survival and regrowth performance of coppiced ash (Fraxinus excelsior) in relation to browsing damage by muntjac deer (Muntiacus reevesi), Q. J. For, vol.92, pp.286-290, 1998.

P. Daget and J. Poissonet, Une me´thodeme´thode d'analyse phytologique des prairies.Critè res d'application, Annl. Agron, vol.22, pp.5-41, 1971.

D. Steven and D. , Experiments on Mechanisms of Tree Establishment in Old-Field Succession: Seedling Emergence, Ecology, vol.72, issue.3, pp.1066-1075, 1991.
DOI : 10.2307/1940606

P. Duchaufour, Pe´dologiePe´dologie Tome 1: Pe´dogenè se et classi- fication2è mend ed, 1983.

M. Duru, G. Balent, and A. Langlet, Mineral nutritional status and botanical composition of pastures. I. Effects on herbage accumulation, European Journal of Agronomy, vol.3, issue.1, pp.43-51, 1994.
DOI : 10.1016/S1161-0301(14)80109-3

J. S. Dukes, Biodiversity and invasibility in grassland microcosms, Oecologia, vol.126, issue.4, pp.563-568, 2002.
DOI : 10.1007/s004420000549

C. S. Elton, The ecology of invasion by animals and plants, 1958.

C. A. Garc?á-robledo and C. Murcia, Comparative habitat susceptibility to invasion by Chinese ash (Fraxinus chinensis: Oleaceae) in a tropical Andean landscape, Biological Invasions, vol.8, issue.3, pp.405-415, 2005.
DOI : 10.1007/s10530-004-2576-4

J. M. Garcia-ruiz, T. Lasanta, P. Ruizflano, L. Ortigosa, S. White et al., Land-use changes and sustainable development in mountain areas: a case study in the Spanish Pyrenees, Landscape Ecology, vol.8, issue.3???4, pp.267-277, 1996.
DOI : 10.1007/BF02059854

A. Gibon and G. Balent, Landscape on the French side of the western and central Pyrenees, 2004.

J. P. Grime, J. G. Hodgson, and R. Hunt, Comparative plant ecology: a functional approach to common British species, 1988.
DOI : 10.1007/978-94-017-1094-7

R. Harmer, The effect of plant competition and simulated summer browsing by deer on tree regeneration, Journal of Applied Ecology, vol.46, issue.5, pp.1094-1103, 2001.
DOI : 10.1046/j.1365-2664.2001.00664.x

A. J. Hester, F. J. Mitchell, and K. J. Kirby, Effects of season and intensity of sheep grazing on tree regeneration in a British upland woodland, Forest Ecology and Management, vol.88, issue.1-2, pp.99-106, 1996.
DOI : 10.1016/S0378-1127(96)03815-7

A. J. Hester, P. Millard, G. J. Baillie, and R. Wendler, ?, Oikos, vol.64, issue.3, pp.536-550, 2004.
DOI : 10.1111/j.0030-1299.2004.12605.x

M. O. Hill, Reciprocal Averaging: An Eigenvector Method of Ordination, The Journal of Ecology, vol.61, issue.1, pp.237-249, 1973.
DOI : 10.2307/2258931

D. U. Hooper and P. M. Vitousek, The Effects of Plant Composition and Diversity on Ecosystem Processes, Science, vol.277, issue.5330, pp.1302-1305, 1997.
DOI : 10.1126/science.277.5330.1302

R. Ihaka and R. Gentleman, R: a language for data analysis and graphics, J. Comput. Graph. Stat, vol.5, pp.299-314, 1996.

F. Jeltsch, S. J. Milton, W. R. Dean, and N. Vanrooyen, Analysing Shrub Encroachment in the Southern Kalahari: A Grid-Based Modelling Approach, The Journal of Applied Ecology, vol.34, issue.6, pp.1497-1508, 1997.
DOI : 10.2307/2405265

P. A. Keddy, Assembly and response rules: two goals for predictive community ecology, Journal of Vegetation Science, vol.119, issue.2, pp.157-164, 1992.
DOI : 10.2307/3235676

T. A. Kennedy, S. Naeem, K. M. Howe, J. M. Knops, D. Tilman et al., Biodiversity as a barrier to ecological invasion, Nature, vol.95, issue.6889, pp.636-638, 2002.
DOI : 10.1126/science.286.5444.1577

J. M. Knops, D. Tilman, N. M. Haddad, S. Naeem, C. E. Mitchell et al., Effects of plant species richness on invasion dynamics, disease outbreaks, insect abundances and diversity, Ecology Letters, vol.379, issue.5, pp.286-293, 1999.
DOI : 10.1126/science.278.5345.1865c

A. Kolb, P. Alpert, D. Enters, and C. Holzapfel, Patterns of invasion within a grassland community, Journal of Ecology, vol.8, issue.5, pp.871-881, 2002.
DOI : 10.1046/j.1365-2745.2002.00719.x

A. T. Kuiters and P. A. Slim, Tree colonisation of abandoned arable land after 27 years of horse-grazing: the role of bramble as a facilitator of oak wood regeneration, Forest Ecology and Management, vol.181, issue.1-2, pp.239-251, 2003.
DOI : 10.1016/S0378-1127(03)00136-1

J. Lauga and J. Joachim, L'e´chantillonnagee´chantillonnage des populations d'oiseaux par la me´thodeme´thode des E.F.P.: inte´re?tinte´re?inte´re?t d'une e´tudee´tude mathe´matiquemathe´matique de la courbe de richesse cumuleé, Acta Oecol., Oecol. Gen, vol.8, pp.117-124, 1987.

M. S. Lett and A. K. Knapp, Consequences of shrub expansion in mesic grassland: Resource alterations and graminoid responses, Journal of Vegetation Science, vol.68, issue.4, pp.487-496, 2003.
DOI : 10.1111/j.1654-1103.2003.tb02175.x

D. M. Lodge, Biological invasions: Lessons for ecology, Trends in Ecology & Evolution, vol.8, issue.4, pp.133-137, 1993.
DOI : 10.1016/0169-5347(93)90025-K

K. S. Maccann, The diversity???stability debate, Nature, vol.405, issue.6783, pp.228-233, 2000.
DOI : 10.1038/35012234

B. C. Maccarthy and J. M. Facelli, Microdisturbances in Oldfields and Forests: Implications for Woody Seedling Establishment, Oikos, vol.58, issue.1, pp.55-60, 1990.
DOI : 10.2307/3565360

A. Macdonald, J. R. Crabtree, G. Wiesinger, T. Dax, N. Stamou et al., Agricultural abandonment in mountain areas of Europe: Environmental consequences and policy response, Journal of Environmental Management, vol.59, issue.1, pp.47-69, 2000.
DOI : 10.1006/jema.1999.0335

G. Marigo, J. P. Peltier, J. Girel, and G. Pautou, Success in the demographic expansion of Fraxinus excelsior L., Trees, vol.15, issue.1, pp.1-13, 2000.
DOI : 10.1007/s004680000061

C. N. Mazia, E. J. Chaneton, C. M. Ghersa, and L. J. , Limits to tree species invasion in pampean grassland and forest plant communities, Oecologia, vol.128, issue.4, pp.594-602, 2001.
DOI : 10.1007/s004420100709

G. R. Mcpherson, Effects of herbivory and herb interference on oak establishment in a semi-arid temperate savanna, Journal of Vegetation Science, vol.4, issue.5, 1993.
DOI : 10.2307/3236134

N. M. Moleele, S. Ringrose, W. Matheson, and C. Vanderpost, More woody plants? the status of bush encroachment in Botswana???s grazing areas, Journal of Environmental Management, vol.64, issue.1, pp.3-11, 2002.
DOI : 10.1006/jema.2001.0486

B. M. Moyle and T. Light, Biological invasions of fresh water: Empirical rules and assembly theory, Biological Conservation, vol.78, issue.1-2, pp.149-161, 1996.
DOI : 10.1016/0006-3207(96)00024-9

O. Connor and T. G. , Composition and population responses of an african savanna grassland to rainfall and grazing, J, 1994.

F. Pasche, M. Armand, P. Gouaux, T. Lamaze, and A. Pornon, Are meadows with high ecological and patrimonial value endangered by heathland invasion in the French central Pyrenees?, Biological Conservation, vol.118, issue.1, pp.101-108, 2004.
DOI : 10.1016/j.biocon.2003.07.012

A. M. Planty-tabacchi, E. Tabacchi, R. J. Naiman, C. Deferrari, and H. Decamps, Invasibility of Species-Rich Communities in Riparian Zones, Conservation Biology, vol.10, issue.2, pp.598-607, 1995.
DOI : 10.1046/j.1523-1739.1996.10020598.x

A. Pornon and N. Escaravage, Till-Bottraud I. and Doche B. 1997. Variation of reproductive traits in Rhododendron ferrugineum L. (Ericaceae) populations along a successional gradient, Plant Ecology, vol.130, issue.1, pp.1-11
DOI : 10.1023/A:1009724216796

K. Prach, J. Leps, and J. Michalek, seedlings in a central European mountain grassland: an experimental study, Journal of Vegetation Science, vol.59, issue.5, pp.681-684, 1996.
DOI : 10.2307/3236379

B. Pre´vostopre´vosto, D. R. Hill, and P. Coquillard, Individualbased modelling of Pinus sylvestris invasion after grazing abandonment in the French Massif Central, Plant Ecology, vol.168, issue.1, pp.121-137, 2003.
DOI : 10.1023/A:1024404214782

A. H. Prieur-richard and S. Lavorel, Invasions: the perspective of diverse plant communities, Austral Ecology, vol.115, issue.1, pp.1-7, 2000.
DOI : 10.1046/j.1442-9993.2000.01033.x

R. Prodon and J. D. Lebreton, Breeding Avifauna of a Mediterranean Succession: The Holm oak and Cork Oak Series in the Eastern Pyrenees, 1. Analysis and Modelling of the Structure Gradient, Oikos, vol.37, issue.1, pp.21-38, 1981.
DOI : 10.2307/3544069

K. G. Roques, T. G. Oconnor, and A. R. Watkinson, Dynamics of shrub encroachment in an African savanna: relative influences of fire, herbivory, rainfall and density dependence, Journal of Applied Ecology, vol.38, issue.2, pp.268-280, 2001.
DOI : 10.1046/j.1365-2664.2001.00567.x

M. Rouget and D. M. Richardson, Inferring Process from Pattern in Plant Invasions: A Semimechanistic Model Incorporating Propagule Pressure and Environmental Factors, The American Naturalist, vol.162, issue.6, pp.713-724, 2003.
DOI : 10.1086/379204

O. Rousset and J. Lepart, Neighbourhood effects on the risk of an unpalatable plant being grazed, Plant Ecology, vol.165, issue.2, pp.197-206, 2003.
DOI : 10.1023/A:1022259905649

A. Stampfli, Accurate determination of vegetational change in meadows by successive point quadrat analysis, Vegetatio, vol.48, issue.2, pp.185-194, 1991.
DOI : 10.1007/BF00044979

T. J. Stohlgren, D. Binkley, G. W. Chong, M. A. Kalkhan, L. D. Schell et al., EXOTIC PLANT SPECIES INVADE HOT SPOTS OF NATIVE PLANT DIVERSITY, Ecological Monographs, vol.69, issue.1, pp.25-46, 1999.
DOI : 10.2307/3898673

T. J. Stohlgren, D. T. Barnett, and J. T. Kartesz, The rich get richer: patterns of plant invasions in the United States, Frontiers in Ecology and the Environment, vol.1, issue.1, pp.11-14, 2003.
DOI : 10.1890/1540-9295(2003)001[0011:TRGRPO]2.0.CO;2

S. Y. Strauss and A. A. Agrawal, The ecology and evolution of plant tolerance to herbivory, Trends in Ecology & Evolution, vol.14, issue.5, pp.179-185, 1999.
DOI : 10.1016/S0169-5347(98)01576-6

M. R. Stromberg, P. Kephart, and V. Yadon, Composition, invasibility, and diversity in coastal california grasslands, Madronõ, vol.48, pp.236-252, 2001.

J. Thioulouse and D. Chessel, A Method for Reciprocal Scaling of Species Tolerance and Sample Diversity, Ecology, vol.73, issue.2, pp.671-680, 1992.
DOI : 10.2307/1940773

URL : https://hal.archives-ouvertes.fr/hal-00698261

J. Thioulouse, D. Chessel, S. Doledec, and J. M. Olivier, ADE-4: a multivariate analysis and graphical display software, Statistics and Computing, vol.7, issue.1, pp.75-83, 1997.
DOI : 10.1023/A:1018513530268

URL : https://hal.archives-ouvertes.fr/hal-00434994

D. Tilman and J. A. Downing, Biodiversity and stability in grasslands, Nature, vol.367, issue.6461, pp.363-365, 1994.
DOI : 10.1038/367363a0

DOI : 10.2307/1940605

T. G. Tutin, V. H. Heywood, N. A. Burges, D. M. Moore, D. H. Valentine et al., The Flora Europaea. Cambridge, 1983.

O. W. Van-auken, Shrub Invasions of North American Semiarid Grasslands, Annual Review of Ecology and Systematics, vol.31, issue.1, pp.197-215, 2000.
DOI : 10.1146/annurev.ecolsys.31.1.197

M. Williamson and A. Fitter, The Varying Success of Invaders, Ecology, vol.77, issue.6, pp.1661-1666, 1996.
DOI : 10.2307/2265769