Thèse-EliseBuisson-1Introduction
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Thèse-EliseBuisson-1Introduction

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Cet ouvrage est issu d’une thèse de doctorat de l’Université d’Aix-Marseille III co-dirigée par le Professeur Thierry Dutoit et le Maître de Conférence Emmanuel Corcket, au sein de l’IMEP, Institut Méditerranéen d’Ecologie et de Paléoécologie. Cette thèse a été présentée et soutenue publiquement le 20 septembre 2005, à l’Europôle de l’Arbois, devant le jury composé de : Mme Karen Holl, Professeur, University of California Santa Cruz, USA, Rapporteur Mr. Richard Michalet, Professeur, Université de Bordeaux 1, Rapporteur Mr. James Aronson, Directeur de Recherche, CNRS-CEFE, Montpellier, Examinateur Mr. Thierry Tatoni, Professeur, Université Paul Cézanne, Aix-Marseille III, Examinateur Mr. Sean Anderson, Docteur, Center for Conservation Biology, Stanford University, USA, Examinateur Mr. Grey Hayes, Docteur, Elkhorn Slough National Estuarine Research Reserve, USA, Membre invité Mr. Emmanuel Corcket, Maître de Conférences, Université de Bordeaux 1, Co-directeur Mr. Thierry Dutoit, Professeur, Université d'Avignon, Directeur. Le texte présenté est issu d’une version corrigée de la thèse dont le titre original était : « Restauration écologique de communautés végétales herbacées méditerranéennes: exemples dans le sud-est de la France et sur la côte californienne » Il a été tenu compte dans la présente version des remarques faites par les rapporteurs et examinateurs lors de la soutenance. 1 Acknowledgements ...

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Cet ouvrage est issu dune thèse de doctorat de lUniversité dAix-Marseille III co-dirigée par le Professeur Thierry Dutoit et le Maître de Conférence Emmanuel Corcket, au sein de lIMEP, Institut Méditerranéen dEcologie et de Paléoécologie.Cette thèse a été présentée et soutenue publiquement le 20 septembre 2005, à lEuropôle de lArbois, devant le jury composé de : Mme Karen Holl, Professeur, University of California Santa Cruz, USA, Rapporteur Mr. Richard Michalet, Professeur, Université de Bordeaux 1, Rapporteur Mr. James Aronson, Directeur de Recherche, CNRS-CEFE, Montpellier, Examinateur Mr. Thierry Tatoni, Professeur, Université Paul Cézanne, Aix-Marseille III, Examinateur Mr. Sean Anderson, Docteur, Center for Conservation Biology, Stanford University, USA, Examinateur Mr. Grey Hayes, Docteur, Elkhorn Slough National Estuarine Research Reserve, USA, Membre invité Mr. Emmanuel Corcket, Maître de Conférences, Université de Bordeaux 1, Co-directeurMr. Thierry Dutoit, Professeur, Université d'Avignon, Directeur. Le texte présenté est issu dune version corrigée de la thèse dont le titre original était : « Restauration écologique de communautés végétales herbacées méditerranéennes: exemples dans le sud-est de la France et sur la côte californienne » Il a été tenu compte dans la présente version des remarques faites par les rapporteurs et examinateurs lors de la soutenance.
 
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Acknowledgements
First, I would like to thank Pr. Thierry Dutoit who supervised my M.S. research and advised me on this Ph.D. work. He has always been there, not only to guide me in my experiments and writing, but also for fieldwork. I thank him also for having trusted me all along. I thank Dr. Emmanuel Corcket, my co-adviser, particularly for advising me on the experimental design of my experiments, brainstorming on statistics and always being enthusiastic. I am grateful to Pr. Karen Holl from the University of California in Santa Cruz; Pr. Richard Michalet from the University of Bordeaux 1; D.R. James Aronson from CEFE, Centre d'Ecologie Fontionnelle et Evolutive in Montpellier; Dr. Sean Anderson, Center for Conservation Biology, Stanford University; and Dr. Grey Hayes, Elkhorn Slough Foundation Estuarine Research Reserve, California, who are judging this work. I am also grateful to the Institute of Mediterranean Ecology and Paleoecology; the team Conservation Biology and Landscape Ecology; Thierry Tatoni; and the 'Ecole Doctorale Sciences de l'Environnement' for having admitted me; Pr. Karen Holl from the Department of Environmental Studies, University of California Santa Cruz; and the Center for Conservation Biology, Stanford University and particularly Dr. Sean Anderson for their collaboration. Financial support for this research was provided by the French Department of Sustainable Development and Ecology (Ministère du Développement Durable et de l'Ecologie): program Espaces Protégés; The French Department of Research and Technology (Ministère de la Recherche et Technologie); the Elkhorn Slough Foundation; the U.S. Department of Agriculture and the Académie d'Agriculture de France. We thank the Conservatoire-Etudes des Ecosystèmes de Provence, Jean Boutin, Axel Wolff and the team of the Eco-Musée de Crau, the Elkhorn Slough Foundation and Kim Hayes for site access and help. For helpful comments on some parts of the manuscript and/or proof reading the English, I thank Didier Alard, Jean Boutin, Laura Castellini, Pascal Campagne, Gilles Cheylan, Alice Endamne, Grey Hayes, Karen Holl, Peter Poschlod, David Pyke, Arne Saatkamp, Marjorie Sweetko, Carey Suehs, and Axel Wolff. I also thank Philip Roche, Maurice Roux and Franck Torre for their help with statistics. For fieldwork, greenhouse and garden experiments, I greatly appreciated the assistance of Pascal Auda, Manuela Bellanger, Markus Bernhardt, Paule  2
Bottone, Emilie Buisson, Valentine Cuillier, Rachel Davis, Charlotte Durand, Sylvain Fadda, Estelle Forey, Pauline Gaignard, Cédric Genest, Eric Gerbaud, Christophe Grand, Fred Guiter, John Gustafson, Grey Hayes, Karen Holl, Jim Leap, Linda Locatelli, Grant Lyon, Charles Mcclain, Agnès Montesinos, Paulo Oliviera, Marie Julie Peters Desteract, Claire Philips, her mum and her grand-mother, Christine Römermann, Arne Saatkamp, Benjamin Salicis, Jeff Schinske, Isabelle Schwob, Daniel Scriver, Courtney Smith, Elise Trivelly, Matthieu Trouvé, Jim Velzy, Virginie Vergnes, Dana, Mo, Patrice, the team Conservation Biology and Landscape Ecology for carrying all these stones and the Creek Monkeys ! I am grateful to Alain Peeters, Bernard Toussaint and the team of the Laboratoire d'Ecologie des Prairies (Louvain-la-Neuve) in Michamps for helping me analyze most of my soil and plant samples. I also thank Christiane Rolando for soil analyses. I would also like to thank the team "Community Ecology" in BIOGECO, BIOdiversité, Gènes, ECOsystèmes, Bordeaux for having welcomed me for several weeks, and particularly Sylvain Delzon for his comments and help in statistics and software. I am grateful to the CIES (Centre d'Initiation à l'Enseignement Supérieur), Mr. Cartapanis, Sonia Amoros and Anne Lapied-Lahaye for the opportunity to teach as an assistant for four years, to Thierry Tatoni for having backed up my candidacy as a teaching assistant and to the various people who helped me prepare or teach these courses, among which Laurence Affre, Alex Baumel, Pascal Campagne, Sophie Dandelot, Evelyne Franquet, Manu Gandouin, Fred Guiter, Laurence Kiss, Martin Lavoie, Brigitte Talon, Franck Torre and Eric Vidal. This research project would not have been possible without housing in California and without decently priced housing in France. I thus thank Laura Castellini, Hakan Guven and various other roommates, Vicki Oswald, Bobby and John Gustafson, Alice Endamne and Kolo Wamba, Marta Bonilla, Marie Guittonny-Larchevêque, Véronique Bonnet, Arnaud Robert and James Carter, Gisèle and Pascal Agostini as well as Claudia, Steve and Quinn. Finally, I would like to thank all the people of our team, Conservation Biology and Landscape Ecology for all this good time we spent together as well as all the people who helped me through advice, stimulation or inspiration, or simply by enjoying relaxed moments with me, botanical walks or slang lessons. To all of you who made this not just a thesis, but an adventure. This endless list starts with Emilie, Sophie, Jean-Pierre and Jacqueline Buisson, Laura, Marie & Philippe, Sylvain, Danito, Errol, Luezi & Alice, Latif & co., Gina, Virginie, Arne, Marie, Jade, Guillou, Otélé, Shéhérazade, Monica & So, Val, Delphine, Murielle
 
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Index   Introduction .....................................................................................................8 Context.............................................................................................................8 Objectives ........................................................................................................9 Basic questions ................................................................................................9 Basic questions applied to the local context ..................................................10 Ecological restoration ....................................................................................14 Ecological restoration and ecological theory .................................................18 Vegetation Dynamics (Chapter 3) .................................................................18 Transition zones between ecosystems (Chapter 4) ........................................19 Resilience (Chapter 3) ...................................................................................20 Plant co-existence and biotic relations (Chapter 5 & 6) ................................20 Herbaceous communities ...............................................................................23 Why study plant community assemblages? ...................................................23 Why study herbaceous plant communities?...................................................23 Study sites: the steppe of La Crau and California Coastal Prairies................24 Methods .........................................................................................................26 Multi-level approach......................................................................................26 Empirical and experimental approaches ........................................................26 Historical ecology ..........................................................................................27 Species availability on site and through dispersal .........................................27 Facilitation and competition ..........................................................................28 Data Analyses ................................................................................................29 Hypotheses (H) and thesis content.................................................................31 Chapter 1...............................................................Erreur ! Signet non défini. History of La Crau ................................................Erreur ! Signet non défini. Abstract.................................................................Erreur ! Signet non défini. Introduction ..........................................................Erreur ! Signet non défini. La Crau: a site of great biological importance ......Erreur ! Signet non défini. Description of La Crau .................................Erreur ! Signet non défini. Vegetation.....................................................Erreur ! Signet non défini. A haven for birds, reptiles and insects ..........Erreur ! Signet non défini. Traditional land-use ......................................Erreur ! Signet non défini. Main Threats.........................................................Erreur ! Signet non défini. The main types of protected areas in France and the case of La Crau ......................................................................Erreur ! Signet non défini. Conservation Plans ...............................................Erreur ! Signet non défini. First proposal: a failure to communicate.......Erreur ! Signet non défini. 
 
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Second proposal: conservation of steppe and surrounding habitats ......................................................................Erreur ! Signet non défini. Third proposal: spatial heterogeneity............Erreur ! Signet non défini. What now ? ...........................................................Erreur ! Signet non défini. Implications for the creation of protected areas....Erreur ! Signet non défini. Conclusion ............................................................Erreur ! Signet non défini. Chapter 2...............................................................Erreur ! Signet non défini. Vegetation dynamics in La Crau...........................Erreur ! Signet non défini. Abstract.................................................................Erreur ! Signet non défini. Introduction ..........................................................Erreur ! Signet non défini. Materials and methods ..........................................Erreur ! Signet non défini. Study area .....................................................Erreur ! Signet non défini. Study sites.....................................................Erreur ! Signet non défini. Vegetation and soil sampling........................Erreur ! Signet non défini. Seed bank sampling and analysis..................Erreur ! Signet non défini. Data analyses ................................................Erreur ! Signet non défini. Results ..................................................................Erreur ! Signet non défini. Vegetation attributes .....................................Erreur ! Signet non défini. Species richness and evenness ......................Erreur ! Signet non défini. Abiotic factors influencing vegetation dynamics.....Erreur ! Signet non défini. Abiotic parameters being correlated with vegetation dynamics .Erreur ! Signet non défini. Soil seed bank results....................................Erreur ! Signet non défini. Discussion.............................................................Erreur ! Signet non défini. Vegetation attributes .....................................Erreur ! Signet non défini. Attributes of the soil seed bank.....................Erreur ! Signet non défini. Conservation management and restoration ecology ........Erreur ! Signet non défini. Chapter 3...............................................................Erreur ! Signet non défini. Resilience of La Crau ...........................................Erreur ! Signet non défini. Abstract.................................................................Erreur ! Signet non défini. Introduction ..........................................................Erreur ! Signet non défini. Methods ................................................................Erreur ! Signet non défini. Study area .....................................................Erreur ! Signet non défini. Sampling .......................................................Erreur ! Signet non défini. Data analyses ................................................Erreur ! Signet non défini. Results ..................................................................Erreur ! Signet non défini. Discussion.............................................................Erreur ! Signet non défini. Interchapter 3-4.....................................................Erreur ! Signet non défini. Seeding experiment in La Crau.............................Erreur ! Signet non défini. Chapter 4...............................................................Erreur ! Signet non défini.  5
Restoration of La Crau..........................................Erreur ! Signet non défini. Abstract.................................................................Erreur ! Signet non défini. Introduction ..........................................................Erreur ! Signet non défini. Methods ................................................................Erreur ! Signet non défini. Site description .............................................Erreur ! Signet non défini. Main experimental design.............................Erreur ! Signet non défini. Transplanting ................................................Erreur ! Signet non défini. Data collection ..............................................Erreur ! Signet non défini. Community and habitat description ..............Erreur ! Signet non défini. Statistical analyses ........................................Erreur ! Signet non défini. Results ..................................................................Erreur ! Signet non défini. Soil nutrient status and plant community characteristics .Erreur ! Signet non défini. Plant nutrient analyses ..................................Erreur ! Signet non défini. Transplant survival 1.5 years after planting ..Erreur ! Signet non défini. Transplant biomass 1.5 years after planting..Erreur ! Signet non défini. Discussion.............................................................Erreur ! Signet non défini. Establishment on the steppe..........................Erreur ! Signet non défini. Establishment on the fields ...........................Erreur ! Signet non défini. Conclusion ............................................................Erreur ! Signet non défini. Chapter 5...............................................................Erreur ! Signet non défini. History of coastal prairies .....................................Erreur ! Signet non défini. Before European settlement..................................Erreur ! Signet non défini. Coastal Prairies after European settlement ...........Erreur ! Signet non défini. UC Santa Cruz campus .........................................Erreur ! Signet non défini. Elkhorn Porter Ranch .........................................Erreur ! Signet non défini. -Stanford foothills ..................................................Erreur ! Signet non défini. Restoring coastal prairies......................................Erreur ! Signet non défini. Interchapter 5-6.....................................................Erreur ! Signet non défini. Seeding experiment in coastal prairies .................Erreur ! Signet non défini. Chapter 6...............................................................Erreur ! Signet non défini. Restoration of coastal prairies 1............................Erreur ! Signet non défini. Abstract.................................................................Erreur ! Signet non défini. Methods ................................................................Erreur ! Signet non défini. Site description .............................................Erreur ! Signet non défini. Main experimental design.............................Erreur ! Signet non défini. Transplanting ................................................Erreur ! Signet non défini. Seeding experimental design ........................Erreur ! Signet non défini. Data collection ..............................................Erreur ! Signet non défini. Statistical analyses ........................................Erreur ! Signet non défini. Results ..................................................................Erreur ! Signet non défini. Soil nitrogen..................................................Erreur ! Signet non défini.  6
Survival 3 months after transplanting ...........Erreur ! Signet non défini. Survival 1.5 years after transplanting ...........Erreur ! Signet non défini. Biomass ........................................................Erreur ! Signet non défini. Discussion.............................................................Erreur ! Signet non défini. Implications to Restoration Practice .....................Erreur ! Signet non défini. Chapter 7...............................................................Erreur ! Signet non défini. Restoration of coastal prairies 2............................Erreur ! Signet non défini. Abstract.................................................................Erreur ! Signet non défini. Introduction ..........................................................Erreur ! Signet non défini. Methods ................................................................Erreur ! Signet non défini. Site description .............................................Erreur ! Signet non défini. Experimental design .....................................Erreur ! Signet non défini. Seeding and transplanting .............................Erreur ! Signet non défini. Data collection ..............................................Erreur ! Signet non défini. Abiotic variables ...........................................Erreur ! Signet non défini. Statistical analyzes ........................................Erreur ! Signet non défini. Results ..................................................................Erreur ! Signet non défini. Abiotic variables ...........................................Erreur ! Signet non défini. Field emergence............................................Erreur ! Signet non défini. Survival 6 months after planting...................Erreur ! Signet non défini. Survival 1.5 years after planting ...................Erreur ! Signet non défini. Biomass ........................................................Erreur ! Signet non défini. Discussion.............................................................Erreur ! Signet non défini. Conclusions and Management RecommendationsErreur ! Signet non défini. General Discussion ...............................................Erreur ! Signet non défini. 1. Impact ...............................................................Erreur ! Signet non défini. 2. Resilience..........................................................Erreur ! Signet non défini. 3. Boundaries ........................................................Erreur ! Signet non défini. 4. Spontaneous restoration ....................................Erreur ! Signet non défini. 5. Restoration........................................................Erreur ! Signet non défini. Perspectives ..........................................................Erreur ! Signet non défini. In La Crau .............................................................Erreur ! Signet non défini. In California coastal prairies.................................Erreur ! Signet non défini. At both sites ..........................................................Erreur ! Signet non défini. The role of the perennial plants studied ................Erreur ! Signet non défini. Pursue restoration with sowing.............................Erreur ! Signet non défini. Population dynamics.............................................Erreur ! Signet non défini. Mycorrhizae..........................................................Erreur ! Signet non défini. Conclusion ............................................................Erreur ! Signet non défini. References ............................................................Erreur ! Signet non défini.    
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Introduction
Context Global environmental changes are the results of human activities which, through agriculture and industry, pollute, alter biogeochemical cycles and induce constant changes in land-use (Fig. 1) (Vitousek 1994; Fig. 1). This has profound effects on climate change, ecosystem functioning and biological diversity, and raises questions about the human relationship to the natural environment (Katz 1997). One of the main global environmental change types, changes in land-use and land cover, has transformed at least 43% of the earth's terrestrial surface (Daily 1995). The losses of pristine ecosystems exacerbate the need for preserving those that remain; e.g. only 0.69% of temperate grasslands are protected worldwide (IUCN 1994). However, often these areas are already too small and too few to preserve biological processes and diversity (Anderson 1995; Hobbs & Norton 1996). Not only have pristine ecosystems been lost, but there is also increasing abandoned degraded land (Urbanska et al., 1997; McMahon & Holl 2001), thus creating a growing potential for ecological restoration both to buffer and link preserved areas and to repair entire ecosystems (Anderson 1995). Young (2000) points out i) that restoration must remain only a second choice because conservation is the only way of preserving high quality habitats; ii) and that mitigation will never equally replace original ecosystems. However, ecological restoration has the potential to help reach conservation goals and to test ecological knowledge (Ormerod 2003).
Industry
Poll
Climate change
Study framework Human activities Agriculture
es in land-nd land cover Biogeochemical cycles
Biological processes and diversity
Fig. 1. Modified from Vitousek 1994.
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Objectives Basic questions This study is driven by two objectives: to improve ecological restoration planning and techniques and to contribute to ecological theory through the use of the applied approach of ecological restoration, in the light of the changes in land-uses and land cover. The thesis is organized in three parts, each of which each answers the following questions on ecological theory and ecological restoration needs: 1) What is the impact of disturbances on plant communities? Are they resilient to these disturbances? Are these communities so degraded, that they might need restoration? 2) Do remnant patches of undisturbed plant communities play a role in the resilience process within the context of a fragmented landscape? Can we assess resilience more precisely? Does spontaneous restoration at the boundaries between remnant patches of undisturbed plant communities and degraded communities occur and if it does, at what rate? Does the rate of spontaneous restoration justify ecological restoration? 3) Were irreversibility thresholds passed through during disturbance? Which ones are they and is there a way back? Can we hierarchize the factors which limit restoration among various factors of the habitat, the disturbance regime and plant dissemination? Can this contribute to the study of ecosystem functioning? The perspectives of this thesis include research on the role of dominant perennial species on species assemblages and on the potential of these species to facilitate the establishment of other species in degraded ecosystems. 
 
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Basic questions applied to the local context 1) What is the impact of strong exogenous disturbances on Mediterranean herbaceous plant communities that have evolved with regular endogenous disturbances for centuries? Are these communities resilient to these disturbances? Are these communities so degraded that they might need restoration? (Chapter 2 & 3). Adisturbance is a relatively discrete event in time that disrupts the ecosystem (community or population) structure and changes the resources, substrate availability or physical environment (White & Pickett 1985) (Fig. 2). In a review on disturbance and ecosystem dynamics, White and Jentsch (2001) commenting on this broad definition, explain that it focuses on the results of the disturbance on the ecosystem and specify the disturbance attributes: duration, abruptness and magnitude. They consider that a continuous disruption in the ecosystem (like continuous herbivory) is not a disturbance and define such non-abrupt processes as stresses. Grime's definition (1979) focuses on the results of the disturbance on biomass: disturbance is a destruction of biomass while stress is an external constraint limiting biomass production. A disturbance can also be described as endogenous if the ecosystem has evolved with it and plants have had a chance to adapt (e.g. herbivory), while an exogenous disturbance is described as a force originating neither from the ecosystem nor from successional development (e.g. changes to the endogenous disturbance regime, or removal of endogenous disturbances are exogenous disturbances) (McIntyre & Hobbs 1999).In this study, I consider sheep grazing, California native ungulate grazing and regular summer drought as stresses or disturbances endogenous to the herbaceous communities studied, while short-duration cultivation is an exogenous disturbance or disturbancesensu lato. Disturbances affect all ecosystems at various temporal and spatial levels and drive ecosystem dynamics (White & Jentsch 2001): they play a major role in structuring ecosystems by causing heterogeneity in competition and resource availability. The impact of a disturbance on an ecosystem is measured by resistance and resilience (Mitchell et al. 2000; Hirst et al. 2003): resistance (called inertia by Westman 1978 and resilience by Holling 1973inMitchell et al. 2000) is defined as the ability of the ecosystem to withstand the disturbance;resilience(called stability by Holling 1973 and May 1973inMitchell et al. 2000) is defined as the process (Westman 1986) or the time period (Hirst et al. 2003) the ecosystem (or community) to return to its reference trajectory after an exogenous disturbance (Fig. 2). Both Mitchell et al. (2000) and Hirst et al. (2003) highlight the importance of assessing resilience for applied ecology. The impact that a disturbance has on an ecosystem includes both the changes occurring just after the disturbance has taken place, for which Neubert & Caswell (1997) proposed various indices, and the resilience of the system and the mechanisms associated with both the changes and resilience (Mitchell et al. 2000).
 
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Exogenous disturbance
Endogenous disturbance = stresses
Reference ecosystem trajectory
?
              Resilience   Time   Fig. 2. Theoretical model showing the definitions of disturbance and resilience. Depending on communities, resilience may be only theoretical. Contrary to succession, assembly rules state that a community does not tend towards one stable dynamic endpoint but several (Lockwood 1997). The community goes extinct or moves to another alternative endpoint when a disturbance forces it (Law & Morton 1996). This view of community assembly implies that there is no guarantee that a natural community will return to its original composition on its own (Lockwood 1997). The impacts of endogenous disturbances (e.i. grazing) and of exogenous disturbances (e.i. cultivation) on herbaceous ecosystems have been widely studied (Poschlod & WallisDeVries, 2002): e.g. Hillier et al. (1990), Gibson & Brown (1992), Pärtel et al. (1999), Hansson & Fogelfors (2000), Sternberg et al. (2000) and Moog et al. (2002) have studied the impacts of endogenous disturbances (grazing mowing) while Booth (1941), Costello (1944), Reichhardt (1982), Hutchings & Booth (1996a), Dutoit et al. (1999) and Critchley & Fowbert (2000) have studied the impacts of exogenous disturbances (cultivation, plowing, fertilization). However, few studies dissociate the impact of a single and abrupt exogenous disturbance from that of a disturbance regime (continuous endogenous disturbance) (Chabrerie 2002).In this study, we aim at assessing the impact of cultivation (exogenous disturbance) on the steppe of La Crau which has evolved with grazing and drought (endogenous disturbances or stresses). We thus carry out a space-for-time substitution study or synchronic study (a study done at a single point in time rather than over the course of a period of time): we compare nine fields abandoned between 37 and 3 years ago (year of study 2001) and six patches  11