ecologia mediterranea Revue internationale d ~écologie méditerranéenne InternationalJournal ofMediterranean Ecology Tome 28 • Fascicule 1 • 2002 Rédacteur en chef • Managing editor Secrétariat • Secretariat FRÉDERIC MÉDAIL MICHELLE DOUGNY - FABRICE TRANCHIDA Rédacteurs • Editors Trésorier • Treasurer LAURENCE AFFRE JACQUES-LoUIS DE BEAULIEC PHILIP ROCHE THIERRY TATONI THIERRY DUTOIT ERIC VIDAL Fondateur • Founder PROFESSEUR PIERRE QUÉZEL Comité de lecture •Advisory board ARONSON]., CEFE-CNRS, Montpellier LE FLOC'H E., CEFE-CNRS, Montpellier BARBERO M., IMEp, Université Aix-Marseille III MARGARIS N. S., University of the Aegan, Mytilène, Grèce BROCK M., University of New England, Armidale, Australie OVALLE c., CSI-Quilamapu, INIA, Chili CHEYLAN M., EPHE, Montpellier PEDROTTI F., Universita degli Studi, Camerino, Italie DEBUSSCHE M., CEFE-CNRS, Montpellier PLEGUEZUELOS J. M., Université de Grenade, Espagne FADY B., INRA, Avignon PONEL P., IMEP, CNRS, Marseille GOODFRIEND G. A., Carnegie Institut, Washington, USA PRODON R., Lab. Arago, Université P. & M. Curie, Paris VI GRILLAS P., Station biologique Tour du Valat, Arles RIDCHARSON D. M., University Cape Town, Afrique du Sud GUIOT]., CEREGE-CNRS, Aix-en-Provence SANS F. X., Université de Barcelone, Espagne HOBBS R. ]., CSIRO, Midland, Australie SHMIDA A., Hebrew University ofJérusalem, Israël KREITER S., ENSA-M-INRA, Montpellier URBINATI c., Agripolis, Legnaro, Italie mediterranea Faculté des sciences et techniques de Saint-Jérôme Institut méditerranéen d'écologie et de paléoécologie, case 461 F-13997 Marseille, cédex 20, France Tél. : + 33 0491 288535 - Fax: + 33 04 91 288051 email: [email protected] - URL: http://www.ecologia.fst.u-3mrs.fr Éditions Édisud 811 La Calade, 3120 route d'Avignon, 13090 Aix-en-Provence Tél. : 00 33 04 42 21 61 44 - Fax: 00 33 044221 5620 email: http://www.edisud.com-Internet:[email protected] © Édisud, 2002, tous droits réservés. Abonnements • Subscription (contacter Edisud) Un an: 2 numéros· One year: 2 issues France: 61 € + 9,12 € de frais de port - Europe: 61 € + 12,2 € de frais de port - Amérique, Afrique, Asie: 61 € + 18,3 € de frais de port ISSN 0153-8756 Changes in structure and function in response to changing diversity within Mediterranean grassland communities C~hangements de structure et de fonction en réponse à des modifications de diversité dans des communautés de pelouses méditerranéennes Dimitri Memtsas) Panayiotis G. Dimitrakopoulos) Akis D. Siamantziouras) Andreas y. Troumbis* BildiVCl'sity Conscrvation Labll1'atoI'Y, Departrnent ofEnviromnental Studies, University of the Aegean, 81100, Lesbos Island, Greece. * AUlhor for correspondence; corresponding address: Fax ++ 30 251 36261, email: atro(il,aegean.gr 5 Abstract Résumé The efficts ofspecies richness, fùnctional group richness andfunc­ Cet article présente les résultats d'une étude expérimentale concer­ tional composition upon structural traits ofvegetation (cover, canopy nant les effets de la richesse spécifique etfonctionnelle ainsi que de height, LAIand PAR) and ecosystem processes (above- and below­ la composition fonctionnelle sur les traits structurels et les processus ground biomass production and short- and long-term decomposi­ écosystémiques de pelouses méditerranéennes synthétiques. L'étude tion) have been monitored in constructed Mediterranean mixed fait partie du projet multinational BIODEPTH grasslands. The experiment is part ofthe european-wide BIO­ 1. Les processus écosystémiques et les traits structuraux de la végé­ DEPTHproject. tation des pelouses manipulées répondent de manière diffirente à The main findings are: la variation des composantes de la diversité de ces communautés. 1. Ecosystem processes andstructural traits ofconstructedgrasslands La production de biomasse ne répond pas de façon significative à showed diffèrent responses to the variation ofthe various commu­ la variation de la diversité. Au contraire, la décomposition rapide, nity diversity components. For instance, biomass production varied le pourcentage de recouvrement végétal et l'index de surfacefoliaire in a non-significant way across manipulated diversity levels. On (LAI) montrent une réponse puissante et curvi-linéaire aux varia­ the contrary, short-term decomposition has showed a strong curvi­ tions de la richesse spécifique. limar response to species richness. Strong significance was also obser­ 2. Les diffirents descripteurs de la productivité (pourcentage de recou­ vedfor plant cover and leafarea index. vrement végétal, LAIet biomasse) répondent de façon diffirente aux 2. Since the various descriptors ofproductivity (plant cover, Leaf variations de la diversité. Ainsi, des mesures directes de la produc­ A.rea Index, and standing biomass) can respond diffèrently to the tivité semblentplus appropriées afin d'acquérir des données robustes variation ofdiversity, a direct measurement ofproductivity would sur la relation diversité-productivité dans ces écosystèmes. o/fér a more robust evidence on the diversity- productivity rela­ 3. La composition spécifique engendre des effets importants sur la tionship in these ecosystems. variation de la production épigée et souterraine de biomasse, la 3. Species composition has significant efficts on above- and below­ hauteur de la végétation et la décomposition. L'identité des espèces ground biomass production, plant cover, canopy height and decom­ semble ainsi avoir une importance significative dans la détermi­ position. Identity ofspecies is ofprimary importance in determi­ nation de la performance globale des processus écosystémiques de ces ning the overall performance ofecosystem processes in grasslands. pelouses. Key-words Mots-clés l'vJediterranean grassland, diversity, productivity, decomposition, Pelouses méditerranéennes, diversité, productivité, décomposition, BroDEPTH BIODEPTH e(ologia meditenanea, tome 28, fascicule 1, 2002, p. 5-18 .. D. MEMTSAS, P G. DIMITRAKOPOULOS, A. D. SIAMANTZIOURAS, A. y TROUMBIS INTRODUCTION tion, mostly fire and grazing (see reviews in e.g. Di Castri & Mooney, 1973; Kruger et al., 1983; Di Castri et al.) The understanding of patterns and mechanisms of 1981). 1t has already been suggested that Mediterranean­ association between the biotic characteristics ofthe com­ type grasslands would be ideal experimental systems munity (such as species numbers, identity of species and (R. Hobbs cited in Richardson & Cowling, 1993), because assemblages and community structure), the ecosystem ecosystems with short-lived species provide fastest res­ functions (such as production and decomposition), and ponses, especially under experimentally controlled condi­ abiotic factors (such as c1imate and soil) is fundamental tions. to the preservation ofbiodiversity and the sustainable use The response curve of ecosystem processes to diver­ of ecosystems. Ecosystem processes determine the levels sity variation has been investigated in many current expe­ of diversity, while they are in turn the consequences of riments which manipulate -directly or indirectly- species diversity. For example, although local productivity can be diversity and monitor the responses of the biogeochemi­ strongly influenced by species richness, the limits of its cal processes that drive ecosystem functioning. Labo­ variation are determined by abiotic factors such as nutrient ratory (e.g. Naeem et al.) 1994) and field experimental availability or c1imatic parameters (e.g. Hector et al.) studies (e.g. Tilman et al.) 1996;Tilman & Downing, 1994; 1999).The loss of biodiversity, at local, regional and glo­ Hooper &Vitousek, 1997; Tilman et al.) 1997; Hector et 6 bal scales, impairs the integrity ofecosystems and at least al., 1999) provide evidence in favour of the hypothesis sorne aspects of ecosystem functioning. At the species that biodiversity influences various ecosystem processes, level, the generic question on the association between e.g. primary productivity or nutrient retention. The diversity and ecosystem functioning is: 'Tf/ill depauperate) conc1usions drawn from them remain contentious as to but nevertheless functionally intact (containing primary pro­ their experimental design, analysis and interpretation ducers) consumers) and decomposers} ecosystems perform dij­ (Givnish, 1994; Aarssen, 1997; Grime, 1997; Huston, ferently from the more species-rich systems from which they 1997; Hodgson et al. 1998; Wardle, 1999; Loreau, 2000). are derived?' (BIODEPTH project 1999). Observational or correlational field studies have also This question is particularly important for hot spot addressed the same question (e.g., McNaughton, 1993; areas, where the severity ofspecies extinction is expected Wardle et al.) 1997b; Troumbis & Memtsas, 2000), to reach its maximum. Within the 2.3 million km2 of the without having however the potential to investigate the Mediterranean Basin occur at least 30,000 plant taxa; in underlying mechanisms for the observed patterns. other words, 1.6% ofEarth's land surface contains ca 10% The purpose of this paper is to provide evidence on of aIl plant species (e.g. Médail & Quézel, 1999). Roughly the diversity-ecosystem function relationship from eas­ half ofthese species are endemic to the area, and ca 4,800 tern Mediterranean grasslands, where experimental plots are endemic to individual countries (Greuter, 1991). with controlled levels of plant diversity (species richness, Approximately 14-15% of this flora is threatened with functional groups and composition) have been establi­ extinction (Greuter, 1994). Mediterranean-type ecosys­