A spatial approach to ecological processes G u e s t Ed i to r s " C o m m e n t

Landscape Ecology vol. 6 no. 3 pp 117-119 (1992) SPB Academic Publishing bv, The Hague

Several characteristics hit the observer of the land- scape of France. First, there is the great variety to be found within a relatively small area. Changing conditions of topography, soils and climate may be found from high mountains to plains and coast- lines. This spatial heterogeneity has been describ- ed in numerous studies of vegetation, and ap- proaches such as those of Braun-Blanquet and Emberger are the basis of phytosociology. Other approaches such as the dynamics series have been utilized by Gaussen in developing the map of the vegetation of France. These studies have also contributed to the emergence of ideas giving rise to modern Landscape Ecology (Forman and Godron 1987).

A second characteristic is that human impacts have taken place everywhere for centuries and this makes the historical perspective essential. Past events have contributed markedly to the diversifica- tion of the landscape of France as well as of other countries in Europe: ancient human settlements, deforestation stages linked to agriculture, proto in- dustrial era, conquest of littoral wetlands, agricul- tural revolution, urbanization.

A third characteristic was mentioned by Crumley and Marquart (1987) in their stimulating work on Burgundian landscapes. 'Although the administra- tive pattern of France may be characterized as a nested and hierarchical organizational structure, one must bear in mind that the administrative tem- plate has been placed over a landscape in which a great number of distinctions of all sorts - linguis-

tic, topographic, climatic, historical, commercial - might reasonably be made. The organizational structure of the landscape as a whole is heterarchi- cal, that is, it possesses the potential of being un- ranked (relative to other elements) or ranked in a number of ways, depending on systemic re- quirements.'

The collection of papers published in this special issue 'Landscape of France at multiple scales' reflects just one of the possible approaches. This approach is process oriented as it considers the spa- tial heterogeneity of the landscape in order to un- derstand ecological processes. Six of the papers (2 to 7) have been selected from results obtained in a program launched in 1987 by the French Ministry of the Environment (Barnaud and Lefeuvre 1988). One (paper 1) results from the 'land-inland water ecotones' project of MAB-Unesco (Naiman et al. 1989), and another (paper 8) from a parallel project on the Mediterranean environment. Papers 1 and 6 were also supported by the Program Environment of the CNRS.

Pinay et al. investigated the ability of riparian forests to retain nutrients and organic carbon along fluvial landscapes. They showed that depositional riparian soils acted as sinks for upstream/down- stream nutrients and carbon flows during floods through accumulation of total carbon, nitrogen and phosphorus from year to year. In contrast ero- sional riparian soils acted as potential nutrient sources during high water periods, since they may release large amounts of easily available carbon,

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nitrogen and phosphorus into the river. Therefore, in fluvial landscapes, riparian forests are hetero- geneous buffering systems whose efficiency de- pends on geomorphic features.

Debussche and Lepart concluded from a study of two common woody plants that the colonization of such plants in Mediterranean ancient fields cannot be reduced to a general rule. Invasion windows in space are largely limited by the dispersal ability of seed-bearers. The rate and extent of colonization depend mainly on the spatial distribution of these seed-bearers, and therefore on the spatial patterns of the landscape.

Manicacci et al. propose a population genetics approach. Their purpose is to explain the mecha- nisms for the maintenance of different traits con- cerned by the shape of the landscape: ability to colonize new sites, growth rate and persistance of a population. Their concern is to know whether the import of genetic diversity is more critical in old or new sites, and whether lack of genetic diversity is more crucial in more fragmented or homogeneous landscapes. They discuss the processes that deter- mine the outcome of selection in a metapopulation and the extent of diversity within a landscape for a given species.

Burel analyses how landscape structure and dy- namics over the last thirty years have affected carabid beetles in hedgerows. She shows that in dense hedgerow networks, some forest species may find good habitats and disperse through the land- scape. When some hedgerow removal occurs, carabid assemblages are highly diversified, and de- pend more on local effects. In this case, forest spe- cies find refuge in the remaining lanes or very dense wooded hedgerows. It is concluded that the knowledge of landscape structure at one period of time is not sufficient to predict carabid assemblages in changing landscapes. Previous states of the land- scape must be considered.

Delettre et al. investigated the impact of land- scape heterogeneity on community structure and population dynamics in two families of Diptera (Empididae and Chironomidae). They showed that a population-centered view of boundaries and patches must be adopted to assess the impact of habitat diversity on species composition and popu- lation dynamics.

Lauga and Joachim assessed the influence of forest fragmentation on the abundance of six forest-breeding bird species on the floodplain of the River Garonne. They showed that the local abun- dance of the birds studied was correlated to a mea- sure of forest fragmentation (the Neighbouring Forest Cover, NFC), and developed an incidence model based on the logistic regression for three spe- cies out of the six studied, which obtained a correct fit. Finally, they built an incidence map of these species up over the whole study area.

Balent and Courtiade modelized the relationship between birds and landscape structure in the agricultural South-Western part of France. They ordinated their relev6s along eoclogical gradients such as: the rate of woody area, the hedgerow net- work complexity and the rate of fallow land. They used this model to measure the importance of the changes induced on landscape by a range of management practises differing in intensity.

Blondel et al. investigated whether a mosaic of habitats of different quality functions as a source- sink system for the Blue Tit. Studying breeding parameters in relation to the food supply in three distinct habitats, they conclude that the rich main- land habitat functions as a source from which birds emigrate into the poor habitat which func- tions as a sink. Those birds which are genetically programmed to breed in the source habitat become mistimed in the sink. Tits on Corsica which are iso- lated from any mainland population have adjusted their breeding traits to the local patterns of food availability and abundance.

The papers were reviewed by colleagues we are pleased to thank: R. Barbault, J. Blondel, P. den Boer, J.F. Dobremez, R. Drent, A. Hansen, G. Merriam, B.T. Milne, P. Opdam, R.C. Petersen Jr., R. Prodon, J.M. Thiollay, E. Van der Maarel, R.C. Wissmar. Dr Ann Say from Durham helped us to translate some of the papers. Thanks are also due to the research department (SRETIE) of the French Ministry of the Environment, particularly to V6ronique Barre and Genevieve Barnaud for their help in the organization and follow-up of the program.

Henri D6camps Jean-Claude Lefeuvre

References

Barnaud, G. and Lefeuvre, J.C. 1988. Le programme 'Ecologie du Paysage' du Comit6 Ecologie et Gestion du Patrimoine Naturel (SRETIE - Ministbre de l'Environnement). Bulletin d'Ecologie 19(4): 563-574.

Crumley, C.L. and Marquardt, W.H. (Eds). 1987. Regional Dynamics. Burgundian Landscapes in Historical Perspective.

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630 p. Academic Press, San Diego. Forman, R.T.T. and Godron, M. 1986. Landscape Ecology.

619 p. John Wiley & Sons, New York. Naiman, R.J., D6camps, H. & Fournier, F. 1989. Role of

land/inland water ecotones in landscape management and restoration. Proposals for collaborative research. 93 p. MAB Digest Unesco, Paris.