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sur le développement des zones arides et semi-arides

Titre : Woody plants as landscape modulators in Mediteranean woodland.

צמחים מעוצים כמעצבי נוף בחורש ים-תיכוני

Auteur : Gabay, Ofri

Etablissement de soutenance : Ben-Gurion University of the Negev

Grade : Doctor of Philosophy (PhD) 2009

Résumé partiel
Recently, an increase attention is given to the issue of non-trophic interaction in ecological systems, through physical modulation of the environment by organisms. A very common non tropic environmental induced change by organism is landscape modulation by patch creation. These organisms are defined as "Landscape Modulators" (Shachak et al. 2008). In this study I investigated theoretically and empirically the interactions between organisms (woody plants) and their environment through patch creation and landscape modification and its impacts on ecological processes. My model system is Mediterranean woodland in which woody plants are the main landscape modulators. Theoretically, woody plants can affect ecosystems at three organization levels. At the landscape level they can affect patch dynamics that shape landscape structure and function. At ecosystem level they are able to control resources flow and the a-biotic conditions. At community level they can affect species dynamics that determined community composition. In the thesis I proposed a conceptual model that links the effects of woody plants as landscape modulators with ecological processes at the above three organization levels .The model integrates the concept of species filtration from community ecology and new ideas on woody vegetation as landscape modulators. I proposed that the Impacts of woody plants at landscape and ecosystem levels are connected to community level by their effects on species filtration and that species composition in a local assemblage is a result of biotic and a-biotic filtration processes that control species flow from a large to a small spatial scale. In the model I integrated three types of filters : dispersal, a-biotic and biotic that operate at two spatial scales : macro – landscape and micro – patch scales. The model suggests that woody plants as landscape modulators affect both dispersal and a-biotic filters at the patch and the landscape scales. At the landscape scale patch formation by woody plants affects dispersal and seed movement by changing the wind velocity. At the same scale modification of resources flow and a-biotic conditions by the mosaic of the woody patches affects the a-biotic filter. At the patch scale woody plant affects local seed dispersal by acting as obstacle for seed movement into and from the patch. The a-biotic filters are affected by the modification of patch environmental condition such as radiation, temperature, soil moisture and organic matter in soil. I developed a penetration index (D) as a method for quantify filtration strength of a patch type or landscape unit consists of a patchwork of several patch types. The index represents a combined effect of several filters and enables quantification of woody plant impact on species movement among various spatial scales. The index facilitates comparisons of species penetration into the environmentally modulated woody patches and the adjacent un-modulated open space. The index also promotes the ability to compare the effect of different species of woody plants as landscape modulators on species filtering. The index also enables to compare the effect of landscape modification by woody plant on species filtering at various landscape structures by comparing species penetration of one, two and multiple-patch types in a landscape.

The main questions in my study were : 1. How does woody plant affect a-biotic conditions and plant species filtrations in the patch it creates ? How does these effects change with spatial scale and transition from a single patch to multi-patches landscape mosaic ? 2. How does goat grazing as a secondary modulation influence the way that woody plants as primary modulators affect their environment at landscape, ecosystem and community levels ? 3. What is the relative importance of a-biotic factors and seed dispersal barrier as species filters at different spatial scales ? 4. What is the effect of grazing and shrub removal on the landscape, ecosystem and plant species filtration in Mediterranean woodland and how they can be used as management tools for promoting biodiversity ?

Mots clés : Canopy cutting ; seed dispersal ; Grazing ; Landscape modulators ; Mediterranean woodland ; Patchiness ; Species filtration ; Woody plants

Présentation et version intégrale (PRIMO)