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Task 2.2.1
Responses of Vegetation to Land Use and Disturbance
Changing land use and climate affect both landscape configuration and disturbance regimes. For example, recent socio-economic changes in many semi-arid areas of the world have been linked with increasing grazing pressures on rangelands, and subsequent modifications in landscape heterogeneity. Gaining a generic understanding of the effects of changes in land use on landscape vegetation patterns requires the development of a conceptual framework based on the characterization of plant species response to disturbance. Previous GCTE research has contributed to the development of plant functional classifications to describe response to climate and atmospheric changes. These classifications recognize that species can be grouped according to similarity of response which in turn, can be related to biological similarities. Likewise, it is proposed that vegetation response to disturbance can be described using a limited set of biological traits of the component species, and that functional classifications for response to different disturbance types can be derived. Previous attempts at these classifications have repeatedly built functional groups that reflect broad life forms. Therefore, a hierarchical approach may be useful to identify relevant traits (morphological, regeneration and disturbance specific) within life forms (Lavorel et al. 1997). This approach will be applied to the selection of relevant traits used in the construction of functional classifications for response to different disturbances. Response to disturbance can be highly context dependent. Vegetation response to a given change in disturbance regime depends both on the long and short-term disturbance history of the local flora, and the resulting landscape patterns. For example, the local impacts of a given grazing pressure depend on overall landscape vegetation patterns. Therefore the identification of plant functional groups for response to disturbance needs to operate in a comparative manner across regions with different disturbance and land use histories. In developing this Task we will use existing data, as well as conduct new experiments and field studies. The results of the analysis of relationships between disturbance regime and species traits will be used to build functional groups based on species response to a given disturbance type. These functional groups will be used to develop landscape-scale models that analyze the interactions between the functional group composition of communities and landscape pattern. Objectives
Implementation The implementation will be developed around a first core network identified in the FAUST (Functional Attributes Underlying Species Traits) core research project, initiated at the end of 1995. FAUST addresses the objectives of the Task through a focus on the effects of grazing and soil disturbance on grasslands and shrublands. The initial core network of FAUST includes intensive studies in Mediterranean Europe (France and Portugal),. Australia (Queensland Australia), and the United States (Texas). These sites represent three different floras (continents), four different climate types (arid and sub-humid Mediterranean, arid and sub-humid tropical), acid vs. limestone-derived basic soils, and different disturbance regimes related to land use associated with different evolutionary and historical disturbance backgrounds. The expansion of FAUST to include a larger number of sites where grazing is the dominant disturbance is an immediate goal. The Task will also be expanded in order to incorporate other ecosystems and disturbance types. It will operate based on three parallel networks focussing on grazing (extension of FAUST), land use change in the old world, and fire in woody-dominated ecosystems. In the second part of the implementation (from 1998), an additional network will be organized for the development of the modelling work. The general objective of that group will be to analyze the interactions between landscape pattern (for example the land cover types present, the grain and connectivity of the landscape pattern), vegetation initial composition, and disturbance regimes. Specifically, simulation models will be run for regions having different functional group spectra and landscape patterns. The effects of changing land use and natural disturbance regimes on different components of landscape pattern will be analyzed. The sensitivity of the models to the resolution in the functional groupings (many detailed functional types vs. a few broad functional types) will also be analyzed in the perspective of scaling up from communities to landscapes and whole regions. This modelling activity will be carried out in close links with the landscape generic modelling activity undertaken in Task 2.2.4. Milestones
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