Spatio-temporal patterns of biodiversity and disturbance in North-Eastern Morocco
Gerald Jurasinski (10/2006-08/2007)
Betreuer: Carl Beierkuhnlein
In the light of land use and climate change which rapidly alter landscapes and ecosystems worldwide there is an urgent need for standardized and comparable data in order to detect changes of biodiversity. Therefore, it is paramount to provide methods for the comprehensive assessment and evaluation of biodiversity. These methods are required to be representative as well as pragmatic due to the fact, that there is insufficient time to obtain complete data sets. If biodiversity is lost rapidly at the landscape level, frequent re-investigations have to be done in order to detect and analyze such changes. The central objective of this thesis is the development and evaluation of spatially explicit, widely applicable methods for the assessment and analysis of phytodiversity, encompassing species richness as well as spatial and temporal heterogeneity of diversity. The conceptual perspective on the one hand and the application of the methodology in order to investigate ecological phenomena on the other represent the two foci of the thesis.
A review of the terminology of biodiversity - especially ‘beta-diversity’ - reveals a multitude of co-existing concepts. This plethora of definitions hampers application and scientific progress. Thus, a new terminology is proposed, which, compared to Whittaker’s concept of diversity (alpha, beta, gamma), provides less ambiguous terms (inventory-, differentiation-, and proportional diversity). It enables a more direct access to the underlying ecological phenomena and key questions. Hence, it can help to structure the scientific discussion and future research.
Spatial patterns of diversity may be best assessed with systematic sampling. However, square sampling grids implemented so far are exposed to the problem of distance decay and deliver indefinite values. Therefore systematic sampling in hierarchically nested equidistant grids is proposed as an appropriate methodology for the assessment of spatial patterns in vegetation.
A new coefficient of multi-plot similarity is developed for the analysis of pattern diversity. For the first time this allows the calculation of similarity between one and many plots while taking species identity into account. It performs superior to all other tested coefficients in detecting vegetation hotspots and gradients. The multi-plot similarity coefficient provides a promising tool for ecological research as well as for nature conservation and monitoring. The developed equidistant sampling grid has been applied in a case study in Northeastern Morocco to investigate the drivers of spatial patterns of biodiversity. The nested equidistant sampling grid with hexagonal plots allows for a detailed evaluation of different aspects of biotic diversity on landscape scale. However, while disturbances play an important role in shaping the emergent patterns of species distribution, the long time disturbance regime, manifested in the coarse vegetation structure, plays an even more important role. Most notably, the relationships between spatial patterns of biodiversity and its drivers vary with scale and exhibit considerable non-stationarity. This has important implications for ecological research. When the relation between pattern and process is under study, the sampling design should address scale issues and enable to study the variation of the relations with scale and extent.
The methodology developed for the comparison of multiple plots has been applied to a data set of vegetation on Alpine summits to evaluate whether the upward shift of mountain plants causes homogenization of the summits. The analysis reveals that this indeed is the case: The increase in species richness on the summits is accompanied by a decrease in differentiation diversity. In the context of this thesis it is to state, that the heterogeneity concept may provide an interesting tool for the evaluation of actual ecological research questions as well as for nature conservation and monitoring.