Factors affecting functional diversity of grassland vegetations

Abstract

The functional diversity of local plant communities is considered to be an important driver of ecosystem resistance and resilience. Various landscape characteristics can influence local functional diversity, but their relative importance is poorly understood. We used a spatially explicit grassland model (TRANSPOP) to simulate competition between 19 functional plant strategies as defined by Grime's C-S-R framework, each with different affinities for levels of Nutrient availability (N) and Disturbance (D). First, we explore the effects of N and D levels on strategy preference. Subsequently, we studied functional diversity in patchy landscapes with various levels of heterogeneity, patch size, connectivity and environmental dynamics (with patches differing in N and D). We evaluated the relative importance of these factors in determining the functional diversity of permanent grasslands of the temperate climatic zone.Simulated N and D optima for occurrence of strategies matched those of Grime. Perpendicular N and D gradients were twice as diverse as correlated configurations. The results show that heterogeneity in N and D was the most important factor determining strategy diversity, followed by environmental dynamics, connectivity and patch size. Grasslands with large heterogeneity and patch size have a high functional diversity, whereas high values for dynamics and connectivity had, in general, a negative impact on functional diversity. The frequent occurrence of significant interactions among characteristics suggests that the optimal spatial design of landscapes with respect to functional diversity is context dependent.Contrary to expectations, connectivity generally had a negative effect on the diversity of plant strategies. This was attributed to the fact that connectivity intensifies competition between strategies. High connectivity and environmental dynamics, low patch size and low heterogeneity intensifies interspecies competition and causes rapid species loss, which strongly reduces resistance and resilience. This shows that high species diversity in itself does not protect against diversity loss, but that factors contributing to the maintenance of high diversity reduce the risk of species extinction and enable resistance and resilience.