EVENT: Long-term studies of California grassland: lessons for restoration

A 27 year study of annual grassland on serpentine soils in northern California elucidated the roles of rainfall variation and disturbance in determining grassland composition and dynamics. The abundance of individual species was found to vary markedly over the study period, in part tracking changes in annual rainfall amounts and distribution, but also varying in relation to animal disturbance and grazing. This led to large variations in species composition both through time and spatially. Of particular importance were the findings that invasion by non-native grasses was episodic and related to above-normal rainfall amounts and that some species which were relatively uncommon in the grassland became dominant under some conditions. These dynamics would not have been elucidated without long-term study. The relevance of the dynamic nature of the grassland, the spatial heterogeneity and the functional roles of individual species are considered within the context of restoration. In particular, the question of setting restoration goals in relation to a reference system is explored. Clearly, the objectives of restoration need to take into account both the dynamic nature of ecosystems and the need to build functional resilience in the system. Similarly, the definition of a reference state needs to recognize the possibility that species which are not abundant at one particular time may nevertheless be important components of the system under changed conditions.