Landscape hotspots of rapid change: Temporal dynamics are mediated by environmental filters and biological legacies in a California oak woodland
Temporal variability in plant community composition can be caused by external drivers such as climate variability and disturbance. These external drivers may interact with intrinsic factors such as soil properties and topographic position either directly if the effects of external drivers are mediated by local conditions, or indirectly if local conditions act as environmental filters that sort the species pool into different subsets at different sites. Suites of species may respond differently to similar external drivers due to variation in functional traits, which could lead to spatial variability in how communities fluctuate and change through time. We compared temporal variability in species composition at 54 plots over 11 years between sites in oak woodlands in which disturbance was experimentally manipulated via the removal of livestock grazing at some sites, and a prescribed burn on others.
Disturbance type influenced temporal dynamics, and sites where grazing was removed during the study had more directional change than sites that were grazed throughout the study and sites that were burned. Temporal fluctuations, turnover, and directional change were all also related to intrinsic factors, suggesting that some locations are more responsive to external drivers than others. In particular, sites on south facing slopes with low nitrogen and high clay content had greater directional change, greater temporal fluctuations, and higher average turnover. We also investigated whether species sorting might influence temporal dynamics by evaluating whether the abundance of species with certain functional traits was associated with greater variability. We found that sites with higher forb and perennial composition the beginning of the study had lower temporal fluctuation than grass-dominated annual sites. These results suggest that different communities respond differently to perturbations, and that pre-existing species composition can create biological legacies that influence how communities might respond to disturbance and climate variability.