The ability of communities to both resist and recover from environmental perturbations is of increasing interest as extreme climate events become more common and species diversity declines. Communities often show synchronized responses to perturbations, which can lead to oscillations in species abundances and ecosystem functions through time. The ability of communities to resist and recover from these perturbations has been shown to depend on environmental variability, species diversity, and the type of perturbation. Here, we apply scale-specific wavelet analysis to detect synchronous events and the time-scales of the resulting oscillations on grassland community productivity. These methods allow us to detect the number, magnitude, and time-scale of synchronous events in a time series, and to compare the resistance and resilience of communities to perturbations. To test for the effects of environmental variability, we examined five long-term data sets of grassland productivity across a precipitation gradient. To test for the effects of species diversity, we looked at within site variability in responses based on species richness. Finally, we also examined sites where perturbations had been experimentally implemented. Concurrently analyzing these different datasets has allowed us to disentangle the effects of environmental variability, species richness, and type of perturbation on the scale and magnitude of oscillations in community productivity.
Results/Conclusions
We found that for all communities, the time-scale of oscillations tends to be around a 5-year timescale. Precipitation variability tended to reduce the time-scale of the oscillations. Across the precipitation gradient, we found that the magnitude of synchronous events is smaller in sites with more species and more rainfall (p = 0.01). When looking at within site variability, we found the opposite trend, where plots with more species had bigger synchronous events. However, when decomposing the type of event into positive and negative effects on productivity, we found that communities with low diversity had more negative events, and communities with more species had more positive events (p=0.01). For experimental manipulations, we found that increasing plant resources tended to increase the magnitude of synchronous events. Our results suggest that both environmental variability and species richness impact the resistance of communities to perturbations, but richness might have different effects across scales. Additionally, long-term perturbations might impact the resistance of similar communities to perturbations.