Plant communities are continually undergoing change; however, we lack a clear understanding of how much change is typical and whether environmental characteristics affect rates of change. Further, it is unknown whether background rates of change relate to the responsiveness of a community to global change drivers (GCDs). Here we first used 38 long-term (>8 years) observational datasets from 22 herbaceous sites around the world to measure background change, using several metrics that capture internal community dynamics. Then, we used 58 experiments with 124 treatment-control comparisons from 26 sites to explore how temporal change in a control plots relates to treatment effect magnitude. Using these two data subsets, we addressed two key questions: (1) In unmanipulated herbaceous systems, how much is the plant community changing from year to year, and do environmental drivers explain any of the variability we see in the background rate of community change across sites? (2) Are sites that change more under background conditions prone to greater responses to GCD treatments? Overall, we aim to provide a baseline for community change in herbaceous dominated systems as well as explore how a community’s baseline change might influence future responses to GCDs.
Results/Conclusions
Communities are changing through time, but the amount of change that occurs varies depending on the metric of change explored, as well as site characteristics. We found that baseline compositional change in herbaceous systems from year to year is 0.20 (scale of 0-1) yet sites ranged from 0.0-0.4. In general, total richness did not change (mean = 0) but sites gained and lost species each year (i.e., species turnover occurred). We also found that the sites that showed the greatest amount of change had greater site level diversity, productivity, and resources (MAP). We are unable to test whether the background change that we observed is due to current rising temperatures, altered precipitation patterns, and increased atmospheric CO2, or if communities are just dynamic and in a constant state of change. However, using an experimental framework we found that the more temporally dynamic sites are also the sites that are most responsive to GCD treatments. Plant communities are constantly changing through time, but how much they change from year to year depends on site characteristics like MAP, diversity, and ANPP. Understanding background year to year change may help to predict the magnitude of response a community might have to future GCDs.