It is necessary to understand how communities shift in response to changes in resources in order to predict how ecosystem function will be impacted as multiple resources are altered with global change. To date most studies have focused on single resource manipulations and found repeatable community responses with similar consequences for ecosystem function. For instance, studies of N addition have found reduced plant diversity with increased productivity. Global change, however, often involves many resources changing simultaneously. We know of three terrestrial studies that have manipulated multiple resources and found that plant communities did not respond in a similar way; instead each replicate within the experiment diverged from the others to form distinct “altered community” types. These stochastic responses result in the inability to predict ecosystem function.
We currently lack an understanding of what brings about divergent communities with multiple global change drivers. During our working group we will brainstorm the potential mechanisms that would lead to community divergence versus convergence. We will also compile a list of long-term (>5 years) LTER community experiments in which multiple or single resources have been manipulated to assess the variability of communities within replicates. Our goal will be to generate a list of experiments from a range of systems that manipulate many different resources (e.g., light, nitrogen, phosphorus, water). If we come up with enough experiments, it is our desire that our working group would then meet again to formalize a conceptual model of community convergence versus divergence, and to test this with empirical datasets.