Long-Term Ecosystem Responses to Directional Changes in Precipitation

Understanding and predicting the effects of changes in climate on ecosystem functioning is currently the most pressing objective of ecology. It is challenging to predict the future functioning of these ecosystems because it is difficult to extrapolate patterns emerging from observations and correlations beyond their original range. Only experimentation can establish cause-and-effect relationships that can be used to predict the future functioning of drylands under novel climatic conditions.

We hypothesize that there are endogenous and exogenous phenomena that interact with each other to generate dryland responses to changes in precipitation. Biogeochemical and demographic phenomena mediate abrupt or continuous changes in populations, communities, and ecosystem processes. In addition, exogenous phenomena such as El Niño events interact with endogenous mechanisms, which affect system resistance, and lead to changes in species composition and ecosystem processes. Results from the first 5 years of this project yielded unexpected results presented in 14 publications.

Our multiple experiments have modified precipitation amount and variability for more than 18 years. These long-term experiments give us the possibility of quantifying independently the effects of the duration changes in precipitation and their magnitude. These experiments provide unique insides to predict the changes in climate that indeed occur in a long-term directionally manner. Recently, we have launched an experiment in which we modified soil water through manipulation of incoming precipitation and atmospheric water by using misters. 

Figure 1: Field experiment modifying soil water via the use of rainout shelters coupled to irrigation systems. The experiment has a factorial design where the effects of soil water is crossed with increases in atmospheric water simulated by misters.