Incorporating environmental variability and competition into climate change predictions for desert annuals
Incorporating the effects of changing rainfall in climate change predictions for plant communities is a major challenge. Plants will react to both average changes in rainfall amount, but also the timing and intensity of individual rainfall events. Additionally, species responses to changing rainfall can be modified by the responses of nearby competitors, either dampening or exacerbating the effects of abiotic changes. Using field experimental manipulations of both rainfall and plant density, as well as natural variation, we have developed a set of demographic models that describe how five Chihuahuan desert annual plant species may respond to climate change. Rainfall in the Chihuahuan desert is expected to decline in the next century, but how the timing and intensity of rainfall will change is uncertain. By downscaling biweekly census data to daily predictions, these models can incorporate the effects of the timing and intensity of individual rainfall events, via soil moisture, on plant whole-season growth, survival, and reproduction. This allows us to investigate many possible climate change scenarios, while still incorporating the effects of neighborhood competition.
Responses to competition and changing soil moisture differ by species. For example, Eriogonum abertianum shows strong positive growth responses to increasing soil moisture and negative effects from increasing competitor density, however the effect of competitors is weakened at lower soil moisture. In contrast, Tidestromia lanuginosa shows positive growth responses to soil moisture, but little to no effect of competitor density at any soil moisture. Preliminary results also indicate that increasing intensity of rainfall, as is expected in many climate change scenarios, could lead to less plant-available soil moisture as more is lost to drainage and surface flow. This decline in available moisture could intensify the effects of already declining rainfall and further favor species that perform best in more xeric environments.