UC Santa Cruz

Many ecological phenomena occur in response to pulses. In desert ecosystems, pulses of moisture drive many ecosystem processes, and without this moisture, pulses of wind can lead to large pulses of dust. These pulses can have different effects depending on antecedent conditions. The first two chapters concern the long-, medium- and short-term effects of soil moisture pulses on the health of the Western Joshua Tree (Yucca brevifolia Engelm.), a foundational and landmark species of the Mojave Desert. The species has been protected under California’s Western Joshua Tree Protection Act. Joshua trees face an uncertain future because of climate change, extreme drought, invasive species, and wildland fire. I found that Joshua trees in the field can respond to precipitation events within a few days even at the hottest and driest time of the year, however, the magnitude of their response is related to the amount of water received in the previous winter. In greenhouse experiments, I found that medium-term changes to the antecedent water conditions of Joshua trees affected their photosynthetic upregulation following rehydration. These experiments show that Joshua trees can quickly respond to summer water pulses, which could open the door to more effective adaptive management of this climate-sensitive iconic species in the face of climate change. Next, I review the effects of pulses of wind and dust on human communities living near the Salton Sea. I analyzed regional air quality and health data and found that there is not yet evidence that the exposed lakebed of the shrinking sea is the major source of particulate matter pollution in the region. Finally, I provide recommendations about how to mitigate the threat of dust to communities in the region.