UC Santa Cruz

This work examines plant response to human alteration in deserts and coastal salt marshes, two systems in which abiotic stress is assumed to limit plants more strongly than biotic factors.

In the desert, I used experimental panels to simulate the effect of solar energy infrastructure on two habitat types. I measured plant diversity and abundance, finding that panels interacted with rainfall and physical features of each habitat type to drive different outcomes. Under panels, diversity and abundance tended to be higher in one habitat type, but lower in the other. I also examined panel effects on the demography of a closely related rare-common species pair. Panel effects on individual demographic rates were rarely strong, but matrix models integrating these effects across the life cycle revealed a negative impact on the rare species, mediated by increased competition under panels. This result highlights the risk of using a common relative to predict impacts on a rare species.

In the coastal salt marsh, I tested whether the Stress Gradient Hypothesis (SGH) can be applied to improve restoration outcomes. The SGH framework predicts that interactions between plants should shift from competition to facilitation as stress increases. I found that soil conditions were more stressful (more negative water potential) at higher marsh elevations, so I expected clustered plantings to do better upslope. I planted two natives in loose and clustered patterns and tracked their performance across elevation for two years. Surprisingly, performance did not vary with elevation during the first year, while clustering had a negative effect on growth. After two years both species showed clear but inverse patterns of cover across elevation – yet across the entire elevation gradient, clustering strongly inhibited cover in both species.

My work demonstrates that even in “stressful” systems, abiotic stress is not always the dominant constraint on plants. To develop effective conservation and restoration strategies in these systems will require a deep understanding of how human disturbance interacts with the biotic and abiotic drivers that govern plant performance.