Interactions between snowpack and competition in post-fire conifer regeneration

Interacting effects of multiple ecological drivers can have dramatic consequences for species recruitment and community assembly not evident from individual effects. To understand how post-fire conifer recruitment varies with interacting abiotic and biotic contingencies, we established an experiment in the Sierra Nevada, California. Working within the King Fire burned area, we crossed a manipulation of snowpack with a removal of surrounding shrubs, which may serve as competitors or facilitators of tree seedlings. We seeded two conifer species, Pinus ponderosa and Abies concolor, within these plots in two consecutive years, one relatively normal and the other with an unusually wet winter and hot summer, and tracked the survival and growth of these seedlings for multiple years. Overall, our results demonstrate that the competitive effect of shrubs on tree seedlings, which is often assumed to be pervasive in this system, is in reality highly context-dependent.

Post-fire regeneration on harsh soils is more resilient to climate change

Plant communities on harsh soils such as serpentine appear to be less sensitive to climate change. However, although disturbance from fire is an important part of grassland, chaparral, and forest communities, the resistance of these serpentine communities has primarily been studied in an undisturbed context. We compared two fires that burned fifteen years apart in a Mediterranean chaparral system to test whether shifting climate patterns—including a historically severe drought—had the same negative impacts on diversity of post-fire communities as it has on unburned communities, and whether those impacts varied by soil type. Our results thus far indicate that disturbance-following communities on harsh soils may be resilient to climate change, but slower recruitment from woody species may lead to eventual type conversion even on harsher soils.

Spatial and temporal contingency in rapid primary succession after dam removal on the Elwha River, Washington

In this study of naturally assembling plant communities after the largest dam removal thus far in the United States, I took advantage of the staged drawdown of the water (and consequent different timings of exposure of the previously inundated soil) as a natural experiment on the effects of temporal contingencies on revegetation. I found that spatial and temporal factors influenced initial community composition of both species and functional traits, and that communities shifted directionally but diverged through time in species composition as well as functional trait composition.