Population dynamics of giant kelp
Forests of giant kelp make up an incredibly diverse and productive underwater ecosystem. My research seeks to determine the most important environmental drivers of giant kelp dynamics and understand how the roles of these drivers change in space and time. I am also examining how variability in kelp abundance impacts the multitude of algae, invertebrates, fish, and marine mammals that inhabit kelp forests. This insight will be critical for predicting the response of kelp ecosystems to changes in climate.
As part of this work I have used satellite imagery to map changes in kelp abundance along the coasts of California and Baja California, Mexico over the past 30 years. Here is a time series of kelp canopy changes off the coast of Goleta, CA from 1984 to 2011:
Metapopulation dynamics and giant kelp genetic diversity
Giant kelp forests are found in discrete patches along many coastlines. This patchiness causes kelp forests to act as what is called a metapopulation, a group of relatively independent subpopulations that are moderately connected to each other through dispersal processes. I investigate how the connectedness of these subpopulations effects how often they go extinct, how long they stay extinct, and how readily they recolonize once they have gone extinct. As part of this project I am examining how kelp genetic diversity changes in space and how much inbreeding occurs in patches as a function of their isolation from other patches. I am interested in understanding if inbreeding depression shortens the lifespan of small, isolated patches.
Mangrove forests and climate change
Over the past few years there have been local scale observations and anecdotal evidence of mangroves migrating pole-ward into salt marsh habitat. Numerous hypotheses have been proposed to explain this phenomenon, however testing these hypotheses has been challenging, because it is difficult to observe these transitions on large scales, and multiple drivers may be responsible. I am currently using field surveys, aerial and satellite imagery, climate data, and land-use data to characterize the dynamics of mangrove abundance on local, continental, and global scales and test hypotheses that relate this expansion to climate and land-use change.
While mangroves are expanding poleward in some parts of the world, these forests face a number of other local- and regional-scale threats such that the net change in global mangrove area may be negative in the near term. Coastal development, aquaculture, and timber production are driving mangrove deforestation losses of 1 to 2% per year. In addition, some impacts of climate change on mangroves are expected to cause reductions in mangrove area. I am also using satellite imagery to track the patterns of this deforestation.
Biodiversity and ecosystem functioning in tropical forests
Many experimental studies have demonstrated positive relationships between biodiversity and ecosystem functioning. However, there has been intense debate over the generality of these relationships in natural systems and the mechanisms that create them. While some argue that mechanisms such as niche complementarity increase ecosystem function, others argue that there is simply an increased probability of encountering a highly productive, dominant species in diverse assemblages (i.e. the sampling effect). Efforts to analyze diversity in natural systems on global scales have been hampered by differences in methods among study sites. I have used data from the Tropical Ecology Assessment and Monitoring Network (TEAM), a global tropical forest biodiversity-monitoring network, to better understand the relationship between biodiversity and aboveground C storage in tropical forests at global scales.