Research

I am a forest ecologist investigating how disturbance and decomposition shape forest ecosystems in the context of global change. My research combines extensive field work, remote sensing, and genomic techniques with modern quantitative tools to investigate the mechanisms regulating forest ecosystems. My approach is to develop a conceptual and mathematical understanding of local processes, and then use big data (e.g., satellite sensors, plot networks, etc) to determine how these processes influence ecosystems at regional to global scales. My work revolves around three fundamental questions.

How do trees die?

Forests play dominant roles in global biodiversity and carbon cycling. Consequently, the local disturbances that regulate forest dynamics – particularly via tree death – have global implications. Although we know what can kill trees, the relative importance of factors that do kill trees is largely unknown. Much of my current and forthcoming research investigates how lightning, pathogens, and drought interact to cause tree death.

Most of my past work on this topic has focused on the direct (i.e., non-fire) effects of lightning in tropical forests. In a collaboration with ecologist Steve Yanoviak and atmospheric physicists Phillip Bitzer and Jeff Burchfield, we have been locating lightning strikes in near real-time throughout a lowland forest in Panama. This work revealed that lightning strikes in this forest typically cause cryptic group tree damage and death events, and initiate interactions with other agents of tree death.  As an Earl S. Tupper Fellow at the Smithsonian Tropical Research Institute, I am now starting an independent research project investigating the physiological and electromagnetic processes by which lightning damages trees and facilitates interactions with other agents of tree death.  Please see the available positions page for information about an opening for a paid internship on this project.

IMG_0221

Pictured are a large group of trees directly killed by lightning in Peru.  Locations where electric current jumped between branches in the canopy are noticeable between the branches in adjacent tree crowns.

Distant lightning strike

This image of a lightning strike was captured by our lightning triangulation system.  We combine images like this from multiple cameras to triangulate lightning strikes and quantify their ecological effects.

How do disturbances shape forest communities and Ecosystems?

After developing an understanding of local disturbances, I use my quantitative toolkit to scale these findings up to landscape and global processes.  In our work with lightning, I combined descriptions of individual lightning disturbances with decades of forest dynamics data and remotely sensed estimates of lightning frequency to calculate the contributions of lightning to total tree mortality.  Using this approach, we showed that lightning was the primary cause of large tree mortality in central Panama.  Stay tuned for my upcoming work quantifying the pantropical geography of lightning caused disturbance and its implications for tropical forest ecosystems.

How does dead wood decompose and contribute to carbon cycling?

Tropical forests are disproportionately important to the global carbon cycle and the vast majority of aboveground carbon is stored in woody tissues.  This carbon is released as dead wood decomposes, yet the process of wood decomposition is poorly studied in tropical forests.  I am investigating the distribution and decomposition of dead wood in tropical forests.   The current stage of this work uses forest plots to understand wood decomposition at large scales and over long time frames.  If you are interested in this work, then please see the available positions page for details about an opening for a paid internship on this project.

I use a variety of approaches to study dead wood dynamics in tropical forests.  In a collaboration with Emma Sayer, Ed Tanner, and Ben Turner, we used a long-term litter removal and addition experiment to determine how soil nutrient availability affects decomposition over a 15 year period.  Separately, I worked with Helene Muller-Landau to quantify the stocks, fluxes, and spatiotemporal variability of dead wood on Barro Colorado Island in Panama.  We found that ca. 50% of wood necromass is separated from the soil, yet we know almost nothing about decomposition above the forest floor.  To address this knowledge gap, I am investigating how decomposition rates change vertically and how these changes are associated with environmental factors (microclimate and nutrient availability) and microbial communities (bacteria, archaea, and fungi).  The next stage of this work is taking an ambitious approach to quantifying long-term and large-scale patterns of decomposition.