Research

My research program is highly interdisciplinary and bridges diverse aspects of environmental science, largely from an ecosystems perspective. Much of my work lies within the mission of unraveling competing and interrelated processes in water-limited ecosystems within the grassland-forest continuum, gradients of woody plant coverage that include shrublands, savannas, and woodlands, as well as grasslands and forests. I am interested in interactions between woody and herbaceous plants and the associated patterns of canopy patches of woody plants and the intercanopy patches that separate them. I have focused on coupled and interrelated processes between ecology and hydrology (the emerging interdisciplinary area of ecohydrology), carbon and water, runoff and runon, evaporation and transpiration, and water and wind erosion. I am also interested in rapid vegetation changes associated with fire and drought and the subsequent hydrological responses. I strive to enable improved decision making and management regarding issues of land use, pollution, and global change.

How can the water budget be evaluated in a more ecologically meaningful way to better determine vegetation dynamics?
How does soil water content vary horizontally under vs. between woody plants, as well as with depth, and how does this variation affect different plant functional types (grasses, shrubs, trees)?
How does the redistribution of water by runoff and runon affect vegetation patterns and dynamics?
How is evaporation vs. transpiration partitioned in various ecosystems and what affects this partitioning?
How can we predict when drought will cause large-scale tree die-off, as has recently occurred across the southwestern USA?
How large is wind erosion relative to water erosion and how does it change following disturbance (e.g., fire, drought)?

(Click thumbnails images to link to Current Research Questions)

Almost all of my research has been conducted with close collaborators. With them, I developed a research program and facility focusing on the interface between ecology and hydrology for which I was recognized with a Los Alamos award for leadership and mentoring in 2004. Working with Craig Allen, I published a paper in the Proceedings of the National Academy of Sciences USA on rapid landscape-scale tree mortality following the regional 1950s drought, which was discussed in the context of potential climate change impacts. Collaborative research on scale-dependencies in runoff and erosion led to development of a conceptual model for erosion thresholds that is being used to guide rangeland monitoring. Recently, my collaborators and I developed a new conceptual framework that led to field-based estimates of relative rates of wind vs. water erosion and transport in semiarid ecosystems. For this work, published in Earth Surface Processes and Landforms, we were awarded the Wiley Prize for best paper of 2003 by the British Geomorphological Research Group. At Los Alamos, collaborative research led to development of a new method for measuring soil carbon based on laser-induced breakdown spectroscopy (LIBS) that allows rapid and high-resolution measurement of soil carbon in the field. Much of my research has focused on piñon-juniper woodlands, including the regional-scale dieoff of piñon in response to the current drought which I highlighted at a recent workshop by the National Academy of Sciences.