We are interested in the response of terrestrial ecosystems to environmental change, and their role in the Earth’s climate system. This is important because as atmospheric CO2 concentrations increase, and temperature and precipitation patterns are altered across much of Earth, we lack the ability to predict if terrestrial ecosystems will be a source or sink of C to the atmosphere.  Our research focuses on C cycling in plants and soils, with expertise in the application of isotopes as tracers of processes.

Our overarching research question is: what is the fate of C in terrestrial ecosystems? This topic spans temporal scales such as whether newly assimilated C is quickly returned to the atmosphere by plant metabolism or sequestered as soil organic matter for centuries to millennia. This topic also covers spatial scales from the study of microbial processes to plant C allocation to landscape-scale climatic controls on ecosystem function.

We combine field measurements, laboratory work, and computational analyses of large continuous datasets. Currently, there are three major themes in our research:

(1) understanding plant C allocation patterns

(2) linking hydrologic controls and ecosystem C cycling

(3) determining mechanistic controls on belowground CO2 fluxes

A methodological tool that is used in most of our research is the application of stable and radioactive isotopic tracers, especially radiocarbon (14C) measured by accelerator mass spectrometry (AMS). In particular, 14C is a novel and powerful tool to study terrestrial C cycling on timescales of hours to millennia. It can be used to determine the age of C, the mean residence time or turnover of C pools, and it can also be used as a source tracer. We use natural abundance, bomb spike, and tracer levels of 14C in our research.

Our past and some ongoing field sites include the Owens Valley and Santa Cruz Island in California, Kohala on the Big Island of Hawaii, Rocky Mountain Biological Laboratory in Colorado, Harvard Forest in Massachusetts, Bartlett Experimental Forest in the White Mountains of New Hampshire, and Howland Forest in Maine.  We are currently working on establishing field sites in the diverse ecosystems of Northern Arizona.