Biodiversity and global change

Research in the Clark lab focuses on biodiversity of forests, including how species coexist and how they are influenced by changing climate and natural and human disturbance.  Studies range in scale from field plots to continental data sets.  Large, long-term experiments are central to the approach.  There is emphasis on modeling innovation to synthesize evidence from many sources.

Summaries of some current projects are below:

Macrosystem Science: forest dynamics and climate change.  Climate change is rapidly transforming forests over much of the globe in ways that are not anticipated by current science.  Large-scale forest diebacks, apparently linked to interactions involving drought, warm winters, and other species, are becoming alarmingly frequent.  Models of biodiversity and climate have not provided guidance on if/where/when such responses will occur.  By sampling and analysis at the individual scale across continental variation in climate, this study can link the individual scale processes to regional responses.  This collabor
ation involves six institutions.

Pathogens and forest biodiversity experiment.  Fungal pathogens may control biodiversity of forest trees through selective mortality of species that would otherwise threaten less competitive species. Climate warming may increase the amount and severity of disease as these pathogens increasingly survive mild winters, their re
productive rates increase, and plant defenses suffer from drought and temperature stress. We are evaluating the extent to which pathogens regulate tree seedling health, the fungi involved, and their effects on tree growth and survival. We are studying how those interactions are affected by the temperature changes predicted for mid-century.  In a warming experiment where tree seedlings are exposed to soil and air temperature increases of 3°C to 5°C in NC and MA, the study allows us to quantify how temperatures affect their hosts when temperatures increase, depending on the competition they simultaneously experience from other tree species.

Forest warming experiment.  Climate change is restructuring forests of the United States, although the details of this restructuring are currently uncertain. Rising temperatures of 2 to 8°C and associated changes in soil moisture will shift the competitive balance between species that compete for light and water, changing the abilities to produce seed, germinate, grow, and survive. We are using large scale experiments to determine the effects of warming on the most sensitive stage of species distributions, i.e., recruitment, in mixed deciduous forests in southern New England and in the Piedmont region of North Carolina.  We are exposing seedlings to air and soil warming experiments in two eastern deciduous forest sites; one at the Harvard Forest in central Massachusetts, and the other at the Duke Forest in the Piedmont region of North Carolina.