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Department of Atmospheric Science

Seminar: Tues.,  25 March, 1:00pm, CL222 

Observing and diagnosing biological fluxes and canopy mechanisms
with implications for climate change and ecosystem disturbance

David Reed
PhD Defense

University of Wyoming
ATSC/Program In Ecology

Improving our predictions of ecosystem responses is an important challenge in ecological science due to the increasing number of stresses applied to biological systems. The assumption that ecosystems are operating in steady-state conditions is far too simple of a model as ecosystems are an integrated part of the earth system. Anthropogenic and non-anthropogenic forces acting on ecosystems within the earth system are numerous and include broad external factors such as climate change to specific internal factors such as infestations causing disturbance. This research quantifies changes in biogeochemical cycling and increases understanding of the mechanisms that control these cycles with the broad goal of better predictive power of ecosystem responses. Eddy covariance methods were used to quantify carbon, water and energy fluxes at two different field sites in sagebrush ecosystems and one field site in a lodgepole pine ecosystem, in south-east Wyoming and northern Colorado. These measurements were supported with environmental and micrometeorological measurements in order to better understand physical mechanisms and canopy processes that control these biological fluxes. Results from the sagebrush component of this dissertation show how semi-arid sagebrush canopies interact with the lower atmosphere in ways that can alter environmental control of water loss with changing leaf area. This feedback has large implications combined with the large land area of these ecosystems and predictions of a dryer and more variable precipitation regime in the future. At the higher elevation lodgepole pine site, the ecosystem is undergoing a major mortality disturbance due to native bark beetles. Interestingly, even with ~80% mortality of the canopy, few changes are observed to carbon and water cycling, as well as water use efficiency and energy cycling at the ecosystem scale. This calls into question predictions of this disturbance altering the net carbon balance of forests across the North American Rockies from an atmospheric sink to a source. This dissertation shows that these two iconic western ecosystems may be more resilient to stresses than previously predicted. 


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