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Biogeochemistry of beetle-killed forests: Explaining a weak nitrate response

Rhoades, Charles C.; McCutchan, James H., Jr.; Cooper, Leigh A.; Clow, David; Detmer, Thomas M.; Briggs, Jennifer S.; Stednick, John D.; Veblen, Thomas T.; Ertz, Rachel M.; Likensh, Gene E.; Lewis, William M., Jr. 2013. Biogeochemistry of beetle-killed forests: Explaining a weak nitrate response. PNAS. 110(5): 1756-1760.

doi: 10.1073/pnas.1221029110

A current pine beetle infestation has caused extensive mortality of lodgepole pine (Pinus contorta) in forests of Colorado and Wyoming; it is part of an unprecedented multispecies beetle outbreak extending from Mexico to Canada. In United States and European watersheds, where atmospheric deposition of inorganic N is moderate to low (<10 kg·ha·y), disturbance of forests by timber harvest or violent storms causes an increase in stream nitrate concentration that typically is close to 400% of predisturbance concentrations. In contrast, no significant increase in streamwater nitrate concentrations has occurred following extensive tree mortality caused by the mountain pine beetle in Colorado. A model of nitrate release from Colorado watersheds calibrated with field data indicates that stimulation of nitrate uptake by vegetation components unaffected by beetles accounts for significant nitrate retention in beetle-infested watersheds. The combination of low atmospheric N deposition (<10 kg·ha·y), tree mortality spread over multiple years, and high compensatory capacity associated with undisturbed residual vegetation and soils explains the ability of these beetle-infested watersheds to retain nitrate despite catastrophic mortality of the dominant canopy tree species.

Keywords: nitrogen biogeochemistry, streamwater chemistry, nitrate loss, watershed disturbance

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Title: RMRS Other Publications: Biogeochemistry of beetle-killed forests: Explaining a weak nitrate response
Electronic Publish Date: January 30, 2013
Last Update:
January 30, 2013

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