Rocky Mountain Research Station

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

Author: Rhoades, Charles C.; McCutchan, James H.; 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.

Date: 2013

Source: PNAS. 110(5): 1756-1760.

Description: 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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Citation

Rhoades, Charles C.; McCutchan, James H.; 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.  2013.  Biogeochemistry of beetle-killed forests: Explaining a weak nitrate response.   PNAS. 110(5): 1756-1760..