Dr. Jonathan O. (Josh) Sharp
Director, Hydrologic Science and Engineering Program
Associate Professor, Civil and Environmental Engineering
Colorado School of Mines
Bark beetle induced tree mortality has resulted in visually stunning and unprecedented swaths of dead trees throughout mountainous regions globally. Exacerbated by a changing climate, this large-scale ecosystem disruption has implications for forest health, fire, climatic feedbacks, and water resources - including water quality. Notably, shifts in the form of dissolved organic carbon export can lead to increased formation of carcinogenic disinfection byproducts during water treatment. While the magnitude of this response is varied, we have established correlations to the percentage of trees impacted within a giving watershed. In exploring this association and underlying biogeochemical shifts, we adopted an interdisciplinary approach combining terrestrial microbiology, hydrology, and geochemistry at the tree scale. A mitigating effect was discerned in Rocky Mountain forests where a sufficient density of actively respiring trees scavenged the release of inorganic nitrogen from proximal bark beetle-impacted trees. The terrestrial microbial community under beetle-impacted trees mirrored this trend suggesting a threshold value of tree mortality where ecosystem buffering was surpassed. Collectively, our research has implications for forest recovery in this nitrogen-limited montane ecosystem and could aid in the prediction of and preparation for water resource challenges.
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