Mountain pine beetle (Dendroctonus ponderosae) outbreaks in North America are currently widespread and have potentially large scale and persistent impacts on forest albedo and evapotranspiration. Despite this, few studies have examined the impact of these outbreaks on surface energy and water fluxes. For my dissertation I utilized multiple datasets for 1) bark beetle outbreak locations, including aerial surveys, tree plots, and dendroecological plots, and 2) remotely sensed indices of vegetation and fluxes, including MODIS products, product inputs and Landsat albedo. We found that mountain pine beetle outbreaks in Colorado and southern Wyoming result in persistent and significant increases in winter, spring and annual albedo in lodgepole pine (Pinus contorta) and ponderosa pine ( Pinus ponderosa) stands. The persistent increase in albedo with time since disturbance combined with the continued progression of the attack across the landscape from 1994-2011, resulted in a rapid increase in the per year winter and annual radiative cooling (MW) effect. When the persistence of albedo effects in lodgepole pine stands was quantified, change in annual albedo and radiative forcing peaked at 14-20 years post-outbreak (0.06±0.006 and -0.8±0.1 W m-2, respectively) and recovered to pre-outbreak levels by 30-40 years post-outbreak. Radiative cooling peaked in winter months at 14-20 years post-outbreak at 3.0±0.4 W m-2. Change to winter albedo and radiative forcing also increased with outbreak severity (percent tree mortality). Persistence of albedo effects were seen as a function of severity which influenced the fraction of albedo recovery through expansion of remaining canopy versus regeneration of new trees. Outbreaks were also found to impact the water cycle. Stands initially experienced a reduction in evapotranspiration of 18.7±1.4% which peaked in summer at 14 to 20 years post-outbreak. This reduction was followed by an elevation in evapotranspiration of 21.6±2.2%, relative to non-attacked stands, in intermediate aged stands (30 to 40 years post-outbreak). MODIS evapotranspiration values responded most strongly to disturbance driven changes in vegetation cover, specifically fraction of absorbed photosynthetically active radiation (fPAR) and leaf area index (LAI). Changes to available energy and sensible/latent heat flux distribution could feedback to affect current climate-influenced mountain pine beetle outbreaks.
|Advisor:||Williams, Christopher A.|
|Commitee:||Kulakowski, Dominik, Masek, Jeffrey, Rogan, John|
|School Location:||United States -- Massachusetts|
|Source:||DAI-A 76/01(E), Dissertation Abstracts International|
|Subjects:||Geography, Biochemistry, Remote sensing|
|Keywords:||Albedo, Bark beetles, Climate change, Evapotranspiration, Forests, Rocky mountains|
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