Date of Award

Spring 1-1-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology & Evolutionary Biology

First Advisor

Carol Wessman

Second Advisor

Timothy Seastedt

Third Advisor

Robert Guralnick

Fourth Advisor

Kendi Davies

Fifth Advisor

Thomas Veblen

Abstract

Forest disturbances are inevitable, and recovery from those disturbances (termed resilience) is required for the persistence of forests through time. Extraordinarily severe or compounding multiple disturbances may, however, exceed that resilience and shift the ecosystems into alternate regimes with potentially large implications for ecosystem structure and functioning. A compound disturbance event (wind, logging, and fire) in a Colorado subalpine forest was studied for the impact of the multiple disturbance events on disturbance characteristics, tree regeneration, and carbon stocks, an important ecosystem service provided by many forests. The regeneration was also grown using the Forest Vegetation Simulator to simulate the effects of climate change and various management/regeneration amounts on carbon stocks in the next century. Results indicate that the disturbances did interact in a mechanistic way, producing a novel disturbance with extreme burn times and temperatures. Regeneration was altered by this interaction, with the serotinous species (lodgepole pine) having reduced regeneration, whereas the seed dispersing species were relatively unaffected. Logging prior to the fire reduced this compound effect, supporting the conclusion that the interaction drove the differential regeneration. Carbon was additively affected by the disturbances, with more disturbances resulting in less carbon and charcoal on the plots. Given literature-derived decomposition rates, the interactions may result in a net loss of charcoal on the landscape over the entire fire return interval. Looking forward, carbon stocks recovered in the near-term despite the loss of conifers in many locations due to the influx of aspen. However, in the majority of the climate change scenarios large tree mortality near the end of the century reduced tree cover and carbon stocks. Aggressive planting of local species was not successful in maintaining tree/carbon stocks; only the establishment of non-local, more warm-climate adapted species maintained the forest. Overall, disturbance interactions create novel, interesting situations with implications for forest resilience, and result in an increase in heterogeneity across the landscape. Carbon is also affected by multiple disturbances. But the growing effects of climate change will likely overshadow the impacts of the disturbances and differential recovery in the next century.

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