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Post-fire tree regeneration in an altered disturbance regime: community dynamics and interactions with land management

  • Author(s): Tubbesing, Carmen Loretta
  • Advisor(s): Battles, John J
  • Stephens, Scott L
  • et al.
Abstract

Fire has long shaped forests across the globe. Anthropogenic forces are reshaping fire regimes, leading to unprecedented forest conditions and unknown long-term consequences. Land management can help mitigate undesired effects of altered fire regimes, but effective management requires information about tree species’ responses to disturbances both historical and modern. In my dissertation, I add to a body of literature examining how novel fire patterns affect tree regeneration and whether forest management strategies can mitigate any undesired effects. I focus on mixed-conifer forests of the Sierra Nevada, where logging, fire exclusion, and climate change have shifted the fire regime from frequent, heterogenous fire to infrequent fire with greater high severity. The tree species that have long comprised these forests are not well adapted to regenerate in large, homogenous fire patches. My dissertation investigates three main questions in three chapters: 1) Can forest management prevent large fire patches and promote post-fire recovery? 2) Will the novel fire regime shift overall species composition toward firs and away from pines? 3) What is the role of post-fire shrub dynamics in determining ecological succession in novel-type fire patches? In Chapter 1, I show that strategically placed fuel reduction treatments effectively reduced fire severity and promoted recovery when burned in a wildfire. In Chapter 2, I explore the idea that the shifting fire regime may lead to regional fir enrichment. I focus on plant interactions following severe wildfire and show that shrub competition affects ponderosa pine more strongly than it affects white fir. However, simulation modeling results in Chapter 3 show that, on net, shrub neighborhood dynamics do not produce an ecological filter favoring firs, though patterns are sensitive to shrub species. These three chapters together illustrate the importance of forest patch dynamics for wildfire resistance and recovery.

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