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CC BY V4.0, Open Access
Thesis
DENDROECOLOGICAL ASSESSMENT AND NICHE MODELING OF A RARE CONIFER SPECIES, PSEUDOTSUGA MACROCARPA, IN LOS PADRES NATIONAL FOREST, CALIFORNIA
Washington State University
Master of Science (MS), Washington State University
01/2021
DOI:
https://doi.org/10.7273/000001859
Handle:
https://hdl.handle.net/2376/120838
Abstract
Widespread forest dieback, often driven by unprecedented wildfires and droughts of the past century, presently impacts all forested continents worldwide. Locally endemic, narrow-ranged tree species suffer disproportionate mortality from drought and wildfire and may be especially at-risk for climate-induced extinction. Pseudotsuga macrocarpa (bigcone Douglas-fir), a conifer species endemic to the Transverse and Peninsular Ranges of southern California chaparral, occupies a narrow range and may be particularly vulnerable to climate-induced extirpation. The 2017/18 Thomas Fire and 2007 Zaca Fire significantly reduced populations at the leading edge of the range in Los Padres National Forest (LPNF). Restoration plans are currently underway yet remain challenged by the effects of the 2011-2016 multiyear drought (MYD). As forests experience progressively warmer and drier conditions, effective and adaptive forest management of P. macrocarpa will require a thorough understanding of how growth and mortality patterns are affected by climate and wildfire including the ecologically-relevant variables that control habitat suitability and distribution. We present the results of two studies: (1) a dendroecological assessment relating 20th and 21st century annual ring width of interior and coastal P. macrocarpa populations to periodic climate oscillations and (2) a habitat niche modeling approach to identify contemporary and future climate change refugia. Regional warming and drying due to climate change and enhanced by longer interdecadal periods of drought and multidecadal variation resulting from the Pacific Decadal Oscillation (PDO), are the most likely climatic drivers of recent P. macrocarpa decline in LPNF. Interior and coastal P. macrocarpa populations responded differently to climate overall, yet began exhibiting similar signs of distress after the 1976-1977 PDO switch. As such, our evidence suggests the MYD likely restricted growth recovery in the perimeter of the 2007 Zaca Fire and primed mortality in the perimeter of the 2017/18 Thomas Fire. Contemporary and future refugia models suggest that P. macrocarpa restoration in LPNF should prioritize low elevation and coastal sites with consistent moisture availability and temperature regimes. Furthermore, conservation of mature, reproductive age populations may be crucial for passive restoration plans in an otherwise fire- and drought-prone landscape.
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- Title
- DENDROECOLOGICAL ASSESSMENT AND NICHE MODELING OF A RARE CONIFER SPECIES, PSEUDOTSUGA MACROCARPA, IN LOS PADRES NATIONAL FOREST, CALIFORNIA
- Creators
- Michelle Devon Wolfgang
- Contributors
- Kevan Moffett (Advisor)Aaron Ramirez (Committee Member)Mark Swanson (Committee Member)Deepti Singh (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Environment, School of the (CAHNRS)
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University
- Number of pages
- 106
- Identifiers
- 99900606550501842
- Language
- English
- Resource Type
- Thesis