The post-fire environment: understory plant recovery following high-severity fire and plant trait responses to increased soil temperature in a ponderosa pine ecosystem

Goodrich, Heidi Kristen (2023) The post-fire environment: understory plant recovery following high-severity fire and plant trait responses to increased soil temperature in a ponderosa pine ecosystem. Masters thesis, Northern Arizona University.

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Abstract

The ponderosa pine forests of the Southwest have experienced dramatic changes since Euroamerican settlement which has led to stands with a closed overstory canopy with few fragmented grass openings intermixed. Long periods of drought combined with overly dense forests have increased the frequency of high-severity, stand replacing fires in forests that are historically adapted to high frequency, low-severity wildfires. Under climate change and the Southwest's changing precipitation pattern, it is anticipated that high-severity wildfires and dry fuel loads will continue to occur at increasing rates. In order to prepare these ecosystems for future change and predict changes in biodiversity, it is imperative to understand how the understory plant community of ponderosa pine ecosystems is altered following a severe wildfire, and how plants respond to an increasingly stressful post-fire environment. We monitored vegetation in understory communities impacted by high-severity fire in 2019 to ask: 1) How does high-severity fire change the proportion of plant functional groups and native/nonnative species in the understory of ponderosa pine ecosystems? 2) Following high-severity fire, do Festuca arizonica, Muhlenbergia virescens, and Ceanothus fendleri occur in different microhabitats? 3) How do the plant communities immediately surrounding F. arizonica, M. virescens, and C. fendleri in the high-severity burn area differ? and 4) How does soil temperature affect trait expressions of F. arizonica, M. virescens, and C. fendleri? Monitoring of plant cover and composition for three years following the Museum Fire determined that high-severity fire promoted an increase in nonnative forb cover, and a decrease in perennial graminoid cover compared to low-severity and unburned patches of forest. Species cover in neighborhoods immediately surrounding three species in the high-severity burn area revealed higher biodiversity near the dominant C4 grass, M. virescens, and a decrease in biodiversity near the C3 grass, F. arizonica. Evenness and Shannon index values were highest near F. arizonica. Increasing soil temperature decreases neighborhood richness for all species, indicating that increased environmental stresses can decrease understory biodiversity. C. fendleri and F. arizonica responded to increasing soil temperatures with opposite leaf dry matter content (LDMC) strategies. This suggests that under increasing temperature stress, some species increase LDMC to be resource conservative, and others can decrease LDMC suggesting they have not hit a temperature stress threshold that is limiting growth rate. Under projected climate change scenarios and following high-severity fire, we may see a decrease in understory biodiversity that needs active management for recovery.

Item Type:	Thesis (Masters)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	plant traits; ponderosa pine; post-fire; understory; high-intensity fire
Subjects:	S Agriculture > SD Forestry
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > School of Earth Sciences and Environmental Sustainability
Date Deposited:	02 May 2025 21:34
Last Modified:	02 May 2025 21:34
URI:	https://openknowledge.nau.edu/id/eprint/6118

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