Biology ETDs

Publication Date

Fall 12-16-2023

Abstract

The ongoing warming associated with climate change is increasing the flammability of southwestern US dry forests. As larger fractions of the landscape are impacted by high-severity fire, the potential exists for forests to convert to non-forest. Given that the forested area in the southwestern US is an important contributor of ecosystem services, quantifying limitations to vegetation establishment is critical to informing post-fire recovery efforts and understanding how ongoing climate change will limit seedling establishment in the future. To that end, this dissertation focuses on post-fire vegetation recovery of southwestern forests. First, I report on the influence of precipitation and topography on post-fire vegetation recovery following high-severity fires between 1986 and 2017. To determine whether the effects of year-of-fire effects persisted through the five years post-fire, we modeled relationships between post-fire vegetation and predictors using Random Forest models, finding that in years four and five post-fire, greenness decreased where year-of-fire precipitation total was greater than 400mm while soil erodibility factor above approximately 0.15 reduced greenness in years one and two. However, year-of-fire effects were small relative to growing season climate, suggesting that while initial conditions could predispose a burned area to different vegetation trajectories, the effects of climate may offset them. Second, I examined the effects of two different shrub species common to post-fire forests in northern New Mexico on planted tree seedling survival. Seedlings planted under Gambel oak had survival rates 10% to 35% greater than those planted under New Mexico locust and higher light availability beneath New Mexico locust corresponded to higher temperatures, lower humidity, and higher vapor pressure deficit, impacting the mortality of planted tree seedlings. Finally, I conducted a growth chamber experiment to address how the physiological limits to heat and drought of southwestern US conifer species may impact post-fire conifer establishment under projected climate. We found that the more mesic conifer species were more susceptible to the effects of hot and dry periods, but their existing ranges are not projected to experience the conditions we tested as early in the 21st century as the more xeric species, leading to lower percentages of their existing ranges predicted to experience seedling-killing conditions. Together, these results indicate that the sensitivity of vegetation to post-fire conditions has created the potential for large scale disturbance-mediated ecosystem conversion, but that the post-fire environment has opportunities to buffer microclimate and increase post-fire planting success in the southwestern United States.

Project Sponsors

United States Department of Agriculture National Institute of Food and Agriculture Interagency Carbon Cycle Science program (Grant No. 2017-67004-26486/ project accession no. 1012226 ); United States Department of Agriculture National Institute of Food and Agriculture Agriculture and Food Research Initiative program (Grant No. 2021-67034-35106/project accession no. 1026366; Joint Fire Science Program (Project JFSP 16-1-05-8, JFSP 20-1-01-9); New Mexico Space Grant Consortium.

Language

English

Keywords

Fire, Climate, Southwestern United States, Conifers, Seedlings, post-fire vegetation

Document Type

Dissertation

Degree Name

Biology

Level of Degree

Doctoral

Department Name

UNM Biology Department

First Committee Member (Chair)

Matthew Hurteau

Second Committee Member

Scott Collins

Third Committee Member

Marcy Litvak

Fourth Committee Member

William Pockman

Fifth Committee Member

Leroy Westerling

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Available for download on Tuesday, December 16, 2025

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