Date of Award:

8-2024

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Committee Chair(s)

Larissa L. Yocom

Committee

Larissa L. Yocom

Committee

Eugene W. Schupp

Committee

James A. Lutz

Abstract

The area burned in high severity fire as well as the proportion of fires burning at high severity have been increasing in southwestern ponderosa pine (Pinus ponderosa) forests since the 1980s. These fires often contain large patches (>100 ha) of 100% tree mortality, which are a concern as they can lead to the establishment of nonnative species and conversion to non-forest vegetation. And, with an increasing amount of fire on the landscape, high severity patches are reburning. However, information on the ecological trajectory of reburns of high-severity patches as well as the utility of remotely sensed burn severity metrics (dNBR) in these reburns is largely unknown. In this thesis I investigate how reburns of high severity patches affect ponderosa pine regeneration and plant community composition, as well as the ecological significance of dNBR in these reburns.

Chapter 1 examines the effects of reburns of high severity patches on ponderosa pine presence and regeneration. Across nine fires in northern Arizona, I found no significant differences in total ponderosa pine regeneration between areas burned once at high severity and those that reburned. This suggests that after high severity fire, at least where seed sources exist nearby, ponderosa pine may be resilient to reburns. However, regeneration was highly variable among fires. Within reburned areas, I found that reburn burn severity (dNBR) had a negative association with post-reburn ponderosa pine regeneration density, suggesting that dNBR is capturing a measure of ecosystem change that affects post-reburn regeneration.

Chapter 2 explores the effects of reburns of high severity patches on plant community composition. Across nine fires and 892 plots, I found that the initial high severity fire defines the ecological trajectory of reburned areas, and reburns generally reinforce changes initiated by the first fire. Additionally, reburns can bolster nonnative species cover, with a small but positive association between nonnative species and higher reburn burn severity.

Collectively, these chapters expand our understanding of how reburns of high severity patches impact ponderosa pine regeneration and plant community composition and the utility of remotely sensed burn severity in these patches.

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