COS 237-1 - Synergistic impacts of wildfire and forest fragmentation on tree mortality

Thursday, August 18, 2022

10:00 AM – 10:15 AM EDT

Location: 516B

Presenting Author(s)

AS

Anna I. Spiers, n/a

Ph.D. student
University of Colorado Boulder
Boulder, CO, United States

Coauthor(s)

BM

Brett A. Melbourne, PhD

Associate Professor
University of Colorado Boulder
Boulder, Colorado, United States
KD

Kendi Davies, PhD

Associate Professor
University of Colorado Boulder, United States

Background/Question/Methods

Understanding how interacting disturbances impact biodiversity is critical in a warming climate. Historically, habitat loss and fragmentation have been the largest causes of biodiversity loss, but forest fires are growing larger and more intense due to fire suppression and extreme climate impacts. Despite the anthropogenic escalation of habitat fragmentation and wildfire, we know little about their synergistic impacts on biodiversity. We document the response of a Eucalyptus forest community following a wildfire in an experimentally fragmented forest.

The area burned in the Australian 2019-20 bushfires was the largest in a single season globally. This area included the Wog Wog Habitat Fragmentation Experiment in southeastern Australia where native Eucalyptus forest was fragmented in 1987, when an exotic pine plantation was established. We combine unoccupied aerial system (UAS) imagery taken before and after the fire at Wog Wog, historical tree surveys, and field assessments of fire impacts to identify burn intensity (scorch height) and severity (tree mortality) across the experiment within a year following the fire. We assess the role of the following in driving intensity and severity: abiotic (e.g., slope, hydrology), biotic (e.g., tree density), individual traits (e.g. species, size), and fragmentation (e.g., fragmentation, edge effects).

Results/Conclusions

Our findings contribute to understanding the synergistic impacts of habitat fragmentation and wildfire on tree communities. The fine spatial resolution (3 cm) of the UAS imagery enabled us to measure fire intensity (i.e., scorch height up tree trunks) and severity (i.e., Eucalyptus tree mortality) for >2,000 trees across the experiment. We found that fire intensity and severity were greater in experimentally fragmented plots compared to continuous Eucalyptus forest controls. A surprising result was higher burn intensity and severity at the center of experimental fragments compared to fragment edges. This result went against our hypothesis that proximity to an exotic pine plantation matrix would lead to higher burn intensity and severity. Satellite imagery suggested that fragment cores were drier than edges before the fire, potentially explaining this result. This study provides a unique case study of how anthropogenic disturbances interact to affect community biodiversity and establishes a baseline for comparison for continued monitoring of ecosystem recovery.