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Wildfire, invasion, and native plant regeneration in montane forests of Hawaii Volcanoes National Park

Authors: Nathan Gill*, Texas Tech University, Tali Hamilton, Texas Tech University, Stephanie Yelenik, U.S. Geological Survey, Tara Durboraw, Texas Tech University, Jeff Stallman, U.S. Geological Survey
Topics: Biogeography, Mountain Environments
Keywords: disturbance, pyrogeography, biological invasions
Session Type: Paper
Presentation File: No File Uploaded

Introduced grasses can alter fire regimes by increasing the abundance and continuity of fine fuels. In montane forests and shrublands of Hawaii Volcanoes National Park, historical land use practices contributed to widespread invasion of numerous grasses, including Ehrharta stipoides, Holcus lanatus, Andropogon virginicus, and Eragrostis grandis. In 2018, the Keauhou Ranch Fire burned 2,978 acres of montane forest and shrubland, including areas with high and low coverage of these invasive grasses at time of fire. One year after fire, we measured in situ burn severity, ground cover, and regeneration of invasive grasses and native species Dodonaea viscosa, Acacia Koa, Sophora chrysophylla, and Deschampsia nubigena. Pre-fire estimates of grass cover were calculated using oblique aerial photographs taken in 2014. This method for evaluating grass cover was evaluated using 21 calibration sites and 39 validation sites in the surrounding unburned forest and shrubland of the National Park. We compared our burn severity measurements against satellite-derived burn severity across cover types. Finally, relationships between burn severity, pre-fire grass cover estimates, and post-fire regeneration densities and cover of native and invasive plants were assessed in R. Accuracy of estimated grass cover was poor in certain land cover types, especially woodlands with dense canopies. Satellite-derived burn severity could be use to estimate in situ measurements of char height, scorch height, and percent mortality with varying degrees of strength, depending on cover type. Results will be used to inform restoration planting strategies implemented by the National Park Service after wildfire.

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