Stephanie G. Yelenik
Tara Durboraw
Robert Cox
Nathan S. Gill
Hamilton Natalia
2021
<div class="art-abstract in-tab hypothesis_container">With invasive grasses increasing wildfire occurrence worldwide, a better understanding of the relationships between native plants, fire, and invasive grass is needed to help restoration plans facilitate ecosystem resilience. Invasive grasses are particularly problematic for altering fire regimes in the tropics, yet in Hawaiʻi, restoration sites are often planted with monocultures of the native tree<span> </span><span class="html-italic">Acacia koa,</span><span> </span>which can promote grass growth via nitrogen fixation. This, combined with the difficulty of estimating pre-fire grass cover under thick canopies, complicates attempts to restore Hawaiian ecosystems. We studied the 2018 Keauhou Ranch Fire in Hawaiʻi to investigate three questions: (1) at what level of precision can pre-fire grass cover be accurately estimated from oblique aerial photos? (2) how are post-fire<span> </span><span class="html-italic">A. koa</span><span> </span>regeneration densities affected by fire severity? and (3) how are post-fire<span> </span><span class="html-italic">A. koa</span><span> </span>regeneration densities affected by pre-fire grass cover and its interaction with fire severity? We collected burn severity and post-fire regeneration data from 30 transects stratified across mid-elevation woodland, montane woodland, and montane shrubland communities. We evaluated visual estimates of pre-fire grass cover from oblique aerial imagery with quantitative in situ data from 60 unburned transects of the same cover types. Pre-fire estimates of grass cover categories were 67% accurate in montane woodland (<span class="html-italic">n</span><span> </span>= 9) and 100% accurate in montane shrubland (<span class="html-italic">n</span><span> </span>= 11), but only 20% accurate in mid-elevation woodland (<span class="html-italic">n</span><span> </span>= 10). In montane woodlands with low pre-fire tree densities,<span> </span><span class="html-italic">A. koa</span><span> </span>regeneration densities were higher with increased fire severity, but this trend reversed when pre-fire tree densities were high. We detected no effect of pre-fire grass cover, nor its interaction with fire severity, on<span> </span><span class="html-italic">A. koa</span><span> </span>regeneration density. This indicates that restoration through the planting of<span> </span><span class="html-italic">A. koa</span><span> </span>may be successful in promoting fire-resilient<span> </span><span class="html-italic">A. koa</span><span> </span>forest, although there are potential issues to consider regarding the effects that<span> </span><span class="html-italic">A. koa</span>’s grass promotion may have on other species within the ecosystem.<span> </span></div>
application/pdf
10.3390/land10090962
en
MDPI
Understanding grass invasion, fire severity, and Acacia koa regeneration for forest restoration in Hawaiʻi Volcanoes National Park
article