Improved wildfire management in Megathyrsus maximus dominated ecosystems in Hawaiʻi

Abstract

Wildfire management in Hawaii is complicated by the synergistic influences of nonnative invasive grasses and increased human ignitions. The frequent, high severity fires that often result threaten surrounding ecosystems and developed areas. The overarching goal of this research was to improve wildfire management in guinea grass (Megathyrsus maximus) dominated ecosystems in Hawaii using in situ fuels data collection, fire behavior modeling, remote sensing, and ecological restoration. Specific objectives included: i) quantification of rates of land cover conversion at the grass/forest ecotone from 1950-2011; ii) an accurate assessment of the spatial and temporal variability in guinea grass fuels; iii) use of in situ fuels data to parameterize a custom fuel model for guinea grass dominated ecosystems; iv) use of MODIS-based vegetation index data to accurately predict real-time fuel moisture content; and v) assessment of whether native species restoration can simultaneously compete with guinea grass and decrease fire potential. The results of this research provide tools to better predict and manage wildfire. The historical analysis showed that type conversion associated with grass invasion and subsequent fire occurred widely prior to active fire management, and that predicted rates of fire spread are 3-5 times higher in grasslands than in forests. Guinea grass total fine fuel loads ranged widely, from 3.26 to 34.29 Mg ha-1, highlighting the importance of real-time, site-specific data for fire management. Field data were used to parameterize a custom fuels model, which better predicted fire behavior than national standard or previous custom fuel models for guinea grass. MODIS-based models better predicted live fuel moisture (R2=0.46) than the currently used National Fire Danger Rating System (R2=0.37) , providing managers with an improved method for assessing this critical component of fire behavior. Native outplant survival averaged 51% twenty-seven months after planting, and outplant treatments successfully suppressed guinea grass (P<0.001). Predicted fire behavior in outplant and untreated control plots, however, did not differ, likely due to the low moisture content of D. viscosa which dominated the restoration trails. Together, this research provides the foundation for improved fire management in guinea grass ecosystems in Hawaii, and can inform similar work throughout the tropics.