Assessment of fire behavior and management options in subalpine vegetation on Mauna Kea, Hawai'i

Abstract

Fire is a major threat to habitat for the endangered Palila (Loxioides bailleui) within subalpine vegetation on Mauna Kea volcano, Hawai‘i. The presence of large amounts of fine fuel from grasses, dry climate, and human ignition sources produces a significant risk of wildfire in this area year-round. The purpose of this report is to provide information on fuels and potential fire behavior that will contribute to fire management of Palila habitat. Recommended actions will contribute to the conservation of these native forests and facilitate restoration in degraded areas. To assess the effects of grass invasion on fuel conditions and potential fire danger, we quantified vegetation and fuels across an elevation gradient from grasslands into sub-alpine forests on the west slope of Mauna Kea. Our results indicated that grass cover was reduced under tree canopy in plots below ~2,500 m elevation, but at higher elevations grass cover was higher under trees than in the open. However, tree canopy cover below 2,500 m elevation was not high enough overall (~25% on average) to result in significant reductions in fine fuels at the landscape level. Sampling directly under and away from tree crowns at multiple elevations suggested that below ~2,500 m, the presence of tree canopy cover can reduce grass fuels significantly. Furthermore, moisture content of live surface fuels was increased under tree canopy compared with open areas. These results suggest that restoration of forest cover may have the potential to alter grass fuels in ways that decrease the threat of fire in some subalpine forests. Fire behavior estimates based on fuel data from grasslands, mixed forest and māmane forest indicated the need for fuelbreaks of at least 20-30 m to limit fire spread in most areas. In many cases, breaks as wide as 40 m are required to limit fire spread risk under extreme weather conditions. Based on our fuels data and fire behavior predictions, recommended actions include: (1) construction of new or expansion of existing fuelbreaks to immediately reduce fire risk to the most sensitive areas adjacent to the core Palila population on the southwest slope and the translocated Palila population on the north slope of Mauna Kea, (2) enhancement of forest restoration activities to increase fuel moisture and reduce grass fuel loads (3) installation of water sources (diptanks) in both areas to decrease firefighter response time, and (4) increased public education and awareness with regard to fire danger on Mauna Kea.