Fuel loads and potential fire behavior within sub-alpine dry forests on Mauna Kea Volcano, Hawaii

Tropical dry forests are one of the most endangered forest types worldwide.  In Hawaii, dry forest decline has been linked to a number of factors including: land use change, ungulate grazing, invasion of alien plant species and altered fire regimes.  In particular, invasion of alien grasses has the potential to convert native-dominated forests to alien-dominated grasslands by increasing fire frequency, spread and severity.  Subalpine dry forests on the slopes of Mauna Kea Volcano, Hawaii Island, are located at 2000-2800 m and are largely dominated by the native tree mamane (Sophora chrysophylla). These forests are of extremely high conservation value, because they contain the only extant populations of the endangered bird palila (Loxioides bailleui).  The forests are bordered by pastures on lower slopes, have been invaded by alien grasses and are particularly at risk from anthropogenic fires ignited downslope.  To assess the effects of grass invasion on potential fire danger, we quantified fuels along transects running from lower slope pastures into upper elevation forests.  Alien grasses contributed the majority of fine fuels sampled in the study.  The relationship between tree density and fine fuels suggested that increasing native tree cover may help to reduce fine fuel loads in some areas.  Given the limited distribution of native subalpine forest on Mauna Kea and highly endangered status of palila within the forest, developing ways to reduce fine fuels and mitigate fire risk are likely to be a conservation and management priority.