Characterization of Masticated Fuelbeds and Fuel Treatment Effectiveness in Southeastern US Pine Ecosystems

I. Abstract Mechanical fuels treatments are being widely used in fire prone ecosystems where fuel loading poses a hazard, yet little research examining fuel dynamics, fire behavior, and ecological effects exists, especially in the southeastern US. In order to broaden our understanding of these treatments, effects of mechanical mastication ("mowing") were examined in a common pine ecosystem of the southeastern US Coastal Plain, where the post-mastication fuel environment is unique among ecosystems where mastication is being employed. Foliar litter dominates surface fuels after understory mastication in palmetto/gallberry pine flatwoods, however rapid recovery of shrubs quickly regains control over fire behavior. Treatments were effective at reducing flame heights during post-treatment prescribed burning in these sites, however compact surface fuels were observed to cause long-duration heating during laboratory burning. Overstory tree mortality observed following summer burning in mowed treatments may have resulted from combustion of the compact surface fuels beneath the shrub layer. Although temperature and humidity at the shrub level were minimally impacted, drier surface fuels existed in masticated sites where shrub cover was reduced, potentially exacerbating combustibility of the surface fuel layer. Treatments had little impact on understory vegetation communities or soil nutrients, however, observed reduction in saw palmetto may alter future groundcover, as slight increases in grass cover were observed. The fast recovery of understory vegetation and generally low impact to ecosystem attributes suggest resiliency of these pine flatwoods following mechanical treatments. However, their effectiveness at reducing fire hazard is likely short-lived. Treatment regimes that utilize prescribed burning to reduce post-mastication fuels will require special attention to treatment timing in order to ensure surface litter consumption, while minimizing potential impacts to the overstory. II. Background and Purpose Fire is a dominant ecological process in many ecosystems worldwide, however maintaining natural fire regimes through active management is often difficult. Ecosystems vary in frequency, intensity, extent, and predictability of their historical fire regime (Agee 1993). While some ecosystems may go several decades or even centuries without fire, some have evolved under frequent and relatively low intensity fire regimes. Infrequently burned ecosystems will often burn with high intensity fire behavior that results in substantial alterations of ecosystem structure and composition due to years of fuel buildup. Fuel accumulation may occur in the tree canopy stratum, the understory and midstory vegetation, and as downed woody and foliar debris. When high intensity fire burns in such an ecosystem, it may take decades or centuries …