Alteration of natural disturbance regimes contributes to anthropogenic disruption of native ecosystems. Fire, once common in numerous ecological communities, has been eliminated across much of the modern landscape. Even when conservation efforts promote prescribed burns it is unclear if ecological needs are being met in the long-term. This is due in part to the challenge of assessing effects over many years. Recently-developed models suggest that large areas of the US once burned multiple times a decade, in some areas more frequently than every 2 years (on average). A once-dominate savanna habitat often dominated by longleaf pine (Pinus palustris) is fire-dependent. Short-term studies support this but often fail to provide insight into the details of effects of moderately different fire regimes, especially what return-interval and/or season of burn is most ecologically useful. Longleaf savanna vegetation is usually dominated by long-lived perennials, including native, often clonal hardwood species. Many species increase in dominance with ineffective burning, slowly decrease light at the ground level, and degrade native habitat structure. This naturally open habitat supports >15 vertebrate species of conservation concern. We report on results from a long-term fire-effects project that demonstrates need for prescribed fire regimes that differ from those often employed.
Study plots reside at Escambia Experimental Forest (USDA Forest Service). During 1984, data were collected on hardwood stems >2.5cm diameter at breast height (DBH) on plots in three blocks. In 1985 all plots were burned using pre-assigned winter or spring fires. Within block and season of burn, plots were assigned fire return intervals of 2, 3, or 5 years. Assessment continues every 3-5 years; reported data covers 1984-2009. Spring burns had significant influence on decreasing hardwood stem density (p= 0.02) compared to only moderate effects generated by shorter fire return interval (p=0.07). Hardwood DBH was also significantly affected by season of burning but there was no difference related to frequency. Historically, regional focus for prescribed fire was to use fire regimes that consumed accumulated hazard fuel rather than those that promoted ecological values. Public land-management agencies push to burn more frequently. However shifting to growing-season burns is logistically challenging and often used on an irregular basis. This long-term study supports the position that to compensate for anthropogenic disruption incorporating aspects of natural fire regimes may be critical for conservation. It also supports the need to focus effects of natural fire regimes rather than simply attempting to recreate the regime itself.