Fire, wind, and water: Disturbance and ecological forestry in pine grasslands of the Southeastern Coastal Plains

Background/Question/Methods

Longleaf grassland ecosystems have the highest floral species richness recorded in the literature (>50 species m^-2), and that richness is dependent on frequent fire.  They exist across a wide ecological gradient from sandhills to flatwoods and the hydrologic gradient regulates both the structure and function of these woodlands. Longleaf systems also produce high quality wood products, and are favored habitat for game species (e.g. quail). Managing these systems through ecological forestry principles including the incorporation of biological legacies, integration of fire as an intermediate stand development process, and maintaining variable and appropriate recovery times results in maintaining high levels of ecological services (such as conservation of biodiversity) and an outflow of consumptive products (timber). Here I discuss some of the critical legacies, including those associated with overstory patterns, regeneration and fuel heterogeneity. I also present recovery patterns after disturbance.

Results/Conclusions

Frequent fires result in open canopy forests with an understory dominated by graminoids but rich in floral species. The openness allows for sufficient light (more than 30% of full sunlight) to allow advanced regeneration of pine to establish. This source of regeneration provides an insurance against catastrophic disturbance, as well as multiple size cohorts and age classes as it is released over time by both natural disturbance and selective harvesting (greater than 60% of full sunlight). This open canopy structure also provides habitat for the endangered red cockaded woodpecker as long as grass and forb cover exceeds a threshold of 40% or greater, and a midstory that is scattered. The variable overstory regulates small scale heterogeneity in fuels that is significantly related to variation in fire behavior at sub-meter scale (more than 2/3 of the variation in fire temperature can be explained by variation in fine scale fuel patterns). Harvesting gaps with distinct edges, and when they exceed 0.1 ha can result in altered litter and microclimate that disrupt fire continuity and result in state changes (from pine grassland to hardwood domination). Harvesting increases bulk density of soil within skidder paths with little recovery after two years, but has little impact on vegetation after short recovery times. The diversity of this system can be sustained only through management. Frequent fire regimes require that pine litter be distributed uninterrupted in time and space through retaining forest structures perpetually.