The first European settlers in what is now the southeastern United States were confronted with an upland forest that was dominated by longleaf pine (Pinus palustris Mill.). The pre-historical fire regime, both lightning and Native American-ignition, in the longleaf pine ecosystem was characterized by frequent burning, producing fire of low-moderate intensity. These fires were usually non-lethal to the dominant vegetation and maintained the forest structure of a herbaceous understory with scattered shrubs and an open-canopy. These fire-maintained forest ecosystems were essentially two-layered, consisting of a high canopy dominated by mature longleaf pine and an understory of grasses and herbs. While much is known about the longleaf pine overstory, less is known about the understory which develops under different overstory densities. In the early 1970's, a study was initiated in south Alabama, USA to examine the understory that develops with a dormant, spring, summer, and no burn treatment under overstory densities of 4.1, 6.1, 8.2, and 10.3 square meters per hectare.

Results/Conclusions

Results after three growing seasons with two biennial growing season burns revealed the grass and legume production was significantly greater under longleaf pine overstories of 5.5 and 7.3 square meters per hectare than heavier densities. Summer burning improved grass production while spring burning increased legume weight. Forb production improved more following burning than under unburned conditions. Overstory density did not significantly affect woody understory basal area, weight, or number of stems. Burning significantly reduced basal area and weight but did not affect number of stems. Stocking of longleaf pine seedlings was not significantly affected by treatment or treatment interaction, although spring burning apparently eradicated 1-year-old seedlings established following a heavy seed crop between the first and second burns. Control of the woody understory by spring burns followed by periodic dormant season maintenance burns would enhance longleaf pine regeneration potential without the need for expensive site preparation.