Document: GOR-3-68-25

Effects of fire frequency on tree demography and community composition.

MINOR, E.* and G.A.FOX

University of South Florida, Tampa, FL 33620-5150, USA ¹

Abstract:
What are the consequences of fire frequency for tree demography and community composition? We have studied age/stage structure of several species of pines and oaks growing in replicated experimental plots that, over a 20-year period, have been burned every 1, 2, 5, or 7 years, or never burned. The study was conducted in the USF Ecological Research Area, 500 acres of sandhill habitat. Sandhill communities occur on well-drained, sandy soil dominated by longleaf pine (Pinus palustris) and deciduous oaks (Quercus spp.), and are naturally maintained by frequent, low-intensity fires. In each plot, we sampled over 1000 m² and measured and identified all woody plants >0.5m. For all species, contingency table analysis showed a substantial difference in size structure among the plots. In the one and two-year burn plots, the smallest and largest size classes were most abundant, with very few intermediate-sized individuals present. In the five- and seven-year plots, size distributions were more "even" in the sense that all size classes were relatively abundant. In the unburned plots, most pines and oaks were large adults and very few seedlings were found. This pattern has different causes in different species. P. palustris seeds germinate well in the 1 and 2 year plots but the young plants, while fire-resistant, do not grow and survive well when subjected to very frequent burns. There are abundant small Q. laevis in the frequent burns, on the other hand, because of regrowth from roots. Our data also allowed us to study changes in community composition with fire frequency. As expected, more frequent fires resulted in open stands of longleaf pine overstory, turkey oak undergrowth, and few other large woody plants. Species richness of both pines and oaks increased with reduced fire frequency. The absence of fire resulted in hardwood-dominated stands. These results suggest that maintenance and restoration of longleaf pine forests in the Southeastern US may depend on maintaining a periodicity of fire that is frequent but less than every year or two.

Keywords: Fire, pine, oak, population structure, stand composition, demography

This abstract is being presented at: 10:30 AM in session:
Poster Session #12: Disturbance Ecology.