PS 32-194 - Effects of 25 years of different fire regimes on growth of young longleaf pine trees and encroaching hardwoods

Tuesday, August 9, 2011
Exhibit Hall 3, Austin Convention Center
Sharon M. Hermann, Department of Biological Sciences and Longleaf Pine Stand Dynamics Laboratory, Auburn University, Auburn, AL, John S. Kush, Longleaf Pine Stand Dynamics Laboratory, School of Forestry and Wildlife Sciences, Auburn University, Auburn, AL, William D. Boyer, G.W. Andrews Forestry Sciences Laboratory, USDA Forest Service, Auburn, AL, Rebecca J. Barlow, School of Forestry & Wildlife Sciences, Auburn University, Auburn University, AL and John C. Gilbert, Longleaf Pine Stand Dynamics Laboratory, School Forestry and Wildlife Science, Auburn University, Auburn University, AL

It is well understood that frequent prescribed fire is necessary to control hardwood encroachment and promote ecological integrity of longleaf pine (Pinus palustris Mill.) forests.  However, there has long been concern that this management tool might also lessen growth and overall volume of young pine trees.  Results of some short-term studies, including one that applied biennial fires for over a decade, showed a decrease in growth of young longleaf pines on burned plots compared to unburned ones.  That information prompted establishment of the current research effort in 1984 to look at effects of fire frequency (2, 3, and 5-year) and season (dormant versus growing season) as well as unburned plots.  This long-term study is located near Brewton, AL, on the Escambia Experimental Forest, a privately own facility managed by the U.S. Forest Service.  The naturally regenerated longleaf pines were 15 years old and had been frequently burned prior to initiation of the study.  During 25 years of frequency and season of burn treatments, plots have been sampled 7 times.  Data were collected on growth of permanently marked longleaf pine as well as on the number and size of hardwood stems in each sample area. 


Although there were minor differences in juvenile longleaf survivorship, after 25 years there is no significant difference in basal area at breast height (DBH) among burn treatments or compared to unburned trees.  In contrast, there are significant differences in hardwood response to different treatments.  Compared to any burn treatment, unburned plots support significantly more small hardwood stems.  Within burn treatments, season contributes to differences in number of hardwood stems; frequency is marginally important.  Mean density of hardwoods (> 1.25 cm DBH) ranged from 0-10 stems/ha on growing season burned plots to 40-125 stems/ha on dormant season burned ones.  Season but not frequency affects hardwood basal area, perhaps in part because only well-established stems were sampled.  Results indicate that burning results in only minimal decrease in longleaf pine growth that but that fire, especially in the growing season, is beneficial in controlling encroaching hardwoods.   The significance of growing season fire was anticipated, however, inconsistent effect of burn frequency was unexpected.  Based on 25 years of burn treatments, similarity of longleaf growth across all fire regimes, including no burn, suggests that this management tool can be applied for hardwood control and other conservation purposes with little negative influence on timber value.

Copyright © . All rights reserved.
Banner photo by Flickr user greg westfall.