Postfire survival in south Florida slash pine: interacting effects of fire intensity, fire season, vegetation, burn size, and bark beetles

Abstract

We used path analysis to examine postfire survival of south Florida slash pine (Pinus elliottii var. densa) at Archbold Biological Station in south-central Florida. We considered the interacting factors of bark beetle infestation, fire intensity (estimated by bark char, percentage of canopy green, and other measures), season of burn, burn size, and vegetation structure and composition. Trees were sampled in 24 burned areas for 3 years after each fire. Fires on recently-burned sites (5–19 years since previous fire) killed fewer trees (44% mortality) than fires on sites > 25 years postfire (71%). For long-unburned sites, we used multiple regression to examine 35 variables and form a path model linking nine variables at four levels. Pine survival was most affected by season of burn; fall burns decreased survival indirectly through increases in fire intensity. Higher mortality was associated with greater char height, larger area burned, more intense attacks by the beetle Platypus, occurrence of hickory scrub or flatwoods vegetation, and complete needle consumption. The final path model explained over 90% of the variation in pine survival. It suggested that beetle effects reflect fire intensity, and detailed many complex interactions. Both preburn and fire intensity data were needed to explain a high amount of variance. Analyses of survival within burns produced similar results, but added some patterns due to vegetation differences within burns and higher survival for larger trees. Fire-induced south Florida slash pine mortality did not spread to trees growing in adjacent, unburned areas. Fire intensity may influence pine densities over the upland landscape in all but the most xeric and hydric sites. Fire management to maximize pine survival is feasible, but management for landscape heterogeneity will tolerate variation in fire intensity and pine survival.