Tree Mortality Following Mixed-Severity Prescribed Fire Dramatically Alters the Structure of a Developing Pinus taeda Forest on the Mid-Atlantic Coastal Plain

David G Ray,Deborah Landau

doi:10.3390/fire2020025

Abstract

This case study documents the aftermath of a mixed-severity prescribed fire conducted during the growing season in a young loblolly pine forest. The specific management objective involved killing a substantial proportion of the overstory trees and creating an open-canopy habitat. The burn generated canopy openings across 26% of the 25-ha burn block, substantially altering the horizontal structure. Mortality of pines was high and stems throughout the size distribution were impacted; stem density was reduced by 60% and basal area and aboveground biomass (AGB) by ~30% at the end of the first growing season. A nonlinear regression model fit to plot data portrays a positive relationship between high stocking (i.e., relative density > 0.60) and postburn mortality. Survival of individual trees was reliably modeled with logistic regression, including variables describing the relative reduction in the size of tree crowns following the burn. Total AGB recovered rapidly, on average exceeding levels at the time of the burn by 23% after six growing seasons. Intentional mixed-severity burning effectively created persistent canopy openings in a young fire-tolerant precommercial-sized pine forest, meeting our objectives of structural alteration for habitat restoration.

Highlights

Fire exclusion has led to dramatic changes in the composition and structure of Eastern US forests, often with negative implications for species and habitat diversity [1,2,3]
Similar to Cain [41], we found a clear separation between the heights of bole scorch and crown scorch on the permanent plots, and further, that average scorch heights followed a linear increasing trend with plot relative density (RD) (Figure 4)
We speculate that our success in generating canopy openings is attributable to a combination of factors, including the relatively short stature of the overstory trees, generally high stocking (60% of plots had RD > 0.6), and the intentionally aggressive approach to burning. The structure of this loblolly pine forest was dramatically altered by a mixed-severity prescribed burn carried out in the early growing season

Summary

Introduction

Fire exclusion has led to dramatic changes in the composition and structure of Eastern US forests, often with negative implications for species and habitat diversity [1,2,3]. Forest management, including the use of prescribed fire, that generates structural and compositional heterogeneity is advocated as a viable approach to promoting adaptation and resilience in the context of a changing climate [4,5,6]. Low-severity disturbances, including conventional forest thinning and understory burning, may not alter stand development trajectories sufficiently to achieve more broad-based management objectives (e.g., [9]). The ecological “work” accomplished by moderate and severe wildland fires is increasingly recognized as important for generating structural heterogeneity and habitat conditions that are often missing from contemporary forests, most conspicuously in the Western US [10,11].

Methods

Discussion

Conclusion