Date of Award
Master of Forest Resources (MFR)
Gerard , Patrick D
The xeric sandhills on Carolina Sandhills National Wildlife Refuge have a monospecific overstory of longleaf pine and an understory dominated by turkey oak and wiregrass. The understory vegetation is spatially heterogeneous within stands, with small patches dominated by either turkey oak or wiregrass, or lacking understory vegetation. I described the fuel complexes created by the variable vegetation structure, in terms of their chemical and physical properties, and used prescribed fire to test for differences in fire behavior among the vegetation types. In addition, I compared the effects of the vegetation structure and below-ground competition on the establishment of wiregrass.
Turkey oak-dominated sites had the highest potential fuel weights, and contained high-energy fuels. The duration of burn above 60 ¡C and the heat output were longest on these sites. Longleaf pine-dominated sites contained energy-rich fuels but low potential fuel weights; they also had a long duration of burn above 60 ¡C, but lower heat output than turkey oak-dominated sites. Wiregrass-dominated sites had low potential fuel weights, the lowest fuel energy content, and a well-aerated fuel bed. These sites had the shortest duration of burn above 60 ¡C and the lowest heat output. Rate of spread and peak fire temperature were highly variable, and did not vary with understory vegetation.
The effect of vegetation structure on wiregrass seedling establishment was only significant directly following planting, which coincided with the driest portion of the growing season. Early in the study, seedlings had the lowest survival rates, and seed the lowest numbers of germinants in the turkey oak-dominated sites. Understory vegetation structure was only marginally linked to measures of above-ground light resources, with longleaf pine-dominated sites having the least available sunlight in the understory, but the most available light at ground level. Below-ground competition limited seedling survival and growth, and establishment from seed during the entire season, and across all vegetation types. Below-ground competition reduced soil moisture, a limiting resource in the xeric sandhills.
Management goals to reduce turkey oak cover will change the fuel structure and fire behavior, but may not be sufficient to increase wiregrass cover in the long term. Where turkey oak is already restricted to the understory through frequent burning, negative effects on wiregrass seedling establishment may only exist during drought conditions or the earliest stages of seedling establishment. At other times, competition from pines and other understory vegetation is comparable to that produced where turkey oak is present.
Wenk, Evelyn, "Effects of vegetation structure on fire behavior and wiregrass seedling establishment in xeric sandhills" (2009). All Theses. 612.