Date of Award

1988

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Forestry, Wildlife, and Fisheries

First Advisor

John R. Toliver

Abstract

A field study was established on a Beauregard silt loam site in central Louisiana to provide basic information on the effects of prescribed burning or hexazinone herbicide when used to control potential competitors of loblolly pine trees (Pinus taeda L.) within a mixed pine-hardwood stand seven years after clearcutting and mechanical site preparation. The design was a randomized complete block, with five blocks of three treatments each: check, hexazinone, and prescribed burn. The burn was a low-intensity winter backfire (87 kJ/s/m) executed on December 20, 1985, after the passage of a cold front, with light northerly winds, relative humidity of 42%, and ambient air temperature of 12$\sp\circ$C. The hexazinone was applied on April 12, 1986 at 3.0 kg active ingredient/ha. The number of suppressed pine trees/ha was greater on the check plots than on the hexazinone and burn plots. Within the hexazinone treatment, the number of potential crop trees decreased significantly after two years. The diameter, height, and stemwood volume growth of the potential pine crop trees was not significantly different among treatments, but within both the hexazinone and burn treatments, the volume/ha of potential crop trees increased significantly over the 2-year period. Therefore, treatments may have affected total stand growth. The insignificant effect of fire on juvenile loblolly pine diameter and height growth is noteworthy, because it shows that cool backfires can be used in relatively young pine stands early in the rotation without severely injuring the majority of the trees. The hexazinone treatment reduced the density of oak and the heights and diameters of oak and sweetgum trees. The winter backfire did not lead to a reduction in the brush after two years. However, the first burn in a stand of trees often is limited in effect, which was expected because safety of the potential crop trees from crown scorch and stem injury was of primary concern. Several burns within this juvenile mixed pine-hardwood stand may be needed before the brush is affected significantly.

Pages

91

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