Date of Award

2003

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Forest Resources

Advisor

Robert G. Wagner

Second Committee Member

Alan S. White

Third Committee Member

George L. Jacobson

Abstract

The creation of natural canopy gaps is an important ecological process in the Acadian forest. Designing harvest gaps that emulate natural gap dynamics may be important for maintaining structural and biological diversity, as well as naturally regenerating desired tree species. We used a controlled study to 1) compare vegetation dynamics among and within harvested gaps, natural gaps, and under a closed canopy, and 2) examine the growth response of mature overstory edge trees of harvests gap and saplings inside of gaps as possible methods for dating natural gaps in the Acadian forest. For the vegetation dynamics study (objective I), we compared plant abundance, diversity, and composition in 45 harvested gaps (four growing seasons after harvest), 23 natural gaps, and 23 closed canopy transects. The percent cover of each species was measured in 4 m2 plots located every 2 m along a north/south transect across each gap. Total plant cover was greatest in harvested gaps (p c 0.001) and was highest in the center of the larger harvested gaps (672 - 2,106 m2) (p c 0.003). Abies balsamea was the most abundant species in all conditions. Diversity (i.e., number of species per sample area) was greatest in harvested gaps and least under the closed canopy (p<0.001). Species evenness (measured as the slope of dominance diversity curves) indicated that harvested gaps had greater evenness than natural gaps and closed canopy conditions. One hundred twelve of the 195 plant species identified occurred only in harvested gaps, and a detrended correspondence analysis indicated that plant composition in harvest gaps was different from natural gap and closed canopy plant composition. Tree regeneration was abundant under all conditions but was not correlated to gap origin (p = 0.15) or location within the gap. Seedlings (< 0.5 m tall) were the most abundant form of regeneration, and saplings (0.5 - 2.0 m tall) were most abundant in harvested gaps. A. balsainea was the most abundant tree species regenerating in natural gaps and closed canopy conditions, while Acer rubrunz was most abundant in harvested gaps- In the gap dating study (objective 2), we examined the growth response of Tsuga canadensis, Acer rubrum, and Betula papyrifera at the edge of 20 harvested gaps as well as A. balsamea and T. canadensis saplings at the center of the harvested gaps and 23 natural gaps. Radial growth increment after harvest and percent growth response were assessed as release criteria in edge trees and saplings seven years before and after harvest. For edge trees, a 50% growth response provided the best release criterion for dating gaps. Gap size (x2 = 7.560, p<0.006) and the interaction of gap size and species (x2 = 4.39, p<0.036) were the best variables predicting release using this criterion. For saplings, a 200% growth response provided the best release criterion for dating harvested gaps. Gap size also was correlated with sapling growth response (x2 = 8.187, p< 0.004). Using a 200% sapling growth response as a criterion underestimated the formation date of natural gaps. A 100% or more growth response provided the best results for dating natural gaps.

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