Date of Award

12-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Forest Resources

Advisor

Wang, G. Geoff

Committee Member

Walker , Joan L.

Committee Member

Shelburne , Victor B.

Committee Member

Rieck , James R.

Abstract

To support the development of silvicultural protocols for restoring longleaf pine (LLP; Pinus palustris Mill.) and its characteristic herbaceous understory in loblolly pine (LBP; P. taeda L.) stands, a three-year study was conducted on moderately well- and well-drained soils in Onslow County, North Carolina. A replicated field experiment was conducted to test the effects of selected silvicultural treatments on planted LLP seedlings, understory vegetation, and plant resources. Seven canopy treatments included four uniform canopy density treatments defined by target residual basal area [Control, MedBA (9 m2/ha), LowBA (4.5 m2/ha), and Clearcut] and three circular gap treatments defined by area [LG (5027 m2), MG (2827 m2), and SG (1257 m2)]. Within each canopy treatment, three cultural treatments including control (C), herbicide (H), and herbicide plus fertilization (H + F) were applied.
Among the canopy treatments, LLP seedlings planted in the Clearcut had higher survival rate after the first three growing seasons compared to Controls. Canopy treatment significantly improved seedling root collar diameter (RCD) growth, but interacted with applied cultural treatment. C within Control had the smallest RCD, and H + F within Clearcut had the largest RCD. Canopy treatment significantly affected the percentage of seedlings in height growth such that Control plots had significantly lower percentage of seedlings in height growth than other canopy treatments. H and H + F also significantly increased the percentage of seedling in height growth compared to C.
Among the uniform canopy treatments, ground layer vegetation cover significantly changed over three years, but showed different trends for different functional groups. By the 2010 growing season, H increased forb cover and proportions of total herbaceous and forb covers, but decreased covers of woody, graminoids and proportion of graminoid cover. Clearcut resulted in greater midstory LBP density by the 2009 and 2010 growing seasons. Herbicide application (H and H + F) significantly decreased target woody density, but increased LBP density by the 2010 growing season. Clearcut resulted in greater aboveground biomass of woody, herbaceous and graminoid species, but it did not affect the proportions of herbaceous, graminoids and forbs. H significantly decreased woody aboveground biomass and graminoid proportion. H + F significantly decreased woody aboveground biomass, but increased herbaceous proportion. Canopy treatment did not affect species richness, but herbicide application (H and H + F) reduced woody species richness at the scale from 0.1 to 100 m2. Non-metric multidimensional scaling (NMS) and multi-response permutation preocudure (MRPP) analyses concluded that the variation of understory vegetation among sampled plots was attributed to soil characteristics, especially soil texture, rather than experimental treatments.
Gap size affected neither survival and growth of planted LLP seedlings after the first three growing seasons nor the abundance of ground layer vegetation and density of midstory woody plants by the third growing season after harvest. Within-gap position significantly affected the growth of planted LLP seedlings, but it did not affect their survival or the abundance of ground layer vegetation. Both gap size and within-gap position significantly affected gap light index (GLI), but they did not affect surface soil moisture and affected soil temperature only in 2009. Although within-gap position did affect foliar P and K concentrations, these effects showed neither consistency over the two years nor followed expected pattern of changes (i.e., high close to center and low at edge or inside forest). Our results supported the hypothesis of light limitation on seedling growth in gaps.
GLI significantly differed among four uniform canopy treatments, nonlinearly increasing with decreasing basal area. H resulted in higher soil temperature in both 2009 and 2010. Foliar Ca, Mg, Zn and Fe concentrations significantly increased after the prescribed fire in 2010, while foliar N, Cu and Na concentrations significantly decreased. The effects of canopy and/or cultural treatments on foliar nutrients were not consistent over the two years. The RCD of planted LLP seedlings was positively correlated with GLI and foliar P, Ca and Zn concentrations, but negatively correlated with soil temperature.

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