Browsing by Author "Thomas R. Wentworth, Committee Co-Chair"

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Characterization of a North Carolina Lower Coastal Plain Wet Pine Savanna.
(2007-10-28) Wall, Wade Alan; Michael J. Vepraskas, Committee Member; William A. Hoffmann, Committee Co-Chair; Thomas R. Wentworth, Committee Co-Chair
Savannas in the southeastern United States formerly occurred from East Texas to southern Virginia. Logging, conversion to agriculture, and fire suppression have reduced their area and extent, and there is an urgent need to catalogue and classify the remaining savannas for both restoration and resource management purposes. The Big Savannah was a unique wet savanna on a geographically-limited Inceptisol in North Carolina that was studied and described by B.W. Wells during the 1920s. Unfortunately, the site underwent agricultural conversion and the unique community it supported was believed to have been eliminated from the North Carolina landscape. Subsequent savanna classifications have either not included this type of community or placed it with savannas occurring on Ultisols. During the late 1990s, vegetation reminiscent of that described for the Big Savannah was discovered 8 km north of the original site in two power line corridors. Shelingoski (2005) used the Carolina Vegetation Survey protocol to survey 13 100 m2 quadrats at Wells Savannah, the name given to the newly-discovered savanna. During summer 2005, we surveyed an additional 56 100 m2 quadrats on the Taylor Tract, private property adjacent to Wells Savannah. We compiled a data set from existing quadrat data inventoried from other lower coastal plain savannas to compare to the natural community at Wells Savannah and the Taylor Tract and to determine the relationship of this community to those found on other savannas in the region. We combined 12 of the Wells Savannah quadrats, 26 of the Taylor Tract quadrats, 6 quadrats from Holly Shelter Game Lands, and 27 quadrats from the Carolina Vegetation Survey (CVS) database. Quadrats from Holly Shelter Game Land and the CVS database were selected because of their similarities to the Wells Savannah and Taylor Tract quadrats, in terms of vegetation and topography, as well as geographical proximity. We used a variety of multivariate techniques to analyze the data. Multi-response permutation procedure (MRPP) results suggested significant vegetation and soil differences between the Wells Savannah/ Taylor Tract and surrounding savannas. Non-metric multidimensional scaling (NMDS), indicator species analysis (ISA), linear discriminant analysis (LDA), and classification tree modeling (CART) also clearly separated Wells Savannah and the Taylor Tract quadrats from other regional wet savannas. Species identified as indicators of Wells Savannah and the Taylor Tract tended to be either obligate or facultative wetland species, while the other wet savannas in the outer coastal plain of North Carolina contained a number of species, such as Aristida stricta, typically associated with areas experiencing shorter hydroperiods. NMDS ordination based on vegetation data separated Wells Savannah and the Taylor Tract from the other wet savannas, and discriminant analysis using soil characteristics correctly identified quadrats as either from Wells Savannah⁄ Taylor Tract or other wet savannas 76% of the time. Important distinguishing soil characteristics separating Wells Savannah and the Taylor Tract from the other wet savannas are the combination of higher clay percentage, higher calcium (ppm), and higher phosphorus. Recognition of a separate community type for Wells Savannah and the Taylor Tract is warranted, based on differences in vegetation and soil characteristics. Further exploration of the area is necessary in order to identify other remaining sites similar to the Big Savannah that may warrant preservation.
Ecological and Physiological Basis for the Distribution of Woody Plants along Water Availability Gradients in the Southeastern United States Mixed Forest
(2008-07-15) Abit, Pamela Po; William A. Hoffmann, Committee Chair; Thomas R. Wentworth, Committee Co-Chair; Mary M. Peet, Committee Member; Edwin L. Fiscus, Committee Member
Effects of site preparation and vegetation control on the plant communities, successional dynamics, and stand structure of a loblolly pine (Pinus taeda) plantation.
(2002-11-11) Jeffries, Stephanie Breard; H. Lee Allen, Committee Co-Chair; Thomas R. Wentworth, Committee Co-Chair
Sustainability has become a focus for forest management all over the United States, but particularly for the South, where harvest intensity has increased in recent years. Considerable interest has focused on the effects of high intensity silvicultural practices and short rotations on ecological processes, biodiversity, and wildlife habitat. In order to better understand these effects, we conducted a comparative study of second and third rotation plant communities and the effects of silvicultural practices on succession, biodiversity and stand structure in a loblolly pine (Pinus taeda) plantation in the Piedmont of North Carolina. Following harvest of the second rotation stand, a 2 x 2 x 2 split-split-plot experiment was established using two harvest (stem only versus complete tree), two site preparation (chop versus shear, pile, and disk) and two cultural (vegetation control versus no vegetation control) treatments. Presence/absence of vascular plant taxa was determined prior to harvest for ages 22 and 41 of the second rotation as well as for ages 1, 2, 6, 12, and 18 in the third rotation. We also obtained cover data for years 1, 2, 6 and 18 in the third rotation. Since the harvest treatments did not differ significantly for any of the parameters throughout the third rotation, our analyses focused on the effects of site preparation and vegetation control. Results indicated a significant difference in species composition from the second to the third rotation, with disturbance-responsive species positively associated with vegetation control in the third-rotation plots. The addition of these species to the vegetation control plots largely accounted for the addition of approximately forty species from the second to the third rotation, although trace numbers of woodland herbaceous species were recruited across all treatments. The least intensively managed third-rotation stands were more similar to the unmanaged stands of the second rotation. We also found that early in the life of the third rotation stand, intensive site preparation influenced species composition and cover across the site. However, following canopy closure, individual treatments converged to similar composition and cover. Despite the lack of long-term treatment effects on the species composition and cover of the plant communities, we found that vegetation control treatments significantly affected stand structure at all height strata, prevented the development of a midstory and promoted the persistence of an herbaceous layer. At the lower shrub and sapling levels, site preparation affected stand structure within the plots with no vegetation control, with chop plots contributing multiple hardwood sprouts and disk plots contributing more individual seed-germinated saplings. Our results indicate that high intensity silvicultural practices, such as shearing, piling, and disking and vegetation control, reduced initial competition and thus permitted the persistence of early successional species, increasing overall diversity from the second to the third rotation. We also found evidence that this stand is evolving from its agricultural legacy to a forest through the recruitment of several late successional herbaceous species. Although intensive silvicultural practices play an important early role in determining species cover and composition and continue to affect forest stand structure after twenty years, they apparently do not disrupt successional processes. Interestingly, differences in species composition due to soil variation across the study site were seen through both rotations, while treatment differences diminished over time during the third rotation. Thus we find that intensive management in a secondary forest stand had little long-term impact on succession and plant species composition, but may have important ramifications for wildlife due to the alteration of stand structure.
Genetic Diversity and Phylogeography in a Tasmanian Rainforest Vonifer (Lagarostrobos franklinii (Hook f.) Quinn Podocarpaceae
(2006-04-27) Clark, Catherine M.; Ronald Sederoff, Committee Co-Chair; Thomas R. Wentworth, Committee Co-Chair; Bruce S. Weir, Committee Member; Henry Amerson, Committee Member
Genetic variation in Huon pine (Lagarostrobos franklinii), a Tasmanian rainforest conifer, was estimated using several marker systems and two spatial scales. Genealogy based methods were used to infer population history of eight Huon pine stands based on chloroplast DNA variation. Chloroplast nucleotide diversity (pi) was low (0.00093) in a multilocus haplotype generated by three universal chloroplast primers (trnS-trnT, trnD-trnT, psbC-trnS). Five haplotypes were identified; two were widely distributed but the most frequently occurring haplotype was found only in trees in the western portion of the range. Genetic differentiation among populations was significant and showed a high degree of structure (GST = 0.26077). Pairwise comparisons between populations revealed significant structure between the southeastern and northwestern watersheds and significant isolation by distance (p < 0.02). Nucleotide variation was also assessed in segments of three nuclear genes, 4Cl (4-coumarate: coenzyme A ligase), ITS2 (intergenic spacer region of ribosomal DNA) and G3pdh (glyceraldehyde 3-phosphate dehydrogenase). A total of 1,154 base pairs were sequenced from 79 individuals (158 alleles) representing seven geographic locations. Estimates of nucleotide diversity (pi = 0.00089) and theta (0.00061) were low for the combined loci and similar to chloroplast estimates. There was a higher level of variation at the 4Cl locus (pi = 0.00167) associated with recombination. Nucleotide diversity for nuclear loci was highest in the subalpine Mt. Read population, previously described as a putative clonal stand. Population differentiation (FST = 0.0130) was lower than estimated in chloroplast DNA, or in a previous allozyme investigation (FST = 0.095). Multilocus genotypes based on RAPD markers (random amplified polymorphic DNA) were generated to further investigate genetic diversity in the Huon pine stand at Mt. Read. DNA was analyzed from 63 trees from Mt. Read and genetic diversity compared to 33 Huon pine samples from a wide geographic range. Twelve random decanucleotide primers amplified a total of 35 alleles. Only three of the alleles (8.6%) from the Mt. Read population were polymorphic in contrast to 18 (51.4%) polymorphic alleles in the reference population. Gene diversity at Mt. Read (0.0316) was six-fold lower than that found in the reference sample (0.1973). Only four unique DNA fingerprints were revealed at Mt. Read and these were spatially clustered in the stand. Each of the 33 isolates in the wide geographic sample exhibited a unique genotype. The three marker systems of this study, along with a previous allozyme survey, are concordant in indications of a low level of diversity in a Southern Hemisphere conifer. The low level of nucleotide diversity, star-like phylogeny and haplotype distribution of chloroplast DNA suggest that Huon pine has experienced a series of population bottlenecks and colonization events from refugial areas. This is congruent with paleoecological data that suggest that there were major refugial areas on the western coast of Tasmania in addition to small, isolated refugia in other portions of the current range. The low level of variation found in nuclear loci is also compatible with a history of demographic events related to Pleistocene and Holocene environmental variability and long-term range reduction. The limited genetic variation in the Mt. Read population may be related to minimal gene flow into this stand due to geographic isolation, and extensive vegetative reproduction in a harsh environment.