Browsing by Author "Daniel J. Robison, Committee Chair"

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Abundance, Fruit Presence, and Growth Enhancement of Prestoea montana and Roystonea borinquena, Two Palm Species of Importance to Amazona vittata (Puerto Rican Parrot), in Rio Abajo Forest, Puerto Rico.
(2007-07-16) Malone, Meredith B.; Daniel J. Robison, Committee Chair; Jaime A. Collazo, Committee Member; Thomas R. Wentworth, Committee Member
Stand Dynamics and Ecological Constraints on Growth in Young, Naturally Regenerated Hardwood Stands
(2006-04-20) Schuler, Jamie L; Douglas J. Frederick, Committee Member; Charles B. Davey, Committee Member; Daniel J. Robison, Committee Chair; H. Lee Allen, Committee Member
In the southern U.S., forests are generally managed as even-aged entities, and commonly regenerated using a clearcut reproduction method. Alternatives to clearcutting, namely low- and medium-density shelterwood methods, were assessed in North Carolina, South Carolina and West Virginia. Results suggested that the alternative methods afforded little to no advantage over traditional clearcut methods. Weeding, fertilization and thinning treatments were employed post-harvest on rising 1-yr-old Hill Forest and rising 3-yr-old Duke Forest upland Piedmont sites. Stems at both sites responded to fertilization. Individual stem volumes increased 2 to 3-fold after three years. Weeding-alone increased growth on the Hill Forest. The response to weeding and fertilization treatments was usually additive. Thinning-alone had little effect on stem growth. However, thinning + weeding treatments simulated large increases in stem growth. For thinned stems, weeding generally had a greater affect on growth than fertilization at both sites. Stems on the rising 1-yr-old Hill Forest site were tagged (>3000 stems) and monitored over three years. Stem survival was greatly affected by the weeding and fertilization treatments. Fertilization reduced survival for most species, especially for the lower initial height and diameter size classes. Weeding, by contrast, tended to increase survival in the small initial size classes. The survival data indicated that some of the growth response associated with fertilization might be due to mortality in the smaller sized stems. Three-year growth and survival models based on initial stem size were generated for each species and treatment combination at the Hill Forest site. Comparisons were made between treatments for each species, and between Liriodendron tulipifera L. and Cornus florida L., Prunus serotina Ehrh., Pinus spp., Acer rubrum L. and Quercus alba L. for each treatment. Generally, most species responded favorably to weeding and fertilization treatments, although these responses were not always statistically significant. However, individual species differed in respect to their ability to increase growth and survival, although yellow-poplar ranked among the fastest growing species in every treatment after 3 years. These last data can be used to develop floristic models to predict species composition for other upland stands.
Thinning and Fertilizing Young Coastal Plain Hardwoods
(2003-07-10) Newton, Leslie Phelps; Theodore H. Shear, Committee Member; Barry Goldfarb, Committee Member; H. Lee Allen, Committee Member; Daniel J. Robison, Committee Chair
A thinning and fertilization study was installed on a 7-year-old naturally regenerated hardwood stand on somewhat poorly drained soils in the Atlantic Coastal Plain of North Carolina (Northampton County). Dominant species were sweetgum (Liquidambar styraciflua L.) and red maple (Acer rubrum L.). Treatments were thinning (to 3000 stems per hectare in February 1997) and fertilization (238 kg/ha N and 58 kg/ha P hand broadcast in May 1998 as urea and diamonium phosphate), applied separately and in combination. Trees were measured for diameter and height in 1997 and again during the dormant season in 2000/2001. Other measured variables included canopy, specific leaf area, foliar nutrients, competition (woody and herbaceous), soil properties and nutrients, and depth to the water table. Fertilization had a significant positive impact on diameter, height, basal area and volume growth, stem densities, foliar N, leaf area, and leaf area duration. In addition, fertilization appeared to limit the growth and development of woody shrubs and coppiced stems, and accelerate natural self-thinning. Thinning had little to no significant impact on tree growth or nutrient levels, and appeared to allow for increased levels of competing vegetation. The canopy on the thinned-only treatment was less dense than any other treatment and there were more shrubs (predominantly wax myrtle [Myrica cerifera L.]) and vines (predominantly poison ivy [Toxicodendron radicans L.]) on the thinned-only treatment. The combined thinning and fertilization treatment resulted in the highest levels of incremental growth between 1997 and 2001, but only the fertilization effect was significant. Based on the results from foliar and soil analyses, the site does not appear to be phosphorus-deficient, and the strong fertilization effect may be the result of ameliorating a nitrogen deficiency. Both sweetgum and red maple responded well to fertilization. Given the lack of significant block effect noted for red maple throughout the study, red maple appears to be the more elastic of the two species. Trees observed in this study would most likely benefit from another application of nitrogen, as would most forest stands on similar sites. This study has shown that it is highly unlikely that stand development at this age can be accelerated through thinning alone, although growth benefits gained from thinning may become more evident as the stand ages. Fertilization alone, or in combination with thinning, not only accelerates stand development, but may also increase long-term productivity.