Fertilization impacts on growth and species composition in a very young naturally regenerated piedmont upland hardwood stand in North Carolina

by 1978- Berenguer, Bryan Jacob

BERENGUER, BRYAN JACOB. Fertilization Impacts on Growth and Species Composition in a Very Young Naturally Regenerated Piedmont Upland Hardwood Stand in North Carolina. (Under the direction of Daniel J. Robison.) Hardwood stands in the southern U.S. are often regenerated naturally following clearcutting, with little or no silvicultural intervention in the early stages of stand development. Fertilizer was applied to a very young naturally regenerating stand in order to evaluate the effectiveness of nutrient addition as a silvicultural tool in recently clearcut stands and to better understand the ecological relationships between site fertility and stand development. The study was installed on a rising 2-year-old naturally regenerated mixed pine-hardwood stand in the Hill Demonstration Forest in the Piedmont region (Durham County) of North Carolina. Dominant species were red maple (Acer rubrum), sweetgum (Liquidambar styraciflua), white oak group (Quercus alba, Quercus phellos and Quercus prinus), redbud (Cercis canadensis), hickory (Carya spp), red oak group (Quercus falcate, Quercus rubra and Quercus coccinea), loblolly pine (Pinus taeda) and tulip poplar (Liriodendron tulipifera). Fertilizer treatments were broadcast applied and consisted of an untreated control (Control), nitrogen (N) only treatments, nitrogen and phosphorus (N+P) treatments, and nitrogen, phosphorus and potassium (N+P+K) treatments (respectively at 200 kg N per ha, 50 kg P per ha and 100 kg K per ha). On a whole stand basis, increased growth rates were observed for N+P and N+P+K plots. Fertilizer treatments did not affect total stand density, but the density of evergreens significantly decreased in N+P plots compared to the Control. The density of stems of stump origin also increased in plots receiving N+P. Density of sweetgum significantly increased and hickory density decreased with the application of N+P. Dominant hardwood species (with the exception of tulip poplar) responded with an increase in height to only N+P fertilizer treatments. Tulip poplar increased in groundline diameter, height and mean tree volume with the application of N+P. Loblolly pine responded to N+P+K fertilizer treatment with an increase in height, diameter and volume over the Control. The 16 largest trees increased groundline diameter (GLD) in response to N+P and N+P+K treatments and had larger mean height with N, N+P and N+P+K treatments over the Control). There was no growth response among treatments for the 10 largest trees per species per plot, with the exception of red oak which responded with an increase in height in N+P plots. There were slight differences among treatments in elemental foliar nutrients in dominant red oak, loblolly pine and tulip poplar trees, but none were found to be deficient. The lack of growth response to N alone suggests the primary nutrient limitations for the site is not N or at least N alone. However, the strong response to N+P in hardwoods and N+P+K in loblolly pine suggests the site is deficient in these elemental combinations. Current and projected growth responses, both on a whole stand level and among individual species, indicate that the use of N+P fertilizer may be an effective silvicultural instrument to increase growth and accelerate stand development in very young naturally regenerated stands, and thereby shorten rotation time. Fertilization Impacts on Growth and Species Composition in a Very Young Naturally Regenerated Piedmont Upland Hardwood Stand in North Carolina by Bryan Jacob Berenguer A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Master of Science Forestry Raleigh 2006