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 Research 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 andQuercus prinus), redbud (Cercis canadensis), hickory (Carya ovata), red oak group (Quercus falcate, Quercus rubra and Quercus coccinea), loblolly pine (Pinus Taeda) andtulip poplar (Liriodendron tulipifer). Fertilizer treatments were broadcast applied and consisted of an untreated control (Control), nitrogen (N) 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 perha). Tree heights were recorded in June 2004 before treatment effects and for height and ground line diameter in October 2005. Stem origin and foliar nutrient concentrations (for red oak, loblolly pine and tulip poplar) were determined. Data was analyzed for treatment differences in ground line diameter, height, mean tree volume, groundline basal area, volume per hectare, density, and species composition on a whole stand basis as well as for the largest 16 trees per plot regardless of species, dominant species, and the 10 largest trees per species per plot for hickory, loblolly pine, red maple, red oak group, sweetgum, tulip poplar and white oak group. 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. 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 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 responded with increases in GLD with N+P and N+P+K treatments and with increases in height with N, N+P and N+P+K treatments 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 larger 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 al 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.
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Fertilization Impacts on Growth and Species Composition in a Very Young Naturally Regenerated Piedmont Upland Hardwood Stand in North Carolina
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