Effects of canopy treatments on early growth of planted longleaf pine seedlings and ground layer vegetation in North Carolina

Background/Question/Methods: Longleaf pine (LLP; Pinus palustris Mill.) restoration is a primary management goal of landowners throughout the southeastern United States.  We installed a field experiment to support the development of protocols to restore longleaf pine to existing mature loblolly pine (LBP; Pinus taeda L.) stands at Camp Lejeune, NC.  The study used a randomized complete block design, with location as the blocking factor, and seven canopy treatments, including four uniform and three gap treatments, were applied in the experiment.  The four uniform treatments were defined by target residual basal area, including no thinning (Control), thinning to a target basal area of 9 m²/ha (BA9), thinning to a target basal area of 4.5 m²/ha (BA4.5), and clearcut (BA0).  The three gap treatments were defined by gap size, including a large gap (LG; 5027 m², a medium gap (MG; 2827 m²), and a small gap (SG; 1257 m²).  We quantified treatment effects on planted longleaf pine seedlings and ground layer vegetation after the first growing season.  

Results/Conclusions: Canopy treatments significantly affected the growth of planted longleaf pine seedlings.  Among the four uniform treatments (Control, BA9, BA4.5, and BA0), there was a consistent increasing trend in RCD as residual overstory LBP basal area decreased.  However, growth of planted LLP seedlings within gaps was not significantly affected by gap size.  Total vegetation cover and total herbaceous cover, measured in both May and September, 2008, were also significantly influenced by canopy treatments.  By the end of the first growing season, all uniform thinning and gap treatments had greater total vegetation cover than Control.  Total herbaceous cover was also greater in uniform thinning or gap treatments than Control, although some of those differences were not statistically significant.  We are currently analyzing available N (NH₄ and NO₃) and soil moisture at different positions within LG, comparing light availability among different canopy treatments, and relating growth of LLP seedlings to available N, soil moisture and light.