Site preparation for longleaf pine restoration on hydric sites: Stand development through 15 years after planting

Abstract

Longleaf pine (Pinus palustris Mill.) restoration is an important land management goal throughout the southeastern U.S. On hydric sites within the Atlantic Coastal Plain, restoration may involve site preparation prior to planting to overcome challenges to seedling establishment, such as abundant competition and poor soil drainage. Investment in site preparation assumes that treatments will result in long-term benefits to stand development, yet lasting impacts of site preparation on longleaf pine are not well understood. We sampled longleaf pine plantations in Onslow County, North Carolina through three years and at 15 years after site preparation and planting. The eight study treatments we tested include an untreated control, six combinations of two vegetation control treatments (chopping or herbicide) with three soil manipulation treatments (mounding, bedding, or flat-planting [no treatment]), and a chopping-herbicide-bedding treatment. Our findings indicate that site preparation significantly improved survival and growth of longleaf pine through 15 years. Herbicide resulted in greater growth, higher survival, and earlier grass stage emergence than chopping. Similarly, soil manipulation treatments resulted in improved stand establishment outcomes relative to flat-planting (no treatment). Effects of site preparation treatments on diameter growth were observed early and maintained through the end of the study period, while effects on survival were not observed within the first three years. Differences in stand height among treatments were more strongly driven by growth rates following grass stage emergence than timing of emergence. Our results demonstrate that site preparation improves longleaf pine stand establishment on hydric sites, although the intensity of site preparation treatments recommended for restoration depends on management objectives.