Response of direct seeded Pinus palustris and herbaceous vegetation to fertilization, burning, and pine straw harvesting
Fallen pine straw (needles) is a renewable biological resource valued as a mulch in horticulture and for landscaping. However, its harvesting may have detrimental long-term effects on forest soils and vegetation. To compare current pine straw harvesting practices, a randomized complete block splitplot study was established during 1990 in a 34-year-old stand of direct-seeded longleaf pine (Pinus palustris Mill.) that had been prescribed burned every 3 years since establishment. Practices included no fertilizer or applications of 50 kg ha-1 N and 56 kg ha-1 P in both 1991 and 1997 as the main plot treatment. The subplot management practices were prescribed burning and the mechanical baling and removal of straw. Pine straw harvesting eventually removed the forest floor and increased soil bulk density by 1993. The growth of longleaf pine was not significantly affected by treatments over a 5-year period from early 1991 to early 1996. Herbaceous plant productivity was determined in July 1997, and there were shifts in plant dominance associated with treatments. Fertilization increased current-year herbaceous plant biomass by 59 percent on an oven-dried weight basis. Among management practices, prescribed burning in early 1991, 1994, and 1997, with two annual straw harvests in early 1992 and 1993, resulted in the greatest herbaceous plant yields by July 1997. The lowest yields in 1997 were on plots that were either annually harvested six times or had been left untreated for over 6 years. Burning every 3 years favored pinehill bluestem (Schizachyrium scoparium var. divergens (Hack.) Gould), which is often the dominant grass on longleaf uplands in the West Gulf Coastal Plain of the U.S.A. Raking straw shifts herbaceous plant dominance to other grasses, principally the panicums (Dicanthelium spp. and Panicum spp.). The cessation of management favored bracken fern (Pteridium aquilinum var. pseudocaudatum (Clute) Heller).
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