Effects of overstory competition on canopy recruitment patterns of naturally regenerated longleaf pine on two site types

摘要

Recent interest in continuous cover forest management of longleaf pine (Pinus palustris Mill.) ecosystems raises questions of long-term sustainability because of uncertainty in rates of canopy recruitment of longleaf pine trees. We destructively sampled 130 naturally regenerated, midstory longleaf pines across an 11 300 ha, second-growth longleaf pine landscape in southwestern Georgia, United States, to reconstruct individual tree height growth patterns. We tested effects of stand density (using a competition index) and site quality (based on two site classifications: mesic and xeric) on height growth and demographics of midstory trees. We also compared height growth of paired midstory and overstory trees to infer stand regeneration and recruitment dynamics. In low-density stands, midstory trees were younger and grew at greater rates than trees within high-density stands. Midstory trees in low-density stands were mostly from a younger regeneration cohort than their paired overstory trees, whereas midstory-overstory pairs in high-density stands were mostly of the same cohort. Our results highlight the importance of releasing midstory longleaf pine trees from local competition for sustained height growth in partial-harvesting management systems. They also demonstrate patterns of long-term persistence in high-density stands, indicating flexibility in the canopy recruitment process of this shade-intolerant tree species.