Growth dynamics of longleaf pine during conversion to uneven-aged stands

Abstract

A growing recognition that uneven-aged silviculture can offer multiple benefits to forested ecosystems has encouraged some landowners in the southern region of the United States to convert even-aged pine stands into multi-aged stands. For shade-intolerant pines of the southern United States, however, few studies have examined residual tree growth following silvicultural treatments that convert even-aged stands to multi-aged stands. Understanding the growth response of residual trees to different kinds of stand conversion treatments is critical to stand development and sustainability, as trees must be recruited into larger size classes during the conversion process to develop the desired stand structure and maintain productivity. In this study, we utilized a replicated, long-term silvicultural experimental trial in the southeastern United States to assess the effects of two cutting treatments (dispersed “single tree cutting” that created small canopy gaps and the “patch cutting” that created 0.1–0.8 ​ha patch openings) and an uncut control on the 14-year growth (∼cutting cycle length) of residual longleaf pine (Pinus palustris Mill.) trees. We found that tree growth, measured as mean basal area increment (BAI), was significantly higher following patch cutting (mean BAI of 16.97 ​cm²) compared to both the single tree cutting (13.33 ​cm²) and the uncut control (12.68 ​cm²) (p ​< ​0.001). In patch cutting, the size of the patch opening, the location of trees surrounding the patch opening, and the position of the tree canopy all had a significant effect on BAI. Trees surrounding patch openings of 0.4 ​ha exhibited greater growth, with a mean BAI of 19.24 ​cm², compared to those surrounding 0.1 and 0.8 ​ha patch openings, which had mean BAI values of 15.89 and 15.71 ​cm², respectively (p ​< ​0.001). The position of a tree around the patch opening also influenced tree growth, as residual trees more to the North, South, and East sides exhibited significantly higher mean BAI than trees on the West side of the patch openings (p ​< ​0.001). However, distance from the patch opening border did not significantly affect the mean BAI (p ​= ​0.522). In all treatments, dominant and co-dominant trees exhibited higher BAI than intermediate and overtopped trees, indicating that tree canopy position significantly influenced tree growth (p ​< ​0.001). Understanding how residual trees grow after these silvicultural treatments is crucial for thoroughly assessing their efficacy with longleaf pine. This study's findings will enhance our understanding of stand dynamics during stand conversion and help land managers anticipate the growth of longleaf pine into larger size categories after single tree and patch cuttings.