Pro-b Selection Method for Uneven-aged Management of Longleaf Pine Forests

Interest in uneven-aged silviculture has increased since advent of ecosystem management programs, which place greater emphasis on ecological values and ecosystem services while also harvesting timber from the forest. However, traditional uneven-aged approaches (e.g., BDq) are often criticized as too complex, costly, and requiring highly-trained staff. The ProportionalB method (Pro-B) addresses these concerns, making uneven-aged silviculture a practical management option. In an operationalscale study, Pro-B was successfully used, by forest staff from a range of professional backgrounds, following less than 3 hours of training, to apply single-tree selection and group selection in longleaf pine (Pinus palustris Mill.) forests. Field crews achieved precision levels within 3 to 5 percent of the target residual basal area. By aggregating many diameter size-classes into only three size-class groups, Pro-B improves efficiency by requiring tree markers to remember only three fractions while making a single pass through the stand. Not being restricted by maximum-diameter rules also allows flexibility to retain larger trees for enhancing structural diversity. Trees of specific species and with good form, broad crowns and cavities can be retained, while adjusting spacing to release residuals. Systematic quantification of tree removal enables different individuals to obtain consistent results. A stable structure is maintained with characteristics of a mature forest, while regeneration is initiated and timber is removed through a periodic cutting cycle. With a focus on forest sustainability and flexibility to retain large trees and biological legacies by mimicking small-scale natural disturbances, Pro-B might be implemented to achieve the production objectives and stewardship goals of retention forestry. INTRODUCTION Ecosystem management policies emphasizing biodiversity and long-term sustainability have, in recent years, increased the interest in and practice of uneven-aged silviculture (O'Hara 1998). This is true nowhere more than in southern pine forests, where even-aged methods for timber production lead to adverse consequences for other ecosystem values (Guldin 2006). Protecting native plant communities, maintaining continuous forest canopy, and facilitating development of large old trees are among the desirable habitat features resulting when uneven-aged silviculture is applied in an adaptive management framework (Brockway and others 2006). Uneven-aged silviculture also affords a major advantage, in that natural regeneration is more or less continuous through time, as late-successional stand dynamics are emulated (Guldin 1996). Despite an historical decline, longleaf pine (Pinus palustris Mill.) forests are highly valued for a variety of resources having ecological, economic and cultural importance and substantial interest has recently emerged in best management approaches for sustaining and restoring them (Brockway and others 2005a, Van Lear and others 2005). Although longleaf pine has been mostly managed with even-aged methods and was formerly thought to be too intolerant for uneven-aged silviculture (Croker and Boyer 1975), recent evidence suggests this to be a viable management alternative (Brockway and Outcalt 1998, Farrar 1996, Gagnon and others 2003, McGuire and others 2001, Palik and others 1997). Longleaf pine can grow in pure stands and also in association with numerous trees species across a wide range of ecosystem types, including slash pine (P. elliottii Engelm.) on flatwoods, loblolly pine (P. taeda L.) and shortleaf pine (P. echinata Mill.) on mesic uplands, and various hardwoods on xeric sandhills, mountains and other site types (Boyer 1990). This natural variety indicates that no single prescription is appropriate for sustaining longleaf pine everywhere. Prudent managers will select approaches suited for their specific environment, which lead to: (1) an overstory dominated by mature longleaf pine occurring as uneven-aged stands or even-aged patches across an uneven-aged landscape, with a lesser component of other tree species; (2) a midstory that is generally absent or mostly composed of ascending longleaf pine in scattered, modestlysized canopy gaps; and (3) an understory with abundant longleaf pine seedlings and groundcover dominated by native grasses and