Response of Planted Eastern White Pine (Pinus strobus L.) to Mechanical Release, Competition, and Drought in the Southern Appalachians

Conversion of low-qual i ty , natural mixedpinelhardwood ecosystems, containing a mountain laurel (Kalmia latifolia L.) dominated understory, to more productive eastern white pine (Pinus strobus L.)l mixed-hardwood systems is a common prescript ion on relat ively xeric southern Appalachian forest s i tes . We examined the ef fects of mechanical release, interspeci f ic competi t ion, and annual precipi tat ion on growth qf planted white pine in four 14-yr-old stands in the southern Appalachians. Two stands were mechanically released at age 6. No s igni f icant di f ferences in biomass, basal area, or diameter were,found between treatments for al l species combined. Radial increment was sign$cantly less during a drought year for both treatments . Height increment was less sensitive to severe moisture limitation than radial increment. Height and radial increment were compared to distance-dependent and distance-independent measures of competi t ion for the nonreleased s tands. Indices based on height and height ldis tance explained the greatest amount of var ia t ion in both radial and height increment . The inf luence ofpost-release severe drought may have delayed or diminished the response to release. The competi t ive inf luence of understory dominant mountain laurel at s tand age 14 appears to be s l ight compared to the i@uence of other competing hardwood vegetat ion. South. . I . Appl. For . 21(1):19-23. A n important component of southern Appalachian forest ecosystems is the mixed oak-pine forest type on xeric midslopes and ridges. In recent years, the pine component of this forest type has been substantial ly reduced by drought and associated southern pine beetle (Dendroctonus ,fi-ontalis Zimmerman) infestations (Smith 1991). As a result, extensive areas are poorly stocked and have dense understories dominated by the evergreen mountain laurel (Kalmia latifolia L.) (Clinton et al. 1993, Swift et al. 1993, Vose and Swank 1993). Historically, these oak-pine stands depended on periodic fire for maintenance; however, in the absence of fire, these stands do not regenerate to commercially productive tree species (Barden and Woods 1973, Barden and Woods Now: This project was funded by the USDA Forest Service, Coweeta Hydrologic Laboratory, in cooperation with the Wayah Ranger District of the Nantahala National Forest. Additional funding was provided through the Southern Appalachian Forest Ecosystem Program. A special thanks to Bill Culpepper for providing historical information on past management in the Blazed Creek watershed and to Patsy Clinton for field assistance. Also, we would like to thank Timothy B. Harrington and Thomas A. Waldrop for providing critical reviews of the manuscript. Manuscript received December 4, 1994, accepted January 22, 1996. 1976, Van Lear and Waldrop 1988); therefore, silvicultural prescriptions are necessary to regain productivity. Chainsaw felling, burning, and planting of eastern white pine (Pinus strobus L.) are currently prescribed to convert these shrub-dominated ecosystems to more productive stands of mixed-hardwood and white pine. A necessary objective is to reduce the competitive influence of mountain laurel sufficient ly to al low the planted white pine to become establ ished. The prescribed fire rarely eliminates the mountain laurel, so competition with the planted pines may intensify over time. A mechanical or other form of release is often prescribed during early stand development to reduce competition from mountain laurel and other vegetat ion. I t is not known whether such release is necessary or effective. Pine growth during early stand development has been documented for the first year following outplanting, where diameter growth and seedling physiology were related to biomass of all competitors (Elliott and Vose 1993), but information on competitive effects later in stand development is lacking. In addit ion to competi t ion, severe drought can have longterm adverse effects on tree growth. Some species never fully