Influence of Planting Density on Diameter and Height in East Texas Pine Plantations

The resp•nse •f diameter and height •f unthinnedplanted stands •fl•bl•lly (Pinus taeda L.) and slash (Pinus elliottii Engelm. ) pine in East Texas to different classes of planting densities were analyzed. After tracking the development ofdiameter and height for 15 yr on a set ofpermanentplots representing a broad range of plantation parameters, average diameter and average height trends were observed. For both species, average diameter values were significantly larger with lower planting densities. In contrast, average height growth is insensitive to planting density at younger age classes for loblolly and at older age classes for slash pine plantations. South. J. Appl. For. 22(4):241-244. Choice of the number of t ees per acre to plant (planting density) is a critical decision facing a plantation manager. The choice can affect the selection of a site preparation technique, planting procedures, and the genetic stock, which in turn can influence the total cost of plantation establishment. Profit on the establishment investment may be realized, if the trees are of sufficient size at harvest to be merchandised into suitable products for the anticipated markets. The effect of planting density on tree size (diameter-measured at breast height and height--total tree height) has been investigated for several species. For young stands of loblolly pine (Pinus taeda L.) in Georgia, lower planting densities resulted in larger diameter trees, while height was not significantly influenced by planting density (P•enaar and Shiver 1993). Similar results were found for slash pine (P. elliottii Engelm.) in Georgia (Sarigumba and Anderson 1974), Choctawhatchee sand pine (P. clausa var. immuginata D. B. Ward) in the southeastern Coastal Plain of the United States (Outcalt 1986), Eucalyptus grandis Hill ex Maiden trees in southwestern Florida (Meskimen and Franklin 1978), and Terminalia superba in Nigeria (Okojie et al. 1988). No information on planting density and tree size is available for southern pines on the western edge of the range. The objective of this study was to determine the effect of planting No•: J. David Lenhart is the corresponding author, and he can be reached at (409) 468-2090; Fax: (409) 468-2489; E-mail: dlenhart@sfasu.edu. Support from companies participating in the East Texas Pine Plantation Research Project•hampion International Corporation, International Paper Company, Louisiana-Pacific Corp., Resource Management Services, Inc. and Temple-Inland Forest Products Corp.--is appreciated. Manuscript received July 17, 1997, accepted December 17, 1997. density on diameter and height development of unthinned planted pine trees in East Texas. Plantation Measurements Observations from an array of 282 permanent plots located throughout East Texas in 196 unthinned industrial 1oblolly and 86 slash pine plantations were utilized in this study. Each plot consists of two adjacent subplots (separated by a 60 ft buffer). When the East Texas Pine Plantation Research Project permanent plots were installed in 19821984, the age of the plantations varied from 1 to 15 yr of age. From either planting records or field measurements, planting density was determined for each subplot. After 15 yr or 5 cycles of measuring the planted pines within each plot, about 25% of the original subplots have been lost due to acts of man or nature. In this analysis, each subplot was treated as a sampling unit. As a result, from the 15 yr period, 1,601 loblolly and 720 slash subplot observations were available for quantifying the development of the planted pines. For each observation: age was known, and average diameter (in.) of all trees and average total height (ft) of the ten tallest rees were calculated. In addition, planting density (trees per acre) was constant for each sampling unit. The nature and character of these five plantation variables are depicted in Table 1. Average planting density for both species could translate into spacings of about 8x 8 ft, 6 x 10ftor 5x 12ft. Observations from the 1oblolly data set were grouped by five planting density classes (_ 800) and four age classes (5, 10, 15, and >20 yr); however, a <400 class was not available for the slash pine data set. Based on these data, one-way ANOVA calculations were conducted