Eleventh-Year Response of Loblolly Pine and Competing Vegetation to Woody and Herbaceous Plant Control on a Georgia Flatwoods Site

Through 1 I growing seasons, growth of Ioblolly pine (Pinus taeda L.) increased after control of herbaceous, woody, or both herbaceous and woody vegetation (total control)for thefirst 3 yr after planting on a bedded site in the Georgia coastal flatwoods. Gains in stand volume index from controlling either herbaceous or woody vegetatkn alone were approximately two-thirds that from controlling both types of vegetation. Pine response throicgh age I1 was approximately equalfor herbaceous control alone and woody control alone, whereas, response through age 5 was greater with control of only herbaceous vegetation. The impact of woody vegetation should continue to have a strong effect on pine growth through midrotation because ofits continued development. This is in contrast to herbaceous weeds that have greatly decreased in abundance since age 6. South. J. Appl. For. 22(2):88-95. s. . . tgmftcant progress has been made in developing herbicide prescriptions for woody plant control in the coastal flatwoods region of the southeastern United States. Good to excellent control can be obtained for most major species (Shiver et al. 199 1, Lauer and Glover 1993). As forest managers evaluate the use of herbicides to control woody and herbaceous plants, there is an increased need to understand the potential longterm response from such control. Large short-term response from control of both woody and herbaceous vegetation from the time of planting on flatwoods sites has been noted for both loblolly (Pinus taeda L.) and slash (Pinus elliottii Engelm.) pines (McKee and Wilhite 1988, Swindel et al. 1988, Colbert et al. 1990, Shiver et al. 1990, and Dalla-Tea and Jokela 1991). Because herbicide treatments may be applied to control primarily herbaceous, primarily woody, or both types of competing vegetation, there exists the need to assess the relative importance of effects of the vegetation type conNOTE: Manuscript received July 5,1996, accepted April 3.1997. Bruce Zutter is the corresponding author and can be reached at (334) 8441033; Fax: (334) 844-1084; E-mail: [email protected]. This is Alabama Agricultural Experiment Station Journal Series No. 9-965258. This research was supported in part by members of the Auburn University Silvicultural Herbicide Cooperative. The authors acknowledge the efforts of Ken Xydias in study installation and early measurement and maintenance, and Bill Garbett and other staff members with Union Camp Corp. for continued measurement and maintenance. trolled. A central question is whether the sum of gains in pine growth from controlling individual vegetation types is equal to the gain when controlling both types. Thus, are the effects additive, or more or less than additive? Understanding stand dynamics, with and without competing vegetation of either or both types, is also needed. As a part of the region-wide Competition Omission MonitoringProject(COMP)(Milleretal. 1991,Milleret al. 199.5). a single location was established in the coastal flatwoods of Georgia. Objectives of COMP are to compare the relative importance of effects of woody versus herbaceous vegetation on the shortand long-term growth of loblolly pine and to document dynamics of associated vegetation. This article summarizes response of loblolly pine through 11 growing seasons on the Georgia flatwoods site as influenced by woody and/or herbaceous vegetation control. The abundance of competing herbaceous and woody vegetation is also examined as an aid to understanding pine response over the 11 yr period. Reasons for focusing on results from this single COMP site are: (1) its uniqueness among the other locations in terms of the type of site-lower coastal plain flatwoods-and dominant form of woody vegetation_shrubsand (2) the opportunity to provide a more detailed examination of both shortand long-term dynamics than would be possible if all 88 Reprinted from the Southern Journal of Applied Forestry, Vol. 22, No. 2, May 1998. Not for further reproduction. COMP study locations were being summarized. As the data are from only one location, and might be considered by some individuals as a case study, results will be discussed in reference to findings from similar and more recently established studies on flatwoods sites.