Growth After Thinning a 35-Year-Old Natural Stand to Different Loblolly Pine and Hardwood Basal Areas

Growth was niorzitoredfoi. 4 yi. in a tlzinnedstancl iii southern A/-/vet-e regressed with I-esid~tal pine u i ~ d Izal-dwood basal areas. Pine basal oreu and volume givwth increased with the pine stoclcii7g leveIiifte1. thinning anddecreased with thc level ofr-etained harilwoods. Foi.basaIar.ea andrner-charztahle i'iilunze, hardwoodgro~-1fiL lar.gely c,onzpe~zsatedfor losses in the pine component, and thus, ha/-dnjuod r-etention had little net effect on the total growth oJ thc. staizcl. The greatest irnpar.f ofhurilwood rete/ztiou was on the staizcl's suwtirnhelg7-owt/z, beiainse har.dwoods did not coiztribute to thi.sprnduc.t c1as.r. Each I ,ji2/ac ofretained harrlwood basal area reducedpiitc ~awtinzbergrowtlz by 6 to I 0 htl ft Doylelaciyr-, depe~zding on the pine stoi,kiiig. Because large d~J?ererzces vistecl irt the i~alue c f t iml~crprod~~c t s , r-etainirzg I5 ai?cl30f$/uc clflzul-dwoorls radcrred [he value oftimberpi-odi~cfion by 13 aizd 2470, respectively, at 4 yr ufter th innin~. South. .I. Appl. For. 2/(4):168-174. Pne-hardwood stands are an important resource in the South, occupying some 27 millioil ac (USDA Forest Service 1988). In addition, mimy oC the 41 million ac in the natural pine type contain a significant hardwood component. Although pine-hardwood stands have occurred naturally for many years, their management and establishment has only been recently proposed (Waldrop I98Y). Two major trends that are shaping the current interest in pine-hardwood stands are environmental issues and changing markcts/processes (Lentz et al. 1989). Markets have been developed for the small-diameter hardwoods typically found on pine sites and are expected to increase In the future. Landowners now have the option to allow hardwoods lo grow to merchantable sire in cstahlished pine stands and harvesting them, rather than applying control treatments. The competition between pines and hardwoods has long been thc subject of southern forestry rcscarch. However, most of this information has focused on the critical establishment phase of even-aged stand development, because success or failurc of pine I-egeneration often depends on controlling hardwood competition. The intcnsity of hardwood control during stand establishment is often directly related to the NOTE. This ~ e s e a ~ c h wa? conduc~ctl in co~rjunction with the Scliool of Forest Resources of the Un~vcrsily of Arkansas dt Montlcello. The autl~ors thank the reviewer? fnr thclr helplul commenrs. Manuscript received February I 1, 1996. acccplcd February 15, 1997. growth rates of the pines (Glover andzutter 1993). However, less definitive results have been obtairled for hardwood coiltrol in well-established pine stands. Soine studies in natural stands have clbserved positive growth responses of overstory pines to hardwood removal (c.g., GI-ano 1970, Cain and Yaussy 1984), while others have not (e.g., Cain 1985). Boyer ( 1986) proposed that a threshold exists for hardwoods, ranging between 10 and 30 ft2/ac of basal area, below which there isno discernible el'fect on thegrowth of ovel-story pines. There appears to be little economic or biological justilication for controlling hardwoods below this rhresholtl. One lnanagement alternativc for pine-hardwood stands is to convert Lhem to pure pine by removing hardwoods through harvesting or control treatments. However. many landowners find this option unacceptable, particularly if conversion requires high capital investments. Other landowners want to retain a hardwood component because they place a high priority on nontimber resources (Haymond 1988). Making wise choices among management alternatives rcquires quantitative info~mation on resource trade-offs between pines and hardwood?. To better understand the growth relationships bctween pines and hnrdwoods, a thinning study was installed in a 35-yr-old natural loblolly pine (Pinus tarcia L.) stand with a significant hardwood component located on a good site in southern Arkansas. In this paper, we report thc growth relationships for the first 4 yr after thinning, which was completed in 1989. 168 Reprinted from the Southern Journnl of Applied Foresfry, Vol. 21, No. 4, November 1997. Not for further reproduction.