Response of loblolly pine plantations to woody and herbaceous control - eight-year results of the region-wide study - The COMProject

Zutter, B.R.; Miller, J.H.; Zedaker, S.M.; Edwards, M.B.; Newbold, R.A.

General Technical Report Southern Research Station, USDA Forest Service ( SRS-1): 75-80


Accession: 003259264

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The COMProject (competition omission monitoring project) was developed to compare the effects of herbaceous and/or woody weed control in loblolly pine (Pinus taeda) plantations in the southeastern USA. Woody weeds (hardwoods and shrubs) were controlled with glyphosate and/or triclopyr, while herbaceous weeds (including vines and semi-woody plants) were controlled with sulfometuron in spring and glyphosate during summer. Eight-year response of planted loblolly pine to woody and herbaceous control following site preparation, studied at 13 locations from Louisiana to Virginia, differed by pine response variable and hardwood level grouping. Treatments affected average pine height the same at both low hardwood (<6 ftsuperscript 2/acre basal area at age 8) and high hardwood (>13 ftsuperscript 2/acre) levels, and ranked: total control (woody + herb control) > herb control > woody control > no control. The same ranking held for pine diameter at breast height (dbh), basal area/acre, and volume index/acre at the low hardwood level. However, at the high hardwood level, dbh response to woody control exceeded that for herb control, while basal area/acre and volume index/acre response were equal for the two treatments. Volume index increases over no control on the low and high hardwood levels averaged 127% and 336% greater with total control; 32% and 57% greater with woody control only; and 92% and 73% with herb control only, respectively. Treatment effects on all pine response variables were additive at the low hardwood level, and more than additive at the high hardwood level.