Growth and Yield Relative to Competition for Loblolly Pine Plantations to Midrotation- A Southeastern United States Regional Study
Loblolly pine (Pinus taeda L.) plantations were studied across 13 southeastern sites grown for 1.5 yr with near-complete control of woody, herbaceous, and woody plus herbaceous components during the first 3-5 yr. This multiple objective experiment (the COMProject) documents stand dynamics at the extreme corners of the response surface that encompasses most competition conditions common to pine plantations. This is the second of two companion reports. Merchantable pine volume after 15 yr with early, near complete competition control reached 2,350-4,415ft3/ac by site compared to 1,132-2,965ft3/ac on the no controls. With control of both woody and herbaceous competition, 15 yr volumes were increased by 23-121% and gains increased as hardwoods and shrubs increased on the no controls. Early woody control increased merchantable pine volume on 11 sites by 14-118%, while herbaceous control yielded somewhat less on average, a 17-50% increase on ten sites. No gains and some volume losses occurred when control of one component released severe competition from an enhanced remaining component, otherwise gains were generally additive for control of both components. Pine volume was decreased by about 1% for each 1 ft2/ac of hardwood basal area (BA) present at age 15. Annual measurements determined that culmination of current annual increment (CAI) with control of both competition components occurred in yr 8-2011 at 250-470ft3/ac/yr. CAIs for pine height, BA, and volume were decreased by about 5-27% when growing season rainfall (March-October) was less than 36 in. Mean annual increment had not culminated for any treatment at any location by yr 15 and ranged from 195-250 ft3/ac/yr with both woody and herbaceous control. Fusiform rust mainstem galls [Cronartium quercuum (Berk.) Miyabe ex Shirai f. sp. fusiforme (Hedge. & Hunt) Burdsall & Snow] in high severity areas increased additively with control of both components, more so with herb control. Contrary to the widespread assumption that hardwood out-compete pine, the hardwood proportion of stand BA decreased from yr 5-2015 on sites where hardwood BA in yr 5 exceeded 10 ft2.