Thinning Methods in Slash Pine Plantations.

Results of a thinning experiment initiated in 1937 in a 13-yearold slash pine (Finus elliottii Engelm.)plantation growing on land of high site quality near Bogalusa, Louisiana were studied.Four thinning treatments (Light Low, Light Crown, Heavy Crown and Selection) and a control (unthinned) were compared.Each treatment included two l/4-acre plots, and individual tree measurements were taken periodically.The Heavy Crown and Selection treatments were applied at ages 13 and 26.The Low and Light Crown treatments were applied at ages 13, 24, and 29.One control plot, one Heavy Crown and one Selection plot were inadvertently thinned at age 30.No additional cutting has occurred.The trees were 40 years old when last measured.No statistically significant differences in either net or gross cubic volume increment per acre were found among the treatments by age 29, but there were indications that frequent light thinnings produced more net volume per acre than heavy thinnings or no thinnings by age 40.Residual trees inadvertently thinned on the Control plot grew rapidly, indicating that age 30 is not too late, on good sites, for' slash pine to respond to thinning.Thinning stimulated tree diameter growth, and the increased growth rate was maintained longer on the more heavily thinned plots.x Increment in individual tree volume was positively correlated with crown length and crown ratio.Crown length was a better variable for predicting volume increment than was crown ratio, but neither vari able had a strong effect on increment.The average height of the trees varied with treatment; unthinned plots had the shortest average height and the Heavy Crown plots had the greatest average height.This result was thought to be a reflection of the sizes of the trees removed in thinnings rather than of growth stimu lation resulting from treatment.Dominant-tree height showed little effect from treatment.A financial analysis of the plots up to age 40 showed that thin ning is financially advantageous.The Light Crown and Selection plots proved to be the most valuable.The plot that was first thinned at age 29 was more valuable than one never thinned, indicating that even deferred thinning is profitable.Mortality was greatest on the unthinned plot; no significant differences in mortality were found among the thinned plots.Fusiform rust appeared to be an indirect cause of most.mortality;those trees that died from suppression were much smaller than the average for the s tand.Random samples, totaling 158 trees, were selected from the plots in order to make a study of individual trees.Tree form class and specific gravity of the outer ten growth rings were apparently unaffected by differences in stand density.The number of suitable xi pole-and-piling trees per plot was unaffected by the thinning treatment.The exterior quality, expressed in terms of the size and number of firstlog knots, seemed to be slightly improved by thinning.A competition index was developed from the sample tree data, based on the hypothesis that a tree's growth is modified by the proximity and relative sizes of the trees that surround it.It was assumed that each tree influences a circular area within a stand.When two such areas overlap, a zone of competition is established.The index of a single tree is defined as the ratio of the sum of the competition-zone areas within that tree's influence circle to the area of this circle.This competition index was inversely correlated with past growth and present crown width of the sample trees.It was concluded that this index may be useful for measuring stand density and thinning intensity and for predicting future tree growth.