Bark Yields of 11-year-old Loblolly Pine as Influenced by Competition Control and Fertilization

Bolts cut from 11-year-old loblolly pines (Pinus taeda L.) were measured to determine the effects of applications of fertilizer and competition control treatments on the amount of pine bark produced. Bark thickness at breast height was not significantly affected by any of the treatments. Regression analysis showed that the dry weight of bark per unit surface area of the bolt increased as the volume of the bolt increased. The regressions for unfertilized and fertilized trees were significantly different: the fertilized trees had less bark. Because bark weight is correlated with bole diameter, bolts were placed in 20-mm-wide inside-bark diameter classes. Fertilizer and woody plant control treatments decreased me in bark weight from 71.6 to 59.7 kg m-3 of wood for bolts in the 1 2 0 m class and from 72.9 to 62.0 kg mP3 for those in the 140-mm class. Introduction We harvested bolts from a stand of loblolly pine (Pinus taeda L.) that had received fertilizer and Weed and treatments weed control treatments. We compared bark weights applied at time of establishment of new plantations to bolt volumes and surface areas to d e , e me increase the growth pines effm of the treatmen& on bark yields. We rrmovpd (Bacon and ZedaLer 1987, Clason 1984, Schmidtling the effects of diameter on bark yields by 1984, Tiarb and Haywood 1986, Zutter and others in regression models and by wg 1987). This reported growth increase is based on comparisons within bolt diameter outside-bark diameter measurements and derived volumes and on the implicit assumption that the treatments do not affect the tree shapes or the proportions of bark and wood in the trees. However, cultural treatments do affect the taper of older trees (Shoulders and others 1989). Because bark has relatively little economic value, even small changes in bark-to-wood ratios could cause significant differences in the economics of a cultural treatment. Because interest has usually centered on determining actual wood volume, most measurements of bark have been of thickness. These measurements have shown that bark thickness changes with d.b.h. (Burton 1962), height (Cochran 1982), and age (Koch 1972). Bark thickness is reduced by fire (MacKinney 1934) and varies with region and soils (Koch 1972). Bark thickness is also difficult to measure accurately (Mesavage 1969) and is highly variable (Judson 1964). Bark weights as a portion of wood volume or weight have been reported but have not been related to silvicultural treatments. Methods Bolts for taper and bark measurements were collected in an 11-year-old loblolly pine plantation established as part of a fertilizer and competition control experiment (Haywood and Tiarks 1990, Tiarks and Haywood 1986). The study site is in Winn Parish, LA, on moderately well-drained Malbis v q fine sandy loam (fine-loamy, siliceous, thennic Plinthic Paleudults). A mature loblolly-shortleaf pine (P. echinuta Mil.) stand was clearcut and the site intensively prepared by V-blading and mot raking. In the winter of 1977-78, 64 loblolly seedlings were planted at a 2.4by 2.4-m spacing on each of 32 19.5by 19.5-m plots. The center 16 trees in each plot were designated as measurement subplot trees. To maintain uniform density, all dead seedlings were replaced in September 1978 with container-grown loblolly seedlings. Paper presented at the Seventh Biennial Southern Silvicultural Reaead Conference, Mobile, AL, November 17-19, 1992. Sod Scientist and Silviculturist, USDA Foreat Service, Southern Fotest Experiment Station, Pinsville, LA. Fertilizer, herbaceous plant control, and woody plant control treatments were applied in a 2 by 2 by 2 factorial experiment with a randomized complete block design. The four blocks served as replicates. Fertilizer was hand broadcast in April 1978 at the rate of 112 kg of nitrogen, 49 kg of phosphorus, and 93 kg of potassium per hectare. Woody plant control was accomplished by two herbicide applications. In 1978, low-volatile ester 2,4,5-T [(2,4,5-trichlorophenoxy) acetic acid] was sprayed on all hardwoods after the pines had been covered. In 1979, the few remaining hardwoods were cut off near the ground and their stumps treated with a picloram (4-amino3,5,6-trichloro-2pyridinecarboxylic acid) and 2,4-D [(2,4dichlorophenoxy) acetic acid] mixture. Herbaceous plant control was achieved by hoeing a 1.14-m radius circle around each pine to remove grasses, grasslike plants, and forbs without damaging pine or hardwood roots. The hoeing was done three times yearly between April and September for the first four growing seasons. Total height and diameter at breast height (d.b.h.) of the 16 loblolly pine trees in each plot center were measured for the &st 10 years. When the pines were 11 years old, the heights and d.b.h. of all living pines on the plots, including those in the border rows, were measured. The measurement data were used to select trees for removal in a thinning operation that would leave 32 living pines per gross plot and 8 evenly spaced, well-formed, crop trees per measurement plot. In each plot, four of the pines identified for thinning and reflecting the diameter distribution of pines on the plot were selected. Whenever possible, trees within the measurement plots were selected, but only if they were from the original planting and not more than one standard deviation smaller in d.b.h. than the mean for the plot. Where this was not possible, trees from the inside border row and having d.b.h. within one standard deviation of the measurement plot d.b.h. mean were selected. Because we preferred to leave good trees in the measurement plots, we took about half of the sample trees from the border rows. After the sample trees were felled, sample bolts were cut from their main stems at heights of 0 to 1, 1 to 2, and 3 to 4 m. These bolts were debarked by hand and the ovendry weight of the bark from each bolt was recorded. The top-end and bottom-end diameters of each debarked bolt were measured with a tape. Single bark thickness was calculated by taking half of the difference between the d.b.h. of the standing tree and the d.b.h. calculated from the upper and lower diameters of the debarked bolt representing the 1-m to 2-m height. Because bark thickness varies around the circumference of the tree (Mesavage 1%9), this method should give better results than does a bark gauge. The surface area and volume of each bolt were calculated from the upper and lower diameters of the bolt and assuming a truncated cone. These results were used to calculate the dry bark weight per unit volume of wood and dry bark weight per unit surface area of the debarked bole. The significance of effects of the treatments on bark thickness was tested by analysis of variance. Linear regression was used to describe the relationship between dry weight of bark per unit surface area and volume of wood. After the bolt data were separated by 20-mm boltdiameter classes, general linear model regression was used to analyze the effects of the treatments on bark weight per unit of wood volume and bark weight per unit of surface area. Results and Discussion