AN INDIVIDUAL-TREE SURVIVAL FUNCTION FOR LOBLOLLY PINE MANAGED UNDER SINGLE-TREE SELECTION

Aspects of the growth and stand dynamics of uneven-aged loblolly pine (Pinus taeda L.) managed under singletree selection were investigated as follows. Eighty-one plots were installed in south Arkansas and north Louisiana. Treatments were three basal areas (40, 60, and 80 ft/acre), three maximum diameters (12, 16, and 20 inches), and three site classes (site index <81, 81-90, and >90 ft at base age 50 years, loblolly pine). Each treatment combination was replicated three times. The logistic function was selected for the individual-tree survival equation, and tree, stand, and site factors were tested as explanatory variables. Initial individual-tree diameter, ratio of initial individual-tree diameter to quadratic mean diameter, and site index were the best variables. The resulting survival equation was used to examine survival patterns for different uneven-aged stand structures. Implications for management are discussed. 1 Research Foresters, USDA Forest Service, Southern Research Station, P.O. Box 3516, Monticello, AR 71655. coastal plain. Each treatment combination was replicated three times, and there are 81 plots in all. Basal areas are kept lower than in even-aged stands to favor the development of pine reproduction. Reynolds (1959) recommended cutting when stand basal area reaches 75 ft/acre to allow pine regeneration to develop. Basal area in uneven-aged loblolly pine stands, therefore, should probably not be much above this level at any time during a cutting cycle. A slightly higher basal area (80 ft/acre) was chosen so that we could investigate its longterm effects on loblolly pine growth and regeneration. The lowest basal area treatment level, 40 ft, probably represents the lower acceptable density limit for management. Densities lower than this approach understocked conditions in which growth is lost without any offsetting gain in regeneration. Maximum d.b. h. in uneven-aged management is somewhat akin to rotation age in even-aged management. Selection of a larger maximum d.b. h. implies a longer term investment. A residual maximum d.b. h. of 20 inches probably represents an upper limit for both economic and product-size goals. A 12-inch maximum d.b. h. represents a lower limit for an adequate seed source. Field Installation and Measurements Each of the stands chosen for plot installation had at least 70 percent of its basal area in loblolly pine; no evidence of cutting within the last 10 years; no evidence of catastrophic loss caused by insects, disease, weather, or fire; and a site index that did not vary more than 10 ft over a plot. Stands that exhibited a reverse J-shaped stand structure were preferred if available. The stands represented a gamut of structures: some already exhibited a reverse J-shaped stand structure, while others had a mound-shaped structure more typical of evenaged stands. Most stands had more than one plot installed in them. All 81 study plots are on the Coastal Plain in southern Arkansas and northern Louisiana (fig. 1). Each square 1.6-acre gross plot included an interior square 0.5-acre net plot. Before harvest, all loblolly pine trees with d.b. h. >3.5 inches were inventoried by 1-inch d.b. h. classes for the 0.5-acre net plots and 1.1-acre isolation strips. Plots were then marked for harvest. Marking was designed to give each plot its assigned residual structure as defined by residual basal area, maximum d.b. h. , and a q of 1.2 for 1inch d.b. h. classes. Any shortleaf pines occurring in the plots were cut. All hardwoods with a groundline diameter ≥1 inch or larger were injected with herbicide prior to harvest, if possible, but no later than the first growing season after treatment. Plot installation and harvesting were carried out over a 3-year period beginning in the fall of 1983. All cutting was completed during the early part of the dormant season of each year, and about one-third of the plots were established each year. After harvesting, all residual loblolly pine trees with d.b. h. >3.5 inches on the net plot were numbered, mapped, and measured. D.b. h. was measured to the nearest 0.1 inch using a tape. A d.b. h. mark was painted on each tree to ensure consistency in subsequent measurements. Total height and height to the crown base were measured to the nearest foot on a sample of 20 percent of the trees in each 1-inch d.b. h. class. Five to 10 height-sample trees suitable for site index calculation were identified and their age determined by increment coring. Trees whose ring widths and growth patterns were indicative of past suppression were not used for site index computation. Site index was computed as suggested by Farrar (1973). The plot trees were remeasured after 4 to 5 years of growth. With the exception of tree age, the same measurements were taken for both surviving trees and ingrowth trees. In addition, tree status (living, dead, ingrowth) was recorded for all trees in both inventories. Cause of death was determined where possible. Data Summary and Analysis Trees that were alive at the time of the first inventory were recorded as alive (1) or dead (0) at the second inventory. The following variables were calculated for trees with d.b. h. ≥ 3.6 inches: Pi t = probability of survival of the ith tree for t years Dmax = maximum d.b. h. (inches) for the plot,