A base-age invariant site index equation for jack pine based on the Chapman–Richards function was produced that satisfied nine criteria of preferred behavior for site index equations. A difference form of the Chapman–Richards equation produced the best behavior; height equalled site index at base age, and the shape of the curves reflected the data. The data structure used to fit the difference equation was all possible differences rather than the conventional nonoverlapping sequential intervals because this improved the behavior of the model. Height-prediction equations typically use height at base age (site index) as a predictor variable. As site index is measured with error, the equation will be biased. This bias will be evident in the predicted height at base age and in the shape of the curves. Base-age invariant equations predict height and site index with the same equation and thus diminish the effect of stochastic predictor variables. The equation performed comparably to a previously published equation with a specific base age of 50 years.

Modeling height in the context of site index involves two processes: (i) estimating height at base age (site index), given height at some other age, and (ii) estimating height at some desired age given height at base age. When these two processes are modeled by individual functions for each process, height is assumed to be measured without error when on the right-hand side of the equation, but possessing error when on the left-hand side of the equation. This assumption causes a bias in the parameters of the site index curves. The bias in the estimated parameters is evident in the magnitude of the curves and in the shape of the curves, the typical change of shape of the curves from low site index to high site index is underestimated. An ad hoc method is presented that solves the problem. The ad hoc method is conceptually related to methods used in linear regression and to maximum likelihood estimation in a measurement errors problem context. A general measurement errors model is presented as an alternative. The measurement errors model requires an independent estimate of measurement error.

On a silt loam soil in central Louisiana, three cultural treatments were applied to a seedling loblolly pine (Pinus taeda L.) plantation. The treatments were in a 2 × 2 × 2 factorial design: (1) no fertilization or a broadcast application of 177 kg N/ha and 151 kg P/ha; (2) no herbicides applied or broadcast or spot applications of hexazinone, sulfometuron methyl, or glyphosate herbicides and felling as required to control competing vegetation during the first three growing seasons; and (3) no litter applied or broadcast application of pine litter to form a 10 to 15 cm layer in the first growing season. Through 12 growing seasons, the fertilization or herbicide treatment significantly increased stand growth (α = 0.05), and these two treatments had an additive effect (no treatments, 209 m3/ha; fertilization, 328 m3/ha; herbicide, 280 m3/ha; fertilization and herbicide, 362 m3/ha). However, because litter application probably had a minor fertilization effect, the fertilizer and litter combination produced the greatest yield (370 m3/ha). The herbicide and litter combination adversely affected pine survival, and so applying all three treatments was no more effective than fertilization alone. The loblolly pine overstory was the dominant factor influencing the long-term development of the understory.

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A stocking guide was developed from the data of Putnam, et al. (1960). The form of the stocking guide follows Gingrich (1967), although the “B”-line is based on the suggested residual stocking of Putnam, et al. (1960) rather than on minimum full stocking. This stocking guide is similar to the stocking guide for central upland hardwoods constructed by Gingrich, except that 100% stocking is 5-7 ft2² of basal area lower for the southern bottomland guide, across a range of quadratic mean diameter. South. J. Appl. For. 19(3):103-104.