Unthinned Loblolly Pine Plantations Research Articles

Economic Feasibility of Managing Loblolly Pine Forests for Water Production under Climate Change in the Southeastern United States

In this study, we assessed the impacts of climate change, forest management, and different forest productivity conditions on the water yield and profitability of loblolly pine stands in the southeastern United States. Using the 3-PG (Physiological Processes Predicting Growth) model, we determined different climatic projections and then employed a stand level economic model that incorporates, for example, prices for timber and increased water yield. We found that, under changing climatic conditions, water yield increases with thinnings and low levels of tree planting density. On average, under moderate climatic conditions, water yield increases by 584 kL·ha−1 and 97 kL·ha−1 for low and high productivity conditions, respectively. Under extreme climatic conditions, water yield increases by 100 kL·ha−1 for low productivity conditions. Land expectation values increase by 96% ($6653.7 ha−1) and 95% ($6424.1 ha−1) for each climatic scenario compared to those obtained for unthinned loblolly pine plantations managed only for timber production and under current climatic conditions. The contributions of payments for increased water yield to the land values were 38% ($2530.1 ha−1) and 30% ($1894.8 ha−1). Results suggest that payments for water yield may be a “win-win” strategy to sustainably improve water supply and the economic conditions of forest ownership in the region.

A biologically-consistent stand growth model for loblolly pine in the Piedmont physiographic region, USA

A theory-influenced dynamical stand growth model formulation described well the behavior of thinned and unthinned loblolly pine plantations. A simplification containing few free parameters performed as well as a fully parametrized version. It seems particularly well suited to situations where available data is scarce. The stand model can be interfaced to additional climate, nutrition and carbon cycling modules for studying the effects of a changing environment.

Top height definition and its effect on site index determination in thinned and unthinned loblolly pine plantations

Seven definitions of stand (top) height: (1) mean height of dominant and codominant trees at the time of plot measurement, (2) mean height of dominant and codominant trees that have always been dominant or codominant over the life of the stand, (3) Lorey mean height, (4) average height of the 100 thickest trees per hectare at the time of measurement, (5) average height of the 100 thickest trees per hectare at the time of last measurement, (6) average height of the 20% thickest trees at the time of plot measurement, and (7) average height of the 20% thickest trees at each measurement that also survived to the last measurement were evaluated for use in site index (SI) determination. Data collected from permanent plots over a 15-year period in thinned and unthinned loblolly pine plantations were used to make comparisons. Except for a few cases at certain measurements, all seven definitions of top height were significantly different from each other. Site index was predicted based on these definitions to determine if one definition is superior. Magnitudes of the maximum range of residuals and the fit statistics indicated that SI estimated using mean height of dominant and codominant trees that have always been dominant or codominant over the life of the stand is more precise than site indices estimated using other definitions. Using this definition of top height, a new SI equation for these stands was developed.

An iterative state-space growth and yield modeling approach for unthinned loblolly pine plantations

A mathematical iteration-based projection approach is applied in developing a management-oriented tree growth model for unthinned loblolly pine ( Pinus taeda L.) plantations according to the biomass balances among the physical compartments of a tree. In this study, the biomass of each tree compartment is used as a state variable. Tree growth is characterized as a dynamic system in which both inputs and outputs are functions of time. This dynamic system can be updated from one state to another by updating state variables, which is based on a hypothesis from tree physiology that suggests the biomass productivity of a tree is proportional to the foliage biomass. The dynamic processes of the system are described using a transition function and an output function of state variables. This approach evaluates the individual growth response to external forces by predicting some coefficients that regulate the growth response based on the input and output of the system. Compared with the traditional empirical growth and yield modeling approach, this method is more easily adjusted to model growth patterns of plantations managed under different growth conditions.

Predicted leaf area growth and foliage efficiency of loblolly pine plantations

Foliage dynamics research is helpful for better understanding the process of forest production and improving silvicultural practice. However, the difficulty of measuring foliage amount has slowed down the research progress. Since leaf area of an individual tree can be reliably predicted from its diameter, growth and yield models that provide detailed information for each diameter class can be used to benefit foliage dynamics research. Simulation results from a growth and yield system for unthinned loblolly pine plantations indicated that foliage area increased with stand age, peaked between ages 36 and 51, and decreased after that. Volume growth increased with leaf area for young stands and decreased for older stands, whereas foliage efficiency consistently decreased with age. Better sites supported higher levels of leaf area index, volume growth, and foliage efficiency. Higher planting densities led to higher maximum leaf area indices and shorter time to reach that level. Initial density had no effect on foliage efficiency through time.

Basal area development in thinned and unthinned loblolly pine plantations

L'objectif de cette etude etait double: analyser la croissance en surface terriere des peuplements de pin a encens (Pinus taeda L.) apres eclaircie et developper une equation generalisee de prediction de la croissance en surface terriere pour differents types d'eclaircie, differentes conditions stationnelles et une variete d'âges de peuplement au moment de l'eclaircie. Les donnees disponibles proviennent de l'etude sur l'eclaircie du pin a encens entreprise par la Cooperative de recherche en croissance et production sur une vaste region et dans une grande variete de conditions de peuplement. En montrant que la surface terriere des peuplements eclaircis s'approche de celle des peuplements non eclaircis, les resultats de l'etude permettent de developper une equation de prediction de la surface terriere. L'equation inclut un facteur de reponse a l'eclaircie et tient compte de la competition des feuillus. La validation du modele demontre qu'en ignorant les differences de reponse a l'eclaircie, les predictions de la surface terriere sont biaisees alors qu'en incluant le facteur de reponse, elles sont precises pour les types d'eclaircie pratiquee dans ces plantations.

Basal area development in thinned and unthinned loblolly pine plantations

Basal area development in thinned and unthinned loblolly pine plantations

Modeling survival in juvenile and mature loblolly pine plantations

Data from a large, region-wide set of permanent plots were used to develop equations for predicting stand-level survival in thinned and unthinned loblolly pine plantations growing in the southeastern United States. A pre-competitive model predicts survival at young ages based on age and total number of trees surviving. A post-crown closure model predicts survival after the onset of intraspecific competition based on age, site index, thinning intensity, percent hardwood basal area and number of trees surviving. Analyses of the pre-competitive data indicated that survival trends differed by drainage class and site preparation method. Thus, separate sets of coefficients were estimated for two drainage class/site preparation groups. Analyses of the post-competitive data indicated that survival trends differed for thinned and unthinned stands and were affected by the amount of hardwood competition. Therefore, the post-crown closure model was developed and parameterized to reflect the changes in survival as a result of hardwood competition and thinning from below.

Predicting Crown-Height Increment for Thinned and Unthinned Loblolly Pine Plantations

Abstract Several nonlinear, individual tree crown-height increment equations were tested for their ability to predict annual crown-height increment in thinned and unthinned loblolly pine plantations. The selected model contained tree height (HT), tree crown ratio (CR) raised to the one-half power, age (A), and a measure of competition. The distance-dependent and the distance-independent models were the same form; however, the competition index (CI) in the distance-dependent model was replaced by the ratio of quadratic mean diameter to tree dbh (DR) for the distance-independent model. The individual-tree increment models were used as a basis for a stand-level crown-height increment model. The independent variables were collapsed to stand-level statistics; the model contained average height of dominant and codominant trees (HD), average crown ratio (R), and age (A). Unlike the individual-tree models, raising the average crown ratio to 0.5 did not improve the fit. Hypothesis tests revealed that thinning, both its intensity and the elapsed time since its occurrence, had a significant effect on crown-height increment. A thinning variable, T, which accounted for thinning intensity and the interval since thinning, was developed and incorporated into the final individual-tree and stand-level increment models. Predictions of crown-height increment were improved using models with the T variable as compared to those with no thinning allowance. For. Sci. 38(3):594-610.

Optimum Plantation Planting Density and Rotation Age Based on Financial Risk and Return

Abstract A stochastic simulation model was developed to estimate the impacts of site index, planting density, and rotation age on the return and risk of unthinned loblolly pine plantations. Return was estimated as the average present value of an infinite series of rotations for each site, density, and age combination. Risk was approximated as the standard deviation of the present value for each combination. Sources of risk were stumpage rate risk, survival risk, and yield risk. Variability in yield estimates (i.e., yield risk), was the major source of financial risk associated with investments in loblolly pine plantations. Volatility in stumpage rates (i.e., stumpage rate risk), had the least impact on the risk of the investment. For average sites (site index 60 base age 25 years), short rotations are less risky than long rotations. But, as expected, short rotations also tend to have lower returns. Risk averse investors should prefer high planting densities and short rotations. Investors who wish to maximize return alone should select high planting densities with longer rotation ages. Low planting densities (less than 600 stems/ac) are not efficient for sites with site index 50 base 25. For. Sci. 37(3):886-902.

Product-Class Proportions for Thinned and Unthinned Loblolly Pine Plantations

Abstract Data from thinned and unthinned loblolly pine plantations on cut-over, site-prepared lands were used to develop equations to predict the proportions of trees by dbh class that qualify as peelers, sawtimber, or pulpwood. This analysis showed that proportion of peelers increased withthinning but proportion of sawtimber (which included chip-n-saw material) remained relatively constant by dbh class regardless of thinning intensity. Equations were developed to predict the proportion of sawtimber by dbh class with data from all thinning intensities (including no thinning)combined. A constrained equation was fitted to predict proportion of peelers by dbh class for unthinned or thinned stands. South. J. Appl. For. 13(4):192-195.

A Production Function Analysis of Loblolly Pine Yield Equations

Abstract A timber production function analysis for unthinned loblolly pine plantations was made using a four-equation system. In the system, the yield equation is the production function. The production function and other equations fit the data well, using biological consistency, significance, goodness of fit, and minimal collinearity as criteria. The system also predicted volume for lightly and heavily thinned stands with a Mean Difference of 2 and 5% of mean volume, respectively. Analysis of the production function coefficients verified the functional form. More specifically, all input factors are complementary, output elasticities indicate a relatively unresponsive production function, the Elasticity of Scale is 2.3, the elasticities of substitution lie between zero and 1.0, and the production function has Variable Elasticity of Substitution (VES). For. Sci. 35(3):775-788.

Relationships between tree crown, stem, and stand characteristics in unthinned loblolly pine plantations

Empirical and theoretical relationships between tree crown, stem, and stand characteristics for unthinned stands of planted loblolly pine (Pinustaeda L.) were investigated. Readily measured crown variables representing the amount of photosynthetic area or distance of the translocation process were identified. Various functions of these variables were defined and evaluated with regard to efficacy in predicting stem and stand attributes. Linear models were used to evaluate the contribution of the crown variables in predicting stem and stand characteristics. The stem attributes modeled included basal area, basal area growth, diameter at breast height, and diameter growth, while the stand attributes modeled were basal area, basal area growth, arithmetic mean diameter, and mean diameter growth. Crown diameter and crown projection area were particularly important in contributing to model fit and prediction of individual stem characteristics, while sum of crown projection areas was found especially important in stand level equations. As these crown measures developed over time so did corresponding stem and stand attributes.

A Ratio Approach to Predicting Merchantable Yields of Unthinned Loblolly Pine Plantations

Abstract A stand-level ratio model is presented which uses the stand attributes age, site index, basal area, and number of surviving trees per acre to portion total stand yield to any desired top diameter and/or threshold dbh limit. A model is also presented which distributes the total number of trees by diameter such that the basal area is consistent with total stand basal area. Comparisons with two Weibull-based diameter distribution approaches showed the ratio approach to be a practical and satisfactory alternative. Coefficients for the equations were developed for unthinned old-field and cutover, site-prepared loblolly pine plantations. Forest Sci. 32:287-296.

Yield Relationships in Unthinned Loblolly Pine Plantations on Cutover, Site-Prepared Lands

Abstract Data were collected in unthinned loblolly pine (Pinus taeda) plantations on cutover, site-prepared lands across much of the southern United States. Initial measurement data from these permanent plots were used to (1) develop regression relationships between yield of the planted loblolly pine and measurements of the planted pine and competing vegetation, and (2) assess relationships between yield and site preparation methods and physiographic regions (Coastal Plain and Piedmont). These analyses showed that yield of the planted pine component could be predicted adequately from age, average height of dominant and codominant trees, and number of surviving planted trees per unit area. Measurements on the competing vegetation did not significantly reduce the error sum of squares after accounting for the planted-pine variables. An analysis of covariance showed that mean yields (after adjusting for the effects of plantation age, site index, and number of surviving trees) were not significantly different for site preparation classes or physiographic regions. Further analyses showed that survival relationships were similar for the physiographic regions and site preparation classes included. Although the height-age relationships for anamorphic site index curve construction were significantly different for the Coastal Plain and Piedmont, there were no significant differences between site preparation classes within the regions.1

Incidence, Severity, and Growth Effects ofHeterobasidion annosumin Unthinned Loblolly Pine Plantations

Incidence, Severity, and Growth Effects of<i>Heterobasidion annosum</i>in Unthinned Loblolly Pine Plantations