Modeling the Effect of Density on the Growth of Loblolly Pine Trees (original) (raw)
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Modeling the Effects of Initial Spacing on Stand Basal Area Development of Loblolly Pine
Forest Science, 2012
Several studies have reported that in loblolly pine stands with high initial density, basal area declines after reaching maximum carrying capacity. This behavior is not reproduced by most basal area development models because the functions used are sigmoid and nondecreasing, tending toward an asymptote. We used a combined exponential and power function to model the impact of initial density on the basal area development of loblolly pine in a spacing trial. The combined exponential and power function is sufficiently flexible to describe both the asymptotic behavior of the wider initial spacing plots and the decrease in basal area after culmination of the closer spacings. We modified the original function to account for the time lag between stand establishment (age ϭ 0) and basal area establishment (age Ͼ 0), by allowing the origin of the function to be different than age ϭ 0. Two final models are presented: a model fitted using the population-average (PA) approach and a model fitted using the mixed-effects (ME) approach. At the fixed-effects level, the PA and ME models are not equivalent, and, therefore, the appropriate model should be selected according to the availability of previous data and the objectives of the prediction. If previous observations are available, they can be used to improve the predictions using the ME model. FOR. SCI. 58 :95-105.
Effects of initial spacing on height development of loblolly pine
The relationship between dominant height and age is the base of site index, the most widely used measure of site quality. In applying the site index concept, one typically assumes that height development is not affected by stand density or thinning treatment. This assumption has been challenged by recent studies on loblolly pine. A detailed data set with initial densities ranging from 6,730 to 750 trees/ha and covering ages 1 through 25 after plantation establishment was used to study and model the effect of initial spacing on height development of loblolly pine. Dominant height was found to be dependent on initial spacing. Height-age models are proposed that take into account the effect of spacing on average and dominant height. The differences among plantation densities are evident from age 6 and are consistent to the end of the 25-year period of study. Previous studies in other conifers have reported an early advantage in terms of height growth in denser stands that tend to disappear with age, producing a crossover of the growth trajectories. No evidence of this crossover effect in height was found. FOR. SCI. 57(3):201-211.
Modeling individual tree growth for juvenile loblolly pine plantations
Forest Ecology and Management, 1996
Modeling juvenile growth of loblolly pine plantations is important for a better understanding of the whole process of stand development and helping to schedule appropriate silvicultural treatments for young stands. This paper evaluates spacing treatment effects on young loblolly pine trees and presents individual tree growth models for loblolly pine plantations. Using data from spacing trials (plot size ranging from 1.22 X 1.22 to 3.66 X 3.66 m2) for loblolly pine plantations, a generalized randomized block design (GRBD) analysis was conducted to test spacing treatment and site quality effects on young tree growth. It is shown that planting density and site quality have significant influence, and spacing rectangularity is negligible. Based on the Bertalanffy differential equation and biologically reasonable assumptions regarding density and site quality effects on tree growth, a general projection model for individual tree diameter and height was developed. A stochastic model for generalizing tree height predictions within each diameter class was proposed. Models for crown ratio, and initial diameter distribution were also developed. The models were estimated with spacing trial data from young loblolly pine plantations. Validation results for these models showed that they are appropriate for predicting the juvenile growth of loblolly pine plantations where competing vegetation has been controlled in a similar manner to these spacing trials.
The effects of spacing and thinning on stand and tree characteristics of 38-year-old Loblolly Pine
Forest Ecology and Management, 2000
The effects of early and continuous density control on tne characteristics of mature loblolly pine (Pinus tuedu L.) were measured at age 38 and analyzed. Trees in plots planted at spacings of 1.8x 1.8, 2.4x2.4, 2.7x2.7, 3.0x3.0, and 3.7x3.,7 m were either left unthinned or thinned every 5 years beginning at age 18, to residual basal areas of 27.5, 23.0, 18.4, and 13.8 m2 haa'. Trees thinned from plot buffer zones at age 38 were selected to represent a final harvest cross-section of each treatment for evaluation of bole form, component biomass, ;and crown architecture. Volume and biomass of cut trees from all thinnings were included with the age 38 data for stand level yield comparisons. Results show thinning effects were generally more pronounced than spacing effects. Trees of the same diameter at breast height and total height from heavily thinned stands had more cylindrical lower boles, more upper stem taper, longer crowns with more and larger branches, more total foliage, and hence more biomass than trees from unthinned or lightly thinned stands. All levels of thinning increased the yield of the stand in terms of foliage and branch biomass, while only light or moderate thinning increased bole biomass and volume yields. 'The magnitude of these differences are presented. 0 2000 Elsevier Science B.V. All rights reserved. fed.us (V.C. Baldwin Jr.). and stand growth and yield and tree form in planted and natural stands of different densities (e.g. USDA, Forest Service, 1929; Mann and Dell, 1971; Burkhart et al., 19X7), information regarding the morphology and yield differences in older plantations is lacking. We analyzed standing-tree measurements and intensive felled-tree measurements (of thinned trees) at age 38 of a long-term, loblolly pine growth and yield study. Our objective was to show the effects of initial planting spacing and thinning (1) on biomass and volume 0378-l 127/00/$ -see front matter 0
Growth-Density Relationships in Loblolly Pine Plantations
Forest Science, 2018
An understanding of relationships between stand volume growth and stand density is important for making informed management decisions. Contradictions concerning these relationships have been attributed to differences in definitions of volume growth and stand density, among other pitfalls. Models were developed to test growth-density relationships using past-growth data from three thinning studies in 11-to 41-year-old loblolly pine (Pinus taeda L.) plantations. Relationships between gross growth and stand density measures of basal area per hectare, stand density index, volume per hectare, and relative spacing were compared. Relative growth-density relationships were also compared by relating the growth and density of thinned plots to unthinned plots. Analyses indicated that gross volume growth increases with increasing stand density when accounting for age, quadratic mean diameter, and site quality. Results from relative growth-density relationships suggested that thinned stands can exhibit increased growth at relatively lower densities compared to that of an unthinned stand on a similar site. The fitted models, across all four density measures, indicated ever-increasing gross volume growth with increasing stand density within the range of observed data for loblolly pine plantations.
Spacing rectangularity effect on the growth of loblolly pine plantations
Canadian Journal of Forest Research, 2002
The effect of spacing rectangularity on tree growth and stand development was evaluated using tree data obtained annually from a loblolly pine (Pinus taeda L.) spacing trial monitored through age 16 years. In this trial, plots with an initial planting density of 2240 trees/ha occur at slightly and highly rectangular spacings. Spacings with rectangularities 3:4 and 1:3 were used to evaluate the rectangularity effect. Survival and the development of height, diameter, volume per hectare, and basal area per hectare of loblolly pine trees were not affected by rectangularity. Diameter and height distributions were found to be a function of age but not a function of the rectangularity of initial spacing. Crown width, however, was affected by rectangularity. The crown width was larger at larger row or column distance than at smaller row or column distance, but the ratio of crown widths between and within rows was not equal to the rectangularity of the original planting spacing.
Regional mixed-effects height–diameter models for loblolly pine (Pinus taeda L.) plantations
European Journal of Forest Research, 2007
A height-diameter mixed-effects model was developed for loblolly pine (Pinus taeda L.) plantations in the southeastern US. Data were obtained from a region-wide thinning study established by the Loblolly Pine Growth and Yield Research Cooperative at Virginia Tech. The height-diameter model was based on an allometric function, which was linearized to include both fixed-and random-effects parameters. A test of regionalspecific fixed-effects parameters indicated that separate equations were needed to estimate total tree heights in the Piedmont and Coastal Plain physiographic regions. The effect of sample size on the ability to estimate random-effects parameters in a new plot was analyzed. For both regions, an increase in the number of sample trees decreased the bias when the equation was applied to independent data. This investigation showed that the use of a calibrated response using one sample tree per plot makes the inclusion of additional predictor variables (e.g., stand density) unnecessary. A numerical example demonstrates the methodology used to predict random effects parameters, and thus, to estimate plot specific height-diameter relationships.
Forest Science, 1992
A•STRACT. The prediction performance of eight height-diameter regression models was compared for estimating mean stand height when fitted to data selected from 175 1oblolly pine (Pinus taeda) sample plots by (i) simple random sampling without replacement, and (ii) stratified random sampling with dbh classes acting as strata. Among the models tested, the nonlinear model of the form H = ae a/ø performed best especially when fitted to data selected by simple random sampling. A small gain in precision obtained by stratification into dbh classes was outweighed by a substantial increase in bias due to the arbitrary allocation of numbers of sample trees to the strata. To update existing height-diameter models, it is recommended that new trees be selected and measured on every occasion instead of retaining the same sample trees used previously for model fitting. FOI•. Scl. 38(1):192-198. ADDITIONAL KEY WORDS. Inventory, height estimation, regression analysis, Pinus taeda. 192/FOP, ESTSCmNCE CITED BASKERVILLE, G.L. 1972. Use of logarithmic regression in the estimation of plant biomass. Can. J. For. Res. 2:49-53. CURTIS, R.O. 1967. Height-diameter and height-diameter-age equations for second growth Douglasfir. For. Sci. 13:365-375. EK, A.R. 1973. Performance of regression models for tree height estimation with small sample sizes. P. 67-80 in Statistics in forestry research, Proc. 4th Conf. Advisory Group of For. Stat., Vancouver, BC. FLEWELL•NG, J.W., and L.V. PmNAAa. 1981. Multiplicative regression with lognormal errors. For. Sci. 27:281-289. GREEN, E.J. 1981. Models of stand basal area distributions, individual tree basal area growth, and FEBRUARY 1992/ 197 height-diameter relationships for lobIdly pine. Ph.D. diss., Va. Polytechnic Inst. & State Univ., Blacksburg.
Forest Ecology and Management, 2013
Loblolly pine (Pinus taeda) is an important timber species in the southeastern US and abroad. A better understanding of loblolly pine crown relationships with growth has implications for improving productivity estimates using process-based models or remote sensing techniques. Four study installations in the Upper Coastal Plain and Piedmont of Georgia were used to examine the effects of planting density and cultural intensity on loblolly pine stand growth and crown attributes. Treatments included six planting densities, ranging from 740 to 4440 trees ha À1 , in a split-plot design with two different levels of fertilization and competition control. The ''low intensity (LI)'' cultural treatment included relatively high nutrient inputs and early competition control. The ''high intensity (HI)'' cultural treatment included even greater nutrient inputs and complete sustained competition control. Treatment effects on stand and crown attributes were examined at age 13. Fertilization and competition control did not have a major influence on stand and crown attributes. Stands planted at lower densities resulted in significantly greater DBH and height but less standing volume per hectare, basal area per hectare, and current annual increment (CAI) volume growth compared to stands planted at higher densities. Stand-level foliar biomass, peak projected leaf area index (LAI), foliar nitrogen (N) content, specific leaf area (SLA), and intercepted photosynthetically active radiation (IPAR) were significantly greater for stands planted at higher densities, while live crown length and crown ratio were significantly greater for stands planted at the lower densities. IPAR efficiency (CAI per IPAR) was significantly affected by planting density, with values of 0.32-0.42 m 3 %IPAR À1 for 740 and 4440 trees ha À1 , respectively. At this stage of stand development, light limitations due to high stocking have a greater influence on growth than soil resource limitations for the loblolly pine plantations analyzed in this study. Higher density stands resulted in increased SLA and IPAR efficiency, supporting the idea that higher density stands utilize light more efficiently than lower density stands.