Richard F. Daniels

An integrated system of forest stand models

Abstract An integrated system of stand models has been developed in which models of different levels of resolution are related in a unified mathematical structure. Detailed models are specified, and from them a set of growth and survival functions is derived to produce models structurally compatible at lower stages of resolution. The most detailed model is a distance-dependent individual-tree model that simulates the growth and competitive interaction of trees in a stand. Tree basal area and height growth were modelled using a modified Chapman-Richards function in terms of potential growth, current size, relative size, crown ratio, and an index of competition. Potential growth was expressed as a function of site quality, age, and open-grown size. Tree survival probability was described using a logistic function in terms of age, crown ratio, and competition. The point density measure used was area potentially available (Ap), calculated as the area of the polygon constructed from lines which divide the distance between a tree and its neighbors. Mean Ap, or average area per tree, is estimated as the inverse of the number of trees per unit area, so that point density reduces to stand density and a distance-independent individual-tree model results. The distance-independent individual tree model was collapsed to consider trees grouped in size classes. Tree growth and survival equations were applied to the mean attributes of each size class, resulting in a size-class projection model. Following through, the dimensions of the model were collapsed to an ‘average’ tree. A stand-level projection model results from applying the tree growth and survival equations to the stands average tree attributes. At the stand level, the basal area growth function provides a transformation which, for a number of probability density functions (pdfs), will regenerate the initial pdf family. Considering a normal pdf to describe basal area distributions, a pdf-based size distribution model was developed, in which the projected parameters were expressed in terms of the growth function coefficients.

Regional variation in wood specific gravity of planted loblolly pine in the United States

Loblolly pine (Pinus taeda L.) is the most important plantation species in the southeastern United States and specific gravity (SG) is its most important wood quality trait. Analysis of annual ring SG of breast height (1.37 m) incre- ment cores from 3957 trees representing 147 plantations across the species natural range showed that ring SG increases with increasing age and varies significantly among physiographic regions. The South Atlantic and Gulf regions had the highest ring SGs, while the Hilly and Piedmont regions had the lowest. Based on ring SG, the juvenile period averages 4.3 years, followed by 8.6 years of transition wood, with mature wood produced by year 13. Whole-core mean SG was significantly higher in the South Atlantic (0.486) compared with the other regions (mean = 0.455), which were not statisti- cally different from each other. Trees from the South Atlantic have significantly higher whole-core SG because they con- tain significantly more latewood (40.1%) compared with trees growing in other regions (33.8%). Maps indicate that stands in the South Atlantic and Gulf regions have the highest SG at a given age. Stands growing on the northern and western fringe of the natural range of loblolly pine have the lowest whole-core SG.

Relationships between acoustic variables and different measures of stiffness in standing Pinus taeda trees

Acoustic tools are increasingly used to estimate standing-tree (dynamic) stiffness; however, such techniques overestimate static stiffness, the standard measurement for determining modulus of elasticity (MOE) of wood. This study aimed to identify correction methods for standing-tree estimates making dynamic and static stiffness comparable. Sixty Pi- nus taeda L. trees, ranging from 14 to 19 years old, obtained from genetic tests established in the southeastern United States, were analyzed. Standing-tree acoustic velocities were measured using the TreeSonic tool. Acoustic velocities were also recorded in butt logs cut from the same trees using the Director HM200. A strong but biased relationship between tree and log velocities was observed, with tree velocities 32% higher (on average) than the corresponding log velocities. Two correction methods, one for calibrating tree velocities and one for accounting for differences in wood moisture con- tent, were used to determine an adjusted MOE. After correction, adjusted MOE estimates were in good agreement with static longitudinal MOE values measured on clearwood specimens obtained from the trees, and no systematic bias was ob- served. The results of this study show that acoustic estimates of MOE on standing trees largely depend on how the data are processed and the reference method used.

Estimation of Microfibril Angle and Stiffness by near infrared Spectroscopy using sample sets having Limited wood Density Variation

Near infrared (NIR) spectroscopy offers a rapid method for the estimation of microfibril angle (MFA) and SilviScan-estimated wood stiffness (EL(SS)). The success of these NIR calibrations may be related to airdry density, because density varies in wood simultaneously with MFA and stiffness. The importance of density variation was investigated by developing calibrations for MFA and EL(SS) using Pinus radiata D. Don (radiata pine) and Pinus taeda L. (loblolly pine) sample sets where the density range was small and the relationships between density and MFA and density and EL(SS) were poor. Excellent calibrations for MFA and EL(SS) were obtained, particularly when sets had densities greater than 500 kg/m3, can provide strong relationships for MFA and stiffness even when density variation is limited. Examination of loading plots from the MFA and EL(SS) calibrations indicates that variation in wood components such as cellulose, lignin and possibly hemicellulose is important.

Comparison of Pinus taeda L. wood property calibrations based on NIR spectra from the radial-longitudinal and radial-transverse faces of wooden strips

Abstract When a radial strip is cut from an increment core it can potentially be cut with two orientations: parallel to longitudinal tracheids, i.e., a radial-longitudinal (RL) strip (the orientation of SilviScan samples), or at an orientation of 90° to the tracheids, i.e., a radial-transverse (RT) strip. Both strips could be used for near-infrared (NIR) analysis, but it is unknown how calibrations based on RT-face NIR spectra compare with those based on RL-face NIR spectra. A total of 20 Pinus taeda L. (loblolly pine) RL strips were characterized in terms of air-dry density, microfibril angle (MFA), stiffness and several tracheid morphological characteristics. NIR spectra were collected in 10-mm increments from the RL and RT faces of matching strips and used to develop calibrations for each property. In general, RL-face NIR spectra gave calibrations that provided stronger relationships. Differences between the two sets of calibrations were small, indicating that either face could be used for NIR analysis.

Estimation of the physical wood properties of Pinus taeda L. radial strips using least squares support vector machines

Near infrared (NIR) spectroscopy offers a rapid method for estimating many important wood properties, including air-dry density, microfibril angle (MFA) and SilviScan estimated stiffness (EL(SS)). Wood property calibrations may be improved by using non-linear calibration methods. In this study, we compare calibrations developed using partial least squares (PLS) regression and least-squares support vector machine (LS-SVM) regression, a relatively new technique for modelling multivariate, non-linear systems. LS-SVM regression provided the strongest calibration statistics for all wood properties. For an equivalent number of latent variables, the predictive performance of the MFA LS-SVM calibrations were superior to those of the corresponding PLS calibration, while predictive results for air-dry density and EL(SS) were similar for both calibration methods.

Comparison of Pinus taeda L. whole-tree wood property calibrations using diffuse reflectance near infrared spectra obtained using a variety of sampling options

A necessary objective for tree-breeding programs, with a focus on wood quality, is the measurement of wood properties on a whole-tree basis, however, the time and cost involved limits the numbers of trees sampled. Near infrared (NIR) spectroscopy provides an alternative and recently, it has been demonstrated that calibrations based on milled increment cores and whole-tree data can provide good estimates of whole-tree properties. Several options exist for sampling standing trees and the aim of this study was to compare wood property calibrations based on NIR spectra collected from samples obtained using different sampling methods. Calibrations for whole-tree lignin and basic specific gravity based on NIR spectra from whole-tree chips (milled or intact) had the strongest statistics, calibrations based on NIR spectra from milled increment cores were similar. Other options for sampling the tree (drill shavings, etc.) gave errors that were too large for practical applications. If an increment core is going to be used to estimate whole-tree properties, it is recommended that it be dried and milled prior to analysis.

Modeling corewood–outerwood transition in loblolly pine using wood specific gravity

A modified logistic function was used for modeling specific-gravity profiles obtained from X-ray densitometry analysis in 675 loblolly pine (Pinus taeda L.) trees in four regeneration trials. Trees were 21 or 22 years old at the time of the study. The function was used for demarcating corewood, transitional, and outerwood zones. Site and silvicultural ef- fects were incorporated into the model. Heteroscedasticity and within-group correlation were accounted for by specifying the variance and serial-correlation structure, respectively. The estimated transition zone was located between rings 5 and 15, and the outerwood demarcation point varied from rings 12 to 15. No effects of treatments on the demarcation points were observed; however, site preparation and fertilization affected the lower asymptotes of the curves in all sites. A geo- graphical trend for the demarcation point was observed, with the northern site requiring more time to reach a plateau in specific gravity compared with the southern sites. The diameter of the juvenile core was increased as a result of the treat- ments. However, the amount of corewood was not statistically affected, ranging from 55% in the north to 75% in the south, except at one site where fertilization decreased the percentage of corewood.

High Resolution Scanning of Radial Strips cut from Increment Cores by Near Infrared Spectroscopy

Near infrared (NIR) spectroscopy provides a rapid method for the determination ofwood properties of radial strips. The spatial resolution of the NIR measurements has generally been limited to sections 10mm wide and as a consequence the estimation of wood properties of individual rings or within rings has not been possible. Many different NIR instruments can be used to collect NIR spectra from the surface of radial strips at relatively high spatial resolution and the purpose of this study was to compare wood property calibrations obtained using NIR spectra collected in 5 mm and 2 mm seetions with several different NIR instruments. We found that calibrations based on spectra collected in 5 mm seetions had good statistics, with those based on the Bruker Vector 22/N spectrometer the strongest. Of the three properties examined (density, microfibril angle and stiffness), density had the weakest statistics. When the spatial resolution was decreased to 2 mm, calibration and prediction statistics were weaker than those at 5 mm. RPDps were relatively low with the highest being 1.76 for predicted stiffness based on NIR spectra obtained using the ASD Field Spec Pro spectrometer. Based on the low RPDps, we conclude that none of the instruments examined were suitable for scanning radial strips at a spatial resolution of 2 mm.

Modeling the longitudinal variation in wood specific gravity of planted loblolly pine (Pinus taeda) in the United States.

Loblolly pine (Pinus taeda L.) is a major plantation species grown in the southern United States, producing wood having a multitude of uses including pulp and lumber production. Specific gravity (SG) is an important property used to measure the quality of wood produced, and it varies regionally and within the tree with height and radius. SG at different height levels was measured from 407 trees representing 135 plantations across the natural range of loblolly pine. A three-segment quadratic model and a semiparametric model were proposed to explain the vertical and regional variations in SG. Both models were in agreement that a stem can be divided into three segments based on the vertical variation in SG. Based on the fitted models, the mean trend in SG of trees from the southern Atlantic Coastal Plain and Gulf Coastal Plain was observed to be higher than in other physiographical regions (Upper Coastal Plain, Hilly Coastal Plain, northern Atlantic Coastal Plain, and Piedmont). Maps showing the regional var...