Browsing by Author "Daniels, Richard F."

Now showing 1 - 4 of 4
  • Thumbnail Image
    An integrated system of stand models for loblolly pine
    Daniels, Richard F. (Virginia Polytechnic Institute and State University, 1981)
    An integrated system of stand models was developed for loblolly pine in which models of different levels of resolution are related by a unified mathematical structure. A “telescoping'' system is presented in which a highly detailed overall model is specified and its components. ''collapsed" around a common set of growth and survival functions to provide structurally compatible models at each successively lower stage of resolution. The most detailed model is a distance dependent individual tree model which simulates the growth and competitive interaction of trees in a stand. Tree basal area and height growth were modeled 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 considered a function of site quality, age, and open-grown size relationships. Tree survival probability was described using a logistic function in terms of age, crown ratio, and competition. The competition or point density index is a function of the size and location of neighbors. Published indices were evaluated and compared on their simple correlation with growth, multiple correlation with growth in the presence of other tree and stand measures, computer execution time, and relationships to stand level density measures. The area potentially available (APA) for each tree was chosen as the most suitable. The APA index is calculated as the area of the polygon constructed from lines which divide the distance between a tree and its neighbors. Mean APA, or average area per tree, is estimated by the inverse of trees per unit area, permitting point density to collapse to stand density, resulting in a distance independent individual tree model. This model was collapsed dimensionally to consider trees grouped in size classes. Tree growth and survival equations are applied to the mean attributes of each size class, resulting in a size class projection model. At the lowest level of resolution, the dimensions of the model are collapsed to one "average" tree. A stand level projection model results from applying the tree growth and survival equations to the stand's average tree attributes. At the stand level, the basal area growth function provides a transformation which, for a number of probability density functions (pdf's), will regenerate the initial pdf family. Considering a normal pdf to describe basal area distributions, a pdf-based size distribution model is presented, in which the projected parameters are expressed in terms or the growth function coefficients. Applications to other pdf families are discussed. Preliminary tree growth and survival equation coefficients were estimated using data from a loblolly pine stand density study in North Louisiana. Structurally compatible models at each level of resolution are detailed. Considerations for numerically consistent estimates from models of different levels of resolution are discussed in terms of model specification, estimation, and implementation. Recommendations for model application and future model development are presented.
  • Thumbnail Image
    Methods for Modeling Individual Tree Growth and Stand Development in Seeded Loblolly Pine Stands
    Daniels, Richard F.; Burkhart, Harold E.; Spittle, Gerald D.; Somers, Greg L. (Virginia Tech. Division of Forestry and Wildlife Resources, 1979)
    Methods were developed to model growth and development of seeded loblolly pine (Pinus taeda L.) stands, using individual trees as the basic growth units. Aggregated spatial patterns and individual tree sizes are generated at age 10. Tree diameters and heights are then incremented annually as a function of their size, site quality, competition from neighbors, and stochastic components representing genetic and microsite variability. Individual tree mortality is determined stochastically through Bernouli trials. Subroutines were developed to simulate the effects of hardwood competition and control, thinning, and fertilization. The overall model was programmed in FORTRAN and initial tests were made with published yields. The initial stand generation components were calibrated using a comprehensive set of data from young seeded stands of loblolly pine, but individual tree growth and mortality components relied on previously published relationships developed for plantations. Results indicated that, in order to accurately model stand structure, the growth and mortality relationships must be calibrated for seeded stands. Data collection procedures, calibration methods, and recommendations for further work are discussed.
  • Thumbnail Image
    Simulation of Individual Tree Growth and Stand Development in Loblolly Pine Plantations on Cutover, Site-Prepared Areas
    Burkhart, Harold E.; Farrar, Kenneth D.; Amateis, Ralph L.; Daniels, Richard F. (Virginia Tech. Division of Forestry and Wildlife Resources, 1987)
    A forest stand simulator, PTAEDA2, was developed to model growth in loblolly pine (Pinus taeda L.) plantations on cutover, site-prepared areas. Individual trees were used as the basic growth units. In PTAEDA2, trees are assigned coordinate locations in a stand and 'grown' annually as a function of their size, the site quality, and the competition from neighbors. Growth increments are adjusted by stochastic elements representing genetic and microsite variability. Mortality is generated stochastically through Bernouli trials, Subroutines were developed to simulate the effects of hardwood competition, thinning, and fertilization on tree and stand development. Options for varying the spatial location of trees to mimic randomness in machine and hand planting operations are also included.
  • Thumbnail Image
    Simulation of Individual Tree Growth and Stand Development in Managed Loblolly Pine Plantations
    Daniels, Richard F.; Burkhart, Harold E. (Virginia Tech. Division of Forestry and Wildlife Resources, 1975)
    A FORTRAN based simulator, PTAEDA, was developed to model growth in managed loblolly pine (Pin us taeda L.) plantations, using individual trees as the basic growth units. In PTAEDA, trees are assigned coordinate locations in a stand and "grown" annually as a function of their size, the site quality, and the competition from neighbors. Growth increments are adjusted by stochastic elements representing genetic and microsite variability. Mortality is generated stochastically through Bernouli trials. Subroutines were developed to simulate the effects of site preparation, thinning, and fertilization on tree and stand development. Comparisons with published yields showed close agreement for thinned and unthinned old-field plantations. Results indicated that, compared to stand-level models used in the past, the simulator is more flexible in terms of growth and yield estimation and evaluation of alternatives under a wide range of management regimes.