Stand-level Models Research Articles

A stand-level model of carbon allocation and growth, calibrated for loblolly pine

A stand-level model of carbon allocation and growth, calibrated for loblolly pine

Linking individual-tree and stand-level growth models

An algorithm is presented to provide a linkage between stand-level models and individual-tree models. The algorithm is based on the assumptions that stand-level estimates of basal area, trees per unit area, and average diameter are correct and that the projected individual trees must be adjusted to equate to the stand-level estimates. The form of the individual-tree model is not important so long as initial and projected tree lists are provided. It is further assumed that the relative growth between individuals is to be maintained and the adjusted survivals are restricted to be less than or equal to 100%. Simplification of the general algorithm are also developed. These simplifications take the form of dropping the survival equation from the individual-tree model and dropping the average diameter estimate from the stand-level model. Examples are provided of a bimodal diameter distribution.

Development of growth models for Pinus radiata in New Zealand — experience with management and process models

The Forest Research Institute (FRI) has recently finished developing a series of management growth models for Pinus radiata within major bio-geo-climatic regions. These are stand-level models consisting of a series of stochastic differential equations, with the state of the stand at any one time being described by the major variables of top height, basal area and number of stems per hectare. Additional state variables and time-scale multipliers are used to account for regional differences in patterns of growth, loss of site occupancy, nitrogen and phosphate fertiliser effects, and increased growth due to improved breeds of trees. The research programme has been driven by the forest manager's need to accurately regulate yield in a period with a greater demand than supply, and to evaluate the profitability of new afforestation. It was necessary to predict the response to extremes of silvicultural regimes, ranging from dense pulpwood to widely spaced, high pruned stands. From 1986 onwards, an FRI/Industry Stand Growth Model Cooperative has facilitated data collection, research and technology transfer. Since the early 1980s, a research programme to construct process models for Pinus radiata has contributed to understanding physiological processes, particularly water balance and interception of solar radiation. However, initial expectations that such models would contribute to improvements in forest management, or to better management growth models have so far not been met. There is no evidence to suggest that either management or process models can be used with confidence outside the range of their experimental data.

Growth of Loblolly Pine Stands After the First Five Years of Uneven-Aged Silviculture Using Single-Tree Selection

Abstract The effects of three levels of residual basal area (40, 60, and 80 ft2/ac), maximum dbh (12, 16, and 20 in.) and site index (< 81 ft, 81 to 90 ft, and >90 ft) on the growth of loblolly pine (Pinus taeda L.) stands after 5 yr of uneven-aged silviculture were determined from plots located in south Arkansas and north Louisiana. Designated levels of basal area and maximum dbh were achieved by harvesting; a q factor of 1.2 (using 1 in. dbh classes) was imposed on all plots as closely as possible. Stand-level models were developed for annual per acre net volume growth (merchantable cubic feet, sawtimber cubic feet, and sawtimber board feet, Doyle rule) and annual per acre survivor growth, ingrowth, and mortality components of basal area growth. Growth for all volume measures increased with an increase in basal area. Site index did not significantly affect merchantable cubic-foot growth but had a positive effect on sawtimber growth in both cubic feet and board feet, Doyle. Increases in maximum dbh decreased merchantable and sawtimber cubic-foot growth but increased growth for board-foot volume, Doyle. South. J. Appl. For. 18(3): 128-132.

Incorporating the effects of interspecific competition and vegetation management treatments in stand table projection models for Douglas-fir saplings

A stand table projection system based on individual-tree and stand-level models for young Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco var. menziesii) plantations was developed from and evaluated with remeasurement data from sites in the Siskiyou Mountains of southwestern Oregon and in the Coast Ranges of Oregon and Washington. A projection equation was developed for relative tree size, defined as the ratio of individual-tree diameter at 15 or 30 cm above ground level (depending on the study location) to quadratic mean diameter. The relative size projection equation for the Coast Ranges study included the effect of total vegetation control, which indicated that diameters of Douglas-fir receiving total vegetation control tended to become more uniform over time in the Coast Ranges. An additional equation was developed to project quadratic mean diameter so that individual-tree diameters could be estimated from projected relative size. The effect of vegetation management treatments on projected quadratic mean diameters in the Siskiyou study was expressed as an interaction between proportion of cover removed by treatments (intensity) and dominant height of Douglas-fir at time of treatment relative to current dominant height. In 1- and 2-year projection periods, the stand table projection system performed similarly to a diameter distribution prediction system based on a Weibull distribution function. However, the difference between projected and predicted diameter distributions became more pronounced as the projection period increased to 5 years.

Eastern cottonwood clonal mixing study: predicted diameter distributions

A parameter recovery procedure for the Weibull distribution function was modified to incorporate monocultures and mixtures of eastern cottonwood (Populusdeltoides Bartr.) clones planted in Mississippi and Kentucky. Components of the system included functions to predict stand-level basal area and four percentiles (0th, 25th, 50th, and 95th) of the cumulative diameter distribution. Basal area was predicted as a function of surviving number of trees, dominant height, age, planting location, and the proportion of each clone planted. Clonal proportions, which accounted for 3.6% of the variation in observed basal area, were more important than differences in planting locations, which accounted for 3.0% of the variation. Interactions between clones in mixtures were not significant (p = 0.5676), but some cases of both over- and under-compensation appeared to be developing. Percentiles of the cumulative diameter distribution were predicted as functions of quadratic mean diameter, and therefore included indirect effects of both genetic and planting site differences. Only the minimum diameter (D0) was directly affected by proportions of clones planted. Most of the monocultures and mixtures of clones had smaller minimum diameters than expected for a given value of quadratic mean diameter. The predicted quadratic mean diameter and percentiles were used to recover parameters of the Weibull distribution such that the predicted diameter distribution has the same quadratic mean diameter as obtained from the stand basal area model. The predicted distributions indicated that a common stand-level model was not sufficient for accounting for variations in diameter distributions of eastern cottonwood clones. As a result of the differences in diameter distributions, monocultures and mixtures of the Texas clones appeared to have less volume and greater stand variance than the Mississippi clones.

Forest ecosystem processes at the watershed scale: incorporating hillslope hydrology

An approach to distributed modeling of watershed hydro-ecological processes over large spatial scales is described. A data and simulation system, RHESSys (Regional HydroEcological Simulation System), combines a set of remote sensing/GIS techniques with integrated hydrological and ecological models in order to automate the parameterization and simulation of a suite of ecological and hydrological flux and storage processes through the watershed. Specifically, we simulate forest canopy net photosynthesis ( PSN) and total evapotranspiration ( ET) through the year with a modeling package that integrates FORESTBGC, a stand level model of forest carbon, water and nitrogen budgets, with TOPMODEL, a quasi-distributed hydrological model. The latter model introduces the effects of hillslope hydrological processes, incorporating surface redistribution of soil water by saturated throughflow processes. The maintainance of regular patterns of soil water by throughflow processes cause forest ecosystem activity to vary dependent on hillslope position. The distributed framework is based on a terrain partition in which each terrain object (hillslopes and stream reaches) comprising the watershed are separately parameterized and simulated. The location of each terrain object within the watershed is explicitly represented while the internal variability of each object is represented as a joint parameter distribution. Generalization of the surface into different numbers of terrain objects (by growing or shrinking the extent of the stream network) is automatically accomplished using digital terrain data. This allows us to flexibly alter the spatial representation of the watershed by shifting surface information either into the internal hillslope parameter distributions or into greater numbers of hillslopes (and stream reaches). Limited simulations of a mountainous watershed in western Montana indicate that incorporation of within hillslope throughflow and the soil, topography and vegetation distribution has the effect of significantly altering the seasonal PSN and ET trends in comparison with lumped surface representations without lateral water flux.

Techniques for assessing the effects of pest hazards on long-run timber supply

Stand-level and forest-level models are developed for the purpose of assessing the effects of pest hazards on long-term timber supply. The stand-level model yields formulas for the long-run average yield and the land expectation value when both the risk of infestation by pests and the risk of total destruction by fire are present. Infestations are assumed to occur with a probability dependent upon stand age. A forest-level harvest scheduling procedure of the model II type, which allows for pest infestation and fire destruction, is developed. Numerical examples are given, using data for lodgepole pine in the Quesnel Timber Supply Area of British Columbia, assuming various patterns of infestation by mountain pine bark beetle.