Validation of forest height–age models

1996 ◽  
Vol 26 (5) ◽  
pp. 810-818 ◽  
Author(s):  
Gordon D. Nigh ◽  
Vera Sit
Keyword(s):  
Forest Management ◽  
Confidence Intervals ◽  
Error Variance ◽  
Site Index ◽  
Random Coefficients ◽  
Multivariate Technique ◽  
Forest Height ◽  
Preliminary Validation ◽  
Age Model ◽  
Validation Procedure

Forest height–age models are used in forest management to estimate height and (or) site index. It is useful to know the bias and precision of these models in order to evaluate their applicability. Methods are available for validating the models; however, many problems exist with the methods because of a lack of independence in the data and nonconstant error variance across a range of ages. A validation procedure is presented that overcomes these problems by using a multivariate technique (random coefficients) to model the structure of the errors associated with the models. Confidence intervals for bias and precision can then be constructed based on the error structure. This method of validation was demonstrated on the white spruce (Piceaglauca (Moench) Voss) height–age model for British Columbia, Canada. The preliminary validation showed the model to be unbiased for estimating both height and site index; however, its precision was poor.

scholarly journals Juvenile Height Development in Interior Spruce Stands of British Columbia

2000 ◽  
Vol 15 (3) ◽  
pp. 117-121 ◽  
Author(s):  
Gordon D. Nigh ◽  
Bobby A. Love
Keyword(s):  
Decision Making ◽  
British Columbia ◽  
Site Index ◽  
Timber Supply ◽  
Breast Height ◽  
Forest Region ◽  
Interior Spruce ◽  
Spruce Stands ◽  
Age Model ◽  
Height Model

Abstract Good estimates of juvenile heights are important for silviculture and timber supply decision-making. These height estimates are particularly important for estimating the number of years it takes a stand to reach green-up and breast height. Thirty-nine 0.04 ha plots were established in managed juvenile stands of interior spruce in the Prince Rupert Forest Region. Four sample trees in each plot were split longitudinally and height-age data were obtained from the exposed pith nodes or branch whorls. The height-age data were fit to a combined exponential and power function to create a juvenile height model for interior spruce. This model is a function of age and site index. Years to breast height and green-up age models were developed with data generated from the juvenile height model. Forecasts from these models indicate that the time to reach breast height and green-up age is less than previously expected. The juvenile height model, years to breast height model, and green-up age model should be used for site indices above 14.2 m. In addition, the height model should only be used up to total age 20. West. J. Appl. For. 15(3):117-121.

Assessing the effect of measurement error in age on dominant height and site index estimates

2011 ◽  
Vol 41 (8) ◽  
pp. 1698-1709 ◽  
Author(s):  
Chengcai Ni ◽  
Gordon Nigh
Keyword(s):  
Measurement Error ◽  
Pinus Ponderosa ◽  
Ponderosa Pine ◽  
Site Index ◽  
Stand Age ◽  
Initial Value ◽  
Dominant Height ◽  
Projection Length ◽  
Age Model ◽  
Projection Error

Stand age is often hard to measure accurately. Measurement error in age affects height estimates when height is projected from one age to another age. In this study, our objective was to derive an estimator for the variance of the component of projection error associated with the error in age. To evaluate the estimator, a simulation approach was employed and the results showed that the estimator worked well in most cases. When the variance of the error in age increases and the projection is forward, however, the estimator might not work as well as in other cases. Another objective was to examine how the error in age behaved under different height–age models and to what extent it affected height and site index estimates. The effect of the error in age depended on its magnitude, the height–age model, initial value of dominant height and age, and projection length. It was also shown that the effect was sometimes negligible, but it could be considerable in other cases. Data from 80 ponderosa pine ( Pinus ponderosa Dougl. ex Laws.) trees in British Columbia, Canada, were used in an illustrative example.

Comparing the Sample-Weighted and Unweighted Meta-Analysis: An Applied Perspective

1999 ◽  
Vol 25 (6) ◽  
pp. 803-828 ◽  
Author(s):  
J. Bryan Fuller ◽  
Kim Hester
Keyword(s):  
Confidence Intervals ◽  
Meta Analysis ◽  
Error Variance ◽  
Actual Data ◽  
Sampling Variance ◽  
Average Correlation ◽  
Simulation Research ◽  
Actual Application ◽  
Sample Error ◽  
Variance Estimates

An extensive comparison of the sample-weighted method (Hunter & Schmidt, 1990), and a newer unweighted method (Osburn & Callender, 1992) of meta-analysis is presented using actual data. Several of the advantages of the unweighted method predicted by Osburn and Callendar’s simulation research did not always hold in actual application. Specifically, the unweighted method did not always produce larger estimates of observed variance, credibility intervals, and confidence intervals than the sample-weighted method when large sample outliers are present. Also, Osburn and Callender’s research on mean sampling variance formulae did not generalize to meta-analysis using the average correlation estimator to measure sample error variance. Finally, results show that while both methods may generate similar parameter and variance estimates in primary meta-analysis, they may lead researchers to reach different substantive conclusions in the analysis of moderators.

Comparing biomass regressions by site and stand age for red maple

1983 ◽  
Vol 13 (2) ◽  
pp. 283-288 ◽  
Author(s):  
T. R. Crow
Keyword(s):  
Predictive Model ◽  
Error Variance ◽  
Site Index ◽  
Stand Age ◽  
Site Conditions ◽  
Red Maple ◽  
Wide Range ◽  
Regional Estimates ◽  
Predictive Relations ◽  
Sampling Procedures

Allometric regressions for estimating red maple (Acerrubrum L.) biomass did not differ by stand age and site index. Significant differences were found only in terms of error variance, not in terms of regression slope or intercept. These trends suggest a single predictive model is valid for regional estimates. More attention should be given to regional sampling procedures and predictive relations that are valid for a wide range of stand and site conditions in developing weight tables and conducting biomass inventories.

scholarly journals A system for estimating height and site index of western hemlock in the interior of British Columbia

1998 ◽  
Vol 74 (4) ◽  
pp. 588-596 ◽  
Author(s):  
Gordon D. Nigh
Keyword(s):  
British Columbia ◽  
Site Index ◽  
Tsuga Heterophylla ◽  
Western Hemlock ◽  
Index Model ◽  
Breast Height ◽  
Age Model ◽  
Site Index Model ◽  
Growth Intercept ◽  
Height Model

The focus of recent site productivity research in British Columbia has been to develop height-breast height age, growth intercept, and ecosystem-site index models. These models, together with a years-to-breast-height model, form a system for estimating site index and height. This system is described for western hemlock (Tsuga heterophylla (Raf.) Sarg.) in the interior of British Columbia. Forty-four western hemlock stem analysis plots were used in the construction of this system. As there are three models for estimating site index, the appropriate model for a given stand depends largely on the stand condition and the precision of the models. A graph of model precision against breast height age gives some assistance in deciding which model should be used to estimate site index. Key words: western hemlock, site index, height-age model, growth intercept model, years-to-breast-height model, ecosystem-site index model, model precision

Confidence Interval for Site Index Using Curves Based on Stem Analyses

1971 ◽  
Vol 1 (4) ◽  
pp. 241-245 ◽  
Author(s):  
L. Heger
Keyword(s):  
Confidence Interval ◽  
Sample Size ◽  
Confidence Intervals ◽  
White Spruce ◽  
Site Index ◽  
Stand Age ◽  
Average Quality ◽  
Breast Height ◽  
True Value ◽  
Index Level

A method was described for the derivation of confidence intervals for site index using site-index curves based on stem analyses. The method allows assessment of effects on index estimates due to stand age, index level, sample size of heights used in entering the curves, index age, and sample size underlying the curves. Of these effects, the first three were evaluated for a set of curves based on stem analyses of white spruce (Piceaglauca (Moench) Voss) and on index age of 50 years at breast height (BH). With sample averages of 20 heights, about 95% of index estimates were within ±5 ft (1.52 m) of the true value in spruce 25–100 years old at BH on both average quality and extreme quality sites. To ensure this precision in spruce younger than 15 years at BH, 50 heights were required on the average sites and more than 50 on extreme sites.

scholarly journals Site Index Curves for White Fir in the Southwestern United States Developed Using a Guide Curve Method

2006 ◽  
Vol 21 (2) ◽  
pp. 87-93 ◽  
Author(s):  
Robert L. Mathiasen ◽  
William K. Olsen ◽  
Carleton B. Edminster
Keyword(s):  
United States ◽  
New Mexico ◽  
Confidence Intervals ◽  
Site Index ◽  
Abies Concolor ◽  
Inventory Data ◽  
Southwestern United States ◽  
White Fir ◽  
Curve Method ◽  
Study Sites

Abstract Site index curves for white fir (Abies concolor) in Arizona, New Mexico, and southwestern Colorado were developed using height-age measurements and an estimated guide curve and 95% confidence intervals for individual predictions. The curves were developed using height-age data for 1,048 white firs from 263 study sites distributed across eight national forests. These site index curves can be used with standard inventory data for estimating potential site productivity for white fir in the southwestern United States.

scholarly journals A Method for the Development of Dynamic Site Index Models Using Height–Age Data from Temporal Sample Plots

Forests ◽  
2019 ◽  
Vol 10 (7) ◽  
pp. 542
Author(s):  
Jarosław Socha ◽  
Luiza Tymińska-Czabańska
Keyword(s):  
Forest Management ◽  
Site Index ◽  
Height Growth ◽  
Strategic Decisions ◽  
Growth Trend ◽  
Potential Productivity ◽  
Forest Sites ◽  
Using Data ◽  
Temporal Sample ◽  
Index Estimation

Knowledge of the potential productivity of forest sites is fundamental for making strategic decisions in forest management. Site productivity is usually evaluated using the site index, and therefore the development of site index models is one of the crucial tasks in forest research and forest management. This research aims to develop an effective method for building top-growth and site index models using data from temporary sample plots (TSP). Exploiting the advantages of the generalised algebraic difference approach (GADA), the proposed method overcomes the limitations of the guide curve method that has been to date used in site index modelling using TSPs data and allows to obtain only a set of anamorphic site index curves. The proposed approach enables the construction of dynamic site index models with polymorphism and variable asymptotes. Such models better reflect local, site-specific height growth trajectories and therefore allow more appropriate site index estimation. We tested the proposed method using data collected from 5105 temporary sample plots in Poland. Our results indicate that growth trend estimates using height–age measurements of TSPs may be valuable data for modelling top height growth. For these reasons, the proposed method can be very useful in forest management.

scholarly journals Site Index and Volume Growth Percentage Determination for Privately Owned Uneven-aged Stands of Quercus pubescens and Quercus ilex along the Croatian Adriatic Coast

2019 ◽  
Vol 10 (1) ◽  
pp. 65-75
Author(s):  
Alen Berta ◽  
Tom Levanič ◽  
Denis Stojsavljević ◽  
Vladimir Kušan
Keyword(s):  
Forest Management ◽  
Quercus Ilex ◽  
Accurate Determination ◽  
Volume Growth ◽  
Site Index ◽  
Holm Oak ◽  
Similar Data ◽  
Quercus Pubescens ◽  
Mediterranean Regions ◽  
Privately Owned

Background and Purpose: Although organized forestry has existed in Croatia for more than 250 years, this mostly entailed state forests. During the last decade, Extension Services have started to support the development of forest management plans for privately owned forests. Lately, FMPs have been developed for nearly 3/4 of privately owned forests in Croatia. During the creation of those plans, yield tables and normal models for state-owned forests, primarily even-aged stands with long-time management, were used because similar data was not developed for uneven-aged and poorly managed forests. This research encompasses privately owned forests in the Croatian Mediterranean and sub-Mediterranean regions where holm oak ( Quercus ilex L.) and downy oak ( Quercus pubescens Willd.) are the prevailing species in forest stands. The main goal was to determine site indices revealed in the analysis of yearly radial increments and to create relevant yield tables. Materials and Methods: In this study, 1286 oak trees were cored to the centre on 377 locations spread in privately owned forests in Croatian Mediterranean and sub-Mediterranean regions. The ratio of trees and locations was approximately 3:1 for Q. pubescens. Some cored trees were more than two centuries old. After the standard sample preparation for dendrochronological analysis, cores were scanned, and tree-ring widths were determined. In total, ring width for over 67,000 rings was determined and measured. Results: Based on the data dispersion of cumulative tree increments at 40 years of age, 2 site index classes for Q. ilex and 3 for Q. pubescens were created based on k-means clustering. Prodan’s growth function was fitted to the created clusters to determine the site’s “model” tree. For the model trees, the percentage of volume growth was calculated. For easier field site index determination, height curves based on field data for each site index were calculated. Conclusions: For the first time in Croatia, systematic and controlled data on the growth (and age) of uneven-aged privately owned forests in the Croatian Mediterranean and sub-Mediterranean area were collected. Based on the data collected in the field, three different site indices for downy oak and two site indices for holm oak were determined. These results could find their application during operational forest management and forest exploitation because they allow for more accurate determination of the site production strength in the explored stands.

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