Estimation of stem volume using laser scanning-based canopy height metrics

The aim of this study was to test different stem volume predictorsthat are capable of utilizing laser scanning-based canopy heightmetrics as independent variables. The three laser scanning-basedmethods compared were (1) a direct prediction model for thestem volume at plot level, (2) a volume prediction system basedon the modelled percentiles of the basal area diameter distribution,and (3) a parameter prediction method used to determinate Weibull-basedbasal area diameter distributions for the plot-level stem volumeprediction. The predicted volumes were also compared with field-measuredvolumes obtained with the Finnish conventional inventory bycompartments. The best results were obtained with the firstmethod, i.e. the model that predicts plot-level stem volumesdirectly, which is logical. Furthermore, the simulated reductionof point density of laser data had no effect on the accuracyof stem volume predictions. The percentile-based modelling ofdiameter distributions was applied, in particular, to the determinationof non-homogenous stand structure; using this method, it iseven possible to fit multimodal distributions. In terms of theaccuracy of the predicted plot-level stem volumes, the volumeprediction method based on modelled percentiles of basal areadiameter distributions was the second best, whereas the volumeprediction method based on the parameter prediction of the Weibull-basedbasal area diameter distributions resulted in slightly worseresults. However, the accuracies of the three laser-based volumeprediction methods tested were superior to the published resultsof spectral value-based remote sensing studies implemented usingdata collected from Finland. Furthermore, the accuracy of plot-levelstem volume estimates calculated from field assessments wasconsiderably weaker than the accuracy of the three volume predictionmethods that utilized measures obtained with laser scanning.     

Weibull and percentile models for lidar-based estimation of basal area distribution

Abstract

The aim of this study was to assess the accuracy of basal area distributions of sample plots in coniferous forest derived from small-footprint airborne laser scanner data, and to compare the accuracy of two methods for derivation of such distributions based on: (1) two percentiles of a two-parameter Weibull and parameter recovery, and (2) a system of 10 percentiles defined across the range of observed diameters. The 12 percentiles were derived from the empirical basal area distributions of 141 plots with size 300–400 m². Regression analysis was used to relate the percentiles to various canopy height and canopy density metrics derived from the laser data. On average, the distance between transmitted laser pulses was 0.9 m on the ground. The plots were divided into three strata according to age class and site quality. The stratum-specific regressions explained 7–91% of the variability. Total plot volume predicted from the estimated distributions was used to assess the accuracy of the regressions. Cross-validation of the regressions revealed a bias of ?1.2 to 2.1% between predicted and ground-truth values of plot volume. The standard deviations of the differences between predicted and ground-truth values of plot volume were 15.1–16.4%. Neither bias nor standard deviation differed significantly between the two validated methods.     

Predicting and calibrating diameter distributions of Eucalyptus grandis (Hill) Maiden plantations in Zimbabwe

Diameter distribution models for even-aged Eucalyptus grandis plantations in Zimbabwe were developed using the two-parameter Weibull function. The analysis was based on data from Correlated Curve Trend (CCT) experiments replicated on four different sites. Parameters of the Weibull distribution were predicted using stand characteristics as regressors. Two sets of parameter models were estimated: a set with and one without stand basal area as a predictor. Stand variables such as dominant height, age, site index and number of stems were used in both sets. The models were further calibrated to result in a given number of stems and stand basal area simultaneously. The usability of constructed models was tested both in prediction of yield in a stand inventory situation and in simulation of growth in connection with different growth models. The results indicated that models not including stand basal area produce considerably less precise stand volume estimates compared to models including also stand basal area. Calibration improved the accuracy of diameter distribution models. In growth simulation diameter distribution models can be connected both to single tree growth models and to stand projection models. The usability of calibration in growth simulation depends on the accuracy of the prediction of stand characteristics.     

Determination of number of stems in coniferous forest stands by means of aerial photo‐interpretation

Two models for determination of the number of stems per hectare in forest stands (N) from attributes derived by aerial photo‐interpretation were developed. The models relied on the assumption that N could be determined by dividing the total stand volume per hectare with the volume of the “average tree”; defined by stand mean height and the diameter corresponding to mean basal area of a stand. Input variables of the models were stand mean height, crown closure and site quality. Additionally, model II required input of average stand volume per hectare and average mean diameter derived from stratified field sample plot inventories. Material for 143 coniferous stands was used for the testing of the models. The stands were recorded by intensive field measurements. Aerial photographs at the approximate scale of 1:15 000 were used for photo‐interpretation. The N value was underestimated in model I by 5.4–47.0%. The standard deviation for the differences was 15.2–26.2% for mature stands and 41.4–44.2% for young thinning phase stands. For model II, the mean difference between the predicted and observed N value was in the range ‐16.1% to 12.2%.     

Comparison of beta,Johnson’s SB,Weibull and truncated Weibull functions for modeling the diameter distribution of forest stands in Catalonia (north-east of Spain)

The purpose of this study was to compare the beta, Johnson SB, Weibull and truncated Weibull functions in describing the diameter distributions of forest stands in Catalonia. The data consisted of permanent sample plots from the Spanish National Forest Inventory in Catalonia. The empirical data represent left-truncated distributions, as the smallest diameter measured in the field was 7.5 cm. A total of 1,242 plots were used to fit the functions and analyze their performance. The distribution functions were fitted to the diameter distributions of the number of stems (DD_N) and stand basal area (DD_G). The performance of the candidate functions was compared by means of their bias and RMSE for different diameter sums measuring the difference between the empirical and fitted distributions. The leftmost part (from 0 to 7.5 cm) of the non-truncated functions was ignored in this analysis. Sensitivity analyses were conducted to check whether the results depended on the number of trees measured in the stand, or the main species of the stand. The truncated Weibull function for the diameter distribution of stand basal area appeared to be in all cases the most accurate and consistent function. Generally, functions describing the distribution of stand basal area performed better than functions that described the distribution of the number of trees. Of the basal area distributions, beta and Johnson’s SB were the second best and nearly equally good with each other. The order of precision of the tested functions was: truncated Weibull for DD_G, truncated Weibull for DD_N, Johnson’s SB for DD_G, beta for DD_G, beta for DD_N and Weibull for DD_G, Weibull for DD_N, and Johnson’s SB for DD_N.     

辽东山区天然次生林林分直径分布模型研究

以峰度、偏度和变动系数为指标研究了辽东山区天然次生林直径株数分布特征。运用Johnson’s SB分布、Gamma分布、3参数和2参数Weibull分布等4种概率密度函数研究了辽东山区天然次生林直径株数分布规律,同时利用Kolmogorov-Smirnov(KS)检验法来检验4种概率分布的拟合效果,结果表明:林分直径的株数分布以Johnson’s SB分布拟合效果最好,Weibull分布(包括2参数和3参数)仅仅适合中度区和弱度区,但不是最好。所有的分布模型均通过了优势度检验,说明均适用于直径株数分布的拟合。     

Evaluation of the growth function of an empirical forest scenario model

Forests have an important role in the global carbon cycle as carbon pools, sinks and sources, and their quantification has become a relevant task. Empirical models based on national forest inventories are widely used for the assessment of carbon sequestration. However, these models do not treat explicitly all the processes occurring in the ecosystem, as they are mainly based on statistical relations to estimate forest development. Therefore, there is a need for validation of these models to increase confidence in the predictions of future forest development. This study evaluates an empirical single-tree model that was developed in Switzerland (MASSIMO). The accuracy and precision of the growth function of the model is evaluated with data from the National Forest Inventory (NFI) of Liechtenstein. MASSIMO was found to predict the basal area per hectare of the Liechtenstein data very precisely (underestimation of 0.65%). The main differences between observed and predicted diameter increment occur mostly for larger DBH classes, where the increment is underestimated by the model. However, these differences may be related to the precision of the input variables. For example, the explanatory variable stand age is determined with relatively low precision; therefore it shows a high variability. For future model development, either the variable stand age should be estimated more reliably, or stand age should not be an explanatory variable of the growth function.     

Modeling diameter distribution of Austrian black pine (<Emphasis Type="Italic">Pinus nigra</Emphasis> Arn.) plantations: a comparison of the Weibull frequency distribution function and percentile-based projection methods

The main purpose of the present investigation is to examine and compare three methods for diameter distribution modeling in terms of their fitness to predict from stand level variables the diameter distributions of even-aged Austrian black pine (Pinus nigra Arn.) plantations in Bulgaria. The percentile-based projection method involving empirical probability density function based on 12 percentiles was the first method tested. A new modified approach based on the first method was proposed as the second alternative. The third method was the 2-parameter Weibull functional model in which parameters were recovered from the first and the second raw moments and the second central moment of the empirical distributions. The Kolmogorov–Smirnov test was applied to compare the experimental distributions with the predicted ones, and estimation of the error indices was employed to evaluate the total absolute deviation of the predicted numbers from the actual ones by diameter class. The two-parameter Weibull function proved superior to the examined alternative percentile-based projection methods and the newly proposed percentile method, without a driver percentile showed improved precision compared to the classical percentile method (with a driver percentile). The parameters of the Weibull frequency distribution function can be easily recovered from the stand quadratic mean diameter. Consequently, this diameter distribution model could be incorporated as a sub-model for stand horizontal structure characterization within the Stand Density Management Diagram modeling framework.     

麻池背油松天然林林分生长结构的研究

依据历年调查资料,对麻池背油松天然林的林分生长结构进行了研究.该林分的植物种类丰富;直径、树高、林龄等林分结构呈正态分布、近似正态分布和多峰状分布;近熟林的林分蓄积生长率为0.82%,材积生长量69年生时连年生长量仍大于平均生长量.由于林分密度过大,油松形状比值偏高,林木自然稀疏强烈,枯损率达32.7%,其中小径木占86.3%,病虫害感染枯死木占29.4%.油松天然更新不良,辽东栎不能成为更新树种,林下有青木杄、落叶松幼树分布.     

抚育间伐对人工红松林生长效应的影响

利用不同间伐强度后40 a的人工红松林,连续抚育3次的长期定位观测资料,分析了抚育间伐对人工红松单木胸径和材积、林分断面积和蓄积、林分枯损和总收获量的影响。研究结果表明:间伐可以增加单木平均胸径和材积的生长率,且不同间伐强度表现为相同的规律,即中度(33.2%)强度(43.4%)弱度(23.1%)对照(0.0%);间伐后林分的断面积和蓄积生长率,具有相似的自然规律,间伐样地的生长率均高于对照;林木枯损率随间伐强度的增加而降低;间伐后的林分总收获量平均增加11.6%,间伐林分之间差别不明显。在整个研究阶段,不同的抚育阶段表现不同的规律,抚育间伐可以延缓单木胸径和材积生长速度的降幅;而不同抚育阶段内,林分断面积和蓄积生长率均为增长,也就是说,在一定阶段内间伐可以有效地提高林分平均断面积和蓄积生长率;从林分枯损状况来看,应该减少间伐间隔期。     

木麻黄生长与收获模型系统的研究

利用海南文昌2005年森林资源二类调查的木麻黄工业原料林样地资料,通过参数置换法,构建了以优势高模型为基础,以断面积预估为中心,将蓄积量作为目标变量的生长与收获模型系统。结果表明：组成模型系统的各模型的拟合精度较高,各模型的预估值与观测值差异不显著,适应性较好,能对木麻黄的优势高、断面积和蓄积量生长进行正确预估,可用于研究区木麻黄工业原料林的生长与收获预估。研究方法为一次性调查数据生长模型及类似模型的研建提供了经验和借鉴,并为当前缺少长期定位观测数据和大量解析木数据的森林经营单位编制森林经营方案提供了理论基础。     

A growth model for Pinus radiata D. Don stands in north-western Spain

A dynamic whole-stand growth model for radiata pine (Pinus radiata D. Don) stands in north-western Spain is presented. In this model, the initial stand conditions at any point in time are defined by three state variables (number of trees per hectare, stand basal area and dominant height), and are used to estimate total or merchantable stand volume for a given projection age. The model uses three transition functions derived with the generalized algebraic difference approach (GADA) to project the corresponding stand state variables at any particular time. These equations were fitted using the base-age-invariant dummy variables method. In addition, the model incorporates a function for predicting initial stand basal area, which can be used to establish the starting point for the simulation. Once the state variables are known for a specific moment, a distribution function is used to estimate the number of trees in each diameter class by recovering the parameters of the Weibull function, using the moments of first and second order of the distribution. By using a generalized height-diameter function to estimate the height of the average tree in each diameter class, combined with a taper function that uses the above predicted diameter and height, it is then possible to estimate total or merchantable stand volume.     

Development of stand structural stage indices to characterize forest condition in Upstate New York

Stand development stages are often used to describe temperate forest dynamics, but defining them using stand history or age can be difficult, especially for extensive surveys. The purpose of this study was to define stand development stage indices for forest stands on state forest land in Upstate New York using stand structure alone. A total of 508 stands were sampled, including 442 in Upstate New York. Two structural stage indices were defined for each of the 442 stands. The first index, based on SILVAH, was calculated using weighted mean diameter of trees in different size classes. The second index, based on work from Frelich and Lorimer, was calculated using the ratio of basal area of large trees to mature trees and either (1) exposed crown area (ECA) of trees in different size classes, or (2) basal area of trees in different size classes. Both indices were tested on stands with known stand histories. The second index was preferred for its superior ability to distinguish old-growth stands and was used to characterize structural stages of major forest types in Upstate New York: hemlock–hardwood (9% of state forest land), red spruce-fir (16%), and northern hardwood (51%). Results showed that the vast majority of stands in Upstate New York are in the mid-developmental stages. Structural characteristics of old-growth stands from this study were found to be in agreement with other old-growth stands in the northeastern United States.     

Modelling the diameter distribution of Pinus sylvestris, Pinus nigra and Pinus halepensis forest stands in Catalonia using the truncated Weibull function

Parameter prediction models for the diameter distribution ofPinus sylvestris L., Pinus nigra Arn. and Pinus halepensis Mill.in Catalonia were developed using the truncated Weibull functionas the theoretical distribution. The parameter models allowone to use individual-tree models in the simulation of standdevelopment when only stand-level data are collected in forestinventories. Parameter models for the diameter distributionof stand basal area were developed. The data consisted of permanentsample plots from the Spanish National Forest Inventory in Catalonia.A total of 1780 empirical distributions of P. sylvestris, 1204distributions of P. nigra and 1535 distributions of P. halepensiswere used as modelling data. The empirical data represent left-truncateddistributions, as the smallest diameter measured in the fieldwas 7.5 cm. Two different approaches, namely, regression (two-stepmethod) and optimization approach (one-step method), were usedto find the coefficients of the parameter models. In the two-stepmodelling method, the Weibull parameters were first estimatedseparately for every empirical distribution by maximizing thelog-likelihood function of the Weibull density function. Inthe second-step, regression analysis was used to find the relationshipbetween Weibull parameters and stand basal area, number of treesper hectare and elevation of the site. The one-step method usedoptimization to find such coefficients for the parameter models,which minimized the mean of the squared differences betweenempirical and predicted cumulative tree frequencies in the wholemodelling data. The one-step optimization method performed betterthan the two-step regression method for all tree species. Theparameter prediction models developed in this study enable theprediction of the diameter distribution of P. sylvestris, P.nigra and P. halepensis in Catalonia from limited stand information.     

Estimating stand structure using digitalized aerial photography

This study estimates the structure of a forest stand using high-resolution data from digitized aerial photography. The study area was conducted on the fifteen plots with the size of 20 m × 20 m or 15 m × 15 m taken as samples of sugi (Cryptomeria japonica D. Don) stands. The stand factor was investigated based on its relation with the digitalized number (DN) on the black and white aerial ortho photos (scale 1:5,000, taken in 1995). We analyzed various stand structure factors and the distribution of DN from the image data using the Weibull function, which comforms well to every shape of distributions. Using the Weibull distribution, a significant negative correlation was observed between the quantity of stand factors (Mean DBH and the stand volume) and the distribution parameterc of DN. A significant positive correlation was also observed between the distribution parameterc of the stand factor (DBH, height and volume) and the distribution parameterc of DN.     

Determining suitable selection cutting intensities based on long-term observations on aboveground forest carbon,growth, and stand structure in Changbai Mountain,Northeast China

We studied the effects of different cutting intensities (0%, 5–10%, 15%, and 20% basal area removal) on stand growth, structure, and net carbon storage in spruce–fir (Picea jezoensis (Sieb. et Zucc.) Carr.–Abies nephrolepis (Trautv.) Maxim.) and broadleaf mixed forests on Changbai Mountain (Northeast China) over 19 years. At this site, inventory-based low-intensity selection cutting was used to maintain a continuous forest canopy. After two cutting events, results showed significant differences in growth, structure, and carbon storage among cutting intensities. When increasing cutting intensity, the growth rate of average diameter, basal area, and volume significantly increased, with the highest increment rates found in the plots with 20% basal area removal. Tree diameters for all plots showed a roughly inverse J-shaped distribution before cutting and a left-skewed unimodal distribution after two cuttings. Volume ratio (the relative amount of volume contained in different diameter classes) for small (6–14 cm), medium (14–26 cm), large (26–36 cm), and very large (>38 cm) diameters remained unchanged in the plots with 5 and 10% basal area removal, but the volume ratio of large and very large diameters increased in the plots with 15 and 20% basal area removal, reaching approximately a 1:2:3:4 ratio in the plots with 20% basal area removal after two selection cuttings. Net carbon storage increased when increasing cutting intensity, reaching maximum storage in the plots with 20% basal area removal (cutting intensity and net C storage increase: 0%, 7.21 Mg C ha^?1, 5–10%: 11.68 Mg C ha^?1, 15%: 21.41 Mg C ha^?1, 20%: 26.47 Mg C ha^?1). Therefore, our results show the potential of low-intensity selection cutting to meet demands of both timber production and maintenance of forest cover for biodiversity values.     

抚育间伐对辽东山区3种林型林分总断面积和总收获量的影响

利用几十年的定位观测数据,分析了抚育间伐对辽东山区红松人工林、天然次生蒙古栎林和人工诱导的阔叶红松林3种林型林分总断面积和总收获量的影响。结果表明:与对照区相比,抚育间伐没有提高红松人工林的林分断面积和蓄积总生长量,但极强度和强度间伐能提高红松人工林的林分断面积生长率。林分总断面积随着间伐强度的增加先升高后降低,各间伐强度均能提高林分总断面积,极强度间伐除外。抚育间伐能提高红松人工林林分蓄积生长率,弱度区除外;红松人工林林分总收获量随着间伐强度的增加先升高后降低,各间伐强度均能提高林分总收获量,中度间伐效果最好。抚育间伐能提高蒙古栎林林分断面积和蓄积总生长量、生长率以及林分总断面积和总收获量,各指标随着间伐强度的增加先升高后降低,中度间伐效果最好。抚育间伐能提高人工诱导的阔叶红松林林分断面积和蓄积总生长量、生长率以及林分总断面积和总收获量,林分断面积和蓄积总生长量、林分总断面积和林分总收获量随着间伐强度的增加而升高,林分断面积和蓄积生长率随着间伐强度的增加先升高后略有降低,强度间伐效果最好。可见,合理的间伐强度能够提高3种林型的林分总断面积和总收获量。