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1.
Allometric equations are required for a rapid estimation of commercial timber volume and forest biomass stocks. In order to preserve the forest ecosystem, this study applied a non-destructive sampling approach to measure biophysical properties of living trees. From these measurements, volume and biomass models were developed for 11 dominant tree species in a semi-deciduous natural forest and for Acacia auriculiformis in a plantation located in southern Benin. The observations were combined to develop also generic models applicable to non-dominant tree species. Wood samples of the tree species were collected with an increment borer and analysed in the laboratory to determine species-specific wood densities. The sample size was composed of 243 trees in natural forest and 21 trees in plantation. The measurements were conducted in 30 plots of 50 m × 50 m. The graphical assessment of correlation between model outputs (biomass and volume) and variables (diameter and height) and the statistical analysis confirmed that the logarithmic model with two variables had the best predictions. The assessment also confirmed that the model using diameter only as a variable had good predictions when observations on height were unavailable. The comparative analysis of model predictions showed that the generic model in this study over-estimated biomass by up to 74.80% for certain species and under-estimated biomass by 21.18% for other species. The study shows that there are no statistically significant differences between the wood densities in this research and that published in previous studies.  相似文献   

2.
Gmelina arborea Roxb. is a fast-growing, deciduous tree species native to Bangladesh. It has been widely planted since 1992 for commercial production of pulpwood in hilly areas of Bangladesh. The purpose of this study was to derive well-fitting allometric models for estimation of aboveground biomass, and carbon and nutrient (nitrogen, phosphorus and potassium) stocks in G. arborea to ensure sustainable production and management of this species. Eight linear models with 64 regression equations were tested for estimation of aboveground biomass, carbon and nutrient stocks in different parts (leaves, branches, bark and stem) of the plant. The best-fitting allometric models were selected in accordance with various relevant statistical criteria.  相似文献   

3.
Allometric models for dominant shade tree species and coffee plants (Coffea arabica) were developed for coffee agroforestry systems in Matagalpa, Nicaragua. The studied shade tree species were Cordia alliodora, Juglans olanchana, Inga tonduzzi and I. punctata. The models predict aboveground biomass based on diameter at breast height (for trees), and the stem diameter at a height of 15 cm and plant height (for coffee plants). In addition, the specific gravity of the studied species was determined.The total aboveground biomass of the shade trees varied between 3.5 and 386 kg per tree, and between 0.005 and 2.8 kg per plant for coffee. The aboveground biomass components (foliage, branch, and stem) are closely related with diameter at breast height (r > 0.75). The best-fit models for aboveground biomass of the shade trees were logarithmic, with adjusted R 2 between 0.71 and 0.97. In coffee plants, a high correlation was found (r = 0.84) with the stem diameter at 15 cm height, and the best-fit model was logarithmic, as well. The mean specific gravity was 0.52 (± 0.11) for trees and 0.82 (± 0.06) for coffee plants.  相似文献   

4.
Forest biomass estimation at large scale has become an important topic in the background of facing global climate change, and it is fundamental to develop individual tree biomass equations suitable for large-scale estimation. Based on the measured data of biomass components and stem volume from 100 sample trees of two larch species (Larix gmelinii and L. principis-rupprechtii) in northeastern and northern China, an integrated equation system including individual tree biomass equations, stem volume equation and height–diameter regression model were constructed using the dummy variable model and error-in-variable simultaneous equations. In the system, all the parameters of equations were estimated simultaneously, so that the aboveground biomass equation was compatible to stem volume equation and biomass conversion factor (BCF) function; the belowground biomass equation was compatible to root-to-shoot ratio (RSR) function; and stem wood, stem bark, branch and foliage biomass equations were additive to aboveground biomass equation. In addition, the system also ensured the compatibility between one- and two-variable models. The results showed that: (1) whether aboveground biomass equations or belowground biomass equations and stem volume equations, the estimates for larch in northeastern China were greater than those in northern China; (2) BCF of a larch tree decreased with the growing diameter while RSR increased with the growing diameter; (3) the proportion of stem wood biomass to aboveground biomass increased with the growing diameter while those of stem bark, branch, and foliage biomass decreased.  相似文献   

5.
A forest biomass yield table based on an empirical model   总被引：1，自引：0，他引：1  
We report an empirical model for estimating unutilized wood biomass, and its application to Cryptomeria japonica D. Don and Larix kaempferi in Tohno City, Iwate Prefecture, northeast Japan. Outputs from the model are the quantity of unutilized wood biomass and merchantable volume produced by timber harvest. The unutilized wood biomass is divided into stumps, tops, branches, foliages, small trees, and unutilized stems due to their defects. Inputs to the model are mean diameter at breast height (DBH), mean tree height, trees per unit area, and timber utilization standards. DBH distribution, DBH–height curve, stem form, bark thickness, and relationship of stem biomass to foliage and branch biomass could be described by the proposed model, indicating its validity. The proposed model enables us to develop the forest biomass yield tables modified from the existing stem volume yield tables. The developed forest biomass yield tables indicated that the unutilized wood biomass due to defects accounted for the largest part of the whole unutilized wood biomass, and that the ratio of unutilized parts in stem volume to total stem volume could vary with stand age and site productivity class. Based on a comparison of the developed forest biomass yield tables with those reported previously, we concluded that the proposed model-based forest biomass yield table would be useful for estimating the quantity of unutilized wood biomass.  相似文献   

6.
The African tulip tree, Spathodea campanulata, the most common tree in Puerto Rico, forms novel forest types with mixtures of native and other introduced tree species. Novel forests increase in area in response to human activity and there is no information about their biomass accumulation and nutrient cycling. We established allometric relationships and chemically analyzed plant parts of African tulip trees to determine the concentration and standing stock of chemical elements (C, N, P, K, Ca, Mg, S, Mn, Al, Fe, Na), and ash. Trees ranged in diameter at breast height from 8 to 85 cm and in height from 8.8 to 28 m. The concentrations of N, P, K, and Ca in leaves of the African tulip tree were similar to those of the native pioneer Cecropia schreberiana and higher than those of mature forest tree species in Puerto Rico. The over bark wood volume of African tulip trees in nine forest stands where it was dominant ranged from 163 to 849 m3/ha. Aboveground biomass ranged from 60 to 296 Mg/ha, and N and P stocks ranged from 190 to 988 and 32 to 137 kg/ha, respectively. Novel forests on abandoned agricultural lands can store more biomass and elements than native and plantation forest stands of similar age.  相似文献   

7.
《Southern Forests》2013,75(4):279-286
The South African government has banned planting of Jatropha curcas L. (Jatropha), potentially a multipurpose tree and biofuel source, owing to insufficient knowledge about the species. Use of allometry as a non-destructive method of monitoring growth and biomass attributes of Jatropha was investigated. The objectives were to examine: reliability of allometry between above-ground variables and basal diameter and crown depth of Jatropha; effects of below-ground interspecies competition and tree spacing on allometry; and validity of these relationships with independent data. The study site was Ukulinga Research Farm, South Africa. Destructive sampling was carried out in March 2008, and tree height and basal diameter were measured periodically during March 2005 to April 2007. Regression analysis and analyses of covariance were used to analyse the data. The height-diameter equation developed by destructive sampling was validated using independent data. Highly significant allometric regressions resulted from using basal diameter (r ≥ 0.89) and crown depth (r ≥ 0.94). Stem diameter had linear relationships with wood and foliage biomass percentages (r = 0.91). Height-diameter equations were equivalent across competition and tree spacing treatments. Predicted and measured tree heights were linearly related (r > 0.97). It could be concluded that above-ground allometry of Jatropha was very reliable and not significantly affected by either below-ground interspecies competition or tree spacing. The site-specific allometric equations are useful for accurate and non-destructive estimations of Jatropha growth under various growing and (non-pruning) tree management conditions. The equations presented here are, however, not universally applicable.  相似文献   

8.
Obtaining accurate estimates of national belowground and whole tree biomass is important to better understand the global carbon cycle and to quantify biomass stocks and changes. However, the availability of individual tree belowground biomass functions is generally low due to the difficulty of extracting roots. Allometric birch (Betula pubescens Ehrh. and Betula pendula Roth) biomass functions were derived from 67 trees for belowground and whole tree biomass using diameter at breast height (dbh) and height as the independent variables. The sampled trees spanned a dbh range from 4.0 to 45.5?cm and the functions provided a good fit to the data (RMSE?=?14.2?kg for BG and 40.7?kg for whole tree with dbh as predictor). Belowground, total stem, live crown, and dead branch biomass comprised 29.2%, 52.2%, 18.1%, and 0.5% of the whole tree biomass, respectively. Observed root-to-shoot ratios were between 0.21 and 0.88 with a mean of 0.42. Comparisons with existing belowground birch biomass functions from Fennoscandia indicated considerable differences in estimates between existing functions. The derived data-set for belowground birch biomass is the largest in Fennoscandia and the developed functions are likely the best available for estimating national birch biomass stock and stock change in Norway.  相似文献   

9.
《林业研究》2021,32(3)
Secondary Miombo woodlands and forest plantations occupy increasing areas in Mozambique, the former due to anthropogenic activities. Plantations, mainly species of Eucalyptus and Pinus, are being established on sites previously covered by secondary Miombo woodlands. This affects the evolution, cycle and spatiotemporal patterns of carbon(C) storage and stocks in forest ecosystems. The estimation of C storage, which is indispensable for formulating climate change policies on sequestrating CO_2, requires tools such as biomass models and biomass conversion and expansion factors(BCEF). In Mozambique, these tools are needed for both indigenous forests and plantations. The objective of this study is to fit species-specific allometric biomass models and BCEF for exotic and indigenous tree species. To incorporate efficient inter-species variability, biomass equations were fitted using nonlinear mixed-effects models. All tree component biomass models had good predictability; however, better predictive accuracy and ability was observed for the 2-predictors biomass model with tree height as a second predictor. The majority of the variability in BCEF was explained by the variation in tree species. Miombo species had larger crown biomass per unit of stem diameter and stored larger amounts of biomass per stem volume. However, due to relatively rapid growth, larger stem diameters, heights, and stand density, the plantations stored more biomass per tree and per unit area.  相似文献   

10.
《Southern Forests》2013,75(3-4):141-146
Volume equations predict the volume of the stem of a tree from dendrometrical characteristics that are easy to measure, such as diameter and/or height. These equations can serve as a surrogate for biomass equations, by converting the stem volume to stem biomass, and then expanding it to the total aboveground biomass. This is especially important for Central Africa where biomass equations are scarce, whereas volume equations are common. We measured the stem volume of 459 trees in the Yoko forest, Orientale province, Democratic Republic of Congo. These trees belonged to three species: Gilbertiodendron dewevrei (limbali), Guarea thompsonii (bossé foncé) and Scorodophloeus zenkeri (divida). Species-specific volume equations were fitted using these data, and biomass estimates were derived from these volume equations. The fitted volume equations were consistent with other location-specific volume equations for the same species. The biomass estimates derived from the fitted volume equations were also found to be consistent with multispecies pantropical biomass equations.  相似文献   

11.
Accurately and non-destructively quantifying the volume, mass or nutrient content of tree components is fundamental for assessing the impact of site, treatment, and climate on biomass, carbon sequestration, and nutrient uptake of a growing plantation. Typically, this has involved the application of allometric equations utilising diameter and height, but for accurate results, these equations are often specific to species, site, and silvicultural treatment. In this study, we assessed the value of incorporating a third piece of information: the height of diameter measurement. We derived a more general volume equation, based on the conical approximation, using a diameter projected to the base of the tree. Common equations were developed which allowed an accurate estimate of stem volume, dry weight and nutrient content across two key plantation grown eucalypt species, Eucalyptus grandis W. Hill ex Maiden and Eucalyptus globulus (Labill.). The conical model was developed with plantation-grown E. grandis trees ranging from 0.28 to 15.85 m in height (1.05 g to 80.3 kg stem wood dry weight), and E. globulus trees ranging from 0.10 to 34.4 m in height (stem wood dry weight from 0.48 g to 652 kg), grown under a range of contrasting cultural treatments, including spacing (E. grandis), site (E. globulus) and fertilization (nitrogen and phosphorus) for both species. With log transformed data the conical function (Vcon) was closely related to stem sectional volume over bark and stem weight (R2 = 0.996 and 0.990, respectively) for both E. grandis and E. globulus, and the same regressions can be applied to both species. Back transformed data compared with the original data yielded modelling efficiencies of 0.99 and 0.97, respectively. Relationships between Vcon and bark dry weight differed for the two species, reflecting differing bark characteristics. Young trees with juvenile foliage had a different form of relationship to older trees with intermediate or adult foliage, the change of slope corresponding to heights about 1.5 m for E. grandis and age 1 year for E. globulus. The Vcon model proved to be robust, and unlike conventional models, does not need additional parameters for estimating biomass under different cultural treatments. More than 99% of the statistical variance of the logarithm of biomass was accounted for in the model. Vcon captures most of the change in stem taper associated with cultural treatments and some of the change in stem form that occurs after the crown base has lifted appreciably. Fertilization increased N and P concentrations in stem wood and bark, and regressions to estimate N and P contents (the products of biomass and concentration) were dependent on treatment. For instance, there was a large growth response to N fertilization in E. globulus corresponding with a change (P < 0.05) in the intercept of the regression to estimate N content.  相似文献   

12.
Agroforestry systems have the potential to contribute significantly to climate change mitigation and adaptation. However, data on tree and soil organic carbon (SOC) pools for most agroforestry systems are lacking because reliable methods for estimating ecosystem carbon (C) pools are scarce. This study quantified the effects of five Leucaena species (L. leucocephala, L. macrophylla, L. diversifolia, L. collinsii and L. pulverulenta) on vegetal and soil C stocks and on mean annual increment (MAI) in aboveground tree C stocks. Specifically, it tested the validity of the CO2FIX model using empirical data from 7?year-old woodlots at Msekera, Zambia, and assessed the impact of converting a degraded agricultural ecosystem to woodlots on C stocks. Measured above- and below-ground tree C stocks and MAI of aboveground biomass differed significantly among the Leucaena species. Measured stem and total aboveground tree C stocks in seven-year old woodlots ranged from 17.1 to 29.2 and from 24.5 to 55.9?Mg?ha?1, respectively. Measured SOC stocks at 0?C200?cm depth in Leucaena stands ranged from 106.9 (L. diversifolia) to 186.0?Mg?ha?1 (L. leucocephala). Modeled stem and branch C stocks closely matched measured stocks, but the soil module of CO2FIX did not predict the soil C. The soil C data are inconclusive at this stage. We recommend that a fractionation and a soil aggregate hierarchy study backed by C dating is carried out to explain soil C dynamics in these soils. However, the model can be used only for estimating changes in aboveground tree C stocks in woodlots until soil C module is proven to predict SOC stocks.  相似文献   

13.
Fractal branching models can provide a non-destructive and generic tool for estimating tree shoot and root length and biomass, but field validation is rarely described in the literature. We compared estimates of above ground tree biomass for four indigenous tree used on farm in the Philippines based on the WanFBA model tree architecture with data from destructive sampling. Allometric equations for the four species varied in the constant (biomass at virtual stem diameter 1) and power of the scaling rule (b in Y = aD b ), deviating from the value of 8/3 that is claimed to be universal. Allometric equations for aboveground biomass were 0.035 D 2.87 for Shorea contorta, 0.133 D 2.36 for Vitex parviflora, 0.063 D 2.54 for Pterocarpus indicus and 0.065 D 2.28 for Artocarpus heterophyllus, respectively. Allometric equations for branch biomass had a higher b factor than those for total biomass (except in Artocarpus); allometric equations for the leave + twig fraction a lower b. The performance of the WanFBA model was significantly improved by introduction of a tapering factor “τ“ for decrease of branch diameter within a single link. All statistical tests performed on measured biomass versus biomass predicted from the WanFBA results confirm the viability of the WanFBA model as a non-destructive tool for predicting above-ground biomass equations for total biomass, branch biomass and the leaf + twig fraction.  相似文献   

14.
[目的]由于激光雷达技术已经能准确测定立木树高及相关树冠因子,应用该技术建立基于树高和树冠因子的立木材积模型,为激光技术在森林蓄积估计中提供技术支撑.[方法]利用云杉、冷杉、栎树、桦树4个树种组的3 010株实测样木数据,分析了立木材积与胸径、树高、树冠因子之间的相关关系;并通过对数回归方法构建了基于树高和树冠因子的立木材积模型,用确定系数R2和平均预估误差MPE等6项指标对模型进行评价.[结果]表明,立木材积与单一因子之间的相关,以胸径最为紧密,其次是树高,再次是冠长和冠幅.基于树高和树冠因子的立木材积模型中,以树高和冠幅作为解释变量的二元模型效果较好,再增加冠长因子的三元模型改进不大.云杉、冷杉、栎树、桦树4个树种组基于树高冠幅的立木材积模型,其R2分别为0.81、0.80、0.76和0.77,MPE分别为4.7%、5.3%、5.4%和5.3%,模型预估精度均能达到95%左右.[结论]本文对材积与林木因子之间相关关系的定量分析,建立了云杉、冷杉、栎树、桦树4个树种的立木材积模型,模型预估精度高.为激光雷达技术定量估测森林参数提供了依据.  相似文献   

15.
There has been an increasing interest in fodder trees and their potential to help the rural poor. However, few studies have addressed the ecological impacts of fodder tree harvesting. We investigated the species harvested and the techniques used, and the effects of fodder harvesting on (1) species’ populations and (2) forest carbon stocks in three montane forests in Kenya. Focus-group discussions were organized in 36 villages to determine which species were harvested and with which techniques. Field observations were made on vegetation plots: stem diameter, tree height, species and extent of harvest were recorded. Carbon stocks were calculated using an allometric equation with (1) observed height of harvested trees, and (2) potential height estimated with a power model, and results were compared. Eight tree species were commonly harvested for fodder using different techniques (some branches, main stem, most branches except stem apex). Fodder harvesting (together with other uses for some species) negatively affected one species populations (Olea europaea), it did not negatively affect four (Drypetes gerrardii, Gymnosporia heterophylla, Pavetta gardeniifolia, Xymalos monospora), and more information is needed for three species (Olea capensis, Prunus africana, Rinorea convallarioides). Fodder harvesting did not significantly reduce forest carbon stocks, suggesting that local communities could continue using these fodder trees if a carbon project is established. Among the fodder species studied, X. monospora could be used in reforestation programs, as it has multiple uses and can withstand severe pruning. Although our study is only a snapshot, it is a baseline which can be used to monitor changes in fodder harvesting and its impacts related to increasing droughts in northern Kenya and increasing human populations.  相似文献   

16.
Estimates of above-ground biomass are required for better planning, sustainable management and monitoring of changes in carbon stocks in agroforestry systems. The objective of this study was to develop and compare biomass equations for Markhamia lutea, Casuarina equisetifolia, Maesopsis eminii and Grevillea robusta grown in a linear simultaneous agroforestry system in Uganda. These species were established in single rows in the middle of fields in 1995 from four-month old seedlings. A total of 57 trees were sampled for this study, 13 for M. lutea, 12 for C. equisetifolia, 16 for M. eminii and 16 for G. robusta. Biomass values of the various tree components (stem, branches and foliage) as well as the total above-ground biomass were fitted to linear and non-linear allometric models using total height, diameter-at-breast height (DBH), crown width as predictor variables. Although both DBH and height are typically used as independent variables for predicting above-ground biomass, the addition of height in biomass equations did not significantly improve model performance for M. eminii, M. lutea and G. robusta. However, addition of height significantly increased the proportion of variation explained in above-ground biomass for C. equisetifolia, while DBH did not significantly improve the prediction of biomass. The study confirmed the need for developing species-specific biomass equations.  相似文献   

17.
Several studies have been conducted in the past on carbon stock measurements in the tropical forests of Indonesia.This study is the first related research conducted in the New Guinea Island.In a degraded logged-over secondary forest in Manokwari Regency (West Papua,Indonesia),carbon stocks were measured for seven parts,i.e.,above-ground biomass (AGB),below-ground biomass (BGB),under-storey biomass (B u),necromass of dead leaves (N l),necromass of dead trees (N t),litter (L) and soil (S) using appropriate equations and laboratory analysis.Total carbon stocks were measured at 642.8 tC·ha-1 in the low disturbance area,536.9 tC·ha-1 in the moderate disturbance area and 490.4 tC·ha-1 in the high disturbance area.B u,N l and N t were not significant in the carbon stock and were collectively categorized as a total biomass complex.The carbon stock of litter was nearly equal to that of the total biomass complex,while the total carbon stock in the soil was eight times larger than the total biomass complex or the carbon stock of the litter.We confirmed that the average ratio of AGB and BGB to the total biomass (TB) was about 84.7% and 15.3%,respectively.Improvements were made to the equations in the low disturbance logged-over secondary forest area,applying corrections to the amounts of biomass of sample trees,based on representative commercial trees of category one.TB stocks before and after correction were estimated to be 84.4 and 106.7 tC·ha-1,indicating that these corrections added significant amounts of tree biomass (26.4%) during the sampling procedure.In conclusion,the equations for tree biomass developed in this study,will be useful for evaluating total carbon stocks,especially TB stocks in logged-over secondary forests throughout the Papua region.  相似文献   

18.
《Southern Forests》2013,75(3):235-245
Global sustainable development goals include reducing greenhouse gas emissions from land-use change and maintaining biodiversity. Many studies have examined carbon stocks and tree species diversity, but few have studied the humid Guinean savanna ecosystem. This study focuses on a humid savanna landscape in northern Sierra Leone, aiming to assess carbon stocks and tree species diversity and compare their relationships in different vegetation types. We surveyed 160 sample plots (0.1 ha) in the field for tree species, aboveground carbon (AGC) and soil organic carbon (SOC). In total, 90 tree species were identified in the field. Gmelina arborea, an exotic tree species common in the foothills of the Kuru Hills Forest Reserve, and Combretum glutinosum, Pterocarpus erinaceous and Terminaria glaucescens, which are typical savanna trees, were the most common species. At landscape level, the mean AGC stock was 29.4 Mg C ha?1 (SD 21.3) and mean topsoil (0–20 cm depth) SOC stock was 42.2 Mg C ha?1 (SD 20.6). Mean tree species richness and Shannon index per plot were 7 (SD 4) and 1.6 (SD 0.6), respectively. Forests and woodlands had significantly higher mean AGC and tree species richness than bushland, wooded grassland or cropland (p < 0.05). In the forest and bushland, a small number of large diameter trees covered a large portion of the total AGC stocks. Furthermore, a moderate linear correlation was observed between AGC and tree species richness (r = 0.475, p < 0.001) and AGC and Shannon index (r = 0.375, p < 0.05). The correlation between AGC and SOC was weak (r = 0.17, p < 0.05). The results emphasise the role of forests and woodlands and large diameter trees in retaining AGC stocks and tree species diversity in the savanna ecosystem.  相似文献   

19.

The main objective of this case study was to explore the possible influence of forest management on the levels and distribution of biomass and carbon (C) in even-aged stands of Norway spruce [Picea abies (L.) Karst.] in Denmark. Data originated from a long-term thinning experiment and an adjacent spacing experiment at stand ages of 58 and 41 years, respectively. Biomass of 16 trees from different thinning and spacing treatments was measured or partly estimated, and soils were sampled for determination of C stocks. All trees in each plot were measured for stem diameter and some for total height, to allow for scaling-up results to stand-level estimates. For trees of similar size, foliage biomass tended to be higher in the spacing experiment, which was located on slightly more fertile land. Foliage biomass increased with increasing thinning grade, but the effect could not be separated from that of tree size. At stand level, foliage biomass tended to increase with increasing spacing as well as with increasing thinning grade. For branchwood, stems and roots (including below-ground stump), the biomass increased with increasing tree size and stand volume at tree and stand level, respectively, but no differences between stands, spacings or thinning grades were observed, apart from that expressed by tree size or stand volume. At stand level, C stocks of all biomass compartments decreased with increasing thinning grade, while the distribution between compartments was hardly influenced. The ratio between above-ground and stem biomass was about 1.21 at stand level, while the ratio between below- and above-ground biomass was about 0.17. Thinning influenced the C stock of the forest floor and mineral soil oppositely, resulting in no effect of thinning on total soil C.  相似文献   

20.
Adequate allometric equations are needed for estimating carbon pools of fast growing tree species in relation to international reporting of CO2 emissions and for assessing their possible contribution to increasing forest biomass resources. We developed models for predicting biomass, stem basic density and expansion factors of stem to above-ground biomass for five fast growing conifers. Data included destructive measurements of 236 trees from 14 sites, covering a wide range of growth conditions. To ensure model efficiency, models for predicting stem, crown and total above-ground biomass for the five species were estimated simultaneously using a linear, mixed effects model that allowed contemporaneous correlations between the different tree components. Models differed among species and included dbh and tree height. The models explained more than 98% of the variation in above-ground biomass and reflected differences in the allometry between tree species. Stem density differed among species but generally declined with increasing site index and dbh. The overall model for predicting stem basic density included dbh, H100 and site index and explained 66% of the total variation. Expansion factors decreased from 1.8–2.0 in small trees (dbh < 10 cm) to 1.1–1.2 for large trees (dbh > 25 cm), but differed among species. The overall model explained 86% of the variation and included quadratic mean diameter and dbh.  相似文献   

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