Bark Volume Research Articles

Quantifying bark thickness and bark volume with alternative modeling procedures for eight species in the southeastern US

Bark thickness is one of the important tree characteristics to assess plant survival following silvicultural treatments or natural disturbances. With an increased number of catastrophic wildfires under changing climate, a reliable approach for modeling bark thickness and bark volume is critical to monitor forest health and quantify carbon stocking in sustainable forest management. The objective of the study was to compare the efficacy of three alternative quantifying approaches and statistical models for both bark thickness and volume. In approach I, bark thickness is quantified from the differences of inside- and outside-bark diameters, which are predicted with two separate stem taper functions. The second approach combines a stem taper function and a bark thickness model, while in the third approach, bark thickness is quantified via a single predictive model with bark thickness at breast height included. The statistical models examined include segmented polynomial regression models (SEG), variable-exponent models (VEM) and generalized additive models (GAM). A total number of 71,187 observations of 2,932 trees were queried from the LegacyTree database, including eight ecologically and economically important species in the southeastern US.Results show that all combinations of approaches and models can quantify bark thickness and bark volume without bias for all eight species examined. Approach III yields higher accuracy and precision levels than approaches I and II. The performance of the models varies among quantifying approaches and species. GAM and VEM generally produce a more reliable quantification than SEG. Although GAM may not be the optimal model for a given species, such a model can provide preliminary quantitative information about bark thickness and bark volume when there is no existing model for the target species. The results of this work provide additional insights for forest ecologists and practitioners to select appropriate modeling approaches for quantifying bark thickness and volume.

The Effect of Age on the Evolution of the Stem Profile and Heartwood Proportion of Teak Clonal Trees in the Brazilian Amazon

Stem profile modeling is crucial in the forestry sector, particularly for commercially valuable species like teak (Tectona grandis Linn F.), whose value depends on its stem dimensions, heartwood proportion, and age. We proposed a nonlinear mixed-effect model to describe the evolution of the stem and heartwood profiles of clonal teak trees with ages between 4 and 12 years in the Brazilian Amazon. Tapering models were used to estimate the bark, bark-free, and heartwood diameters. Dummy variables were included in each tapering model to estimate each type of diameter and enable compatibility. We used mixed models with age as a random effect in order to improve the accuracy. The Demaerschalk model provided the most accurate and compatible estimates for all three types of stem diameter. Also, age as a random effect significantly improved the model’s accuracy by 7.2%. We observed a progressive increase in the heartwood proportion (14% to 34%) with advancing age, while the proportions of bark (23% to 20%) and sapwood (63% to 45%) showed inverse behavior. The growth rate of the heartwood differed from that of the bark volume, emphasizing the importance of considering the age of heartwood maximization when determining the cutting cycle of the species.

Estimation of Scots pine bark biomass delivered to the wood industry in Northern Germany

Abstract Scots pine (Pinus sylvestris L.) is the most widely distributed pine species in the world. In Germany, as in many other European countries, it is a very important species both culturally and economically. Few studies have focused on bark volumes being delivered to the wood industry together with the roundwood, being potentially a valuable resource for material or energetic utilization. Therefore, logs from six different forest sites were collected and bark variables including double bark thickness (DBT) in three different categories, diameter, and bark damage (as a degree of miss-DBT) in three different categories, diameter, and bark damage (as a degree of missing bark) were measured and analyzed in order to model bark volume (Vbark) and bark mass (Mbark). The correlation analysis using Pearson’s method showed that the highest correlation coefficients were observed from the correlation between DBT and Vbark, as well as between DBT and Mbark. Also, results demonstrated that with DBT greater than 20 mm, the percentage of Vbark exceeded 20%. Finally, different linear regression models were recommended to predict Vbark and Mbark based on the other variables. The results of this study can be used in different wood industries in order to predict bark volume and bark mass of e.g. truckloads or roundwood stacks.

Модели для оценки биомассы и объема коры деревьев липы мелколистной (Tilia cordata Mill.)

The research is aimed at analyzing variability and developing mathematical models for estimating bark biomass and volume, volume of trunk with bark, and bark proportion of small-leaved linden (Tilia cordata Mill.) trees growing in natural coppice and artificial stands. The models are based on data from 107 and 95 destructively sampled trees in natural coppice and artificial stands, respectively. There were 10 sampling areas per stand type, representing different growth stages. The model trees were sawn into 2-meter sections, the volumes of which with and without bark were calculated using the Huber formula. The total volume of the tree trunk with and without bark is obtained by summing the volumes of all sections and the conical volume of the tree top. The bark volume was the difference between these two parameters. The bark biomass was determined by direct weighing, followed by conversion to absolutely dry mass. The correlations between the dendrometric parameters and the selected tree characteristics were estimated. The effectiveness of 3 regression models using the diameter at breast height (dbh = 1.3 m) and the tree height (h) as independent variables was studied in a comparative aspect. The bark biomass and volume, and the volume of trunk with bark are strongly influenced by these values. This correlation is very weak for the bark volume proportion in natural coppice stands, and insignificant in artificial stands. The bark volume proportion for each tree was calculated as the ratio of the difference between the volume of trunk with and without bark and the volume of trunk with bark. The equation that showed the best statistical characteristics in terms of consistency was chosen in order to predict the bark biomass and volume, the volume of trunks with bark of small-leaved linden trees. These models were estimated using the weighted least squares method taking into account the inherent errors and heteroscedasticity, by assigning each model its weight function separately for natural coppice and artificial stands that differ significantly from each other in morphometric features.

Characteristics and factors driving the variations in bark thickness of major woody plants in China

Bark is an important protective tissue and vegetative organ of woody plants. Variations in bark thickness have a direct effect on plant growth and development, forest community structure, and terrestrial ecosystem function. However, the characteristics of these variations in tree bark thickness (BT) and adaptation to environmental factors remain unclear. In this study, we established comprehensive BT traits and environmental factor dataset for 75 major woody plant species in China and analyzed the spatial pattern and factors driving BT traits in the major woody plants of China. As results, the BT of major woody plants in China varied significantly with spatial location (latitude and longitude) (P < 0.001). A significant difference was observed in the relative age bark thickness among different plant types (gymnosperms and angiosperms) and life forms (evergreen and deciduous) (P < 0.001). Significant differences in relative bark thickness (RBT) were detected among the different bark phenotypes (smooth and rough) (P < 0.05). However, no significant difference in the relative bark volume was observed among the three groups (plant types, life forms, or bark phenotypes). All BT traits had particular phylogenetic signals. The Mantel test results showed that all BT traits except RBT were correlated with the environmental factors (Mantel’s P < 0.05). The redundancy analysis revealed that the spatial variation in BT traits was significantly affected by the annual mean temperature, the mean diurnal range, and altitude (P < 0.05). The results of variance decomposition showed that the BT traits were affected by spatial factors (20 %), climatic factors (8 %), and their interaction (8 %), while the effects of soil factors could be ignored. Our results demonstrate that the biotic factors affecting the BT of woody plants in China were the different plant types, life forms, and bark phenotypes, while the abiotic factors were the spatial and climatic factors and their combined effects.

Bark volume and thickness in teak trees with different spacings

The bark in some forest species may represent a significant volume of the trunk, demanding the use of efficient methods to estimate bark volume indirectly through equations. The aim of this study was to evaluate bark volume and thickness in teak (Tectona grandis) trees planted at different densities. Volume data were used to evaluate the percentage of bark in different portions of the trunk. Averages were compared by the Tukey test (p &lt; 0.05%) and regression analysis (polynomial model) was used to predict bark thickness along the trunk. The effect of spacing on bark thickness was compared by the model identity test. The percentage of bark in more densely planted teak trees was higher. The percentage of bark decreases from the base to the top of the tree trunk, with an average volume of green bark reaching 24% to 30% of the total volume. Increasing spacing promotes higher absolute average bark thickness.

Stacking factor in transporting firewood produced from a mixture of Caatinga biome species in Brazil

ABSTRACT The energetic requirements of the Brazilian gypsum industry are mainly provided by firewood transported by road. The cost of transporting firewood is greatly affected by the stacking factor. In this study, we determined how the stacking factor for trailer trucks varied for the firewood harvested from forest species in the Caatinga biome, Brazil. For this purpose, the following steps were carried out: i) the logs were stacked in a frame (volume, 1 stere) and weighed; ii) the solid over bark volume of each log was obtained by scanning and by xylometry (immersion in water); iii) the stacked volume of logs on the truck was measured; and iv) the stacking factor, the stacking density and the apparent density of the unpeeled wood were computed for each of 60 truck trips. The stacking factor was, on average, 1.12. This value is lower than reported for other species; the greater compaction of the timber represents an advantage in terms of transport costs. However, the maximum variation in the load weight was 20%, which is not negligible from an economic point of view because of the associated loss of energy efficiency in the supply chain for the lowest volume loads.

Stem volume functions for Melaleuca cajuputi trees in Southwestern Region

The objective of this study was to construct standing stem and commercial timber volume functions at the individual tree level of Melaleuca cajuput plantations. The inside bark and outside bark stem volume functions were constructed from 56 sample trees at the diameter classes of 4 to 16 cm. The appropriate volume functions are tested from five candidate functions. The applicability of the volume functions were tested from 10 trees that were not included in the construction of the volume functions. The research results showed that the function V = a + b(D2 * H)c was a suitable function to build the inside bark stem volume function of Melaleuca cajuput. The function V = a + b(D2H) + c(DdHe) was a suitable function to build the outside bark stem and commercial timber volume functions of Melaleuca cajuput. The volume functions gave errors less than 5.0%. Compared with the inside bark stem volume, the average ratio for the outside bark stem volume, inside bark and outside bark commercial timber volume, and bark volume was 65.7%, 95.2%, 60.6% and 34.3%, respectively.

Interpreting the uncertainty of model-based and design-based estimation in downscaling estimates from NFI data: a case-study in Extremadura (Spain)

ABSTRACT Remotely sensed data are increasingly used together with National Forest Inventory (NFI) data to improve the spatial precision of forest variable estimates. In this study, we combined data from the 4th Spanish National Forest Inventory (SNFI-4) and from the 2nd nationwide Airborne Laser Scanning (ALS) survey to develop predictive forest inventory variables (total over bark volume (V), basal area (G), and annual increase in total volume (IAVC)) and aboveground biomass (AGB) models for the eight major forest strata in the region of Extremadura that are included in the Spanish Forest Map (SFM). We generated maps at 25 m resolution by applying an area‐based approach (ABA) and 758 sample plots measured with good positional accuracy within the SNFI-4 in Extremadura (Spain). Inventory performance is mainly influenced by spatial scale and vegetation structure. Therefore, in this study, we conducted a comparative analysis of statistical inference methods that can characterize forest inventory variables and AGB uncertainty across multiple spatial scales and types of vegetation structure. Predictions at pixel level were used to produce county, provincial, and regional model-based estimates, which were then compared with design-based estimates at different scales for different types of forest. We developed and tested both methods for forested area (cover, 19,744.15 km2), one province (9126.78 km2), and two counties (1594.42 km2 and 2076.76 km2, respectively) in Extremadura. The resulting relative standard error (SE) for regional level forest type-specific model-based estimates of V, G, IAVC, and AGB ranged from 3.34%–14.46%, 3.22%–12.50%, 4.46%–16.67%, and 3.63%–12.58%, respectively. The performance of the model-based approach, as assessed by the relative SE, was similar to that of the design-based approach at regional and provincial levels. However, the precision of SNFI model-based estimates was higher than that of estimates based on only the plot observations in small areas (e.g. at county level). The standard errors (SE) for model-based inferences were stable across the different scales, while SNFI design-based errors were higher due to the small sample sizes available for small areas. The findings indicate that SNFI-model based maps could be used directly to estimate forest inventory variables and AGB in the major forest strata included in the Spanish Forest Map, leading to potentially large economic savings.

HEARTWOOD FUNCTIONS AND COMPATIBLE TAPER AND MERCHANTABLE VOLUME SYSTEMS FOR Acacia mangium Willd. IN, TABASCO, MEXICO

In the last 20 years in Mexico, 30 % of the plantations supported by the Comisión Nacional Forestal (National Forestry Commission, CONAFOR) were made for timber purposes and established in the states of Tabasco, Veracruz, and Campeche, in Mexico. The economic valuation and management of plantations for these purposes are optimized by estimating the timber volume by type of product. The objectives of this study were to fit three compatible systems of segmented equations of taper and merchantable outside-bark volume; identify functions of taper and cumulative volume of heartwood; and analyze the dendrometric types based on the system developed by Fang et al. (2000) for plantations of clonal trees of Acacia mangium Willd., located in Huimanguillo, Tabasco, Mexico. Ninety-one (91) trees (2, 3, 7 and 8 years old) were cut down and two data groups were formed: 60 trees for fitting, and 31 for validation. The stem volume per section was calculated using the overlapping bolts method. The selection of the models was made according to the classification of four goodness-of-fit statistics. The system developed by Fang et al. (2000) showed reasonable estimates with both groups of measurements. The heartwood volume function overestimated the average percentage of heartwood relative to the inside bark volume in 2-year-old trees. However, it estimated them logically for the other ages: 34.7 % at 3 years, 61.8 % at 7 years, and 67 % at 8 years. The ratio heartwood taper to inside bark taper decreased after reaching 70 % of height.

Modelling bark volume for six commercially important tree species in France: assessment of models and application at regional scale

Modelling bark volume for six commercially important tree species in France: assessment of models and application at regional scale

Machine learning and regression models to predict multiple tree stem volumes for teak

The quantification of a stand’s wood stock is one of the most important procedures for Tectona spp. (teak) management. An optimal method for estimating tree volume must accommodate the variation of the data collected in the inventory. This study evaluated alternative methods to estimate the volume on stems of teak trees. We cut and measured the outside bark, inside bark, and heartwood diameters at heights of 0.1, 0.5, 1.5 m and every meter thereafter until the minimum outside bark diameter reached 3 cm, using 180 trees of ages 3 to 12 years. We tested two approaches (A1 and A2) to estimate stem volumes of the outside bark, inside bark, and heartwood (v ob, v ib and v hw, respectively): modelling the tree volume in A1, and the taper model in A2, with the techniques of regression, artificial neural network (ANN) and support vector regression (SVR). In addition, we obtained the percentages of heartwood, sapwood and bark in the stem. The accuracies of the estimates were evaluated using bias, correlation and root-mean- square error (RMSE). Validation was made for the outside bark, inside bark and heartwood volumes, and the outside bark, inside bark and heartwood diameters, from the taper models. In A1, the ANN technique more accurately predicted v ob and v ib, with RMSE% values of 18.88% and 18.54%, respectively; for v hw, the regression technique was more accurate, with RMSE% equal to 26.87%. In A2, the regression technique obtained the highest precision in the prediction of v ob, v ib and v hw, with RMSE% values of 13.99%, 13.31% and 26.50%, respectively. Approach A2 showed more accurate results compared with A1 for predicting the multiple volumes of teak trees with the three tested techniques.

Construction of the additive model system for heartwood, sapwoodand bark taper of Pinus koraiensis plantation in different regions of Heilongjiang Province, China

With the commonly used variable-exponent taper models developed by Kozak (1988), Muhairwe (1999), Lee (2003) and Kozak (2004), we aimed to develop taper functions of diameter outside bark (DOB), heartwood diameter (HD), sapwood width (SW), and bark thickness (BT) based on the data of 2977 discs from 103 sample trees of Pinus koraiensis plantations under different conditions in Mengjiagang Forest Farm, Dongjingcheng and Linkou Forestry Bureau in Heilongjiang Province. We selected the optimal basic model after comparison. By using seemingly unrelated regression (SUR) method in the PROC MODEL of SAS software, we established an additive model system for the taper equations of DOB, HD, SW and BT. By introducing the region as a dummy variable, the models were evaluated by coefficient determination (Radj2), root mean square error (RMSE), Akaike information criterion (AIC) and Bayesian information criterion (BIC). The results showed that the taper model developed by Kozak (2004) was the optimal one for the DOB, HD, SW and BT. When satisfying the additivity of each component and total amount, the additivity model system got better prediction effect, with a prediction precision of more than 98%. The additive model system with dummy variables improved the prediction ability to varying degrees, especially the prediction precision of HD and SW models. Minor differences existed in DOB and BT among different regions, while enormous differences in HD and SW. The additive model system with dummy variables not only had high prediction accuracy but also satisfied the additive logic of DOB, HD, SW and BT, which provided a basis for accurate estimation of heartwood, sapwood and bark volume of P. koraiensis.

Total and Merchantable Volume Equations for 25 Commercial Tree Species Grown in Canada and the Northeastern United States

Accurate estimates of tree bole volume are fundamental to sustainable forest management. Total inside and outside bark and merchantable volume equations were developed for 25 major commercial tree species grown in natural stands in eastern and central Canada and the northeastern United States. Data used to develop these equations was collected from 9647 trees sampled from natural stands across the study area. The number of trees sampled varied among species. Jack pine (Pinus banksiana Lamb.) had the most observations (1648 trees) and American basswood (Tilia americana) and red oak (Quercus rubra L.) had the fewest (28 trees each). Two mathematically consistent volume equations (dimensionally compatible and combined variable) were fitted to inside and outside bark and merchantable tree volume data from these tree species. The final volume equation was selected based on fit statistics, predictive accuracy, and logical consistency. Its predictive accuracy was compared with a volume equation previously developed by Honer. Both (total and merchantable) volume equations were fitted using a nonlinear mixed-effects modelling approach. However, random effects were significant for total volumes for only four tree species. A weight (power function) was used to address heteroscedasticity in the data. The modified form of the dimensionally compatible volume equation outperformed the combined variable volume equation in terms of fit statistics and predictive accuracy and was selected as the total inside and outside bark and merchantable volume equations for all tree species. This equation produced logically consistent estimates of total and merchantable volumes and was more accurate than that previously developed by Honer to estimate volumes for most of the tree species used in this study. This new equation can be used to estimate total inside and outside bark and merchantable volumes of major commercial tree species in eastern and central Canada and the northeastern United States.

Comparison of different approaches to estimate bark volume of industrial wood at disc and log scale

Within the wood supply chain, the measurement of roundwood plays a key role due to its high economic impact. While wood industry mainly processes the solid wood, the bark mostly remains as an industrial by-product. In Central Europe, it is common that the wood is sold over bark but that the price is calculated on a timber volume under bark. However, logs are often measured as stacks and, thus, the volume includes not only the solid wood content but also the bark portion. Mostly, the deduction factors used to estimate the solid wood content are based on bark thickness. The aim of this study was to compare the estimation of bark volume from scaling formulae with the real bark volume, obtained by xylometric technique. Moreover, the measurements were performed using logs under practice conditions and using discs under laboratory conditions. The mean bark volume was 6.9 dm3 and 26.4 cm3 for the Norway spruce logs and the Scots pine discs respectively. Whereas the results showed good performances regarding the root mean square error, the coefficient of determination (R2) and the mean absolute error for the volume estimation of the total volume of discs and logs (over bark), the performances were much lower for the bark volume estimations only.

Effects of site and tree size on wood density and bark properties of Lebombo ironwood (Androstachys johnsonii Prain)

Background: Wood and bark are important renewable natural resources. Density is an important property that is used to describe wood and bark quality for a number of end uses. However, wood and bark density, bark proportion and dimensions vary with age and site, as well as among and within trees. The aim of this study was to investigate the effect of site, diameter class, and vertical position within the stem on the density of wood and bark, bark volume, bark dry-mass and thickness of Lebombo ironwood (Androstachys johnsonii Prain). Methods: The study was conducted on 93 Lemombo ironwood trees growing in Mozambique. Eight discs were sampled from each selected tree and diameter over and under bark was measured. Bark thickness, bark mass and bark density were determined along with the basic wood density of each disc. Results: The overall average whole-stem properties were estimated at: 786 kg m–3 wood density, 586 kg m–3 bark density, 19% bark volume, 19% bark dry-mass, and 9 mm bark thickness. Height level uniquely explained most of the variation in bark mass (97%), bark volume (95%) and wood density (86%). Diameter class explained most of the variation in bark density (51%) and bark thickness (51%). Site only explained a small proportion of the variation in all dependent variables. Conclusions: Overall, the patterns of variation of all wood and bark properties were highly dependent on tree diameter class and vertical position within the stem. Site differences were not a significant source of variation in the properties studied. Improved knowledge of the wood and bark properties of this species will aid its sustainable management and utilisation.

Development of a Taper Equation for Teak (Tectona grandis L.f.) Growing in Western Thailand

Teak is an important and valuable tropical hardwood species. In this study, we developed and evaluated suitable taper equations for teak growing in Western Thailand using a formulation of Goodwin cubic polynomial model combined with a bark thickness model. The best taper model calibration was selected based on goodness-of-fit and leave-one-out cross validation statistical testing. In total, 12 different model calibrations were tested, with Thong Pha Phum (TPP) 2 being the most suitable for teak in Western Thailand. The mean prediction error of three validation statistics: (prediction of diameter under bark given height; prediction of height given diameter under bark; and prediction of under bark volume given log length) were within 10% and the overall validation index was 5.454, which was the lowest when compared to other calibrations. A comparison of TPP 2 with a teak taper equation developed for Northern Thailand, using a graphical analysis of the stem shape and bark thickness, indicated that the teak trees growing in the two regions have similar stem shapes, but the trees in Western Thailand tend to have a thicker bark. These results will also help in further work as they indicate that bark thickness equations are particularly important.

Bark proportion of Scots pine industrial wood

Bark characteristics are not only used in the forest-wood supply chain, for example to calculate standing volumes, but also to transform wood volumes and masses. In this study, bark thickness, bark volume and bark mass were analyzed on the basis of 150 Scots pine discs, with a mean diameter of 13 cm. The mean double bark thickness was 3.02 mm, the mean bark volume proportion was 5.6% and mean bark mass proportion was 3.3%. Bark proportions were significantly affected by the log-specific variables ‘diameter over bark’, ‘proportion of bark damage’ and ‘double bark thickness’.

A Taper Equation for Loblolly Pine Using Penalized Spline Regression

Abstract Stem profile needs to be modeled with an accurate taper equation to produce reliable tree volume assessments. We propose a semiparametric method where few a priori functional form assumptions or parametric specification are required. We compared the diameter and volume predictions of a penalized spline regression (P-spline), P-spline extended with an additive dbh-class variable, and six alternative parametric taper equations including single, segmented, and variable-exponent equation forms. We used taper data from 147 loblolly pine (Pinus taeda L.) trees to fit the models and make comparisons. Here we show that the extended P-spline outperforms the parametric taper equations when used to predict outside bark diameter in the lower portion of the stem, up to 40% of the tree height where the more valuable wood products (62% of the total outside bark volume) are located. For volume, both P-spline models perform equal or better than the best parametric model, with taper calibration, which could result in possible savings on inventory costs by not requiring an additional measurement. Our findings suggest that assuming a priori fixed form in taper models imposes restrictions that fail to explain the tree form adequately compared with the proposed P-spline.

Quantifying carbon in tree bark: The importance of bark morphology and tree size.

Bark contributes approximately 20% to the total above‐ground biomass of trees, yet bark is not properly accounted for when estimating carbon sequestered by trees. Current allometric functions estimate tree volume from diameter measured over the bark, and derive bark density and carbon content from estimates for wood. As the bark density of hardwood species is 40%–50% lower than the wood density, but nearly equivalent in conifers, bark carbon is overestimated for most species. The latter is further exacerbated by variation in bark volume with bark surface morphology.Fissured bark volume is overestimated by diameter over bark measurements by up to 40%. The vacant space in fissures can be accounted for by a bark fissure index (BFI). We calculate bark carbon for Australian species from a non‐destructive and effective BFI using bark thickness measured in the field.Bark volume, and in turn bark carbon, scaled inversely with tree size (diameter) so that bark volume comprised 42% of small trees (10 cm diameter at breast height, DBH) but 23% of large trees (50 cm DBH). Our BFI method using a bark thickness gauge (BGM) yielded similar results than using the less time‐efficient contour gauge method (CM) to estimate BFI (bias BGM‐CM −1.3%, non‐significant at p = 0.72). Both BGM and CM had an error of <4% compared to digitized BFI from destructive sampled stem disks. An average of 15 bark gauge measurements per tree estimated bark thickness (and inconsequence BFI) for both fissured and unfissured bark with <20% error relative to the exact value.Using the bark gauge method, BFI can be rapidly measured from large numbers of trees needed for estimating bark carbon at the community level and modelling carbon uptake, storage and cycling in woody biomes.