Stem Volume Estimation Research Articles

Accuracy comparison of various remote sensing data sources in the retrieval of forest stand attributes

Recent advances in developing new airborne instruments and space-borne missions and in SAR technology, especially in interferometry and coherence estimation, have roused questions: can such new SAR data be utilized in operational forest inventory? What is the accuracy of different satellite data for forest inventory? This paper verifies the explanatory power and information contents of several remote sensing data sources on the retrieval of stem volume, basal area, and mean height, utilizing the following data: Landsat TM, Spot PAN and XS, ERS-1/2 PRI and SLC (coherence estimation), airborne data from imaging spectrometer AISA, radar-derived forest canopy profiles (obtained with HUTSCAT), and aerial photographs. Ground truth data included three different sets ranging from conventional forest inventory data to intensive field checking where one man-day was spent for assessing one stand. Multivariate and neural network methods were applied in data analysis. The results suggested that (1) radar-derived stand profiles obtained with 100 m spacing was the most accurate data source in this comparison and was of equivalent accuracy with conventional forest inventory for mean height and stem volume estimation, (2) aerial photographs (scale 1 : 20,000) gave comparable results with the imaging spectrometer AISA, (3) the satellite images used for the estimation in the decreasing explanation power were Spot XS, Spot PAN, Landsat TM, ERS SAR coherence, JERS SAR intensity images (PRI); and ERS SAR intensity images (PRI). It appears that optical images still include more information for forest inventory than radar images, (4) from all satellite radar methods, the coherence technique seemed to be superior to other methods.

Estimation de la hauteur des peuplements forestiers par diffusiomètre radar

This paper presents the results of an analysis of radar airborne scatterometer data obtained over an Austrian black pine (Pinus nigra Arnold ssp. nigricans Host.) forest in Lozère, France. This system provides vertical sounding inside canopy from which can be derived tree height estimations. The objective of this paper is to analyse the validity of these measurements and, then, to study the interest of this kind of sensors for better forest management. The mean and top height estimations give very good results with a relative error of about 6%. The radar measures the back scatter coefficient of the vegetation from which can be estimated other parameters such as stem volume or basal area. The radar backscatter coefficient is found to be sensitive to the biomass in a low to intermediate range of values (0-200 m3/ha), particularly when the canopy backscattering is separated from the ground echo. The estimation of stem volume using a regression with both tree height estimations and backscatter measurements gives satisfying results. Finally, we discuss the interest of this kind of sensor data for an improved and detailed forest management giving an example of application on the evaluation of the variability of the local site index within a stand.

Estimating Stem Volume and Basal Area in Forest Compartments by Combining Satellite Image Data with Field Data

The weighted k - nearest neighbour (kNN) method was used for estimating stem volume (m3 ha?1) and basal area (m2 ha?1) on a compartment level (average 19 ha) by combining satellite image data with measurements from Swedish National Forest (NFI) inventory plots. In the kNN method each estimation location (target plot) is assigned a value that is an average, which is weighted, of the attribute data from the k closest reference plots (NFI plots). The distance between target and reference plot was measured on different scales, which were transforms of spectral values and/or ancillary data. The standard error (assuming bias with no trend) of stem volume estimates in the compartments was 36% using only spectral data. This estimation accuracy improved to 17% if site index, age of the forest and mean tree height (ancillary data) were known for the compartments. Low volumes were overestimated and high volumes underestimated. This bias was reduced if ancillary data were added but was also dependent on the transform of the original scales.

Retrieval of biomass in boreal forests from multitemporal ERS-1 and JERS-1 SAR images

The response of JERS-1 and ERS-1 synthetic aperture radar (SAR) to the forest stem volume (biomass) was investigated by employing a digital stem volume map and weather information. The stem volume map was produced from the National Forest Inventory sample plot data together with a LANDSAT thematic mapper (TM) image. A new indirect inversion method was developed and tested to estimate the forest blockwise stem volume from JERS-1 and/or ERS-1 SAR images. The method is based on using a semiempirical backscatter model for inversion. The model presumes that backscatter from a forest canopy is determined by the stem volume, soil moisture, and vegetation moisture. The area of interest is divided into a training and test area. In this study, the training area was 10% of the test site, while the remaining 90% was used for testing the method. The inversion algorithm is carried out in the following three steps. 1) For the training area, the soil and vegetation moisture parameters are estimated from the backscattering coefficients and stem volume (must be known for training areas) with the semiempirical backscatter model. 2) For the area of interest, the stem volume is estimated from the moisture parameters and backscattering coefficients with the semiempirical backscattering model. 3) If several SAR images are used, the stem volume estimates are combined with a multiple linear regression. The regression equation is defined using the stem volume estimates for the training area. The results for the stem volume estimation using L-band and/or C-band SAR data showed promising accuracies: the relative retrieval rms error varied from 30 to 5% as the size of the forest area varied from 5 to 30000 ha.

Estimation of stem volume in boreal forests using ERS-1 C- and JERS-1 L-band SAR data

Multi-temporal ERS-1 C- and JERS-1 L-band Synthetic Aperture Radar (SAR) data were analysed to determine the relationship between radar backscattering and forest stem volume. The test site is located within the boreal conifer belt in northern Sweden with stem volume in the range of 0-300m3 ha-1. The statistical analysis was carried out using the water cloud model and various linear regression models. It was confirmed that the L-band of JERS-1 shows a consistently higher sensitivity to stem volumes in boreal forests with a larger backscatter contrast between nonforested areas and areas having dense tree cover in comparison with the C-band of ERS-1. The saturation levels for the ERS-1 and JERS-1 SAR sensors were estimated at 64m3 ha-1 and 143m3 ha-1, respectively. Furthermore, the temporal analysis shows that the backscattering coefficient can differ by approximately three decibels, atmost, between acquisitions for a given stem volume. However, a major finding is that the temporal variation could be modelled as an additive effect that is constant throughout the range of stem volume. For operational forestry purposes this would imply that stem volume can be predicted after calibration of the radar response using clear felled areas as reference targets. The multi-temporal JERS-1 dataset was used to develop a radarbased model of stem volume. The model was tested on a validation dataset resulting in a correlation coefficient of 0.78 between SAR estimated stem volume and ground data.

Architectural analysis of relationship between biomass and basal area based on pipe model theory

To better understand and thus quantify an ecosystem function such as carbon sequestration and water relations, the biological implications of basal area ( BA), which is one of the most convenient variables often used for the estimation of stem volume and aboveground biomass, are theoretically examined on the basis of pipe model theory. Quantitative analysis of profile diagrams leads to the formulation of plant architecture that simplistically describes the bifurcation manner in plant organs: i.e. the plant weight above a given position is in proportion to the stem cross-sectional area at that position. This simple linear relationship was shown to be applicable to the aboveground biomass estimation using BA in forest stands. Specifically, the linearity of the relationships between aboveground biomass and BA was validated for various forest stands. Pipe model theory, developed to describe tree architecture and forest profile, successfully explains the present relationships, and will contribute to the evaluation of forest ecosystem functions.

Monitoring of boreal forests with multitemporal special sensor microwave imager data

The feasibility of multitemporal special sensor microwave imager (SSM/I) data for monitoring boreal forests was evaluated. The parameters of interest were forest coverage fraction and forest stem volume (biomass). The employed test sites covered almost the whole of Finland. Two measurement periods were used: July through September in 1993 and January through February in 1994. The apparent emissivities of various land cover types were determined with the mixed pixel approach under summer and winter conditions. The aim was to define the dominating factors on emissivity under winter and summer conditions. The mixed pixel approach was tested for the estimation of forest coverage fraction. The results with multitemporal SSM/I data show that the pixel‐wise fractions of water, nonforested, and forested area can be estimated with rms errors of around 10 percent units. The correlation between the estimates and the ground truth was over 0.85. A new inversion method for stem volume estimation was presented. At SSM/I frequencies the forest canopy and the snow‐covered ground dominate the emissivity behavior under winter conditions in the boreal forest zone. The method is based on the fact that the emissivity of forest canopy is close to 1, while that of dry snow cover is relatively low. The results with the method showed promising accuracies when wintertime SSM/I data were employed. The rms error was from 13 to 19 m3/ha per pixel (25 km by 25 km), which was 15–16% of the mean stem volume. In the test area the stem volume ranged from 40 to 160 m3/ha per pixel.

Leaf Area and Above- and Belowground Growth Responses of Loblolly Pine to Nutrient and Water Additions

Abstract A 2 x 2 nutrient and water factorial experiment with four replications was installed in an 8-yr-old stand of loblolly pine (Pinus taeda L.) growing on an infertile, excessively drained sandy site in Scotland County, North Carolina. After the fourth year of treatment, estimated stem volume increment, total biomass production, and peak leaf area index (LAI) increased 152%, 99%, and 101%, respectively, with fertilization and 25%, 23%, 16%, respectively, with irrigation. Stem volume growth efficiency (growth per unit LAI) increased 21% with fertilization, 9% with irrigation, and 30% with both fertilization and irrigation. Total biomass production efficiency increased 91% with fertilization, 29% with irrigation, and 120% with both fertilization and irrigation. The observed increase in stem volume growth efficiency may have been due, in part, to changes in biomass partitioning. However, altered partitioning patterns alone did not explain the observed increase in total biomass production efficiency. We hypothesized that the change in total biomass production efficiency may have been a result of greater allocation to foliage (photosynthesizing tissue) and less allocation to fine roots (a high maintenance respiration tissue) under fertilization and irrigation treatments. For. Sci. 44(2):317-328.

Subpixel Land Use Classification and Retrieval of Forest Stem Volume in the Boreal Forest Zone by Employing SSM/I Data

T he use of microwave radiometry for the retrieval of land use distribution (subpixel proportions) and forest stem volume for 25 km and 50 km pixels is investigated, with new algorithms introduced for the spaceborne multichannel SSM/I instrument. The test sites are located in the boreal forest zone in Finland. SSM/I data from snow-free periods (from May to September) are used in the study, together with a digital high-resolution land use map as reference data. A stepwise algorithm is developed, in which the surface emissivity is estimated for each of the pixels in the first stage of the algorithm. By using a training data set (50% of all data), empirical coefficients for the subpixel land use and forest stem volume are determined. The results for subpixel land use classification (retrieval of fractions of individual land use categories contained within study pixels) are promising. When there are two or three categories to retrieve, the rms errors range from 3% to 9%, and the respective relative errors from 3% to 32%. When there are six categories to retrieve, the performance is less satisfactory, with relative errors exceeding 100% for some categories. For the retrieval of forest stem volume, a similar approach is used. The validation data set shows rms errors (standard errors) of approximately 20 m 3/ha when the mean estimated forest stem volume is around 70 m 3/ha. When compared to reported Landsat TM-based biomass estimates for a study area in Finland, the r 2 (coefficient of determination) values are comparable. The methods are also validated for a wider use by limiting the training data set to either northern or southern Finland, since the surface and forest types in these areas are systematically different (subgroups of boreal forests). The results show that the methods are applicable to remote areas with less training data. This is especially true for the stem volume estimation and limited (two or three classes) subpixel land use classification. These can be considered as promising results for a coarse resolution, high-frequency microwave instrument such as the SSM/I.

Radar-derived standwise forest inventory

The application of remote sensing methods in the estimation of forest stand characteristics, especially biomass and stem volume, has been intensively investigated during the last few years. The new methods, however, have not been accurate enough for operational standwise inventory with a required accuracy typically of 15% for main stand characteristics (stem volume, basal area, and mean height). The present work demonstrates the feasibility of a nonimaging helicopter-borne ranging scatterometer for standwise forest inventory. The radar-derived stand profiles were compared with the standwise field inventory data by applying multivariate data analysis methods. The 1300 ha Teijo test site, locating 130 km west of Helsinki, was divided into 18 parallel radar flight lines with a 150 m spacing. A total of 28 radar variables, including profile information and ground and crown backscatter contributions at 5.4 and 9.8 GHz (polarizations VV, HV, and HH), were used in regression model development. The capability of a ranging radar to classify development class, land use class, bog type and fertility (site) class was demonstrated for the first time. The accuracy of the radar-derived estimates for mean height was 1.6 m (13%) meeting the requirement of operational use. The obtained stem volume accuracy of 31 m/sup 3//ha (26%) was slightly better than has been obtained by aerial photographs. The accuracy of stem volume estimation could be easily improved by decreasing the space between flight lines. However, this leads to considerable increase in flight costs, and, therefore, a scanning ranging radar capable of producing three-dimensional (3D) images of forests would be a better alternative.

Retrieval of forest stem volume using VHF SAR

The ability to retrieve forest stem volume using CARABAS (coherent all radio band sensing) SAR images (28-60 MHz) has been investigated. The test site is a deciduous mixed forest on the island of Oland in southern Sweden. The images have been radiometrically calibrated using an array of horizontal dipoles. The images exhibit a clear discrimination between the forest and open fields. The results show that the dynamic range of the backscattering coefficient among the forest stands is higher than what has been found with conventional SAR using microwave frequencies. The backscatter increases with increasing radar frequency. This work shows an advantage compared to higher frequencies for stem volume estimation in dense forests.

Compatible stem taper and volume ratio equation for Korean pine

Based on 29 stems analysis and 140 sample trees of nature Korean pine (Pinus koraiensis Sib.et Zucc.) measured on the Xiaoxing’an Mountain, effects of age ranged from 20 to 300 years on stem form were discussed and a compatible taper and volume ratio system was developed. The merchantable cubic-metre volume ratio table of varying log rules was constructed for nature Korean pine in this paper. Results indicated that age classes were regarded as a totality to develop taper equation. The compatible tree profile and volume ratio equation developed in this paper can be used to obtain estimates of individual tree volumes and stem profile or volume of varying merchantability limits.

Point accuracy of a non-parametric method in estimation of forest characteristics with different satellite materials

Abstract The reference sample plot (RSP) method is a distance-weighted k nearest neighbour estimation method, which allows simultaneous interpretation of several variables. In the RSP method, the k spectrally nearest field plots are looked at separately for each unknown pixel, and the area weight of the unknown pixel is divided as a function of the spectral distances to the nearest plots. The RSP method was examined in a forest inventory for estimating stem volumes by tree species groups using different satellite materials. Two methods were tested both in searching for and weighting the nearest field plots. Euclidean distance functions worked steadily with all the volume variables studied. The other distance measure tested was based on regression modelling. With more than 15 plots, both covariance weighting and inverse distance weighting gave similar results. Considering the field data of this study, the suitable number of the nearest plots in plotwise estimation appeared to be between 10 and 15 plots. Wi...

Seasonal dynamics of C-band backscatter of boreal forests with applications to biomass and soil moisture estimation

The seasonal changes of the C-band backscattering properties of boreal forests are investigated by applying 1) a semiempirical forest backscattering model and 2) multitemporal ERS-1 SAR data from two test areas in Finland. The semiempirical modeling of forest canopy volume backscattering and extinction properties is based on high-resolution data from the authors' ranging scatterometer HUTSCAT. The response of ERS-1 SAR to forest stem volume (biomass) and other forest characteristics is investigated by employing the National Forest Inventory sample plots, stand-wise forest inventory data and LANDSAT- and SPOT-based digital land use maps. The results show that the correlation between the backscattering coefficient and forest stem volume (biomass) varies from positive to negative depending on canopy and soil moisture. Additionally, the seasonal snow cover and soil freezing/thawing effects cause drastic changes in the radar response. A novel method for the estimation of forest stem volume (biomass) is introduced. This technique is based on the use of: 1) multitemporal ERS-1 SAR data; 2) reference sample plot information; and 3) the semiempirical backscattering model. It is shown that the multitemporal ERS-1 SAR images can be successfully used for estimating the forest stem volume. The effects of soil moisture variations to ERS-1 SAR results have been analyzed using hydrological soil moisture model and in situ data. The results indicate that the semiempirical model can he used for predicting the soil and canopy moisture variations in ERS-1 images.

Long-term effects of superphosphate fertilization on stem form, taper and stem volume estimation of Pinus radiata

The long term effects of superphosphate fertilization on stem form, taper and stem volume estimation of Pinus radiata on a phosphorus-deficient site was examined using data from a fertilizer experiment which had been maintained for 30 years. The application of superphosphate resulted in long term and statistically significant changes in stem form. Mean cylindrical form factor ranged from 0.33 for the control trees up to 0.40 for trees fertilized with 100 kg P ha −1. Stem form was also examined through taper curves which provided detailed depiction of average relative stem profiles. The increase in cylindrical form factor of fertilized trees was largely attributed to a significantly broader profile of the lower third of the stem. In comparison with the control trees, the fertilized trees also had a broader, although not statistically significant, profile of upper and middle stem which could also contribute to the increase in their cylindrical form factor. With increased form factor a greater proportion of the stem became merchantable because of increased log length to tree height ratio. Mean average taper of trees did not show a consistent trend with increasing lelevels of superphosphate application. It largely reflected the differential response of DBH and height growth to the treatments. The volume equation based on control trees underestimated the underbark stem volume of fertilized trees by 5–12% on average. Developing separate volume equations for the fertilized trees is warranted.

A simple volume estimation system and its application to three coniferous species

A simple system for the estimation of stem volume is presented based on the compatible stem profile and volume equations. This system can directly predict the stem volume above breast height from measurements of stem diameter at breast height and at an another point along the upper stem, and does not require any sample data for determining a parameter of volume equation. In comparison with the prediction accuracy of existing volume equations from the literature, using data from Cryptomeriajaponica D. Don, Chamaecyparisobtsusa Endl., and Pseudotsugamenziesii (Mirb.) Franco, this system has the advantage of reducing prediction error.

Improving stem volume estimation of regrowthEucalyptus fastigatawith a lower stem form quotient

Summary Stem volume equations were developed and validated using data from 877 sample trees. Initially, three commonly used models were compared. The least biased and most precise estimates of underbark stem volume was obtained using equations based on the combined variable model. A lower stem form quotient, calculated as the ratio of diameter at 4.5m above ground to diameter at breast height, was subsequently included resulting in a substantial improvement in precision.

Production physiology and morphology of Populus species and their hybrids grown under short rotation. I. Clonal comparisons of 4-year growth and phenology

Height and diameter growth, stem volume production, leaf phenology and leaf number, and number of branches of Populustrichocarpa Torr. & Gray, Populusdeltoides Bartr., and their F1 hybrids (P. trichocarpa × P. deltoides) were studied for 4 years in a research plantation in western Washington, United States. Twelve clones (three of each species and six of the hybrids) grew under a short-rotation silviculture regime in monoclonal plots at spacings of 1 × 1 m (10 000 stems/ha). Clones represented a north-south gradient within the geographic distribution of both the two North American poplar species and the parentage of the hybrid material. The results support earlier work by contributing additional evidence for the superiority of the hybrids. However, the relative hybrid superiority in these monoclonal plots was less pronounced than that found earlier in field trials with single-tree plots because of heightened intraclonal competition. After 4 years, mean estimated stem volume of the hybrids was 1.5 times that of P. trichocarpa and 2.3 times that of P. deltoides. Total tree height of the hybrids was 1.1 times that off. trichocarpa and 1.3 times that off. deltoides. Clonal variation was the dominant theme in height and diameter growth, stem volume productivity, time of bud break and bud set, tree mortality, and number of branches. Populustrichocarpa had the highest number of sylleptic branches, P. deltoides had the lowest, and hybrids were intermediate. Significant clone by replicate interactions were observed in height, diameter, and volume growth. Phenological traits, such as the dates of bud break and bud set, and the length of growing period only partly explained the observed differences in growth between the P. trichocarpa × P. deltoides hybrids and the parental species.

The power function as a simple stem profile examination tool

Formulae are presented for calculating the volume, surface area, centre of gravity, centre of mass, form, taper, and instantaneous slope of the power function. A profile plotting technique is also used that allows visual comparisons between average stem profiles independent of the size and taper of individual stems. The technique is used to demonstrate that the position near 30% of the height from the base of the stem is a position of form stability for volume estimation. Using the paracone profile model (a power function midway between a paraboloid and a cone) with the diameter at the 30% position and the total stem height, individual stem volume estimates within 10% of the true volume (95% confidence) are obtained once again using a sample of 50 yearling aspen (Populustremuloides Michx.). The plotting technique is then applied to the aspen sample, and the average profiles support the hypothesis that juvenile stems may begin life as paraboloids. The average centre of gravity, the average centre of mass, the sectional form, the average form, and the taper of the stems are also examined and are shown to be quantitative indicators of the plotted profile characteristics.

Effects and Adjustments of Competition Bias in Progeny Trials with Single-Tree Plots

Abstract A competition model based on the height difference between a subject tree and its neighbors was used to adjust annual growth data (age 1-5) in a close-spaced single tree plot trial of 25 open-pollinated Pinus banksiana progenies. Competition effects in tree height, basal area, and volume growth were estimated within each of eight classes of dominated oppression. This procedure allowed a differential adjustment of family performances of their large plot expectations. It is limited to the absence of competition effects on height growth. Response to competition was the same in all families. Variance components and heritability estimates of basal area and stem volume were inordinately inflated by competition. For. Sci. 35(2):532-547.