A note on the slope correction and the estimation of the length of line features

2002 ◽  
Vol 32 (4) ◽  
pp. 751-756 ◽  
Author(s):  
Christoph Kleinn ◽  
Berthold Traub ◽  
Christian Hoffmann
Keyword(s):  
Line Length ◽  
National Forest Inventory ◽  
Hilly Terrain ◽  
Forest Inventories ◽  
Circular Field ◽  
Slope Correction ◽  
Fixed Area ◽  
Line Features ◽  
Field Plots ◽  
Individual Line

Length of line features, such as forest border, is among the ecologically interesting attributes estimated from forest inventories. In hilly terrain, observed line lengths must be corrected for slope. Contrary to the correction for standard area-related attributes (like volume per hectare), an overall correction of plot size is not sufficient, but the actual inclination of each individual line segment must be used for slope correction. This topic is discussed, and a mean correction factor is calculated as a function of terrain inclination assuming a uniform angular distribution of lines on the slope. Furthermore, the question is discussed whether the standard slope correction procedure for fixed-area circular field plots may possibly introduce a systematic error into the estimation of line length and also of standard area-related attributes. It is concluded that no relevant error is to be expected, neither with respect to point estimates nor to interval estimates. Data from the second Swiss National Forest Inventory serves for illustration.

scholarly journals Zur Auswirkung der Hangneigungskorrektur auf Schätzwerte im Schweizerischen Landesforstinventar (LFI) | Investigation of the effect of the slope correction method as applied in the Swiss National Forest Inventory of estimates

2001 ◽  
Vol 152 (6) ◽  
pp. 215-225 ◽  
Author(s):  
Michael Köhl ◽  
Peter Brassel
Keyword(s):  
Forest Inventory ◽  
Basal Area ◽  
Correction Method ◽  
National Forest Inventory ◽  
National Forest ◽  
Average Deviation ◽  
Forest Inventories ◽  
Slope Correction ◽  
Number Of Stems ◽  
Elliptical Area

For forest inventories on slopes, it is necessary to correct the test areas, because the circular areas, when projected, become elliptical. Based on 93 samples from the Swiss National Forest Inventory (FNI), it was determined whether the simplified method, which increases the radius to match that of the elliptical area, leads to a distortion of the results. An average deviation of 2% was found between the FNI estimated values and the actual values for the basal area and the number of stems. For estimations of smaller units, greater distortions of the results are expected.

scholarly journals How to Evaluate Downed Fine Woody Debris Including Logging Residues?

Forests ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 881
Author(s):  
Nathalie Korboulewsky ◽  
Isabelle Bilger ◽  
Abdelwahab Bessaad
Keyword(s):  
Wood Density ◽  
Stock Assessment ◽  
Woody Debris ◽  
Diameter Class ◽  
Density Measurements ◽  
Fine Woody Debris ◽  
Forest Inventories ◽  
Test Zone ◽  
Fixed Area ◽  
Volume Estimates

Volume or biomass estimates of downed woody debris are crucial for numerous applications such as forest carbon stock assessment, biodiversity assessments, and more recently for environmental evaluations of biofuel harvesting practices. Both fixed-area sampling (FAS) and line-intersect sampling (LIS) are used in forest inventories and ecological studies because they are unbiased and accurate methods. Nevertheless, most studies and inventories take into account only coarse woody debris (CWD, >10 cm in diameter), although fine woody debris (FWD) can account for a large part of the total downed biomass. We compared the LIS and FAS methods for FWD volume or biomass estimates and evaluated the influence of diameter and wood density measurements, plot number and size. We used a Test Zone (a defined surface area where a complete inventory was carried out, in addition to FAS and LIS), a Pilot Stand (a forest stand where both LIS and FAS methods were applied) and results from 10 field inventories in deciduous temperate forest stands with various conditions and amounts of FWD. Both methods, FAS and LIS, provided accurate (in trueness and precision) volume estimates, but LIS proved to be the more efficient. Diameter measurement was the main source of error: using the mean diameter, even by diameter class, led to an error for volume estimates of around 35%. On the contrary, wood density measurements can be simplified without much influence on the accuracy of biomass estimates (use of mean density by diameter class). We show that the length and number of transects greatly influences the estimates, and that it is better to apply more, shorter transects than fewer, longer ones. Finally, we determined the optimal methodology and propose a simplification of some measurements to obtain the best time-precision trade-off for FWD inventories at the stand level.

Realized and potential efficiency for post-stratified estimation in a national forest inventory

2021 ◽  
Author(s):  
James A. Westfall ◽  
Andrew J. Lister ◽  
John W. Coulston ◽  
Ronald E. McRoberts
Keyword(s):  
Remotely Sensed ◽  
National Forest Inventory ◽  
Data Types ◽  
Remotely Sensed Data ◽  
Large Area ◽  
Forest Inventories ◽  
Temporal Misalignment ◽  
Total Tree ◽  
Potential Efficiency ◽  
Post Stratification

Post-stratification is often used to increase the precision of estimates arising from large-area forest inventories with plots established at permanent locations. Remotely sensed data and associated spatial products are often used for developing the post-stratification, which offers a mechanism to increase precision for less cost than increasing the sample size. While important variance reductions have been shown from post-stratification, it remains unknown where observed gains lie along the continuum of possible gains. This information is needed to determine whether efforts to further improve post-stratification outcomes are warranted. In this study, two types of ‘optimal’ post-stratification were compared to typical production-based post-stratifications to estimate the magnitude of remaining gains possible. Although the ‘optimal’ post-stratifications were derived using methods inappropriate for operational usage, the results indicated that substantial further increases in precision for estimates of both forest area and total tree biomass could be obtained with better post-stratifications. The potential gains differed by the attribute being estimated, the population being studied, and the number of strata. Practitioners seeking to optimize post-stratification face challenges such as evaluation of numerous auxiliary data sources, temporal misalignment between plot observations and remotely sensed data acquisition, and spatial misalignment between plot locations and remotely sensed data due to positional errors in both data types.

scholarly journals Improving precision of field inventory estimation of above ground biomass through an alternative view on plot biomass

2020 ◽  
Author(s):  
Christoph Kleinn ◽  
Steen Magnussen ◽  
Nils Noelke ◽  
Paul Magdon ◽  
Juan Gabriel Álvarez-González ◽  
...  
Keyword(s):  
Remote Sensing Data ◽  
Current Approach ◽  
Tree Level ◽  
Alternative View ◽  
Above Ground Biomass ◽  
Ground Biomass ◽  
Forest Inventories ◽  
Continuous Approach ◽  
Continuous Surface ◽  
Fixed Area

Abstract We contrast a new continuous approach (CA) to estimation of plot level above-ground biomass (AGB) in forest inventories with the current approach of deriving the AGB estimate exclusively from the tree-level AGB predicted for each tree in a plot; henceforth called DA (discrete approach). In CA the AGB in a forest is modelled as a continuous surface and the AGB estimate for a fixed area plot is computed as the integral of the AGB surface taken over the plot. Hence with CA, the portions of biomass in plot-trees that extend across a plot perimeter is ignored while the biomass from trees outside the plot reaching inside the plot is added. We use a sampling simulation with data from a fully mapped 2 ha area to illustrate, that important differences in plot-level AGB estimates can emerge, and that one should expect CA-based estimates of AGB to be less variable than with the DA, which translates to a higher precision of estimates from field plots: in our case study, for a target precision of estimation of 5%, the required sample size was 27% lower for small plots of 100m2 when using the CA and 10% lower for larger plots of 1700m2. We discuss practical issues to implementing CA in field inventories and discuss the expected potential for applications that model biomass from remote sensing data.

scholarly journals Area-based lidar-assisted estimation of forest standing volume

2008 ◽  
Vol 38 (11) ◽  
pp. 2911-2916 ◽  
Author(s):  
Piermaria Corona ◽  
Lorenzo Fattorini
Keyword(s):  
Confidence Interval ◽  
Laser Scanning ◽  
Auxiliary Information ◽  
Lidar Measurement ◽  
Sampling Variance ◽  
Ratio Estimator ◽  
Lowland Forest ◽  
Fixed Area ◽  
Scanning Lidar ◽  
Field Plots

Airborne laser scanning (lidar) technology is increasingly being applied in forest ecosystem surveys. This research note proposes a design-based approach for the lidar-assisted estimation of forest standing volume when ground surveys are performed by means of fixed-area plots. The lidar measurement of the height of the upper canopy (digital crown model) is performed for the whole study area, and the resulting pixel heights are adopted as auxiliary information to couple with the standing volume acquired on the ground by means of sample plots. The ratio estimator for the total volume of the forest is derived in a complete design-based framework together with an unbiased estimator of its sampling variance and the corresponding confidence interval. The proposed procedure has been tested in Bosco della Fontana, a lowland forest in Northern Italy, obtaining a 95% confidence interval for the total volume, which is approximately 2/3 smaller than that obtained by solely using information arising from field plots.

Improved stand structure characterization from nested plot designs in the Spanish National Forest Inventory

2020 ◽  
Author(s):  
Daniel Moreno-Fernández ◽  
Isabel Cañellas ◽  
Iciar Alberdi ◽  
Fernando Montes
Keyword(s):  
Spatial Pattern ◽  
Null Model ◽  
National Forest Inventory ◽  
Second Order ◽  
Order Moment ◽  
National Forest ◽  
Nearest Neighbour ◽  
Nested Design ◽  
Forest Inventories ◽  
Moment Functions

Abstract National forest inventories, in which trees are often mapped within the plots, provide a tool for the quantification of large-scale forest structure since they cover all forest areas. Many National Forest Inventories follow a nested design in order to reduce the sampling effort for smaller trees. We propose and test a methodology that allows the spatial pattern of trees, species mingling and size differentiation to be characterized using the nearest neighbour indices and second-order moment functions from nested plot data. The nearest neighbour indices and second-order moment functions for the actual distribution are compared with simulations of the appropriate null model: spatial randomness for spatial pattern characterization or spatial independence for species mingling and size differentiation. The proposed method consists of constraining the null model to fit the nested plot design. For the purposes of the study, we simulated 120 plots and used 26 real plots located in pure and mixed stands in Central Spain, for which a complete census with detailed information about trees was available. The nested design used in the Spanish National Forest Inventory (SNFI) plots was simulated to test the performance, taking the complete census as reference. Despite of the limited accuracy for some structural measures, the proposed method based on nested design data performed better for most of the nearest neighbour indices and second-order moment functions than the strategy currently used in the SNFI for structure assessment in a subsample of SNFI plots, consisting of mapping the 20 trees closest to the plot centre. Nearest neighbour indices provided greater accuracy for species mingling assessment than second-order moment functions, whereas the opposite occurred when describing spatial pattern and size differentiation. The methodology proposed provides the first insight into the characterization of forest structure in nested designs although more evaluations are required for different forest types.

scholarly journals Waldindikatoren zur Artenvielfalt – Erkenntnisse aus LFI und BDM Schweiz | Forest structures and species diversity – Findings from the NFI and BDM

2007 ◽  
Vol 158 (8) ◽  
pp. 243-254 ◽  
Author(s):  
Urs-Beat Brändli ◽  
Christoph Bühler ◽  
Adrian Zangger
Keyword(s):  
Species Diversity ◽  
Vascular Plants ◽  
Monitoring Program ◽  
Stand Density ◽  
Species Group ◽  
National Forest Inventory ◽  
Study Data ◽  
Species Density ◽  
Site Factors ◽  
Forest Inventories

In order to monitor species diversity, surveying indicators in habitats has often been recommended as more cost efficient than assessing species directly. In this study data from the Swiss National Forest Inventory (NFI)and the Biodiversity Monitoring Program (BDM) were used to verify the correlation of species density for vascular plants, mosses, and molluscs with 58 variables of forest structure, site conditions and forest management. The analyses show that site factors, in particular the biogeographic regions, the altitude, slope and the soil acidity,explain 18 to 49% of the observed variance in species density, depending on the species group (taxon). Of all the factors influenced by management, only the availability of light (stand density) was found to play an important role primarily on vascular plants. In addition the density of molluscs is positively correlated to shrub cover. However, none of the regression models tested explains more than 54% of the variance of species density. Therefore, the authors conclude that the species richness of the species groups investigated can be assessed reliably only by direct survey. The analyses confirm that certain data assessed in forest inventories is ecologically very important and relevant for environmental policy.

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