Nonuniform random sampling: an alternative method of variance reductionfor forest surveys

2001 ◽  
Vol 31 (12) ◽  
pp. 2080-2088 ◽  
Author(s):  
Micheal S Williams
Keyword(s):  
Standard Deviation ◽  
Random Sampling ◽  
Large Scale ◽  
Basal Area ◽  
Substantial Improvement ◽  
Spatially Correlated ◽  
Forest Inventories ◽  
Equal Variance ◽  
Fixed Area ◽  
Areal Sampling

Areal sampling has been used extensively in forest inventories. Prior to the 1950s, areal sampling used fixed-area plots exclusively. The advent of variable radius plot (VRP) sampling provided a substantial improvement in efficiency, both in terms of reducing the variance of the estimator for attributes such as basal area and volume and in the amount of fieldwork required to collect samples. However, since the advent of VRP sampling, there have been few substantial improvements in the efficiency of areal sampling. The purpose of this paper is to illustrate how varying the distribution of sampling points to account for large scale spatial variation can further improve the efficiency of forest inventories. While this is not a new idea, the approach taken here attempts to present the material in such a way as to make it accessible to the broadest spectrum of inventory practitioners. The method, referred to as nonuniform random sampling, is developed using a small forest population where the attribute of primary interest is the total number of trees. A simulation study, drawing samples of 20 fixed-area plots, was performed to compare the new method with current practice. The standard deviation of the estimator of the number of trees was reduced by a factor of about 1.4, meaning that almost 40 sample plots would be needed to achieve equal variance of the estimator using plot locations that were uniformly distributed over the population. To illustrate the potential shortcomings of this approach, the performance of the estimator of the total basal area was studied concurrently. The standard deviation of this estimator actually increased by a factor of more than 2, meaning that fewer than five sample plots would have been needed if the plot locations had been located in accordance with a uniform distribution over the area. Thus, while this technique can substantially reduce the variance for a single or small set of spatially correlated attributes for which the inventory is designed, the estimators of other attributes can be seriously compromised.

scholarly journals The impact of precision of tree position measurements and different plot designs on the estimates of tree level production and diversity parameters

2017 ◽  
Vol 63 (4) ◽  
pp. 195-202
Author(s):  
Ján Merganič ◽  
Katarína Merganičová ◽  
Ľubomír Scheer ◽  
Milan Mistrík ◽  
Federico Costantini ◽  
...  
Keyword(s):  
Basal Area ◽  
Tree Level ◽  
Forest Change ◽  
Forest Inventories ◽  
Multi Criteria Evaluation ◽  
Fixed Area ◽  
Economic Constraints ◽  
The University ◽  
The Impact ◽  
Level Production

AbstractSample plots are basic units of statistical forest inventories. The choice of their shape and size, and sampling methods have changed over time due to economic constraints, efficiency and changes in human demands on data about forests. In the presented study we analysed the impact of three different sampling units: fixed-area plots, fixed-different-area plots, and nested concentric plots, on the estimates of tree level production and diversity parameters. These sampling units were measured during the regional inventory at the University Forest Enterprise of Technical University Zvolen, Slovakia, which was repeated four times (1986, 1992, 1998, 2012). Within each inventory plot, all positions of trees were repeatedly and independently measured three times (1986, 1998, 2012) by different operators using different tools. From these data we quantified the error of tree position resulting from human and technological factors and analysed its impact on the estimates of tree level diversity and production parameters. The selected parameters were: number of trees, stand basal area, standing volume per hectare, number of tree species and number of vertical tree layers. The results indicate that the plot design primarily affects ecological characteristics of forests. Fixed-area plots seem to be the most suitable sampling unit from the point of multi-criteria evaluation of forest status and forest change.

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.

scholarly journals Deriving Tree Size Distributions of Tropical Forests from Lidar

2021 ◽  
Vol 13 (1) ◽  
pp. 131
Author(s):  
Franziska Taubert ◽  
Rico Fischer ◽  
Nikolai Knapp ◽  
Andreas Huth
Keyword(s):  
Size Distribution ◽  
Spatial Scales ◽  
Basal Area ◽  
Tree Height ◽  
Tree Size ◽  
Diameter Distribution ◽  
Forest Inventories ◽  
Allometric Relations ◽  
Lidar Measurements ◽  
Derived Data

Remote sensing is an important tool to monitor forests to rapidly detect changes due to global change and other threats. Here, we present a novel methodology to infer the tree size distribution from light detection and ranging (lidar) measurements. Our approach is based on a theoretical leaf–tree matrix derived from allometric relations of trees. Using the leaf–tree matrix, we compute the tree size distribution that fit to the observed leaf area density profile via lidar. To validate our approach, we analyzed the stem diameter distribution of a tropical forest in Panama and compared lidar-derived data with data from forest inventories at different spatial scales (0.04 ha to 50 ha). Our estimates had a high accuracy at scales above 1 ha (1 ha: root mean square error (RMSE) 67.6 trees ha−1/normalized RMSE 18.8%/R² 0.76; 50 ha: 22.8 trees ha−1/6.2%/0.89). Estimates for smaller scales (1-ha to 0.04-ha) were reliably for forests with low height, dense canopy or low tree height heterogeneity. Estimates for the basal area were accurate at the 1-ha scale (RMSE 4.7 tree ha−1, bias 0.8 m² ha−1) but less accurate at smaller scales. Our methodology, further tested at additional sites, provides a useful approach to determine the tree size distribution of forests by integrating information on tree allometries.

On the error of estimates from successive forest inventories with SPR

1987 ◽  
Vol 17 (5) ◽  
pp. 442-447
Author(s):  
Tiberius Cunia
Keyword(s):  
Forest Inventory ◽  
Random Sampling ◽  
Regression Coefficients ◽  
Partial Replacement ◽  
Forest Inventories ◽  
Continuous Forest ◽  
Regression Functions ◽  
The Given ◽  
Linear Regressions ◽  
Continuous Forest Inventory

The approach used by Cunia to combine the error from sample plots with the error from volume or biomass tables when Continuous Forest Inventory (CFI) estimates of current values and growth are calculated is extended to the CFI systems using Sampling with Partial Replacement (SPR). The formulae are derived for the case of SPR on two measurement occasions when (i) volume or biomass tables are constructed from linear regressions for which an estimate of the covariance matrix of the regression coefficients is known, and (ii) the sample plots or points are selected by random sampling independently of the given volume or biomass regression functions.

scholarly journals Modelling Tree Growth in Monospecific Forests from Forest Inventory Data

Forests ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 753
Author(s):  
Guadalupe Sáez-Cano ◽  
Marcos Marvá ◽  
Paloma Ruiz-Benito ◽  
Miguel A. Zavala
Keyword(s):  
Tree Growth ◽  
Large Scale ◽  
Temporal Dynamics ◽  
Carbon Sink ◽  
Size Variation ◽  
Biotic Interactions ◽  
Richards Equation ◽  
Tree Level ◽  
Forest Inventories ◽  
Large Scale Data

The prediction of tree growth is key to further understand the carbon sink role of forests and the short-term forest capacity on climate change mitigation. In this work, we used large-scale data available from three consecutive forest inventories in a Euro-Mediterranean region and the Bertalanffy–Chapman–Richards equation to model up to a decade’s tree size variation in monospecific forests in the growing stages. We showed that a tree-level fitting with ordinary differential equations can be used to forecast tree diameter growth across time and space as function of environmental characteristics and initial size. This modelling approximation was applied at different aggregation levels to monospecific regions with forest inventories to predict trends in aboveground tree biomass stocks. Furthermore, we showed that this model accurately forecasts tree growth temporal dynamics as a function of size and environmental conditions. Further research to provide longer term prediction forest stock dynamics in a wide variety of forests should model regeneration and mortality processes and biotic interactions.

The Perceived Stress Scale (PSS): Normative Data and Factor Structure for a Large-Scale Sample in Mexico

2013 ◽  
Vol 16 ◽  
Author(s):  
Mónica Teresa González-Ramírez ◽  
María Noel Rodríguez-Ayán ◽  
René Landero Hernández
Keyword(s):  
Standard Deviation ◽  
Factor Structure ◽  
Perceived Stress ◽  
Normative Data ◽  
Large Scale ◽  
Age Groups ◽  
Perceived Stress Scale ◽  
Stress Scale ◽  
Large Samples ◽  
Adequate Reliability

AbstractOne of the most widely used scales for the evaluation of stress is the Perceived Stress Scale (PSS), and it has been adapted into different languages. However, few studies have presented normative data from large samples, and there do not appear to be any studies of the PSS that provide normative data based on large samples for Mexico. Thus, the goal of this study was to provide normative data regarding gender and different age groups for a sample of 1990 Mexican subjects to validate the factor structure of the construct for this sample. The analysis of the 10- and 14-item versions of the PSS revealed that the scale had adequate reliability and that the factor structure was consistent with previous studies. With respect to the normative data, the means of the different groups ranged from 20.93 to 25.63 for the PSS14 and from 14.52 to 17.73 for the PSS10. We propose that scores within one standard deviation of these means be used as reference values for each group.

Synchronous Issue of IR-Based Large Scale Volume Localization System

2014 ◽  
Vol 496-500 ◽  
pp. 1643-1647
Author(s):  
Ying Feng Wu ◽  
Gang Yan Li
Keyword(s):  
Standard Deviation ◽  
Mobile Robot ◽  
Large Volume ◽  
Large Scale ◽  
Image Acquisition ◽  
Mean Value ◽  
Network Synchronization ◽  
Localization System ◽  
Localization Performance ◽  
The Mean

IR-based large scale volume localization system (LSVLS) can localize the mobile robot working in large volume, which is constituted referring to the MSCMS-II. Hundreds cameras in LSVLS must be connected to the control station (PC) through network. Synchronization of cameras which are mounted on different control stations is significant, because the image acquisition of the target must be synchronous to ensure that the target is localized precisely. Software synchronization method is adopted to ensure the synchronization of camera. The mean value of standard deviation of eight cameras mounted on two workstations is 12.53ms, the localization performance of LSVLS is enhanced.

Assessment of Biomass and Carbon Stock of planted teak forest in Terai region of Kumaun Himalaya, India

2018 ◽  
Vol 41 (4) ◽  
pp. 397-402
Author(s):  
Tanuja Gahlot ◽  
◽  
Prachi Joshi ◽  
Y.S. Rawat ◽  
◽  
...  
Keyword(s):  
Climate Change ◽  
Carbon Sequestration ◽  
Human Disturbance ◽  
Carbon Stock ◽  
Large Scale ◽  
Basal Area ◽  
Stand Density ◽  
Positive Contribution ◽  
Teak Plantation ◽  
Forest Division

The ability of forests in atmospheric carbon sequestration is increasingly gaining attention. Present study deals with the estimation of biomass and carbon stock of the teak plantation in the terai central forest division in Kumaun, Uttarakhand State of India. Very few scientific studies were done regarding the teak plantation and the estimation of its biomass in Kumaun. Therefore this study was carried out in this region to assess the role played by teak plantation in climate change. The information regarding the changes in pattern of carbon storage is vital and important because it can be used by government and policymakers to predict the deposit pattern for changing climate. Three sites i.e., Kamola block (Site I), Kamola beat (Site II) and East Gadappu beat (Site III) were selected for the study. Large scale variations in biomass and carbon stock were noted among all three sites. Site III (East Gadappu) showed the maximum biomass and carbon stock (297.03 tha-1 and 143.18 tha-1) followed by site I (Kamola block) (241.9 tha -1and 117.27 t ha-1) and site II ( Kamola beat ) (175.76 t ha-1and 85.79 t ha-1). Although stand density and total basal area of the forest showed almost similar value on all three sites, still the differences in biomass and carbon stock at all sites indicated the positive contribution of biodiversity as shown in the results and negative implications of human disturbance to the forest.

On the Early Cambrian age of two late orogenic granites from. west-central Ahaggar (Algerian Sahara)

1969 ◽  
Vol 6 (1) ◽  
pp. 25-37 ◽  
Author(s):  
J. Boissonnas ◽  
S. Borsi ◽  
G. Ferrara ◽  
J. Fabre ◽  
J. Fabries ◽  
...  
Keyword(s):  
Random Sampling ◽  
Field Data ◽  
Large Scale ◽  
Early Cambrian ◽  
Basement Complex ◽  
West Central ◽  
Algerian Sahara ◽  
Igneous Activity ◽  
Made In

The Pharusian belt of west-central Ahaggar belongs to the 'basement complex' underlying the Paleozoic and later sediments of the Sahara. This paper reports and discusses the Rb–Sr ages obtained on total rocks and minerals from two granitic stocks of the belt: the Tioueiine and Iskel intrusions.Both plutons gave good whole-rock isochrons, which show that the systems were closed 560 ± 40 m.y. ago with respect to Rb and Sr. This is, most probably, the age of crystallization. Three of the four values obtained on biotites are somewhat lower and scattered in the range 502–526 m.y. The discrepancies are probably due to deuteric reactions or incipient weathering. They can be ascribed neither to the loss of 87Sr during the cooling down of the granites, nor to rejuvenation by some later thermal or tectonic event.These studies confirm previous results of random sampling in Ahaggar and prove that large-scale igneous activity took place during the Early Cambrian Epoch. Knowing from field data that the Tioueiine and Iskel are late orogenic granites, it must be concluded that the Pharusian orogeny came to an end at that time.Such a result contradicts early assumptions, made in the field, of a middle Precambrian age for the Pharusian orogeny. It gives further weight to modern ideas concerning the 700–500 m.y. events in Africa, and it leaves time for erosion to create the Saharian platform before the deposition of the first Paleozoic sandstones.

Scale-to-scale anisotropy in homogeneous turbulence

2017 ◽  
Vol 827 ◽  
pp. 250-284 ◽  
Author(s):  
Douglas W. Carter ◽  
Filippo Coletti
Keyword(s):  
Large Scale ◽  
Velocity Structure ◽  
Longitudinal Velocity ◽  
Reynolds Numbers ◽  
Homogeneous Turbulence ◽  
Mean Flow ◽  
Spatially Correlated ◽  
Air Jets ◽  
Image Velocimetry ◽  
Definition Of

We experimentally investigate scale-to-scale anisotropy from the integral to the dissipative scales in homogeneous turbulence. We employ an apparatus in which two facing arrays of randomly actuated air jets generate turbulence with negligible mean flow and shear, over a volume several times larger than the energy-containing eddy size. The Reynolds number based on the Taylor microscale is varied in the range$Re_{\unicode[STIX]{x1D706}}\approx 300{-}500$, while the axial-to-radial ratio of the root mean square velocity fluctuations ranges between 1.38 and 1.72. Two velocity components are measured by particle image velocimetry at varying resolutions, capturing from the integral to the Kolmogorov scales and yielding statistics up to sixth order. Over the inertial range, the scaling exponents of the velocity structure functions are found to differ not only between the longitudinal and transverse components, but also between the axial and radial directions of separation. At the dissipative scales, the moments of the velocity gradients indicate that departure from isotropy is, at the present Reynolds numbers, significant and more pronounced for stronger large-scale anisotropy. The generalized flatness factors of the longitudinal velocity differences tend towards isotropy as the separation is reduced from the inertial to the near-dissipative scales (down to about$10\unicode[STIX]{x1D702}$,$\unicode[STIX]{x1D702}$being the Kolmogorov length), but become more anisotropic for even smaller scales which are characterized by high intermittency. At the large scales, the direction of turbulence forcing is associated with a larger integral length, defined as the distance over which the velocity component in a given direction is spatially correlated. Because of anisotropy, the definition of the integral length is not trivial and may lead to dissimilar conclusions on the qualitative behaviour of the large scales and on the quantitative values of the normalized dissipation. Alternative definitions of these quantities are proposed to account for the anisotropy. Overall, these results highlight the importance of evaluating both the different velocity components and the different spatial directions across all scales of the flow.

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