scholarly journals A comprehensive comparison of perpendicular distance sampling methods for sampling downed coarse woody debris

2012 ◽  
Vol 86 (1) ◽  
pp. 129-143 ◽  
Author(s):  
J. H. Gove ◽  
M. J. Ducey ◽  
H. T. Valentine ◽  
M. S. Williams
Keyword(s):  
Coarse Woody Debris ◽  
Sampling Methods ◽  
Woody Debris ◽  
Distance Sampling ◽  
Perpendicular Distance ◽  
Comprehensive Comparison

scholarly journals Distance-limited perpendicular distance sampling for coarse woody debris: theory and field results

2012 ◽  
Vol 86 (1) ◽  
pp. 119-128 ◽  
Author(s):  
M. J. Ducey ◽  
M. S. Williams ◽  
J. H. Gove ◽  
S. Roberge ◽  
R. S. Kenning
Keyword(s):  
Coarse Woody Debris ◽  
Woody Debris ◽  
Distance Sampling ◽  
Perpendicular Distance

Estimating the Carbon in Coarse Woody Debris with Perpendicular Distance Sampling

2008 ◽  
pp. 73-87 ◽  
Author(s):  
Harry T. Valentine ◽  
Jeffrey H. Gove ◽  
Mark J. Ducey ◽  
Timothy G. Gregoire ◽  
Michael S. Williams
Keyword(s):  
Coarse Woody Debris ◽  
Woody Debris ◽  
Distance Sampling ◽  
Perpendicular Distance

Assessing surface area of coarse woody debris with line intersect and perpendicular distance sampling

2005 ◽  
Vol 35 (4) ◽  
pp. 949-960 ◽  
Author(s):  
M S Williams ◽  
M J Ducey ◽  
J H Gove
Keyword(s):  
Surface Area ◽  
Coarse Woody Debris ◽  
Mean Squared Error ◽  
Woody Debris ◽  
Distance Sampling ◽  
Field Work ◽  
Single Measurement ◽  
Stem Form ◽  
Important Conclusion ◽  
Perpendicular Distance

Coarse woody debris (CWD) plays an important role in many terrestrial and aquatic ecosystem processes. In recent years, a number of new methods have been proposed to sample CWD. Of these methods, perpendicular distance sampling (PDS) is one of the most efficient methods for estimating CWD volume in terms of both estimator variance and field effort. This study extends the results for PDS to the estimation of the surface area of CWD. The PDS estimator is also compared to two line intersect sampling (LIS) estimators, where one of the LIS estimators requires the measurement of surface area on each log and the other estimates surface area using a single measurement of log circumference at the point of intersection between the log and the line. The first estimator approximates the true surface area by assuming either a conic or parabolic stem form and requires measurements of the end diameters of each log, which is more time consuming than a single measurement. The performance of the three estimators was compared using a computer simulation. The results of the simulation indicate that, given the same number of pieces of CWD sampled at each point, equal variances can be achieved with PDS using sample sizes that range from about 10% to in excess of 100% the size of a comparable LIS estimator. When the LIS estimators were compared, the estimator that required the measurement of surface area was only about 3%–6% more efficient than the alternative estimator, but the bias associated with assuming a conic or parabolic stem form ranged from roughly 5% to 15%. We conclude that PDS will generally outperform either of the LIS estimators. Another important conclusion is that the LIS estimator based on a measured surface area is likely to have a higher mean squared error than an LIS estimator that employs a single measurement of circumference. Thus, LIS sampling strategies that require the least amount of field work will often have the smallest mean square error.

Perpendicular distance sampling: an alternative method for sampling downed coarse woody debris

2003 ◽  
Vol 33 (8) ◽  
pp. 1564-1579 ◽  
Author(s):  
M S Williams ◽  
J H Gove
Keyword(s):  
Coarse Woody Debris ◽  
Woody Debris ◽  
Distance Sampling ◽  
Sampling Technique ◽  
Sampling Techniques ◽  
New Methods ◽  
Unequal Probability ◽  
Perpendicular Distance ◽  
The Difference ◽  
Primary Advantage

Coarse woody debris (CWD) plays an important role in many forest ecosystem processes. In recent years, a number of new methods have been proposed to sample CWD. These methods select individual logs into the sample using some form of unequal probability sampling. One concern with most of these methods is the difficulty in estimating the volume of each log. A new method of sampling CWD that addresses this issue is proposed. This method samples each log with probability proportional to the volume of each piece of CWD. While this method generally has a smaller variance than the existing methods, the primary advantage is that a design-unbiased estimator of CWD volume is achieved without ever actually measuring the volume of any logs. This method, referred to as perpendicular distance sampling (PDS), is compared with three existing sampling techniques for CWD using a simulation study on a series of artificial populations. In every case, the variance of the PDS estimator of CWD volume was smaller than the variance of the competing methods, but the difference in the variance was not large between PDS and two of the competing methods. When estimating the number of pieces of CWD, the variance of the PDS estimator was one of the largest amongst the tested methods. An equally important result is that the variant of line intersect sampling used in this study, where the orientation of the line is the same at all sample points, performed poorly in every situation. This and other problems suggest that the suitability of this sampling technique for estimating CWD is questionable.

Additional results for perpendicular distance sampling

2005 ◽  
Vol 35 (4) ◽  
pp. 961-966 ◽  
Author(s):  
M S Williams ◽  
H T Valentine ◽  
J H Gove ◽  
M J Ducey
Keyword(s):  
Coarse Woody Debris ◽  
Woody Debris ◽  
Distance Sampling ◽  
Sampling Technique ◽  
Field Testing ◽  
Field Trials ◽  
Field Techniques ◽  
New Methods ◽  
Perpendicular Distance ◽  
Slope Correction

Over the last decade a number of new methods have been proposed to sample coarse woody debris. Of the new methods, both field trials and computer simulations suggest that perpendicular distance sampling is often the most efficient method for estimating the volume and surface area of coarse woody debris. As with any new sampling technique, further research and field testing are required to address some of the practical problems associated with the implementation of perpendicular distance sampling. This paper provides further results associated with the sampling of curved and multistemmed logs and field techniques for both slope correction and the measurement of elevated logs.

scholarly journals Assessment of coarse woody debris following selective logging in Caspian forests: implications for conservation and management

2013 ◽  
Vol 59 (No. 3) ◽  
pp. 117-124
Author(s):  
F.K. Behjou ◽  
O.G. Mollabashi
Keyword(s):  
Coarse Woody Debris ◽  
Forest Ecosystems ◽  
High Efficiency ◽  
Sampling Methods ◽  
Woody Debris ◽  
Forest Health ◽  
Selective Logging ◽  
Survey Method ◽  
Fuel Loading ◽  
Fixed Area

Information on the amount, distribution, and characteristics of coarse woody debris (CWD) in forest ecosystems is highly demanded by wildlife biologists, fire specialists and ecologists. Owing to its important role in wildlife habitats, fuel loading, forest productivity, and carbon sequestration, coarse woody debris is an indicator of forest health. Two sampling methods including fixed-area plot and line intersect sampling were compared for accuracy and efficiency in measuring CWD. Data were selected from mature beech stands following selective logging in Caspian forests. Line intersect sampling consistently provided estimates similar to the results of a 100% survey (high accuracy). This method also took the least amount of time and effort to map the layout and field line location (high efficiency). Finally, line intersect sampling as an easy and fast survey method is suggested to monitor coarse woody debris (CWD) in Caspian forests.  

Analysis of sampling methods for coarse woody debris

2004 ◽  
Vol 198 (1-3) ◽  
pp. 133-148 ◽  
Author(s):  
G Woldendorp ◽  
R.J Keenan ◽  
S Barry ◽  
R.D Spencer
Keyword(s):  
Coarse Woody Debris ◽  
Sampling Methods ◽  
Woody Debris
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