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Field Note: A Comparison of Prism Plots and Modified Point-Distance Sampling to Calculate Tree Stem Density and Basal Area

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Two common methods of measuring forest stand woody stem attributes include prism plots for basal area and modified point-distance for stem density. The data from each method can be used for the other calculation; that is, prism data can provide stem density, and point-distance data can provide estimated basal area. We examined data from the same 10 stands using the two techniques to determine whether the results for each calculation were comparable and/or consistent. There was a significant correlation between the estimated tree (defined as stems >10 cm) basal areas, and between tree stem densities, derived from the two methods (P < 0.01). Prism plots provided significantly higher estimated tree stem densities (+23.5%; P < 0.05) compared to estimates from the point-distance technique, but there was no difference between estimated tree basal area. For all stems, that is also including stems <10 cm dbh, there was no difference between the two methods for estimated basal area or stem density. There was no correlation between total stem densities derived from the two methods. This is likely because the prism plot method (two-factor metric prism) sampled relatively few trees with small diameters, whereas the point distance technique, as used, sampled small trees independently from trees using a diameter distinction. When we removed two young stands with <50 trees/ha, there was no difference in estimates of stem density. We concluded that, for boreal forest stands with a normal density of trees (i.e., >10 cm dbh and 900 to 3,000 stems/ha), either method would provide comparable estimates of stem density and basal area. We found no time difference in conducting surveys using either method.

Keywords: Density estimation; basal area; methods; modified point-distance; prism

Document Type: Research Article

Publication date: 2006-09-01

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  • Each regional journal of applied forestry focuses on research, practice, and techniques targeted to foresters and allied professionals in specific regions of the United States and Canada. The Northern Journal of Applied Forestry covers northeastern, midwestern, and boreal forests in the United States and Canada.
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