Influence of transect length and downed woody debris abundance on precision of the line-intersect sampling method
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Background: Accurate downed woody debris (DWD) volume or mass estimates are needed for numerous applications such as fuel loading, forest carbon, and biodiversity/habitat assessments. The line-intersect sampling (LIS) method of inventorying DWD is widely used in forest inventories and ecological studies because it is timeefficient and unbiased. Despite its widespread use, the appropriate transect length needed to achieve a desired precision at a particular location has received relatively little attention. Methods: We conducted intensive LIS sampling at 33 locations representing eight mature or old-growth forest types in northeastern USA, providing a range of forest conditions and DWD volumes (from 17 to 323m3∙ha−1). We used these empirical field data to test, through simulations, the effect of increasing transect length (up to 340m at each location) on precision of associated LIS volume estimates. Importantly, we used a novel application of copula models to account for within-transect spatial autocorrelation of DWD volumes during our simulations, thereby properly addressing variance estimates. Results: As expected, precision consistently improved with increasing cumulative transect length, and locations with lower DWD volumes required longer transects to achieve a given level of precision. We developed models relating precision, transect length, and DWD volume that allows us to gauge a suitable LIS transect length for desired precision levels. Conclusions: LIS provides an attractive method for estimating DWD volume for a given localized area of interest. For the forest types sampled here, and for the particular copula model framework employed, transect lengths of ca. 120m provide a reasonable level of precision, ranging from 18% to 60% coefficients of variation.
Fraver, Shawn; Ducey, Mark J.; Woodall, Christopher W.; D'Amato, Anthony W.; Milo, Amy M.; Palik, Brian J. 2018. Influence of transect length and downed woody debris abundance on precision of the line-intersect sampling method. Forest Ecosystems. 5(1): 139. 10 p. https://doi.org/10.1186/s40663-018-0156-9.