Influence of transect length and downed woody debris abundance on precision of the line-intersect sampling method

• Published in: Forest Ecosystems Vol. 5; no. 1; pp. 1 - 10
• Main Authors: Fraver, Shawn, Ducey, Mark J., Woodall, Christopher W., D’Amato, Anthony W., Milo, Amy M., Palik, Brian J.
• Format: Journal Article
• Language: English
• Published: Singapore Springer Singapore 05.12.2018; Springer; Elsevier Limited; KeAi Communications Co., Ltd
• Subjects: Biodiversity; Biomedical and Life Sciences; Coarse woody debris; Coefficient of variation; Computer simulation; Copula model; Data processing; Dead wood; Debris; Ecological monitoring; Ecological research; Ecological studies; Ecology; Ecosystems; Estimates; Evaluation; Forest carbon; Forest ecology; Forest structure; Forestry; Forests; Fuel loads; Life Sciences; Methods; Sampling; Sampling (Statistics); Spatial distribution; Forest structure; Coarse woody debris; Copula model; Forest carbon; Dead wood; Fuel loads
• DOI: 10.1186/s40663-018-0156-9
• ISSN: 2197-5620; 2095-6355

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 time-efficient 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 323 m 3 ∙ha − 1 ). We used these empirical field data to test, through simulations, the effect of increasing transect length (up to 340 m 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. 120 m provide a reasonable level of precision, ranging from 18% to 60% coefficients of variation.