Abstract
Standing dead trees (snags) are crucial habitats for fauna in mature and diverse forests along the Interior Douglas-fir Zone of British Columbia. The objective of this study is to evaluate whether snag density and snag metrics differ between three categories of at-risk and irreplaceable Old Growth Priority Deferral Areas (ancient, big-treed and remnant) and their neighbouring areas with no deferral status. Using airborne LiDAR data, we detect snags using 1) area-based forest metrics paired with random forest modelling, and 2) an individual snag detection algorithm.
Snag density was highest along ancient deferral areas (20.7 snags per ha), while snag presence, sampled at 20m x 20m spatial resolution, was highest along remnant forests (65.6% total sampled area). Overall, snags in big-treed deferral areas were the tallest (15.1m), largest (diameter at breast height, DBH = 9.38cm) and exhibited the largest height variation (7.3m). Snag presence was lowest in non-deferral areas (39.3% total sampled area). However, where snags are present, their density and diameter in non-deferral areas are similar to those in deferral areas.
Of the pairwise tests between Old Growth Areas, presence vs absence values of remnant-ancient and remnant-big treed pairs yielded significantly different results (P = 0.0047 & 0.00016 respectively). This suggests that snags found in ancient and big-treed areas are more clustered than those in remnant areas. Snag heights were also significantly different (P = 0.0024) across the three deferral types, with ancient areas possessing lower snag heights. This study validates the merits and weaknesses of the area-based forest metric and individual detection approaches through LiDAR data, and their potential use to inform habitat suitability and connectivity for snag-dwelling fauna along old growth forests.
MGEM Student: Robin Zuo Feng Ong
Community Partner: BC Ministry of Forests, Lands, Natural Resource Operations and Rural Development
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Ong, Robin Zuo Feng, 2022, “Evaluation of snag density and snag metrics in Old Growth Deferral Priority Areas in the Cariboo region using airborne LiDAR data”, https://doi.org/10.5683/SP3/LYPIWG, Borealis, V1