Line Intersect Sampling of Forest Canopy Gaps

Abstract Line intersect sampling (LIS) is commonly used to measure the fraction of forest area under canopy gaps (gap fraction) and the size distribution of gaps. The typical application of this technique makes assumptions about the shape of the gaps. Potential errors associated with these assumptions were quantified. To measure the gap regime in an old-growth, subalpine spruce-fir forest, regression equations were used to describe empirically gap area and perimeter. Most gaps in the spruce-fir forest were shaped like nonconvex polygons. Mapped gap areas were 22% less than estimates based on an elliptical model of gap shape and 22% more than area estimates based on a rhomboidal model of gap shape. An LIS method was developed that works for nonconvex shapes and was used to assess gap fraction in a subalpine, spruce-fir forest. The LIS approach for irregularly shaped gaps provided an estimate of gap fraction that was significantly smaller (35%) than the one based on an elliptical model of gap shape. The modifications in the application of LIS to the study of gap regimes seemed to preserve the efficiency and power of LIS while improving the accuracy of the results. For. Sci. 42(2):131-138.