Separate terrain from surface
A digital terrain model describes bare ground; a digital surface model includes the upper envelope of vegetation and structures. Subtract aligned surfaces to estimate height, then review bridges and buildings before calling the result canopy.
Density is not biomass
A plan-view cover fraction measures the area occupied by canopy above a threshold. It does not directly measure timber volume, carbon storage or ecological quality. Narrow gaps may vanish at coarse raster resolution.
Ground returns beneath foliage
Dense foliage can reduce the number of ground returns. Interpolation then bridges unsupported areas. Keep a ground-support mask beside the DEM and exclude unsupported cells from the canopy denominator rather than assigning them zero cover.
Season and corridor geometry
Leaf-off and leaf-on surveys can produce different cover estimates. State the acquisition season and buffer construction rule. At confluences, dissolve overlapping corridors before calculating area to avoid counting the same trees twice.