Estimation of crown and canopy cover from airborne lidar data

Tests were carried out in mature Scots pine, Norway spruce and Silver birch stands at Järvselja, Estonia, to estimate canopy cover (K) and crown cover (L) from airborne lidar data. Independent estimates K_c and L_c for K and L were calculated from the Cajanus tube readings made on the ground at 1.3 m height. Lidar data based cover estimates depended on the inclusion of different order returns significantly. In all the stands first order return based estimate K₁ was biased positively (3-10%) at the reference height of 1.3 m compared to ground measurements. All lidar based estimates decreased with increasing the reference height. Single return (K_y) and all return (K_k) based canopy cover estimates depended more on the sand structure compared to K₁. The ratio of all return count to the first return count D behaved like crown cover estimate in all stands. However, in spruce stand D understimated L_c significantly. In the Scots pine stand K₁(1.3) = 0.7431 was most similar canopy cover estimate relative to the ground estimate K_c = 0,7362 whereas K_y(1.3) and K_k(1.3) gave significant underestimates (>15%) of K. Caused by the simple structure of Scots pine stand - only one layer pine trees, the Cajanus tube based canopy cover (K_c), crown cover (L_c) and lidar data based canopy density D(1.3) values were rather similar. In the Norway spruce stand and in the Silver birch stand second layer and regeneration trees were present. In the Silver birch stand K_k(1.3) and K_y(1.3) estimated K_c rather well. In the Norway spruce stand K_y(1.3) and K₁(1.3) were the best estimators of K_c whereas K_k(1.3) underestimated canopy cover. Lidar data were found to be usable for canopy cover and crown cover assessment but the selection of the estimator is not trivial and depends on the stand structure.