The canopy length is useful in that it can be used to estimate forest density based on ALS measurements. However, when quantifying the canopy length, the heterogeneity in canopy length within individuals occurring on sloping terrain becomes an issue. In this study, a theoretical forest stand consisting of model trees with canopy geometry represented by quadratic ~ polynomial equations were assumed to assess the effect of the heterogeneity in canopy length that occurs on the upper and lower sides of a slope site on the assumption of the forest density at the slope site. When the slope angle of the stand was varied in a theoretical forest stand consisting of 3,000 standing trees ha^－1 with a quadratic (parabolic) canopy shape and a canopy length of 4 m, canopy length was estimated to be 4.54 m on the lower slope at 30° slope and 5.74 m at 60° slope. The densities estimated from the canopy length on the lower side of the slope were 2,641 trees ha^－1 at 30° slope and 2,092 trees ha^－1 at 60° slope. A similar trend was observed when a polynomial was assumed for the canopy geometry. The effect of heterogeneity in canopy length on the assumption of the forest density can be compensated for by using the average canopy length on the upper and lower sides of the slope, and it can be inferred that the average slope and population density can be compensated for when the upper or lower side is only measured.

Japanese oak wilt, which is caused by the ascomycetous fungus Dryadomyces quercivorus and its vector, the ambrosia beetle Platypus quercivorus, has been spreading across Japan, resulting in massive mortality of Quercus crispula on Honshu Island. However, there have been no recorded cases of Japanese oak wilt in Hokkaido, the northernmost island of Japan. In 2023, field surveys were conducted at five locations in Matsumae and Fukushima, situated at the southern edge of Hokkaido. The surveys revealed 10 damaged trees (16 damaged stems), attacked by P. quercivorus. The damaged trees were identified as Q. crispula. Dryadomyces quercivorus was isolated from the entry holes of P. quercivorus in two damaged trees. The number of entry holes in the nine dead trees ranged from 1 to 17, with many holes located near the ground. The number and density of entry holes in dead trees were higher than those in surviving trees. The number of entry holes was greater in damaged trees with larger basal area at breast height. However, damaged trees were not necessarily larger than surrounding undamaged trees when comparing their diameters at breast height. The characteristics of the first Japanese oak wilt damage in Hokkaido were consistent with previous studies in Honshu in that the number of entry holes was greater in dead trees than in surviving trees. However, there were some characteristics different from those of Japanese oak wilt in Honshu, such as the death of trees with few holes and attacks on trees other than large diameter trees.