Forest fire survival in young, dense Betula ermanii stands on scarification sites

A forest fire (May 2019) in northern Japan, provided an opportunity to examine the impact of the disturbance on dense birch (Betula ermanii) stands on soil scarification sites. Two plots (Plot 1, 10×50 m; Plot 2, 20×20 m; 500 m apart) were set up six months after the fire. To assess the severity of the fire, burn marks on tree trunks (scorch height), burned litter depth, and understory regrowth were examined. Trunk diameter at breast height (DBH) and survival were investigated for all surviving birches (Plot 1; N = 112, Plot 2; N = 115). Scorch height, which correlates with fire intensity, did not reach the tree canopy. Burned litter was found only in the surface layer. New leaves and culms from belowground rhizomes were observed in the dwarf bamboo Sasa kurilensis, the dominant understory vegetation. Fire severity was low enough to avoid damage to the tree canopy, but damaged tree trunks and above-ground parts of understory plants. The survival of B. ermanii was similar in Plots 1 and 2 (24.1 and 27.8 %, respectively). Survival probability, estimated by simple logistic regression, was size dependent; the average DBH of surviving birches was larger than that of dead birches. Therefore, the stand structure, including density and size composition, was shifted because young birches (