Survival of young, dense Betula ermanii stands after wildfire at top soil removal sites

Abstract

Abstract A forest fire in a cool-temperate broadleaved forest in northern Japan, from 26 May to 19 June 2019, provided an opportunity to examine the post-fire dynamics of young, dense birch (Betula ermanii Cham.) stands that had previously undergone top soil removal through soil scarification. To characterize the post-fire responses (survival and resprouting) of birch trees, we set up two plots, 6 months after the fire. We investigated the trunk diameter at breast height and burn marks on the trunks (scorch height and bole charring percentage) of all B. ermanii trees in both plots. Survival and resprouting of each tree were monitored over a 10-month period (6 and 16 months after the fire). To quantify post-fire vegetation recovery of the forest floor, we manually mapped the dominant understory plant, dwarf bamboo (i.e. Sasa kurilensis (Rupr.) Makino et Shibata), from orthomosaic images obtained using an unmanned aircraft vehicle, and estimated the recovery rate in the second year after the fire. Additionally, the seedlings of woody species were counted in both plots. A logistic generalized linear model revealed that the size-dependent survival rates of the plants in each plots were similar in the first year after fire. All B. ermanii trees died without resprouting in the second year after the fire, indicating the lethal effects of fire on young birch trees in top soil removal sites. Moreover, a high recovery rate of dwarf bamboo over 2 years in both plots and limited woody seedling establishment of woody plants suggest that the fire resulted in the regeneration failure of young stands in the top soil removal sites. Based on these findings, we suggest that the vulnerability of young trees can lead to the rapid change in vegetation from young forest to dense dwarf bamboo cover after a fire.