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The frequency and intensity of typhoons are expected to increase over time due to climate change. These changes may expose forests to more windthrow in the future, and increasing the resilience of hemiboreal forests through forest management after windthrow is important. Here, we quantified forest structure recovery using aerial photos and light detection and ranging (LiDAR) data after catastrophic windthrow events. Our aims are to test the following three hypotheses: (1) forest structure will not recover within 30 years after windthrow, (2) forest recovery will be affected not only by salvaging but also pre-windthrow attributes and geographical features, and (3) various post-windthrow management including salvaging will drastically alter tree species composition and delay forest recovery. Our results revealed that hypothesis (1) and (2) were supported and (3) was partially supported. The ordination results suggested that more than 30 years were needed to recover canopy tree height after windthrow in hemiboreal forests in Hokkaido, Japan. Salvage logging did not delay natural succession, but it significantly decreased the cover ratio of conifer species sites (0.107 +/- 0.023) compared with natural succession sites (0.310 +/- 0.091). The higher the elevation, the steeper the site, and the higher the average canopy height before windthrow, the slower the recovery of forest stands after windthrow and salvaging. Scarification and planting after salvage logging significantly increased the number of canopy trees, but those sites differed completely in species composition from the old growth forests. Our study thus determined that the choice and intensity of post-disturbance management in hemiboreal forests should be carefully considered based on the management purpose and local characteristics.

Post-windthrow management delays forest biomass recovery by altering the situation of disturbance legacies and can change the species composition. Although the short-term effects of post-windthrow management have been well studied, we do not have enough knowledge about the long-term effects of post-windthrow management on species composition and biomass recovery. Those effects associated with an increase in the windthrow frequency are also unknown. Although forest landscape models can effectively evaluate these effects, conventional models do not represent the regeneration process on downed logs, which is essential for simulating forest succession. We focused on hemiboreal forests in northern Japan and aimed to (1) incorporate the regeneration process on downed logs into LANDIS-II, which is one of the most used forest landscape models; (2) evaluate the long-term effects of post-windthrow management on tree species composition and aboveground biomass recovery; and (3) evaluate the associated long-term effects of interactions between post-windthrow management and increased windthrow frequency. We incorporated the regeneration process on downed logs into LANDIS-II by regulating the probability of the establishment of species that depend on dead wood, such as spruce, according to the availability of well-decayed dead wood. The incorporation of this process resulted in simulations of trends in species composition and aboveground biomass recovery after post-windthrow management that were more accurate than those produced by the original model. In the modified LANDIS-II simulation, reductions in dead wood and advanced seedlings due to salvage logging had little effect on the tree species composition or aboveground biomass recovery; however, the complete destruction of advanced seedlings by scarification induced a delay in aboveground biomass recovery and a shift to birch-dominated forests that continued for 100 years. In addition, the reduction in dead wood due to salvage

To mitigate the negative effects of climate change, it is necessary to conserve carbon stocks in forests. Typhoons fell many standing trees and generate a substantial amount of coarse woody debris (CWD). In boreal forests, CWD contributes to maintaining carbon stocks for a long time after a disturbance because the decomposition rate of CWD is relatively low. We know that salvage logging after a disturbance tremendously decreases the forest carbon stock over the short term after logging but know little about its long-term effects. We targeted a catastrophic windthrow caused by a super typhoon in 1954 in boreal forests in northern Japan and estimated the long-term effects of salvage logging after the windthrow on the above- and belowground carbon stocks by comparing old-growth forests with low damage from the super typhoon in 1954 or any subsequent typhoons (OG), forests damaged by the typhoon with remaining CWD (i.e., windthrow, WT), and forests damaged by the typhoon followed by salvage logging (WT + SL). The CWD carbon stock of decay class 5 (i.e., the most decayed CWD) in WT was significantly larger than that in OG and WT + SL, suggesting that the CWD in decay class 5 in WT had been generated by the typhoon 64 years ago, and the negative effect of salvage logging on the carbon stock still remains apparent in the CWD carbon stock of decay class 5. The carbon stock of the organic (0) layer in WT was larger than that in WT + SL, probably because of three factors: (1) the slower decomposition rate of fallen leaves and twigs of conifers than broadleaves, as conifer litter is abundant in WT; (2) greater carbon transition from the CWD to the 0 layer in WT; and (3) the occurrence of a lower decomposition rate in the 0 layer in WT. However, the total carbon stock in WT + SL has almost recovered to the level of that in WT within the last 64 years. The carbon stocks of broadleaves that grew rapidly after the disturbance and the newly accumulated dead trees generated througho