Natural disturbances and subsequent management activities strongly affect forest species composition and carbon stocks. Windthrow is a major natural disturbance in East Asia. The short-term effects of salvage logging after windthrow are well known, i.e., vegetation recovery delays due to the destruction of advanced regeneration, changes in species composition, and reductions in aboveground carbon stocks. However, the long-term effects of salvage logging are less clear. Although forest landscape models are effective tools for evaluating these effects, conventional process-based models do not represent the process of regeneration on downed logs, which is essential for simulating forest succession in northern Japan.
We implemented the process of regeneration on downed logs in the LANDIS-II model and simulated the long-term effects of salvage logging after windthrow on forest species composition and carbon stocks in 2 scenarios in a boreal mixed forest (350 ha) in Hokkaido, northern Japan: windthrow only (WT) and windthrow with salvage logging (WT+SL). We modified the model to track coarse woody debris (CWD) carbon stocks by five decay classes and estimated the occupation areas of CWD in decay classes 3-5 for each site. Then, we regulated the probability of establishment of CWD-dependent species, such as spruce, by the CWD occupation areas.
Results/Conclusions
By modifying LANDIS-II, we successfully evaluated the effects of regeneration on downed logs on forest carbon stocks and species composition. As simulated by the modified LANDIS-II, the aboveground carbon stocks (live trees and CWD) in WT+SL were lower than those in WT even 100 years after those impacts. Regarding species composition, the ratio of broadleaves to live trees as biomass in WT+SL was larger than that in WT because pioneer species such as Betula ermanii and Betula maximowicziana established easily in WT+SL due to the destruction of advanced regeneration by salvage logging. These results are in line with the results of an empirical study that evaluated the effects of salvage logging 64 years after windthrow and salvage logging. Furthermore, it took 30 years for the CWD-dependent species Picea jezoensis and Picea glehnii to establish after the windthrow in WT, whereas it took over 70 years for them to establish in WT+SL. Our simulation revealed that salvage logging affects not only forest carbon stocks but also species composition in the long term.