Incorporating the regeneration process on downed logs into LANDIS-II
(Hotta et al. 2021 Forest Ecology and Management)
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We incorporated regeneration on downed logs into LANDIS-II forest landscape model.
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We revealed the long-term effects of post windthrow management on forest recovery.
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Birch-dominated forests regenerated and persisted over 100 years at scarified sites.
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Salvaging after a first windthrow delayed biomass recovery after a second one.
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CWD-dependent species hardly recover after multiple windthrows in case of salvaging.
Forests have the ability to store atmospheric carbon dioxide and reduce climate change. However, when subjected to "natural disturbances" such as fires and typhoons, forests become a source of carbon dioxide. Furthermore, the removal of fallen trees after natural disturbances prevents the recovery of vegetation and delays the recovery of the forest's carbon sequestration and carbon storage functions. However, previous studies have only evaluated the period of about 20 years after disturbance, and the extent to which forest carbon stocks recover after 50 years or more has not yet been revealed.
The 1954 Toyamaru typhoon caused large-scale windfalls in forests in Hokkaido, northern Japan. In order to assess the long-term effects of windthrow on forest carbon stocks, we conducted a survey in and around the windthrow area of Typhoon Toyamaru in the Taisetsu region of Hokkaido.
As a result, 64 years after the windthrow, the carbon stocks in the forests where the fallen trees were removed were not significantly different from those in the forests where the fallen trees were left. It is thought that the reduction in carbon stock caused by the removal of fallen trees was compensated for by the invasion of many fast-growing broad-leaved trees, and the generation of many dead trees in the process of forest development after the windthrow. On the other hand, carbon stock in the decayed dead trees and the sedimentary organic layer (O layer) was lower in the forests where the fallen trees were removed than in the forests where the fallen trees were left behind.
In forest ecosystems, turnover is constantly occurring, as canopy trees die and young trees grow on the forest floor. The triggers for this change in generation are the death of mature trees that have reached the end of their life span, or the death of canopy trees due to large-scale disturbance. One of the most interesting phenomena in forest regeneration is "regeneration on downed logs" in which dead woods lying on the forest floor serve as regeneration sites for young trees, which in turn nurture the next generation. Compared to the forest floor, downed logs have several advantages such as less pathogens and higher location, which makes it easier to get light. The regeneration process on downed logs has been studied extensively based on field research. It has been shown that Spruce and Hemlock depend on downed logs for most of their regeneration sites (e.g. Harmon and Franklin 1989; Takahashi et al. 2000; Weaver et al. 2008). In addition, in the snowy regions of East Asia, where the forest floor is densely covered with Sasa dwarf bamboo, downed logs also function as a place to avoid shading by Sasa, and is thus essential for forest regeneration (Hiura et al. 1996).
Forest landscape models are useful tools for predicting how forest landscapes will change in the future under various climate, disturbance, and management scenarios. However, because models are to some extent simplifications of natural phenomena, they fail to represent some important ecological processes (Albrich et al. 2020). The regeneration process on downed logs is one such process that has not yet been reproduced in forest landscape models.
In this study, we incorporated the regeneration process on downed logs into the forest landscape model LANDIS-II.
As a case study, we also simulated the effect of post-windthrow management on species composition of forests in the future using an improved version of the model.