open access

https://doi.org/10.14943/doctoral.r7052

https://hdl.handle.net/2115/70218

北海道の森林における樹洞木と立枯れ木の動態及び機能に関する研究

日本語

2018-03-22

Hokkaido University

113p

Wise use of multiple ecosystem functions is critical to the sustainable development of human society. As a result of the continued increase in demand for timber production, declines in forest biodiversity have become serious problems worldwide. Cavity trees and snags provide essential habitat for many species, and are considered important elements in forest biodiversity conservation. The objectives of this study were to develop cavity and snag management plans, integrating biodiversity conservation with timber production in managed forests. Various species, from small-bodied rodents to large-bodied raptors, use cavities as their essential habitat (e.g. breeding and foraging sites). Because the size of a functional cavity varies for the different cavity users, I classified cavities by their entrance width and internal dimensions, and estimated the occurrence probabilities of cavities of each size. Internal dimensions were measured using a charge-coupled device camera attached to a 5-m pole. The results showed that most cavities were too small for occupation by cavity users. The occurrence probability of a cavity having a 5-cm entrance width and internal dimensions of both >10 cm lateral depth and >5 cm downward or upward depth was only about 5% in the case of Fagus crenata trees having 60 cm diameter at breast height (DBH). This study indicates that the classification of cavities by their sizes contributes to reliable estimates of cavity availability. Recruitment and fall down drive the dynamics of snags in forests. Information on snag longevity is necessary to manage snag availability. Several studies have reported that snag longevity increased with increasing DBH of snag in conifer-dominated forests, but the DBH effect on hardwood snags is inadequately understood. I investigated whether and how the DBH effect varies by tree species, and estimated snag longevities of the main species in mixed forests. This study showed that DBH positively affected snag longevity only for Abies sachalinensis and Phellodendron amurense among the six main species in this study. Managers of species-rich mixed forests should consider the variability in DBH effects and their longevity in tree species. Saproxylic beetles are part of a diverse group of species that contributes to overall forest biodiversity. The beetles depend on deadwood substrate for all or part of their life cycle. Shortage of deadwood will have a significant effect on many species and may lead to a decline in forest biodiversity. A snag is a vertical structure that may provide stratified habitats for saproxylic beetles, and so I studied the vertical distribution of saproxylic beetles within snag trunks to examine methods for retaining snags in plantation forests. The results showed that the species richness was not significantly different between three vertical positions of snag trunk, but that the species composition of beetle assemblages within the sample logs was different among the vertical positions. Many snags should be retained, tall enough to promote species richness and composition, to conserve saproxylic beetle assemblages within plantation forests. On the basis of the results of this study, I propose “retention thinning” as a method for integrating snag retention plans with plantation forest management. Plantation managers can ensure an abundance of snags during thinning operations, which are often conducted several times before final harvest. The required abundance of snags to be retained during plantation management can be estimated by snag longevity models. The economic cost of snag creation can be minimized by girdling or topping trees with defects such as wood decay or multiple trunks. I also propose a “retention patch” as a plan for cavity tree management in naturally regenerated forests. By combining the cavity occurrence models with a forest growth model, forest managers can calculate the area needed for a retention patch that will provide a sufficient number of cavities. Combining snag longevity models with forest growth and tree mortality models also allows snag and cavity abundance – as well as timber yield – to be managed simultaneously.

2018-03-22

乙第7052号

博士(農学)

(主査) 特任教授 小池 孝良, 教授 秋元 信一, 教授 齋藤 隆 （北方生物圏フィールド科学センター）, 教授 原 登志彦 （低温科学研究所）

農学院（環境資源学専攻）

博士論文

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