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To make a quantitative prediction on forest road failures in the future under the influence of climate change, forest road failure frequency depending on rainfall intensity needs to be clarified. The forest road failure frequency at a certain rainfall intensity should vary regionally because of the variability in susceptibility. In the current situation of a lack of nationwide detailed forest road failure inventory data and GIS-based forest road data, this study analyzed the relationship between rainfall intensity and forest road failure frequency based on Bayesian inference using data available for all the 47 prefectures in Japan; the annual number of forest road failures, forest road length, analyzed precipitation data and polygon data of forest areas. The predicted forest road failure frequency varied broadly by prefecture; 10−4–10−2 km−1 at a rainfall event of 100 mm/24 h, while 10−2–100 km−1 at that of 400 mm/24 h. The frequency at the same rainfall intensity tended to be lower in conventionally rainy prefectures. The results imply that the number of forest road failures in currently less rainy regions may show a larger increase in the future as intense rainfall events are predicted all over Japan due to climate change. [ABSTRACT FROM AUTHOR]

Although the causes of and impacts against forest road failure differ according to the type of damage that occurs, the statistical understanding of the trends in the type of failure is insufficient. In this study, we collected data on 526 forest road failures due to heavy rainfall during 2006–2010 in the mountainous regions of Japan and statistically analyzed the characteristics. The forest roads covered in this study include those used primarily for timber extraction as well as those used for public purposes. Forest road segments were classified into four categories: streamside, stream crossings, zero-order basin, and others, and comparisons were made regarding the length of damage, the relative probability of occurrence, repair costs, and induced rainfall intensity in each category. Streamside segments accounted for only 15% of the total length of routes analyzed but 42% of all damaged segments. Furthermore, the relative risk of the streamside segments was about 6.0 times higher than that of the other categories of segments, indicating that they were the most likely to be damaged in this analysis. It is clear that the most important issue in the target area is to prevent damage to streamside segments. [ABSTRACT FROM AUTHOR]

To utilize timber and forest biomass resources for bioenergy, technically feasible and economically viable timber and forest biomass resources should be estimated accurately considering their long-term availability. This study focuses on five prefectures, namely, Aomori, Iwate, Miyagi, Akita, and Yamagata, and considers trade between these prefectures. The annual availability of timber and forest biomass resources, such as small-diameter or defect stem logs, rather than logging residues in Japan was estimated as supply potential from profitable forests where expected revenues surpassed all costs, from planting to final harvest. As a result, the supply potential and annual availability of timber were estimated at 11,388,960 m3/year and 1,631,624 m3/year, whereas those of forest biomass resources were estimated at 2,277,792 m3/year and 326,325 m3/year, respectively. Therefore, the rate of annual availability to supply potential was 14.3%. Since timber production and wood chip usage from thinned woods and logging residues in 2018 were 4,667,000 m3/year and 889,600 m3/year, the rates of annual availability for timber and forest biomass resources to those values were 35.0% and 36.7%, respectively. Furthermore, the demand was estimated at 951,740 m3/year from 100,000 m3/year with a generation capacity of 5 MW. The rate of forest biomass resource availability to demand was 34.2%. A thinning subsidy was provided for operational site areas larger than 5 ha in Japan. The rates from subcompartments and aggregated forests with a thinning subsidy increased to 91.4% and 190.3%, respectively. Thus, the estimated availability from aggregated forests with a thinning subsidy met the demand sufficiently in this region. [ABSTRACT FROM AUTHOR]