In the present study, the productivities and costs of row- and selective-thinning operations using a tower yarder were compared to develop a low-cost broad-leaved biomass supply system. In both cases, the operation system comprised felling using a chainsaw, yarding using a tower yarder with a high lead cable system and zigzag pulleys, and processing using a chainsaw and grapple loader. The productivity of felling, which was a one-person operation, was 4.7 m³ /hour for row thinning and 2.7 m³ /hour for selective thinning. The productivity of yarding, which was a three-person operation, was 2.2 m³ /hour for row thinning and 1.5 m³ /hour for selective thinning, whereas the operation time of the wire rope reeving system was 7.6 person-hours for row thinning and 8.2 person-hours for selective thinning. Finally, the productivity of processing, which was a one-person operation, was 3.2 m³ /hour for row thinning and 1.7 m³ /hour for selective thinning. Thus, the overall labor productivity of this cable yarding system in a broad-leaved forest was 2.9 m³ /person-day for row thinning and 1.5 m³ /person-day for selective thinning. Moreover, the logging costs were 11,355 yen/m³ for row thinning and 22,920 yen/m³ for selective thinning, giving total costs of 13,955 yen/m³ and 25,520 yen/m³ , respectively, once transport costs were included. This study suggests that row thinning is more productive and cost-effective system than selective thinning; row thinning can be further improved by 30 % if yarding is conducted as a two-person operation.

The Global Navigation Satellite System (GNSS) is a satellite-based navigation system used to determine the geographic location of any point on the Earth’s surface. The technology is key for increasing forest resource management efficiency, in addition to wood production and distribution. However, large positional errors under forest canopies that block and attenuate GNSS signals have posed significant challenges since the introduction of the Global Positioning System (GPS) in forestry in the 1990s. In addition, GNSS receivers with post processing differential correction functions are relatively unaffordable for small-scale forest owners in Japan, which is partly the reason for more than half of forest ownership boundaries in Japan remaining undetermined, which further makes the large-scale management and joint operations in Japanese forestry difficult. In the present study, a novel method of geographical positioning that employs low cost GNSS receivers without post-processed differential correction is proposed and validated in field trials. Five-hour GNSS measurements were made beneath a forest canopy using five GNSS receivers positioned in a crisscross arrangement. The positional data were logged and averaged every five seconds and 300 sets of one-minute GNSS measurements were extracted from the five-hour dataset. As a result, the one-minute GNSS measurements using the arrangement produced lower precision and accuracy errors compared to the conventional averaging method at a single measurement point, and the multi-satellite GNSS measurements further reduced the degree of positional error. The present study demonstrates the potential of carrying out GNSS positioning beneath forest canopies with lower degrees of error and costs and shorter logging times than required previously. However, it is still necessary to improve the portability and practicality of using GNSS equipment in a crisscross arrangement.

We investigated wound healing in trees after thinning operations using a cable logging system with a tower yarder. An observation plot was set up in a plantation of Japanese cedar and Japanese cypress near Kami City, Kochi Prefecture, Japan. A total of 130 wounds were recorded on 45 of 322 trees immediately after thinning and 6 years later in November 2017. Wounds were scored based on their appearance using a scale of five degrees of severity including “healed”. Width, length, and area were recorded, excluding healed wounds in subsequent surveys. Diameter at breast height (DBH) was measured as an index of tree growth. Comparison of wound statuses at two-time points revealed that all wound sizes reduced; however, some of the initially larger wounds had healed less completely. Most of the wounds with an initial width less than 0.04 m healed completely. The average DBH, which represented growth, was not significantly different between trees with healed and unhealed wounds. Wounds at 0.5 m or lower on the trunks exhibited significantly lower healing rates than those of wounds at 2.00–2.99 m.

In safe and accurate felling work, it is required to determine the height of gravity position in the standing tree. In addition, even in special cutting which sawing is performed in a state with tree lifted, it is necessary to set the hanging position at higher than the height of gravity position to ensure safety, so it is important to grasp the height of gravity position in the standing tree. However, almost no knowledge is found about specific model formulas for estimating the height of gravity position in the standing tree with branches. In this study, we tried to construct a model equation to estimate the height of gravity position in the standing tree using parameters that indicate the individual shape of the tree. The height of gravity position in which the lifted tree by using a rough terrain crane becomes horizontal was measured, the average height ratio of the height of gravity position to the tree height was 37.8%. We performed multiple regression analysis with the parameters that indicate the individual shape of the tree, and obtained a model equation to estimate the height of gravity position from the parameters of tree height and branch height. According to this result, the position about 6% of the branch height added to about 34% of the tree height was the height of gravity position. In the future, it is necessary to verify with a larger number of samples such as regionality and differences in three species.