We investigated the combined effects of line-thinning and high browsing pressure by sika deer (Cervus nippon) on undergrowth dynamics and surface soil erosion over a seven-year period in a planted Japanese cypress (Chamaecyparis obtusa) forest located on steep slopes. We applied a line-thinning treatment to a 52-year-old stand by using a two-cut method, leaving four or five rows between the cut rows. We also established four experimental conditions based on two factors: deer exclusion (inside or outside the exclosure) and row type (cut or uncut rows). We monitored the light environment and undergrowth development annually and evaluated the soil surface conditions seven years after thinning. Thinning increased relative light intensity within the stand across all treatments, providing favorable conditions for undergrowth development. Inside the exclosure, the abundance of undergrowth increased gradually throughout the period in both the cut and uncut rows. In contrast, in both types of rows outside the exclosure, it increased slightly in the first two years but remained unchanged thereafter. Outside the exclosure, browsing pressure and surface soil erosion suppressed undergrowth development, with no significant differences between the cut and uncut rows, even for deer-unpalatable species. The cut rows inside the exclosure had significantly higher undergrowth and litter cover ratios, as well as a lower soil erosion susceptibility index (which indicates the relative risk of surface soil erosion), compared to all other conditions. These results suggest that, although line-thinning can promote undergrowth recovery and mitigate surface soil erosion, its effectiveness is reduced under high deer browsing pressure.

The effectiveness of fire prevention function of trees, used in homestead windbreaks and roadside trees in Okinawa Prefecture, was investigated. In recent years, reports of fires, such as the wildfire on Yanaha Island in Okinawa, attributed to rising temperatures and climate change, have been constant. Therefore, we investigated the fire prevention function of the major tree species by measuring moisture content of tree leaf, cubic volume of the leaf, calorific value of combustion and tree form characteristics. In this study, in addition to Garcinia subelliptica (fukugi), which has been commonly used for coastal windbreaks and other purposes in Okinawa Prefecture, we also investigated the effects of fire prevention functions of Calophyllum inophyllum (terihaboku), Diospyros ferrea (ryukyu-kokutan), Pinus luchuensis (ryukyu-matsu), Distylium racemosum (isunoki), Podocarpus macrophyllus (inu-maki), Viburnum odoratissimum (sango-ju), which has been used as a windbreak for a long time, and other trees such as Elaeocarpus zollingeri var. zollingeri (horutonoki), Quercus glauca (amami-arakashi), Cinnamomum yabunikkei (yabu-nikkei), Machilus thunbergii (tabunok), and Fraxinus griffithii (shima-toneriko). P. macrophyllus and P. luchuensis are coniferous trees, while the other ten species are broad-leaved trees. As a result of comparing moisture content of branch and leaf, calorific value of combustion, cubic volume of the leaf, and tree form, it was found that D. ferrea exhibited high fire prevention effectiveness, owing to its high moisture content, low combustion heat value, large leaf volume, and dense tree form. Similarly, G. subelliptica, D. racemosum, C. inophyllum, C. japonicum, and V. odoratissimum also demonstrated effective fire prevention properties due to characteristics such as high moisture content and dense tree form. In contrast, M. thunbergii, E. zollinger, F. griffithii, Q. glauca, and P. macrophyllus did not show effective fire prevention properties, due to features such as low moisture content or high combustion heat value. Furthermore, the conifer P. luchuensis exhibited both high combustion heat value and low moisture content, indicating a low level of fire prevention effectiveness.

Recently, a candidate gene (CJt020762) for MALE STERILITY 1 (MS1) was identified in Cryptomeria japonica, and two male-sterile alleles (ms1-1 and ms1-2) have been found at the MS1 locus. In this study, we developed a PCR primer set (DNA markers) that amplifies the entire coding sequence of CJt020762 including portions of its introns and identifies differences in the length of the amplified fragments. We also conducted marker-assisted selection (MAS) on 1,500 breeding materials collected throughout Japan and selected individuals with insertion or deletion mutations. As a result, we selected two heterozygous trees with a new four-nucleotide deletion mutation in the coding sequence from Iwate Prefecture breeding materials. We named this new male-sterile allele ms1-3. Furthermore, artificial crossing revealed that individuals carrying both ms1-1 and ms1-3 (ms1-1/ms1-3) were male-sterility, indicating that ms1-3 can be used for the breeding of male-sterile C. japonica. In addition, this study showed that individuals carrying a duplication mutation within an intron do not exhibit male-sterility.