Deer browsing damage is a serious problem in woodland ecosystems and forestry in various regions of the world (Gill and Beardall 2001), including Japan (Takatsuki 2009). In Japan, the area of forestry negatively affected by wild animals reached 4,900 ha in 2019, of which deer accounted for more than 70% (Forestry Agency 2021). Although deer exclusion fences have been employed, mainly at plantation sites for conifer timber production, the associated high cost and amount of labor constrained its application in some cases. Deer hunting has already been carried out to the maximum degree possible, and the current cohort of hunters is aging without younger replacements, precluding the possibility of meaningfully increasing the number of deer hunts any further in Japan. This situation may be similar in various parts of the world suffering from deer browsing damage. Therefore, development of alternative options that can be selected according to the forest conditions and deer population density is required to protect seedlings effectively from deer browsing. Treeshelters are single tree protection devices that have been used mainly in Europe and North America (Potter 1991). They have been used in Japan since the 1990s, but their effectiveness has proven to be variable, with many cases of failure. Possible factors included the hot summer conditions in Japan and the species characteristics of major timber trees such as Japanese cedar (Cryptomeria japonica) and hinoki cypress (Chamaecyparis obtusa), but such cases in Japan have never been reported in international journals. In this special feature, we will mainly focus on treeshelters as countermeasures against deer browsing damage, and provide information on their effects and limitations, estimation of deer density, which can be a criterion for decision making about selecting countermeasures, and findings on the latest research including countries other than Japan.

We studied the microclimate inside treeshelters to examine how they affected growth of Japanese cedar (Cryptomeria japonica) seedlings in western Japan. Air temperature (T), relative humidity (RH), and photosynthetic active radiation (PAR) were measured inside and outside of commonly used design of tubular treeshelters made of translucent polypropylene at a nursery throughout a year. Vapor pressure deficit (VPD) was calculated from T and RH data. Results indicated that the inside T and VPD above the seedling foliage were extremely higher than ambient air. However, T within the seedling foliage showed 2.7 degrees C higher than ambient T even though 10.3 degrees C higher above the foliage in August. The VPD within seedling foliage was lower than ambient VPD in summer, and increased with decreasing RH when the precipitation was low. Microclimate in an empty treeshelter showed higher T and VPD than those in treeshelter with seedling. These results indicated that high T and VPD were mitigated by transpiration from needle leaves of seedling, and Japanese cedar seedlings could grow in treeshelters at sufficient water supply.

Treeshelters are used in a variety of environments for forestry and forest restoration purposes. Although their use is often effective, in some cases treeshelters are ineffective. To clarify the effects of treeshelters on seedling performance, a systematic literature review and meta-analysis was conducted. Of the 296 studies related to treeshelters, 139 studies were suitable for extraction of data on mortality rate, browsing damage rate, height growth, or diameter growth. The quality of the literature did not affect the results of the meta-analysis. Mortality, browsing damage, and height growth were positively affected by treeshelters in many subgroup analyses, but diameter growth did not conform with the perceived inhibitory effect of treeshelters. Regarding conifer species, treeshelters had no effect on mortality rate and non-ventilated treeshelters promoted diameter growth. However, many subgroup analyses showed publication bias as indicated by the significantly fewer negative-effect studies. Therefore, the effects of treeshelters may be overestimated although the effects revealed by the meta-analysis were reasonable from the viewpoint of plant physiological reactions. Heterogeneity was high in most of the subgroups, suggesting that factors other than the analyzed subgroups may contribute to the variance in treeshelter effects. Studies on treeshelters are concentrated under specific conditions, such as on species of the genus Quercus and a temperate climate. Thus, other under-represented conditions are considered to constitute research gaps. Further studies in these research gap areas are required to perform a meta-analysis with low heterogeneity.

Tree shelters are used in forestry to prevent large herbivores from browsing on young trees. Although tree shelters can generally prevent browsing damage while the young trees are within the tree shelters, they have been observed to fail in some cases. In this study, to clarify the protective capacity of tree shelters against damage due to deer browsing, the condition of tree shelters on planted Japanese cedar (Cryptomeria japonica) seedlings 2 to 7 years after installation was investigated at 42 sites in southwestern Japan where the density of sika deer (Cervus nippon) is high. The results showed that tree shelters failed for three reasons. Firstly, the shelter had collapsed or incline and could no longer protect the saplings within. Secondly, the saplings in the shelters died relatively shortly after they were planted. Thirdly, and possibly most importantly, the saplings are browsed upon by deer after they extended beyond the top of the shelter. Since there was no correlation between the damage rate and the number of years after planting, it is likely that the damage occurred immediately after the young trees protruded form the shelter. Shelters with a height of only 140 cm, which are widely used in Japan, may be too short to completely prevent herbivory damage by deer.

Insular ecosystems reflect processes by which organisms have colonized from continents and are known as “experimental laboratory for evolution”. Islands have an order of magnitude more endemic species in only a few percents of the global land surface (Kier et al. 2009) and insular forests contribute as a biodiverse habitat. The insular ecosystems, however, are vulnerable to anthropogenic disturbance because of their long periods of isolation. Indeed, insular ecosystems around the world have deteriorated considerably since human settlement and there are few examples that remain intact today. As a result, the extinction rate of insular endemic species becomes much higher than that of continents (Whittaker and FernandezPalacios 2007). These facts make the islands a top priority for ecosystem conservation and increase the need for conservation based on scientific evidence. The Ryukyu Archipelago is a continental island chain and consists of more than 200 continental islands between Kyushu and Taiwan. These islands have been repeatedly connected and isolated from adjacent land because of sea-level fluctuations at least known in the Quaternary Period. This region belongs to the warm temperate to subtropical climate and subtropical evergreen forest (Brown and Lomolino 1998; Kira 1991) that includes roughly the East Asia continent. The unique biota reflects the process of being separated from the continent due to sea-level fluctuations, and a border of the Wallace’s biogeographic region crosses th Ryukyu Archipelago (Brown and Lomolino 1998; Wallace 1876). Given such biogeographical background, this arc is highly valuable for biodiversity conservation and some preserved islands (Amami Ohshima Island, Tokunoshima Island, northern Okinawa Island and Iriomote Island) have been recommended as a World Natural Heritage Site (Government of Japan 2019). However, these islands have problems not only with invasive alien species but also with various human activities such as land use, illegal collection and roadkill. Under these circumstances, it is essential to accumulate scientific information in order to establish appropriate protected areas for biodiversity conservation.

We present the largest freely available herbivory dataset for Japan representing data collected from a network of 19 natural forest sites across the country. Sampled network sites were part of the Monitoring Sites 1000 Project organized by the Ministry of the Environment. Sites were located across a range of climate zones, from subarctic to subtropical, and broadleaf trees (both evergreen and deciduous) were targeted at each site. Litterfall traps were used to assess leaf damage caused by leaf-chewing insects in 2014 and 2015. Using a standardized protocol, we assessed herbivory on 117,918 leaves of 39 dominant tree species. Preliminary analyses suggest that insect herbivory increases with increasing latitude for deciduous broadleaf species. In particular, oak (Quercus crispula) and beech (Fagus crenata) were subject to increased insect herbivory with increasing latitude. In contrast, insect herbivory decreased with increasing latitude in evergreen broadleaf species. The latitudinal gradient of herbivory differed according to leaf type (i.e., evergreen or deciduous). This dataset offers excellent opportunities for meta-analysis and comparative studies of herbivory among various forest types. The complete dataset for this abstract published in the Data Paper section of the journal is available in electronic format in MetaCat in JaLTER at .

ABSTRACT Epiphytic orchids, which account for 68% of vascular epiphytes, contribute substantially to plant species diversity in forest canopies. Many orchid species are naturally rare and have limited geographical distributions. All orchids rely on mycorrhizal fungi for nutrient acquisition during seed germination and seedling establishment, and many species retain these associations throughout their lifecycle. Due to their reliance on mycorrhizal fungi, epiphytic orchid species with highly specific mycorrhizal associations may be geographically restricted and are often rare. Dendrobium okinawense is a rare epiphytic orchid endemic to the Yambaru Forest in Japan and to southern Taiwan. We hypothesized that this species exhibits high mycorrhizal specificity and tested this hypothesis via identification of the species’ mycorrhizal associates. We collected root samples of this orchid from four tree species and assessed mycorrhizal fungi in 25 root fragments harvested from 10 plants. Fungi were identified using molecular methods based on fungal isolates and DNA extracted from mycorrhizal roots. Detected fungi were assigned to 21 operational taxonomic units (OTUs) based on 97% sequence similarity of nuclear ribosomal DNA internal transcribed spacer region sequences. TU11, an OTU belonging to Tulasnellaceae (Basidiomycota), was the most frequently detected OTU, occurring in 20 root fragments from all 10 sampled individuals. Our results indicate that Dendrobium okinawense has a highly specific association with TU11. Further, this specificity may be high relative to the Dendrobium species assessed in other studies. These findings support the hypothesis that Dendrobium okinawense exhibits high mycorrhizal specificity.

Degradation of old-growth forests is an important issue for global biodiversity conservation. Robust indicator species greatly facilitate the identification of old-growth forests requiring protection. Understanding why particular species are associated with priority forests is necessary for assessing the reliability of indicator species. Here, we surveyed the vegetation of 69 sites in Yambaru forests (Okinawa Island) varying in forest age and analyzed the relationships between the dominance of vascular species and three criterion parameters (forest age and species richness (SR) of epiphytes and endangered plants). Eleven species showing significant positive correlations with three parameters were designated as potential candidate indicator species, ten of which were woody species. Of the above eleven candidate indicator species, Distylium racemosum was considered one of the most useful indicator species because it can be easily identified in the field and its ecological characteristics are well documented. Regarding three woody traits – sprouting ability, annual growth rate and wood density – which are expected as the cause of indexing, endangered SR increased when tree species with low sprouting ability and high wood density were dominant, and epiphyte SR increased when tree species with low annual growth rate and high wood density were dominant. These woody species traits were associated with forest age and could explain why D. racemosum is an indicator of priority forest. These results suggest that large trees with such woody characteristics are effective indicators of priority forests.

Oceanic islands are biodiversity hotspots with highly endemic ecosystems that are vulnerable to invasive alien species. Understanding the status of endangered species and identifying threats have the highest priority for insular biodiversity conservation. The two remaining populations of endangered Crepidiastrum grandicollum on Chichi-jima Island were studied for 5 years to describe their status and evaluate the impacts of feral goats (Capra hircus). The main cause of population decline was browsing by goats. The populations protected by the exclosures were stable but declined after an exclosure was removed. Even in the protected population, regeneration was limited outside the exclosures and in 1 year of the survey, a high proportion of feeding damage by moth larvae was observed in one population. These facts indicate that exclosures are not a sufficient conservation measure, and eradication of goats and population restoration in novel habitats are necessary to reduce the extinction risk of C. grandicollum.

Invasive alien tree species can exert severe impacts, especially in insular biodiversity hotspots, but have been inadequately studied.Knowledge of the life history and population trends of an invasive alien tree species is essential for appropriate ecosystem management.The invasive tree Bischofia javanica has overwhelmed native trees on Hahajima Island in the Ogasawara Islands, Japan.We explored forest community dynamics 2 years after a typhoon damaged the Sekimon primary forests on Haha-jima Island, and predicted the rate of population increase of B. javanica using a logistic model from forest dynamics data for 19 years.During the 2 years after the typhoon, only B. javanica increased in population size, whereas populations of native tree species decreased.Stem diameter growth of B. javanica was more rapid than that of other tree species, including native pioneer trees.Among the understory stems below canopy trees of other species, B. javanica grew most rapidly and B. javanica canopy trees decreased growth of the dominant native Ardisia sieboldii.These competitive advantages were indicated to be the main mechanism by which B. javanica replaces native trees.The logistic model predicted that B. javanica would reach 30% of the total basal area between 2017 (in the eastern plot adjacent to a former B. javanica plantation) and 2057 (in the western plot distant from the plantation site), which is a maximum percentage allowing to eradicate under the present guideline of the National Forest.The results suggest immediate removal of B. javanica is required to preserve native biodiversity in these forests.

To support conservation and restoration, it is important to understand how differences in species functional traits relate to the distribution and demographic performance (i.e., changes in rates of growth, survival and recruitment) of co-occurring endemic, indigenous, and alien species on oceanic islands, where species are especially vulnerable to invasion. We examined interspecific differences in leaf and wood traits, and their associations with species origin (endemic, indigenous, and alien), distribution patterns, and demographic performance after typhoon disturbance for 22 co-occurring woody species at Sekimon on Hahajima Island in the Ogasawara Islands. Principal components analysis showed that the first and second principal components were associated with trait variations along spectra of leaf and wood economics (LES and WES). Species origin was not significantly associated with these components. Conservative species with low resource acquisition along the LES were abundant before the typhoon but acquisitive species had higher recruitment after the typhoon. After the typhoon, acquisitive species along the WES showed higher recruitment, relative growth rates but low survival rates on soil substrates. Endemic and indigenous species had lower recruitment and relative growth rates and endemic species had lower survival rates than alien species. Alien, endemic and indigenous species have similar functional space along the LES and WES, but these functional differences do not simply explain high demographic performance of alien species after the typhoon under the conditions of the species composition shifting from endemic species to alien species after repeated typhoon disturbances.

We investigated the epiphytic habit and distribution of Dendrobium okinawense, an endangered orchid in Yambaru (northern Okinawa), Japan. Fifty individuals of D. okinawense were detected on 46 host trees. From the canopy size in chronological aerial photographs, the habitat stands where D. okinawense was found were estimated to be mature. Host trees tended to have larger diameters. The most common host species was Castanopsis sieboldii, which dominates in Yambaru; several other tree species were described as hosts for the first time to our knowledge. However, the orchid was mainly associated with one of these, Distylium racemosum, irrespective of this tree’s small basal area relative to other trees. We attribute this preference by D. okinawense to the external form and longevity of D. racemosum. The presence of D. okinawense and its host D. racemosum with large diameter is a good indicator of the existence of old-growth forests containing endemic rare species in Yambaru.

Native forests on oceanic islands are among the most threatened ecosystems. The forests formed on Sekimon uplifted limestone in Haha-jima Island (Ogasawara Islands) have not yet been destroyed by human activities and remain as primary forests harboring several narrow endemic endangered plants. In this paper, we described the plant species diversity, community structure, and status of invasion by alien plants in the mesic forests of Sekimon. The Sekimon forest was characterized by low tree diversity (37 species), high stem density (1731 ha−1), and high basal area (63.9 m2 ha−1), comparing with natural forests in world islands. The forests were dominated in the number of stems by the sub-tree Ardisia sieboldii followed by the trees Pisonia umbellifera and Elaeocarpus photiniifolius. The invasive tree Bischofia javanica ranked fourth for basal area and third for the number of stems (DBH ≥ 10 cm), and its distribution expanded, especially near a past plantation site. Surveys of forest floor vegetation revealed that species richness of vascular plants was 109 species and that many alien plants had already invaded the forests. Despite the low species richness of alien (16% for vascular flora and 8% for trees), the high frequency of aliens on the forest floor suggests that they have colonized successfully in the Sekimon forest. Extrapolation analysis based on the rarefaction curves predicted that the vascular plants in the Sekimon (25 ha) accounted for 135 species (29.9% of the vascular flora of the Ogasawara Islands) and endemic plants were 85 species (62.0%). The fact that the 39 vascular species recorded in our plots were listed in Japanese Red List suggests that the Sekimon forest should be conserved as a sanctuary of biodiversity. Because alien plants are invading the forests without apparent anthropogenic disturbance, immediate action to eradicate these invaders is highly needed.

本研究では造林地内の空間不均質性に着目し，1）造林木の成長および造林木と雑草木との競合関係が地形により異なるか，さらに，2）場所によるランダム効果の取り扱い方の異なるモデル間で地形の効果が異なるか，を斜面長100 m傾斜角約30 度の4 年生のスギ若齢林で検討した。地形変数（尾根からの距離と傾斜角）が3，4 年生時のスギの樹高およびスギと雑草木の競合関係に与える影響を三つの統計モデル（ランダム効果を考慮しないモデル，場所のランダム効果を考慮したモデル，空間自己相関を考慮したモデル）で解析した。結果，尾根からの距離が大きいほどスギの樹高が高かった。スギの樹高が低い，または，尾根からの距離や傾斜角が大きいほど，雑草木から被圧されやすかった。他のモデルと比べ，空間自己相関を考慮したモデルでは地形変数の効果の信用区間は広がり，効果の評価が下がった。スギの成長や雑草木による被圧が斜面位置によって異なることから，斜面位置によって下刈頻度を変えることも下刈省力化の選択肢の一つとして考えられるが，一方で，要因の検出において空間情報の取り扱い方やサンプリングの方法を十分に検討する必要があると結論付けた。

The degradation of biodiversity caused by anthropic habitat destruction is a global issue. The recovery of natural habitats from invasive alien weeds in order to conserve endemic ecosystems is especially important on small oceanic islands. Planting of endemic trees may be an effective measure, but a complete restoration process within the island is essential to avoid accidental introduction of invasive aliens. To test planting techniques, we planted two endemic tree species whose regeneration was hindered by alien species on degraded lands on Chichi-jima (Ogasawara Islands) and monitored vegetation changes. During an 11-year period, about half of the Elaeocarpus photiniifolius seedlings survived in gap areas, but all Morus boninensis failed. The E. photiniifolius trees reached a height of 4.7 ± 2.4 m. The restored canopy created a dark environment that greatly reduced the volume of the predominant invasive weeds. These results suggest that E. photiniifolius is suitable for restoration of forests on degraded land and for the suppression of weeds on the island. Low species diversity in the restored forests, however, was a remaining issue to be addressed. Herein we discuss potential improvement measures to facilitate the recovery of species diversity, including other native tree candidates.

More than 3,000 species are listed as critically endangered worldwide, and various conservation measures such as habitat restoration, assisted reproduction and establishment of ex situ populations would be required to prevent their extinction. We determined the genotype of all 15 known wild clumps using nuclear microsatellite markers for Stachyurus macrocarpus var. prunifolius, a critically endangered shrub endemic to the Ogasawara (Bonin) Islands of Japan. In addition, the seedlings propagated from seeds taken from one wild clumps were genotyped. The results of complete genotyping showed that both wild and nursery populations had population-specific alleles. Two alleles were detected only in the nursery population, indicating the existence of undiscovered mature individuals in the wild. Four alleles were found only in the wild and were detected in two geographically isolated clumps, and this finding may propose that re-introduction and transplantation between different sites requires sensitive handling in terms of the conservation of evolutionary significant units. These results show that complete genotyping can provide essential genetic and ecological information for effective management of endangered species.

This study investigated the effect of loading on the bond strength to dentin and microleakage of MOD indirect composite restorations bonded with self-adhesive and self-etching resin cements with or without acid etching of the proximal enamel margins. Class II MOD cavities were prepared in 48 molar teeth into dentin and divided into three groups of 16 teeth. Impressions were taken and indirect composite inlays fabricated (Estenia C & B). The enamel margins of the proximal boxes of half the specimens were phosphoric acid etched, and the inlays were cemented with one of three cements (Panavia F 2.0, SA Cement, or Rely X Unicem). After luting, eight teeth in each cement group were mechanically loaded at 2.5 cycles/s for 250,000 cycles. Unloaded teeth acted as controls. Teeth were stored in Rhodamine B solution for 24 hours, sectioned buccolingually at the proximal boxes to examine microleakage using confocal microscopy, and further sectioned for μTBS testing of the resin-dentin interface. Analysis of variance was performed to assess the effect of loading and acid etching on microleakage and bond strength. Acid etching had no effect on microleakage. No significant difference in the dentin bond strengths between the three cements existed after loading. Panavia F 2.0 exhibited a significant reduction in bond strength. With regard to microleakage at the proximal boxes, loading had no effect on dye penetration at the cavity floor. However, at the axial walls, loading had a significant deleterious effect on Panavia F 2.0. No difference in microleakage existed between the three cements at both sites before and after loading. In conclusion, the two tested self-adhesive cements exhibited similar bond strengths before and after loading to the self-etching resin cement. Loading reduced dentin bond strengths and increased microleakage at the resin-dentin interface. However, acid etching of the enamel margins had no significant effect on microleakage in the approximal regions of the bonded inlays.

Insular ecosystems can be dramatically affected by alien species, and records of pre-eradication status are essential to evaluate the effects of eradicating alien species. Nishi-jima Island is a small island of the Ogasawara group on which the first program of complete eradication of alien herbivorous mammals (black rats and feral goats) will be conducted. After eradication, the government plans to conduct ecosystem restoration on the island. This paper reports the angiosperm flora and vegetation of Nishi-jima Island before eradication of the rats and goats, with the objective of aiding ecosystem management after the eradication. Our surveys indicate that vegetation cover by the alien tree, Casuarina equisetifolia has expanded compared with its distribution in a 1974 aerial photograph of the island. The predominant vegetation in 2006 was C. equisetifolia forests and Zoysia tenuifolia grasslands, with fragmented native tree vegetation. The flora of the island comprised 69 angiosperm species (50 indigenous species) of which 30% were endemic, far less than for the Ogasawara Islands as a whole (45%). However, several populations of endangered plants remain. To restore the native ecosystem on Nishi-jima, eradication of C. equisetifolia is important in addition to eradication of alien herbivorous mammals.

We examined seasonal patterns of twig cutting by the introduced black rat, Rattus rattus, on Haha-jima Island, an island in the Ogasawara (Bonin) group of Japan. Censuses were conducted along seven routes to count the number of trees damaged by twig cutting in each month. Overall, 42.6% (23/54 species) of woody species were damaged. Twig cutting was greatest in spring (March-May). Probability of damage by twig cutting was not correlated with species frequency in the vegetation. This suggests that twig cutting is associated with particular characteristics of target species. Endemic plants experienced a significantly higher probability of twig cutting than alien plants. This may be due to an evolutionary loss of plant defense mechanisms in the absence of herbivorous mammals. Because the overall proportion of individuals damaged by twig cutting was not high, the behavior is unlikely to influence the population dynamics of trees and cause vegetation change. But intense twig cutting was also found on critically endangered plants, so twig cutting by black rats could be a threat to those species.