Daisuke Fujiki

The overabundance of sika deer has become a significant threat to plant communities across Japan. As a result of the deer overgrazing, rare plants are undergoing a demographic bottleneck, leading to a loss of genetic diversity. Genetic diversity is crucial for the reproductive success of self-incompatible plants, and it also provides evolutionary potential, which increases their long-term population viability. Therefore, it is essential to appropriately manage the remaining genotypes to conserve local genetic resources. In this study, we exemplify this, via a conservation genetic analysis of Parasenecio peltifolius populations impacted by deer. Genetic data revealed that the small populations confined to isolated refugial sites consisted of effectively single genets. Recent reproductive failures in these populations may be attributed to the loss of genotypic diversity. Despite the bottlenecks, the remaining genets exhibited high individual heterozygosity, which is a good indicator that they have not been affected by severe inbreeding. Hybrid simulations suggested that interpopulation outbreeding between the unique genotypes can be a viable option to promote sexual reproduction and re-establish genetic diversity within the local populations. Establishing artificial progenies in botanical gardens can serve as a vital genetic resource for the long-term viability of threatened P. peltifolius populations.

Almost all ecosystems are open systems, meaning that significant changes in one ecosystem can lead to unexpected changes in others. Deer overabundance has become a problem worldwide, leading to forest degradation that has impacts on not only terrestrial, but also aquatic ecosystems. This study aims to investigate the regional-scale importance of large herbivores in inter-ecosystem interactions by examining the effects of deer-induced forest degradation on fish populations. We selected similar-scale catchments from river systems in Hyogo, Japan, that differed in the time since deer-induced forest degradation. Conventional surveys for fish densities and microhabitat environments were conducted in 23 catchments, and surveys using quantitative eDNA metabarcoding were conducted in 95 catchments. We examined the relationships between fish population densities, microhabitats, and time since forest degradation, considering confounding effects. Data from 8 and 17 fish taxa detected by snorkeling and eDNA methods, respectively, were available for statistical analysis. Snorkeling-counts (Individuals/1 m transect) and eDNA concentrations (Copies/L) in river water were strongly correlated. Fine sediments on riverbeds were increased in the 3–15 years following forest degradation and decreased after 16 years. Population densities of sand-preferring fishes, as inferred from both eDNA and snorkeling, reasonably followed this pattern. These patterns may be caused by the depletion of fine sediments on mountain slopes. The results of this study suggest that deer-induced worldwide alternation may also occur in aquatic ecosystems.

Ungulate overbrowsing is a growing problem in forests worldwide due to its prolonged and pervasive impact on plant biodiversity and ecosystem functioning. It has been shown that overbrowsing not only reduces plant species diversity and biomass (i.e., direct effects) but also causes a loss of associated trophic levels that could potentially feedback to influence plant community structure (i.e., indirect effects). One of the primary pathways of such indirect effects that have not been fully examined is the impact of overbrowsing on soil microorganisms. Recent studies have shown that soil microorganisms maintain vegetation diversity and drive succession, so it is of critical importance to understand how soil microbial communities might be affected by or protected from the deer impact. To assess the consequence of creating artificial grazing refugia on the structure and composition of soil microbial communities, we compared the distribution and abundance of soil microbial taxa (bacteria, archaea, fungi) at the fenced versus unfenced control sites in the context of a catchment-scale field experiment in Japan. The eDNA metabarcoding analysis of soil microbial communities showed that the numbers of archaea and basidiomycetes fungal species were greater in the fenced site than in the control, while no such pattern was found for bacteria and ascomycetes fungi. Despite the lack of significant influence of the fence treatment on taxonomic composition in the soil fungal communities, their functional guild composition was influenced by the fenced treatment, with significant changes in the abundance of animal pathogens. Thus, although the effect of fencing on soil microbial communities is characterized by complex responses that vary from taxon to taxon, our work suggests that creating ecosystem-scale refugia from deer overgrazing might help sustain certain, if not all, taxa of soil microbial communities.

Deer species were repeatedly overexploited and protected for their meat and fur and they had strong impacts on ecosystems and human society by damaging crops and planted trees, altering vegetation, deer vehicle collision, and increasing ticks that vector zoonosis. To accomplish appropriate population management, the historical demography and its main driver need to be clarified. In this study, we estimated the historical demography of effective population size (Ne) of sika deer (Cervus nippon Temminck) in Hokkaido and Hyogo Prefectures of the Japanese archipelago. We estimated Ne of >100 generations from present (2020) by folded single nucleotide polymorphisms (SNP) frequency spectra and, within 100 generations from present, by linkage disequilibrium between SNP. In Hokkaido, Ne drastically increased around 3.0 ky BP and decreased around 100–150 years ago with the assumption of their generation length as 4 or 9 years. The Ne decreased by a 10th before the recent bottleneck. In Hyogo, Ne increased around 80 and 1 ky BP and decreased around 100–250 years ago. Ne decreased by a 100th before the recent bottleneck. After these recent bottlenecks, Ne of both regions recovered and the current Ne has nearly reaches the highest level of the last 100 ky BP. Literature survey and paleoclimate indicates that the decrease and increase of Ne of sika deer in Japanese archipelago may be caused by variations in the hunting activity of humans rather than climate change or the top predator extinction.

A field experiment was conducted involving deer exclosures and planting of Quercus acutissima, a deciduous oak, to reveal forest recovery patterns and factors following clear-cutting at overcrowded conifer plantation sites. Sites were selected in a warm temperate region in western Japan, which is dominated by deciduous broad-leaved secondary forests and extensive conifer plantations. Thirteen years after clear-cutting in the study area, naturally regenerated stands were established with exclosures. The exclosures housed vegetation dominated by pioneer trees, such as Mallotus japonicus or Zanthoxylum ailanthoides. In contrast, naturally regenerated stands without exclosures had limited pioneer trees present. Vegetation dominated by pioneer shrubs (e.g. Aralia elata) was established in these stands. Reduced canopy height and total basal area were observed for vegetation outside the exclosures. In stands where Q. acutissima was planted immediately after clear-cutting, the vegetation that is dominated by this species in the canopy layer was established in both stands with and without exclosure. Most of tree species that emerged after clear-cutting across all stands were of the frugivore seed dispersal type. However, results from this study suggest that these frugivore seed dispersal type trees are more vulnerable to deer browsing than trees from the Fagaceae family. Natural forest recovery following plantation clear-cutting could be inhibited due to deer herbivory at relatively low deer density if a major source of tree regeneration in clear-cut plantations is non-Fagaceae trees.

This study analyzed how 3 Fagaceae species (Fagus crenata, Quercus crispula, and Q. serrata) affect the occurrence of Asiatic black bears (Ursus thibetanus) in and around residential areas from generalized linear mixed models based on monitoring data of bear occurrence and masting over 14 years (2005-2018) in municipalities in Hyogo Prefecture, Japan. The constructed models suggest that it is important to consider the effects of mast production by multiple dominant Fagaceae species, not only within a municipality but also in the surrounding area, to predict bear occurrence with practical accuracy at the municipal level. The accuracy of the predictive model increased as the number of Fagaceae species in the model increased. Models differed among municipalities in their accuracy to predict bear occurrence, which was related to the effect of F. crenata mast production, which was correlated with the proportion of F. crenata forests in each municipality. I suggest that the accuracy of prediction at the municipal level depended on the effect of F. crenata mast production because the spatial and temporal synchrony of F. crenata mast production was stronger than that of other species. To take preventive action to reduce conflict between humans and bears, it would be useful to construct a model to predict bear occurrence at the municipal level based on monitoring data of mast production in multiple Fagaceae species.

・兵庫県内のニホンジカの生息密度が高い地域において、間伐や皆伐などの伐採の実施や、筋工や丸太柵工などの土壌保全施設、あるいは植生保護柵の施工が、森林表土の侵食防止にどの程度の効果があるのかを調査した。・伐採(特に皆伐)に伴い、表土侵食量が増加する場所がみられた。土壌保全施設や植生保護柵を施工した場所においても、ニホンジカの影響による表土侵食量の増加がみられ、その原因は、ニホンジカの採食による林床被覆の減少とともに、ニホンジカの歩行が表土侵食量の増加に直接的に影響している可能性が示唆された。・ニホンジカの生息密度の高い地域では、土壌保全施設だけでは十分な保全効果が得られず、植生保護柵を併用し、ニホンジカの侵入を排除しなければならない場所があることがわかった。

・ニホンジカによる食害を回避するために設置した植生保護柵のうち、設置後4～5年で柵延長がほぼ同じであるステンレス入りポリエチレンネット柵(ネット柵)と亜鉛メッキ鉄線製金網柵(金網柵)の破損状況を調査したところ、ネット柵に比べ金網柵の破損率が約1/8も低いことがわかった。・点検・補修が行われない場合、ネット柵は設置後1-3年でほぼ全ての柵に破損が見つかった。一方、金網柵は設置年数が5年以上になると破損率が急激に高まった。・破損状況としては、ネット柵と金網柵ともに柵の有効高を損なう破損が最も多く、全体の約8～9割を占めていた。・破損原因として、ネット柵では「不適な地形での無理な設置」と「ネット下部への落葉や土砂の堆積」が半数を占めた。金網柵では「倒木」、「不適な地形での無理な設置」、「支柱留め具の脱落」が約3/4を占めた。・ネット柵と金網柵とも程度の差はあれ、点検・補修が不可欠である。両者とも破損原因を防ぐ工夫によって、破損率を減少させることが可能であると結論づけられた。

・シカの影響により下層植生が衰退し、立木密度が低くなった落葉広葉樹林では、土壌侵食被害が発生するケースが増加しており、森林のもつ公益的機能を維持するうえで問題となっている。・そこで本章では、立木密度を基準とした土壌侵食の発生予測ができるモデルを構築し、林分の斜面傾斜角度別に立木密度に応じた土壌侵食リスクが簡易判定できる早見表を作成した。・早見表を参照すれば、森林整備の対象となる林分の土壌侵食リスクと、土壌侵食防止のために誘導するべき立木密度の基準が、簡易判定できる。・早見表は、土壌侵食防止を目的とした落葉広葉樹林の立木密度管理を実施していくうえでの簡便な手引きとなるだろう。

・筆者のこれまでの野外調査の経験に基づき、兵庫県におけるニホンジカの嗜好性植物および不嗜好性植物に関するリストをリストした。・今回、嗜好性植物に区分されたのは8科11種、不嗜好性植物に区分されたのは64科118種であった。・シカの簡易な生息指標として活用しやすい嗜好性植物としては、イヌツゲ、アオキ、ナガバモミジイチゴ、リョウブ、イタドリの5種が考えられた。・シカによる植生の改変度の強さの簡易な指標となる特定不嗜好性植物として、イワヒメワラビ、コバノイシカグマ、マツカゼソウ、ジャケツイバラ、ニワウルシ、レモンエゴマ、ハスノハカズラ、ナルトサワギクの8種が考えられた。・章末に、特定不嗜好性植物8種の生態写真を参考資料として掲載した。

・兵庫県本州部を対象にニホンジカによる落葉広葉樹林の下層植生衰退状況の2010年から2014年にかけての変化を下層植生衰退度に基づいた広域多地点調査に基づいて推定した。・その結果、県本州部全体としては、過去8年に渡って一貫して、下層植生の衰退の進行が止まらない状況が継続していることが明らかとなった。・一方で、下層植生衰退の進行速度は、2010年以降の4年間はそれ以前の4年間に比べて緩やかになっていることも示された。・この期間における捕獲目標達成率は市町間で8.7～262.6%と大きな変異があった。・捕獲目標を達成した市町では、下層植生の衰退に歯止めがかかる傾向がある一方、達成できなかった市町では衰退の進行が止まらない傾向があった。・下層植生の衰退防止のための今後の課題としては、捕獲が足らない市町における捕獲の推進と扇ノ山や六甲山へのシカの影響拡大防止が挙げられる。・章末に附表として、県内各市区町における落葉広葉樹林のSDR別分布面積とその変化の推計をまとめた。

・淡路島における広葉樹林植生のニホンジカによる衰退状況をモニタリングするため、島内の50地点において、簡易植生調査を2012年と2015年の2回実施した。・各調査地点の植生の衰退状況については、密度比数という指標を用いて評価し、地理情報システム上で密度比数データに空間内挿処理を施すことにより、各年における島内の密度比数の地理的分布を推定した。・推定結果から、2012～2015年の期間を通して、シカにより広葉樹林植生が衰退している地域は諭鶴羽山地内にほぼ限定されることが明らかになった。諭鶴羽山地では立木密度が半減以上している樹林域が多数存在していることが推定されたが、この期間を通して植生の衰退の顕著な進行は認められなかった。・諭鶴羽山地では、現在のシカの生息個体数が今後も維持されるようであれば、長期的には緩やかに植生の衰退は進行していく可能性が十分に高い。・章末に附表として、密度比数別広葉樹林面積とその変化の推計を市町毎まとめた。

The impacts of deer browsing on forest ecosystems, including effects on woodland bird species, are now rapidly being felt in western Japan, and quick assessments regarding the spatial and temporal expansion of deer effects are urgently needed in forest management. We gathered multisite profiles of local bird communities together with information on deer-induced changes in forests' physical structure and evaluated deer effects on bird communities by using an ordination approach. Forty-two survey sites were established in mountainous cool-temperate forests in the Mt. Hyonosen region, western Japan. Bird abundance at each site was estimated in June 2012 by using the conventional fixed-radius point count method. Deer-induced changes in forests' physical structure were evaluated by using the shrub-layer decline rank (SDR; ranked D0-D4 based on visual categorization of the shrub-layer vegetation cover). The most recent SDR scores varied from D0 to D4, and by considering previously published scores (5-6 years previously), the intensity of deer effects on vegetation during the intervening period were classified as continuously low at 18 sites, increasing at 11 sites, and high at 13 sites. In the nonmetric multidimensional scaling plot of bird community dissimilarity, sites with lower and higher SDR scores were plotted in a mutually exclusive way. SDR scores explained 11.6% of the among-site differences in bird communities over the effects of various microhabitat differences in a partial canonical correspondence analysis. Another advantage of using SDR scores to assess multisite profiles of local bird communities is that the local indicator species for a forest with a lower impact of deer browsing can be roughly estimated without requiring well-defined control data. In the study region, six potential indicator bird species were identified as being closely associated with low-SDR sites based on an indicator species analysis. SDR-guided management of deer density is being considered in western Japan due to its easy application, even at a regional scale. An SDR-guided management strategy might also be preferable for maintaining local bird communities because it would be possible to infer resulting changes in native bird communities using SDR scores. (C) 2014 Elsevier B.V. All rights reserved.

We assessed the decline in deciduous hardwood forests due to sika deer in 835 stands in the Kansai region (Hyogo Pref., Kyoto Pref., Shiga Pref. and Fukui Pref.) by using the shrub-layer decline rank (SDR), determined by combining the shrub-layer vegetation cover and the presence of signs of grazing by sika deer in a stand. The results showed a SDR rise in with an increase in an index of density of sika deer and declines in several components in forests in most of the prefectures. We estimated the spatial distribution of deciduous hardwood forests with each SDR in the Kansai region, based on the collected data, using a spatial interpolation method in the Geographic Information System. By checking the estimation by leave-one-out cross validation, it was confirmed that most of the errors are within one rank in SDR. From these results, we conclude that the approach using SDR would be applicable not only to the prefectures adjacent to Hyogo Pref. in the Kansai Region but also to multiple prefectures in the other regions. The results of the spatial estimation in the Kansai region showed that there are three areas in the region in which forest decline is very severe. The these area are the inland area of Hyogo Pref. and Tango Mountains excluding Tango Peninsula, Tanba Highland centered on Ashiu Forest Research Station, Kyoto University, and Suzuka Mountains.

A method for obtaining a relative deer population density index with low cost and effort is urgently needed in wildlife protection areas that need their own deer management guidelines. We recorded the number of deer sighted during our daily trips on forest roads by car in Ashiu Forest at Kyoto University, Japan, beginning in 2006. We used generalized additive mixed models (GAMMs) to estimate among-year trends in the number of deer sighted. We applied models for the total number of deer (TND), number of adults (NA), and number of fawns (NF) sighted, which included both current-year and 1-year-old fawns. Full models included the terms of year (2007, 2008, 2009, and 2010), weather (fine, cloudy, and rain/snow), and nonlinear effects of season (date) and time (time). The optimal GAMMs for TND, NA, and NF did not include the effect of weather but included those of time, date, and year. The detected among-year trends in deer population may be influenced by differences in snow environments among the years. The modeling of road count data using GAMM quantitatively determined among-year variation in the number of deer sighted. This trend was similar to that of the population density estimated using a block count survey conducted in Ashiu Forest. © 2012 The Japanese Forest Society and Springer Japan.

The effects of deer overgrazing on soil nitrogen dynamics and streamwater chemistry were examined using deer exclusion fence established around a 13 ha watershed in a cool-temperate forest in Ashiu, Japan, in comparing to its adjacent 19 ha control watershed. Line transects along the valley and ridge lines in each watershed were established. At 339 quadrats along the transects, the soils were sampled and their water contents, FH layer thickness, ammonium and nitrate nitrogen contents, net mineralization and nitrification rates, and carbon: nitrogen ratio were measured. Streamwater was collected at the outlet of watershed. The FH layer in the ridge line was significantly thicker at the fenced watershed than at the control, suggesting that a decrease in understory vegetation accelerates the litter and soil movement to the lower slope. Nitrate concentration in mineral soil was significantly higher in the control watershed than in the fenced watershed both along the valley and ridge lines, whereas there was no difference in net nitrification rate between watersheds. Stream nitrate concentration was also higher in the control watershed than in the fenced watershed two years since the fence was constructed. These results indicate nitrogen uptake by understory vegetation plays a crucial role in nitrogen retention in the forested watershed. Deer overgrazing of understory vegetation can alter soil nitrogen dynamics and increase hydrological nitrate loss.

We investigated the current distribution of the sika deer population and its impact on vegetation around Mt. Hyonosen, Hyogo Prefecture. Based on a vegetation survey that was conducted at a regional scale, we estimated that understory vegetation in deciduous hardwood forests has declined significantly over mountain ranges on the east- and south-sides of Mt. Hyonosen. A pellet group count survey indicated that there has been an overabundance of sika deer since 1999 in these areas. It is hypothesized that a neighboring population of sika deer with high density expanded into these mountain ranges. Moreover, recent decreases in snow in this region could have promoted population expansion. Vegetation around the peak has not declined yet, but deer grazing has occurred seasonally due to migratory individuals traveling from the foot of the mountain. Signs of deer grazing were observed on 230 plant species, including 13 red-listed species, on Mt. Hyonosen. Moreover, we found that a community of red-listed species had declined because of deer grazing. We note that serious declines in vegetation could expand to the peak of Mt. Hyonosen if management of the deer population is not rapidly introduced.

We investigated the validity and efficiency of a survey using sight per unit effort (SPUE) of sika deer and shrub-layer decline rank (SDR), which is an index of decline in the physical structure of a whole stand caused by sika deer, based on data collected on a broad scale. This survey was to be used to manage a deer population in order to conserve a forest ecosystem. First, we evaluated the spatial and temporal scales of deer density that are most appropriate for predicting decline in the status of under-story vegetation. The model with SPUE calculated in a buffer with a radius of 4.5 km using data for the past 4 years was found to be the best. We showed that our knowledge of the relationship between deer density and status of shrub-layer vegetation is improved by identifying the most suitable spatial and temporal scales of SPUE for predicting SDR. Next, we quantified the effects of SPUE and environmental components on SDR in stands. We found that SPUE had the greatest effect on SDR among all explanatory variables. Moreover, the area under the curve (AUC) was large in a model that only used SPUE (AUC = 0.718). This result suggests that the variation in SDR among stands was explained well by SPUE regardless of differences in the forest environment. Furthermore, we identified the effective values of SPUE for preventing shrub-layer vegetation from declining through deer density control. We conclude that a management system based on SPUE and SDR is a simple and valid method for managing deer populations in order to conserve forest ecosystems.

For 345 stands of deciduous hardwood forest in Hyogo Prefecture, Western Japan, we assessed the decline of shrub-layer vegetation due to sika deer in each stand by using the shrub-layer decline rank (SDR), determined by combining the shrub-layer vegetation cover and the presence of signs of grazing by sika deer in a stand. Since there was a geographical correlation between SDR and sighting per unit effort (SPUE), which is an index of the relative density of sika deer, it appeared that decline of shrub-layer vegetation in a stand can be accurately evaluated by SDR. There were correlations between SDR and several variables that indicate the status of components in forests (presence of saplings of tall trees, occurrence of bark stripping of tall trees, proportion of bark-stripped stems of Clethra barvinervis, decline of subtree-layer vegetation by bark stripping, cover of litter on the ground, and area of soil surface erosion). These results indicate that the status of these components changes with decline of shrub-layer vegetation by sika deer grazing. It is thought that such synchronizations are caused by sika deer grazing or a direct or indirect effect by decline of shrub-layer vegetation due to sika deer. Therefore, it is reasonable to assess decline in physical structure due to sika deer for stands of deciduous hardwood forests according to SDR.

We conducted a phytosociological survey in the primeval lucidophyllous forest of Kawanaka, Aya, Miyazaki Prefecture in 1988. Since the 1990s, the population density of the Sika deer (Cervus nippon) has increased, and their feeding pressure on vegetation has been conspicuous. In 2009, we conducted a phytosociological survey in primarily the same stands as in 1988 to compare the layer structure, the species richness and species composition of the forest in 1988 with those in 2009. The coverage of the second shrub layer and the herb layer was decreased significantly by feeding pressure. Species richness in the second shrub layer significantly decreased; however, there was no significant difference in that of the herb layer. The species richness of four life forms, i.e., lucidophyllous tree, lucidophyllous small tree, lucidophyllous shrub and terrestrial herb significantly decreased. The total number and the mean number of component species of the lucidophyllous forest decreased from 109 and 60.3 in 1988 to 92 and 45.6 in 2009, respectively. The numbers of species that decreased and increased in frequency or coverage between 1988 and 2009 were 25 species and 6 species, respectively. Representative decreased species were Trachelospermum asiaticum var. intermedium, Ardisia pusilla, Rubus buergeri, and Diplazium subsinuatum. On the other hand, the 12 species, including Actinodaphne longifolia, Ardisia crenata, and Arisaema japonicum, were considered to be unpalatable plants by studies from other regions. This investigation clarified that feeding pressure of Sika deer was responsible for the changes in the layer structure, species richness and species composition of the primeval lucidophyllous forest.

We reported on the current status and issues involved in the Specified Wildlife Conservation and Management Plans (SWCMP) for the Japanese black bear (Ursus thibetanus) in 2003&ndash;2007 in Hyogo Prefecture, Japan. Two populations of black bear in Hyogo Prefecture are distributed in the east-Chugoku and north-Kinki regions, and each of these populations has been isolated and endangered. However, the numbers of human-bear conflicts in these regions have been increasing. After the SWCMP was implemented, 86% of all bears captured for nuisance control and miss-trapping have been released with aversive conditioning. We fitted 44 bears with transmitters and monitored their subsequent behavior as long as possible. By such careful monitoring, we could avoid unneeded control-killing of bears. And we could euthanize bears in case of aversive-conditioning when captured again in the same or different village according to the guidelines of the SWCMP. These releases may have prevented the local extinction of the bear populations. We still have at least two problems related to bear management. First, we must develop more effective methods to drive away bears, release with aversive conditioning, and educate local people. Another issue to be solved is large scale management of bear populations distributed over multiple prefectures.<br>

In areas with high sika deer density the loss of regenerated vegetation at previously deforested sites, due to herbivory, is a serious problem. However, there are plant species with anti-herbivory strategies, such as Hypolepis punctata, that form a relatively large community at deforested sites under severe feeding pressure by sika deer. This suggests that planting H. punctata may be effective in improving the revegetation of such places. In order to evaluate the effectiveness of revegetation using H. punctata, we investigated stands of the H. punctata community and areas of bare ground at deforested sites in the southern part of Awaji Island in Hyogo Prefecture, Japan. We also investigated secondary forests in the vicinity of the deforested sites. The stands of the H. punctata community were similar to the secondary forests with regards to soil depth and soil chemistry. Soil erosion was clearly observed at the bare ground sites. The number of forest species per 25m^2 was higher in the stands of the H. punctata community than in the secondary forests. Comparison of species composition between the three types of site showed that most species found in the secondary forests were also present in the stands of the H. punctata community. These results suggest that the H. punctata community has a high capacity to reduce erosion and maintain forest species richness. Thus, we concluded that H. punctata is a useful species for the revegetation of deforested sites that are under severe feeding pressure by sika deer.

We have investigated stem turnover strategy for Lindera umbellata, an understory shrub that sprouts from its rootstock under natural conditions to replace constituent stems, on the basis of the hypothesis that the multiple-stemmed form of woody species is an adaptation enabling efficient reproduction in high-stress environments. We tested the hypothesis that the timing of stem replacement maximizes sexual reproduction for the shrub. We developed a model for the time of optimum replacement of a stem by a daughter stem which maximizes the sexual reproduction of a shrub and tested the model using L. umbellata growing in the field. From the model, the optimum time of replacement of a stem with a daughter stem is when cumulative sexual reproduction per unit time for the stem is maximum. In practice, this will be the last age (t(opt)) at which annual sexual reproduction in a stem can potentially exceed cumulative sexual reproduction per unit time for the stem. Half of the stems died at almost t(opt) and had sexually mature daughter stems at that time. Other stems, however, died at times more remote from t(opt) when daughter stems were sexually immature. It is thought that normal replacement of the latter stems was prevented by accidents such as breakage. We conclude that clumps of L. umbellata achieve efficient sexual reproduction by stem replacement at the optimum time, although accidents can, to some extent, determine when the stem actually dies.

We investigated the structures of communities and populations of the component species in four stands of abandoned charcoal secondary forests that differed in the density of sika deer (Cervus nippon), to clarify the effects of herbivory by deer. Densities of stems in the lower height classes were markedly lower in stands affected by deer herbivory than in stands with no herbivory. In stands with herbivory, the effect of herbivory was not evident in Type I species that had a unimodal or flattened distribution in the upper height classes. However, in Type II species that had modes in the lower height classes, the patterns of stem height distributions changed from L-shaped to bell-shaped in the stands. Most late-successional species of tall trees were of Type II, and their saplings were sparse in stands affected by deer herbivory. This suggests that recruitment and regeneration of these species have been prevented in the stands due to herbivory by sika deer. If herbivory by deer continues over a long time in these stands, it may be difficult for the stands to maintain the framework of forest structure. On the other hand, stand regeneration may be attained by late-successional species of Type I. In this case, the future species composition of these stands should be determined through the processes of plagiosere succession, not by general secondary succession.