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Severe browsing pressure from deer may have great effects on the regeneration dynamics of woody seedlings by affecting seedling mortality and seedling demography. This study quantified the seasonal impact of deer browsing on the relationship between seedling survival and the timing of seedling germination. We established a fenced deer exclosure in a cool-temperate forest in Chichibu that experienced browsing pressure from deer. Newly germinated seedlings of the dominant beech, Fagus japonica, were marked and monitored frequently in the fenced plot and outside the deer fence (open plot). To compare the demography of currentyear seedlings, the effects of the timing of germination, light conditions, and total seedling density in each monitoring quadrat were analyzed considering their differences between the two types of plots. The survival rate at the end of the growth period was significantly lower in the open plot (2.0%) than in the fenced plot (9.4%), mainly because of deer browsing (73.8% of the total mortality in the open plot). Intensive browsing was observed only during the early growth season, while damping off was the major cause of mortality in the fenced plot (79.0% of total) during the middle season. Statistical analysis detected opposite effects in the open and fenced plots; early germination was disadvantageous and advantageous for survival, respectively. Seedling demography relating to the advantage of the timing of germination may change depending on the impact of deer browsing, which has clear seasonality. Key word: early emergence advantage, deer browsing, Fagus japonica, seedling demography 石塚 航・梶 幹男・後藤 晋:冷温帯林におけるイヌブナ実生動態への季節的なシカ摂食害の影響 摘要:シカの高い摂食圧は樹木の実生生残数のみならず,生残条件をも変え,更新動態に大きな影響を与えると みられる。本研究では,実生発生タイミングと当年生残との関係における,シカの季節的な摂食害の影響を評価 するため,シカ害のみられる秩父地方の冷温帯林にてシカ防護柵を設置し,柵内外の調査枠内に発生した優占種 イヌブナの当年生実生を調査対象とした。個体識別して実生の消長を追跡し,当年生残に対する発生タイミング の効果を,生育地の光条件や実生密度の影響とともに分析し,柵内外で比較した。柵外区の実生当年生残率(2.0 %)は柵内区の生残率(9.4%)よりも有意に低く,死亡実生の 73.8%がシカ摂食害によるものだった。死亡要 因は顕著な季節性を示し,シカ害は実生発生初期に,柵内区の主たる死亡要因である菌害(全実生の 79.0%) は生育中期に集中していた。統計解析によって,柵内外で実生の発生タイミングが当年の生残に影響しているこ とがわかったが,柵外区では早い発生が不利に,柵内区では早い発生が有利になっており,対照的な影響が検出 された。早い発生の有利性はシカの存在下では失われ,季節性のあるシカの摂食によって実生生残の動態が変わ ることもあると示唆された。 キーワード:早い発生の有利性,シカ食害,イヌブナ,Fagus japonica,実生生残過程 日緑工誌,J. Jpn. Soc. Reveget. Tech., 39(2), 232―240,(2013) ing. In cool-temperate forests, low seedling recruitment because of increased deer populations may affect forest regeneration negatively. Therefore, deer browsing is regarded as a severe limiting factor for seedling survival in these forests. However, seedling germination and subsequent establishment are the most vulnerable life stages for temperate forest trees. Therefore, seedling survival for such trees is affected strongly by deer browsing, damping off, small mammals, and other predators such as insects. In addition to those mortality factors, the conditions of each seedling may also affect its survival, e.g., the germination phase, light conditions, and vegetation density. Several studies have demonstrated an advantage of early germination on seedling survival over late germination. In deciduous forests, the forest canopy becomes closed during leaf flushing; therefore, there is a seasonal limitation on the available resources in the understory (i.e., ephemeral light). Early germinating seedlings, therefore, can utilize these limited resources efficiently and grow sufficiently during the early growing season. An advantage of early germination may be detected if the timing of seedling germination is related to the resistance to mortality caused by pathogens and/or the preferences of predators such as small rodents. Madsen reported that emerged beech seedlings (Fagus sylvatica L.) were browsed immediately by deer, which suggests that the advantage of early germination may not be maintained if deer browse severely. However, the relationship between the effect of deer browsing and the timing of germination on seedling survival remains unclear. Observational study was, then, conducted to trace the demography of woody seedlings at cool-temperate natural forest in central Japan. Browsing pressure from Sika deer (Cervus Nippon Temminck) has increased since, at least, the last two decades. Using a dominant tree species, Fagus japonica Maxim., we monitored the date of seedling germination and its subsequent fate inside and outside deer exclosure. We tested the advantage of early germination considering the effect of the presence of deer. We asked the following questions. What was the limiting factor for germinated seedlings and what was its effect on seedling survival? Was seedling demography, especially the advantage of early germination, affected by deer browsing? 2. Materials and Methods 2.1 Study species Japanese beech, F. japonica, is a deciduous broad-leaved tree. It is mainly distributed in the cool-temperate forests of Pacific Ocean-type regions. In central Japan, F. japonica is one of the dominant species in climax forest, together with Fagus crenata Blume, which is another Japanese beech species, and a coniferous tree, Tsuga sieboldii Carrière. These two beech species are well-known of exhibiting a habitat of mast seedling at intervals of several years. Mature seeds are mainly dispersed by gravity and germinate during the next spring. After germination, the seedling establishment process of beech is strongly affected by multiple limiting factors, especially during the initial growth period. Seedling mortality seems to be high under a closed canopy or dwarf bamboo layer because of their light demand and susceptibility to pathogenic fungi. Predation by small mammals, other vertebrates, and insect larvae also increase the mortality of beech seedlings. Therefore, the seedling recruitment of F. japonica is highly limited in natural stands. 2.2 Study area and the two experimental plots Our study was conducted on the southwestern steep slope of Mt. Hakutai (1,794 m a.s.l.) in the University of Tokyo Chichibu Forest (35°55′N, 138°50′E, 1,210―1,260 m a.s.l., with a slope inclination of approximately 33°), which is located in central Japan. The mean temperature and annual precipitation between 1993 and 2001 at the nearest meteorological station (200 m apart from the study area on 1,160 m a.s.l.) were 8.9°C and 1,416 mm, respectively. This region belongs to the cool-temperate zone and is categorized as having a Pacific Ocean-type climate because there is more precipitation in the summer than in the winter. The study area was covered by an old growth forest with a total basal area of 48.7 m/ha, and no management activities were done to facilitate monitoring the ecosystem during long-term research. The relative abundances of three dominant species, F. japonica, F. crenata, and T. sieboldii, in this area were 24.9%, 23.1%, and 26.5%, respectively. Although the dwarf bamboo (Sasamorpha borealis (Hack.) Nakai) was widely distributed in this region, retrogression occurred associated with deer browsing at our study site (M. Kaji, pers. obs.). In 2006, no dwarf bamboo but several shrub and herbal species (such as Pieris japonica (Thunb.) D. Don ex G. Don, Pertya glabrescens Sch. Bip. ex Nakai, Ainsliaea acerifolia Sch. Bip. var. subapoda Nakai, and Chloranthus serratus Thunb.) can be seen on the forest floor. Only P. japonica was an evergreen and unpalatable species for deer, which was the first major plants among the vegetation of the forest floor, despite its patch distribution. In the growth season (from late spring to autumn), forage biomass increased with the emergence of the saplings of the upper tree species. Based on the periodic deer route-census survey by the Univ. Tokyo Forest, the average number of observed deer around our study site was 1.0/km in 2006 and varied with season; nearly 0.0/km during December to February. Seasonal impact of deer browsing on the demography of Fagus japonica seedlings in a cool-temperate forest 233

nihon ryokka kogakkaishi/nihon ryokka kōgakkaishi

SPECIAL ISSUE &amp;ldquo; Protection and Restoration of Vegetation Damaged by Deer Grazing &amp;rdquo; Seasonal impact of deer browsing on the demography of &lt;I&gt;Fagus japonica&lt;/I&gt; seedlings in a cool-temperate forest