Mitsue Shibata

Seed and Seedling Demography of Four Co‐Occurring Carpinus Species in a Temperate Deciduous Forest

In order to clarify regeneration traits and their fitness, we compared seed fall, seedling emergence, and first-year seedling survival of four co-occurring species, Carpinus tschonoskii, C. japonica, C. laxifiora, and C. cordata, in an old-growth temperate deciduous forest in Ogawa Forest Reserve, central Japan. Seedling emergence ratio of C. cordata (5.5%), whose seeds mostly germinated 1.5 yr after seed fall, was lower than the other species (8.5-11.2%). First-year seedlings of Carpinus tschonoskii and C. japonica had much lower survival rates (2.7%, both species) than C. laxifiora and C. cordata (7.5- 8.5%) under closed canopy, suggesting that the former two are more disturbance dependent than the latter two. They are characterized by their seed and seedling performances as seed rain type fundamentally; however, C. cordata and C. laxiflora are able to establish a seedling bank, and C. cordata has a seed bank too. These regenerative strategies partly explain the abundance and population structure of the four species in this old-growth forest. Multiple regression analyses showed that topography was important for survival of all species but C. cordata. This result was consistent with the adult distribution of these species in this forest. Wind dispersal of Carpinus is effective, both to escape from density- or distance- dependent high mortality and to increase the chance of arriving at canopy gaps, where seedling survival rate is high. However, escaping high mortality seems relatively more important for C. laxifiora and C. cordata (seedling bank strategy), and arriving at a canopy gap is relatively more important for C. tschonoskii and C. japonica (seed rain strategy).

SYNCHRONIZED ANNUAL SEED PRODUCTION BY 16 PRINCIPAL TREE SPECIES IN A TEMPERATE DECIDUOUS FOREST, JAPAN

To investigate synchronized annual fluctuation of seed production and its advantage for regeneration at the community level, for nine years (1987–1995) we monitored the flowering, seed production, and seedling emergence of the 16 principal tree species in a temperate deciduous forest, Ogawa Forest Reserve, in central Japan. We found that the species with higher synchronized flowering within a population had larger fluctuation of annual seed production at the population level. The coefficient of concordance of flowering and the coefficient of variation of annual seed production were continuously distributed among species, making it difficult to distinguish masting from nonmasting species. The annual seed production patterns of the 16 species were classified, by cluster analysis, into groups that synchronize their fluctuation of annual seed production. This analysis showed a highly synchronized annual seed production, not only among congeneric species, but also among species of different families. Although our results have some insufficiency of statistical significance, they did show that predator satiation, both in a population and a guild, effectively operated for many species to enhance seed survival at the pre-dispersal stage. They also showed that pollination efficiency was likely to be operating at the population level for half of the wind-pollinating species. However, generalist predator satiation at the postdispersal seed stage may not operate in a simple, detectable manner in this species-rich forest community. It is highly probable that there are combined effects of several factors: limited weather triggers for flowering, common flowering physiology among taxonomically related species, and the ecological advantages at the population and guild levels, may cause multiple species to have synchronized fluctuation patterns of seed production.

Community dynamics of Ogawa Forest Reserve, a species rich deciduous forest, central Japan

Forest community dynamics were studied for 4 years in a 6 ha permanent plot of species rich, old-growth, temperate deciduous forest in Ogawa Forest Reserve, central Japan. The gap formation rate, recruitment, mortality, gain and loss rate in basal area during 4 years were 42 m2 ha−1 yr−1, 1.74% yr−1, 1.19% yr−1, 1.12% yr−1 and 0.88% yr−1, respectively. The turnover time calculated from them ranged from 58 to 240 years. Both the mortality and mortality factors were size dependent; trees in middle size class had smallest mortality, and the proportion of the trees killed by disturbances increased with size. Gap creations were concentrated in a particular year, suggesting a large heterogeneity in time. Spatial distribution of recruited trees were biassed to the old gaps (older than 4 years), especially that of the species with Bell-shaped dbh distribution (shade intolerant) strongly associated with the gaps. Recruitment in tree stems and the loss of basal area, thus had the larger variability than mortality of stems and this forest, and the species with L-shaped dbh distribution seemed to going to increase the importance in the future if the present trend continues to be held. The turnover time of population is positively correlated with the maximum dbh size of the species, indicating the slow change of the population of large sized species.

CAUSES AND CONSEQUENCES OF MAST SEED PRODUCTION OF FOUR CO-OCCURRING CARPINUS SPECIES IN JAPAN

To test two hypotheses for mast fruiting, i.e., (1) pollination efficiency and (2) pre-dispersal predator satiation, we investigated annual fluctuation in seed production and demography from flower to seed of four Carpinus species (family Betulaceae). We monitored flowering, seed production, and seed fall for seven years (1987-1993) for Car- pinus laxiflora, C. tschonoskii, C. japonica, and C. cordata, which co-occur in a temperate deciduous forest, Ogawa Forest Reserve, central Japan. We also monitored the seasonal development of pistillate aments in 1995. These Carpinus species are known to show highly synchronized, fluctuating annual seed production. Total seed production (the sum of sound seeds, seeds suffering predation, empty seeds, and immature seeds) was proportional to the quantity of staminate aments and was synchronized among the four species during the observation period. The percentage of mature seeds (the sum of sound seeds and seeds suffering predation) out of the total seed production was positively correlated with annual staminate ament production. This result supports the pollination efficiency hypothesis. The observation that most ovaries in this study did not fall after the pollination season and grew into normal, mature-sized seeds irrespective of fertilization (empty or not) also sup- ports the hypothesis. The percentage of seeds suffering predation by insects significantly decreased in relation to sound seed production, suggesting that predator satiation also operated for these Carpinus species. If the four species have common seed predators (pos- sibly some curculionid species), mutually synchronized fluctuation of seed production among them would be effective for escaping from pre-dispersal predation.

The response of forest floor vegetation and tree regeneration to deer exclusion and disturbance in a riparian deciduous forest, central Japan

The response of forest floor vegetation and regeneration of major treespecies to deer exclusion in a riparian forest were studied for 3 years withtheinteractive effects of natural disturbances. At the start of this study, deerdensity had quickly increased to a fairly high level (29–31 individualskm−2) during the last decade and had severely reduced theamount of forest floor vegetation in the study area. Dwarf bamboos, which weredominant before, had almost diminished from the forest floor. During the studyperiod, aboveground biomass increased steadily but species diversity did notchange much in the exclosures. Outside the exclosures, the seedlings of alltreespecies were damaged greatly by deer browsing, especially the taller ones. Deerbrowsing had little effect on the emergence of tree seedlings, but deertrampling might have accelerated emergence indirectly by disturbing the soilsurface for some species. Differences in plant responses were also observed fordeer browsing and the presence of dwarf bamboo that strongly inhibits therecruitment of tree seedlings. The nine major species were classified intothreegroups according to the response of seedlings to deer browsing and disturbance.Group 1 consists of the species whose seedling survival is affected bybrowsing,but seldom by disturbances (Phellodendron amurense,Kalopanax pictus, Quercus crispulaandMalus toringo). Groups 2 and 3 consist of species adaptedto tree-fall disturbance (Betula spp.) and ripariandisturbance (Alnus hirsuta var.sibirica, Ulmus davidiana var.japonica, Populus maximowiczii andSalix sachalinensis), respectively, and seedling survivalof these two groups is principally affected by light conditions. The effect ofdeer browsing on seedling survival and growth was greater for Group 2 than forGroup 3.

Riparian disturbance and community structure of a Quercus-Ulmus forest in central Japan

Population structure and ecological characteristics of component species of a riparian Ulmus-Quercus forest in central Japan were analyzed with special reference to riparian disturbance regime. Though the dbh distribution of the whole community was L-shaped, those of several component tree populations had several modes, suggesting intermittent regeneration periods in the past. Correlation of spatial distributions among tree populations and subpopulations showed 6 major groups reflecting riparian disturbances in the past and different establishment patterns among species. A cluster of small-sized tree populations (Salix sachalinensis, Alnus hirsuta and Populus maximowiczii <30 cm dbh) were distributed on the lower terrace along the active river channel, while large-sized subpopulations (dbh ≥60 cm) of Quercus crispula and Ulumus davidiana var. japonica occurred on the higher terrace. The Phellodendron amurense population also occurred on the higher terrace in small clumps though the trees were small (less than 55 cm dbh). Subpopulations of intermediate-sized individuals (30 ≤ dbh < 60 cm) of Q. crispula and U. davidiana var. japonica, together with Betula and Acer spp. populations occurred on the intermediate terrace. Dendrochronological analyses indicated that the large and intermediate-sized tree groups were established about 330 and 90 years ago, respectively, while the small-sized tree group established about 35 years ago. A survey of historical disturbances showed that these periods of establishment of the former two groups almost coincided with the historically major floods occurring in 1662 and 1902. However, the disturbance that resulted in the establishment of the youngest group could not be precisely identified. Thus, the forest is a mosaic of three differently-aged patches, which is closely related to the frequency and scale of riparian disturbances. Longevity of trees and the preferred conditions for seed germination and/or seedling establishment were particularly important for the guild structure in this forest community.

Evaluating increased fitness through dispersal: A comparative study on tree populations in a temperate forest, Japan

Abstract:It is essential to investigate both the spatio-temporal pattern of seed dispersal and the subsequent fate of offspring to evaluate the effect of dispersal on plant fitness. This paper examines the effectiveness of seed dispersal in terms of three selective advantages (i.e. avoidance of high mortality around the parent plant, finding ‘safe sites’, and directional dispersal) by synthesizing the results of studies on seed dispersal, post-dispersal mortality of seeds, and seedling survivorship of several tree species in an old-growth temperate forest community, the Ogawa Forest Reserve (OFR), Japan. Some species in the OFR apparently avoid high offspring mortality around parents in much the same way as other species have been found to do in other forests. Finding ‘safe sites’ and directional dispersal could also be important elements of seed dispersal; however, the importance of ‘safe sites’ in this context and their spatio-temporal distribution have not been sufficiently characterized to discuss the...

Comparative demography of three coexisting Acer species in gaps and under closed canopy

Abstract Questions: 1. Is there a trade-off between gap dependency and shade tolerance in each of the life-history stages of three closely related, coexisting species, Acer amoenum (Aa), A. mono (Am) and A. rufinerve (Ar)? 2. If not, what differences in life-history traits contribute to the coexistence of these non-pioneer species? Location: Ogawa Forest Reserve, a remnant (98 ha), species-rich, temperate deciduous forest in central Japan (36°56′ N, 140°35′ E, 600 - 660 m a.s.l.). Methods: We estimated the demographic parameters (survival, growth rate and fecundity) by stage of each species growing in gaps and under closed canopy through observations of a 6-ha permanent plot over 12 years. Population dynamics were analysed with stage-based matrix models including gap dynamics. Results: All of the species showed high seedling and sapling survival rates under closed canopies. However, demographic parameters for each growth stage in gaps and under closed canopies revealed inter-specific differences and ontogenetic shifts. The trade-off between survival in the shade and growth in gaps was detected only at the small sapling stage (height < 30 cm), and Ar had the highest growth rate both in the shade and in the gaps at most life stages. Conclusions: Inter-specific differences and ontogenetic shifts in light requirements with life-form differences may contribute to the coexistence of the Acer species in old-growth forests, with Aa considered a long-lived sub-canopy tree, Am a long-lived canopy tree, and Ar a short-lived, ‘gap-phase’ sub-canopy tree. Nomenclature: Satake et al. (1989).

The seed bank dynamics of Cornus controversa and their rote in regeneration

Seed-bank dynamics of C. controversa , a common tree in Japanese temperate forests, were investigated at Ogawa Forest Reserve by direct measurement of seed input, soil seed density, and seedling output (germination of soil seeds), together with two field experiments on postdispersal seed mortality. Soil seed density varied from 4 to 233 m −2 in the site near conspecific adults ( −2 in far sites (≥5 m) during the 1988–92 period. Seed input occurred only in 1988 and 1990: 190–740 m −2 at the sites near conspecific adults, and 4–20 m −2 at the far sites. Seedling output was observed every year and accounted for 0–15% of the loss from the seed bank, occasionally 30–60%. Seeds buried at 5-cm depth suffered moderate mortality ( c. 0.2 year −1 ) by fungal pathogens. In contrast, seeds experimentally placed on the ground suffered higher mortality (0.5–1 year −1 ) through predation by ground mammals, probably wood mice. In the experiment, seeds whose mesocarp was removed survived much better. On the other hand, distance itself did not appear to affect post-dispersal mortality of seeds. Seeds in canopy gaps also tended to suffer higher mortality. Current spatial pattern and mode of seed dispersal should decrease the potential ability of the seed bank of this species to colonize safe sites. Rare and unpredictable events might increase the contribution of the seed-bank strategy to regeneration in this forest.

Interspecific variation in the size-dependent resprouting ability of temperate woody species and its adaptive significance

Summary Resprouting of woody species after above-ground damage may help plants to persist longer at a given site and quickly reoccupy disturbed sites, thereby strongly influencing forest dynamics. Resprouting has been discussed from two adaptation perspectives: recovery from damage by catastrophic disturbance and survival in frequently disturbed shaded understorey. However, few studies have comprehensively dealt with both adaptation types to understand resprouting strategies. To understand the adaptive significance of resprouting, we assessed the size dependence of resprouting ability after stem clipping for 24 deciduous broad-leaved species, including shrubs, sub-canopy and canopy trees, in a cool-temperate forest in Japan. The community assembly includes species adapted to past catastrophic disturbances (e.g. fire, logging) and to stable forest with intermittent treefall (currently the dominant disturbance). We correlated resprouting ability with life-history strategies based on demographic parameters and plant functional traits, such as leaf mass per area (LMA), leaf toughness and wood density. All the studied species could resprout in juveniles, and resprouting ability increased as stump size increased. Most sub-canopy and canopy trees lost their ability to resprout after attaining a particular stump size, whereas shrub species retained the ability to resprout throughout their lifetimes. The relative growth rate, LMA and foliar nitrogen did not greatly influence the resprouting ability of a species. In contrast, species with smaller maximum size, lower leaf toughness and lower wood density had better juvenile resprouting ability. This better resprouting ability may have evolved because these characteristics make them more vulnerable to shaded understorey. However, species with larger maximum size and lower leaf toughness retained their ability to resprout to a larger size. Synthesis. A better resprouting ability is related to the ability to survive frequent disturbances, in juveniles, which are characteristics of both forest understorey and frequent fire or drought. To retain resprouting ability until grown seems to be an adaptation to survive infrequent large disturbances. Light-demanding species, which generally have better resprouting ability than shade-tolerants both in juveniles and adults, are adapted to disturbances of various scale and frequency; however, shade-tolerants could survive well in the understorey due to a combination of stronger physical defences and resprouting ability.