Yoshihiko Hirabuki

POST‐DISPERSAL CHANGES IN THE SPATIAL DISTRIBUTION OF FAGUS CRENATA SEEDS

The spatial distribution of tree seeds is influenced by the behavior of seed dispersers and seed-killing agents. In this study we evaluated the relative importance of multiple seed-killing agents on changes in the spatial pattern of Fagus crenata seeds. The dispersal of seeds and causes of seed death following dispersal were investigated on a 0.6- ha study plot in northern Japan. Seeds were collected using seed traps (n = 110) in the autumn of 1995, as well as directly from the AO layer of the soil, including leaf litter, intermediate, and humus layers (n = 110), in the spring of 1996. A total of 44075 seeds were disseminated into the seed traps, including 17 964 mature seeds; 15% of these were viable the following spring, indicating a large decrease in the abundance of viable seeds during the post-dispersal seed stage. Spatial association of undamaged seeds changed from a positive to independent association between the different dispersal stages, indicating rearrangement of the spatial pattern of seeds through time. During this period, numbers of living seeds generally decreased beneath nonspecific adults compared to those located away from the adults. This change resulted from the spatially different behavior of several biotic and abiotic killing agents. Rodents and fungi attacked the seeds, depending on seed densities and presence of nonspecific adult crowns, respectively, but desiccation was independent of both seed density and nonspecific crowns. The multiple killing agents with different spatial behavior jointly influenced the distributions of recruits entering tree populations.

Heterogeneous dispersal of tree litterfall corresponding with patchy canopy structure in a temperate mixed forest

Spatial dispersal patterns of fine litter were analyzed in relation to forest structure within a temperate mixed stand, in northeastern Japan. The canopy layer was a mosaic of two types of patches, those of shade-tolerant Abies firma (estimated age being 81–146 yrs.) and early successional deciduous broad-leaved trees (about 45 yrs. of age). Litter input to the forest floor was observed for a period of three years using 38 traps set at a height of 1.2 m. The average annual total of fine litter was 6.233 (dw.) metric tons hectare-1, 85.7% of the total litterfall. Fine litter was mostly leaves from the overstory (about 64%). Litter distribution maps were drawn, using the Daviss grid method, of the total fine litter and its two main elements, namely A. firma (a 36.1% share) and deciduous broad-leaved species (36.7%). The mosaic distribution of heterogeneous patches of litter was seem to corresponded with distribution of the canopy structure.

Geographical variation in the early regeneration process of Siebold's Beech (Fagus crenata BLUME) in Japan

The causes and timing of seed death in early regeneration process of Siebolds beech (Fagus crenata Blume) was studied at 15 sites along a snowfall gradient in Japan, in order to clarify why the seedling density of the species has geographic difference remarkably. Seed production did not significantly differ along the snowfall gradient. Pre-dispersal seed mortality by insect damage was higher at sites with light snowfall than at sites with heavy snowfall, but this only seemed to be a minor factor influencing the population. A large proportion of the viable nuts that fall in autumn ware killed in winter before germination. Winter mortality was much higher at sites with thin snow cover than that at sites with thick snow cover, and this factor was strongly correlated with the geographic variation of seedling regeneration probability. There was little seed mortality by winter desiccation. The main factor contributing to the geographic difference seemed to be a seed predation by rodents in winter. Deep snow cover may reduce the success of rodents finding seeds in winter. Thus the observed relationship between snowpack depth and early mortality may be due to an indirect effect through the process of seed predation.p>

Population dynamics of four understorey shrub species during a 7-yr period in a primary beech forest

Shrubs persist in the understorey layer of forests throughout their lives, while tall trees remain there only during the juvenile stage and then grow into the canopy layer. Thus demographic parameters (recruitment-, mortality-, and growth- rates) of shrub species are expected to differ from those of tall tree species. We investigated aspects of the demography of four dominant deciduous-shrub species (Viburnum furcatum, Lindera umbellata var. membranacea, Magnolia salicifolia, and Hydrangea paniculata) in Fagus crenata forests at the beginning and at the end of a 7-yr period in a 1-ha permanent plot. For each species, the number of stems changed little (within ± 10%) during the study period, while total basal area increased markedly (11.7 - 33.8%), because (1) new stems continuously recruited by vegetative growth replaced the sub- stantial number of dead stems, and (2) vegetative stems grew vigorously, probably due to nutrient support from parents. The results indicate that these four understorey shrub species have high ability to maintain their population size in the shaded forest understorey. While in each species more than half of the dead stems were standing dead, a substantial proportion of the dead stems (9.0 - 38.5%) showed signs of mechanical damage, such as stem breakage and suppression by fallen branches or trees. Snow pressure that resulted in decumbent stems was also an important mortality agent for V. furcatum (20.7%) and L. umbellata var. membranacea (5.6%). Probability of dam- age was constant across all DBH-classes for all study species. In each species, newly recruited stems and dead stems were spatially aggregated, largely due to habits of vegetative growth and mechanical damage, respectively. This study revealed that several demographic traits, resulting from recruitment by veg- etative growth and death by mechanical damage, were shrub- species specific and markedly different from those of tall tree species.

Influence of micro-landforms on forest structure, tree death and recruitment in a Japanese temperate mixed forest

The micro-landform unit system offers an effective way of analyzing vegetation–geomorphology relationships at a 10-m scale in areas such as the hilly regions of Japan. We analyzed relationships between micro-landforms and tree population parameters over a 9-year interval to elucidate the influence of geomorphic processes on vegetation dynamics. A 2.16-ha permanent plot was established in a temperate mixed forest. Each 5 m × 5 m quadrat within this plot was classified according to six types of micro-landform units: (i) crest slope (CS); (ii) upper sideslope (US); (iii) head hollow (HH); (iv) lower sideslope (LS); (v) foot slope (FS); and (vi) river bed (RB). All living trees larger than 10 cm in diameter at breast height (d.b.h.) were identified, mapped and marked in 1989 and resurveyed in 1998. Almost all of the 23 common tree species persisted in their own core habitats (i.e. the micro-landforms) between the two surveys. The species distribution in both surveys showed that the six micro-landforms could be combined into two larger groups: upper and lower hillslope areas. The upper hillslope area had higher tree densities and larger basal areas than the lower hillslope area. It is possible that these differences result from the longer lifespans of trees on the upper hillslope area rather than from differences in mortality and recruitment rates. In addition, the different ways in which trees die in the different micro-landform units may affect the regeneration process in hilly regions through different gap formation. The effects of different geomorphic processes are reflected in the lifespans of the trees and may result in different forest structure and dynamics among micro-landform units.

Population dynamics of four understorey shrub species in beech forest

Abstract Question: In the population dynamics of four understorey shrub species (Hp, Hydrangea paniculata Sieb. et Zucc.; Lu, Lindera umbellata Thunb. var. membranacea (Maxim.) Momiyama; Ms, Magnolia salicifolia (Sieb. et Zucc.) Maxim.; Vf, Viburnum furcatum Blume ex Maxim.), (1) What is the relative importance of seedling regeneration versus vegetative growth? (2) Can these shrubs persist stably for a long time in the understorey? (3) What kind of variation in demographic features is observed among these shrubs? Location: 780m a.s.l., north-eastern Japan. Methods: Population dynamics were analyzed by using stage-classified matrix models. Models were mainly constructed from five years stem-census data, including current-year seedlings and sprouts. Results: Current-year sprouts emerged every year in every species. Current-year seedlings emerged every year in Lu and Vf, but densities were very low. In every species, population growth rate (λ) was close to the equilibrium value 1.0 and no statistical difference was found among species. The stable stage-distribution predicted from the matrix model was similar to the observed distribution for Lu, Ms and Vf, but much different for Hp. Elasticity matrix was also similar among Lu, Ms and Vf, but was quite different for Hp. Conclusions: Lu, Ms and Vf were considered as climax shrubs that can regenerate and maintain their population stably in the understorey, even if canopy gaps form infrequently. Hp is a pioneer shrub that require more frequent formation of canopy gaps for long-term persistence in the understorey. Abbreviations: Hp = Hydrangea paniculata; Lu = Lindera umbellata var. membranacea; Ms = Magnolia salicifolia; SL = Current-year seedling; SP = Current-year sprout; Vf = Viburnum furcatum.

The relationship between stem vessel parameters and the development of strata in the early stages of secondary forest succession in Amazonia

In order to compare the development of strata in the early stages of secondary forest succession with vessel parameters of the tree species, a forest inventory was carried out in 4-year (Q1: 48 m2), 11-year (Q2: 400 m2) and 20-year (Q3: 400 m2) forests and vessel parameters were investigated from stem cross sections of 18 species obtained in Q2. Thirty three species (21 families), 77 species (35 families), 39 species (20 families) were found in Ql, Q2, Q3, respectively. The percentage of dead individuals, dead stems and the percentage of individuals with multiple stems increased with time after clear cutting. Also, the total D2H of Q3 was 26.1 times that of Q1, and the development of strata started in Q2 and Q3. The image analysis of vessel size, area and number of vessels revealed that species which reach the forest canopy had a large D2H value, vessel diameter and area, while species which remain near the forest floor had smaller ones. Poecilanthe effusa (Huber) Ducke is an example of the latter case, with a large number of individuals and abundant sprouting of new stems from stumps, but with high mortality.

Potential of High-Resolution Satellite Imagery for Mapping Distribution and Evaluating Ecological Characteristics of Tree Species at the Angkor Monument, Cambodia

Abstract Large trees play several vital roles in the Angkor monuments landscape. They protect biodiversity, enhance the tourism experience, and provide various ecosystem services to local residents. A clear understanding of forest composition and distribution of individual species, as well as timely monitoring of changes, is necessary for conservation of these trees. using traditional field work, obtaining this sort of data is time-consuming and labour-intensive. This research investigates classification of very high resolution remote sensing data as a tool for efficient analyses. QuickBird satellite imagery was used to clarify the tree species community in and around Preah Khan temple, to elucidate differences in ecological traits among the three dominant species (Dipterocarpus alatus, Lagerstroemia calyculata and Tetrameles nudiflora), and to identify crowns of the dominant species. Population structures of trees were determined using a 14.26ha study plot. Species name, DBH, height, height under the crown and crown area were recorded for all trees over 40 cm in DBH. Tree locations were also recorded so as to provide references for the imagery analysis. Ecological traits of the dominant species were estimated using regressions by an expanded allometric equation for both large and small trees, based on DBH, height, height under the crown and crown width. The total number of species in the study plot was 45. From a spatial perspective, the three dominant species over 100 cm in DBH were segregated from each other. D. alatus, L. calyculata and T. nudiflora were concentrated, respectively, along the approach to the temple, near the centre of the complex, and on the walls of the monument. Object Based Image Analysis (OBIA) conducted using QuickBird satellite imagery, showed that crowns of D. alatus were largely determined by maximum of NIR layer and mean of digital number in panchromatic layer. Differences in the parameters for both asymptotic height and spatial distribution among the dominant species, result from differences in ecological traits, and enhance the value of the tourism resource by providing a dramatic shift of forest scenery that can be enjoyed by visitors to the monument.