We investigated gap attributes : the species of gap maker, the mode of gap formation (standing dead, stem broken and uprooted), gap area and gap age, together with gap successors (2m≦height<10m)in a mixed forest in Shiretoko National Park, northern Japan. Canopy gap was defined as the vertical projection area where no stems reached 10m height or 10cm d.b.h. We focused on the effects of gap attributes on the occurrence pattern of gap successors for each species, and then discussed the mechanisms of the regeneration processes of the component species. The stand was composed of 25 tree species, and the canopy (>10 m height) was dominated by Abies sachalinensis, Quercus mongolica var. grosseserrata and Acer mono, bringing about a stratified structure. Mean expanded gap area was 210m^2,and the ratio of gaps in the canopy was 37%. Most gaps were due to multiple tree death. Most gap makers were Abies sachalinensis. In minor species (relative biomass and density ratios<5%), the occurrence pattern of gap successors was mainly governed by the gap attributes. Betula ermanii, Fraxinus mandshurica var. japonica and Prunus maximowiczii were associated with uprooted gaps. Kalopanax pictus and Prunus maximowiczii were associated with large and small gaps, respectively. Phellodendron amurense was associated with young gaps. In major species (relative biomass and density ratios ≧5%), however, the occurrence pattern was governed by the distributional pattern of advance regenerated saplings under the closed canopy, rather than by gap attributes. In conclusion, the species richness of a northern mixed forest was promoted by the co-occurrence of minor species associated with the diversity of the gap attributes, whereas the species diversity of the major species was ascribed largely to the persistence mechanisms of trees under the closed canopies prior to gap creation.
Successional patterns of vegetation on abandoned paddy fields and their levee slopes were analyzed in mountainous regions of central Japan. The samples were classified into two types, the Miscanthus sinensis type and Phragmites australis type, at the first division level of TWINSPAN, based on the dominant species regardless of location or fallow duration. The M. sinensis type occurred at dry sites on convex slopes and the P. australis type at wet sites on concave slopes. M. sinensis and P. australis have dominated paddy field stands for 20 years. Both the clump size and litter accumulation of M. sinensis increased with fallow duration, and this litter effect would be one of the important factors related to the long-term dominance of M. sinensis. During 20 years of fallow in the M. sinensis type, however, woody species invaded the gaps among the M. sinensis clumps. As individuals of M. sinensis become clumped and form heterogeneous spatial patterns including gaps, seeds dispersed from the levee slope vegetation and surrounding forests and /or buried seeds may establish themselves. On levee slopes, most stands were of the M. sinensis type, and dominated by woody species except in those that had lain fallow for three years. These results suggest that the succession of abandoned paddy fields in the surveyed regions is affected by soil moisture conditions related to micro-landform, litter accumulation, the growth form of dominant species and the levee slope vegetation as a seed source.
Systems of sexual reproduction and costs of seed production of Alnus japonica STEUD, a pioneer and anemochore tree species, were studied in two young stands. The annual production rates of each component of the sexual organs were measured using 10 litter traps during five consecutive years from 15 December 1982 to 25 December 1987. The rates of pollen production were estimated by multiplying the number of fallen male catkins per stand by the mean amount of pollen per inflorescence before flowering. The fall of male catkins (buds) before flowering showed a marked peak in the period August-late September every year, amounting to 22% to 54% of the total male catkins in Stand A. This late summer fall was thought to be a saving in the investment of photosynthates to the reproductive organs of A. japonica. Annual pollen production rates (by number) for A. japonica were higher than those of other trees. Furthermore, the production rates for A. japonica were the highest of four Alnus species. There was a low P/O (pollen vs ovules by number per ha) ratio compared with the values for other species. The mean annual production rate of reproductive organs, including pollen, during the five years was 1,545 kg/ha・yr for Stand A and 572 kg/ha・yr for Stand G. However, the photosynthates or dry matter necessary for producing a single seed was 12 to 13 mg in both stands. The specific cost, or the ratio of this invested dry matter to a single seed weighing 1.45 mg, was about eight, being larger than the values (2 to 4) in good seed years for other tree species with larger seeds. It is suggested that the cost of seed production for trees with small-sized seeds is large.
The influences of sample size on the index values of species diversity were examined for various indices which have been used hitherto in community studies, together with several indices newly proposed in this paper. Samples of various sizes ranging from 50 to 4,000 individuals were taken randomly from each of nine types of artificial communities which were set up using paper tips, each representing an individual, and the calculated index values of these samples were compared with each other for each community. The paper tips were made by cutting a card board in about 1×1 cm size. The indices which were least affected by sample size were divisible into three groups. The first group included the β index and allied ones. The indices of the second and third groups had values corresponding to the square root and the logarithm of the respective index values in the first group. The first and the second group satisfied the following quantitative relationship, which has preferable characteristics of diversity index : diversity=richness×evenness. A new method was proposed for estimating the total number of species in the mother community from a sample. The results of comparison between the estimated and actual numbers of species in artificial communities showed that the method might be effective for practical use. The samples of artificial communities were compared with the samples of natural communities, and a number of examples which showed fairly good similarity of structure were found in both communities. It is suggested that not only in artificial communities but also in natural ones, the number of species found in a sample would not reach half the number of species in the mother community when the sample size is smaller than 100 and the value of the β index is larger than 10.
Studies on food selection in non-human primates were reviewed from the viewpoint of optimal food selection. Key factors in the classical model of optimal food selection were "maximization" of the "intake rate" of "energy". Later, the key factors were changed to "maximization" of the "contents" of "energy-essential nutrients" and "minimization" of the "contents" of "digestion inhibitor-toxins" in a modified model for herbivores. Most studies on food selection in herbivorous non-human primates have been based on the modified model, and revealed that primates choose food so as to maximize protein, and to minimize digestion inhibitiors (fiber, condensed tannin). However, the present review points out that the above key factors of the classical model are also important because food availability relating these factors correlates positively with feeding frequency.