We established a miniature seed orchard of Cryptomeria japonica trees with a heterozygous male-sterility gene (Aa). From the result of frequency of open-pollinated male-sterile seedlings (aa) in the seed orchard, it was presumed that the pollen contamination rate was about 62%. Seed yield, 100-seed weight and germination frequency did not differ between the miniature and present seed orchard. If pollen contamination could be prevented by using a greenhouse, it was thought that the miniature seed orchard with a male-sterility gene would become an effective pollinosis measure in the future.

View full abstract

For the problematic erosive tendencies of Chamaecyparis obtuse Endl. (hinoki) forest, fast fragmentation of the scale like leaves due to raindrops striking the soil surface is often referred to. The objective of this study is to evaluate sediment movement in the form of erosion and deposition at three plots set on a steep slope reforested with hinoki in Kochi Prefecture, Shikoku. In case of Plot I having 8 years' observation period, the erosive tendency of whole observation period has turned gentle on the way due to the thinning effect. Fair soil compaction seemed to contribute to an immediate fall in erosion tendency. We found mean erosion heights of 7.412.31 mm per year in three plots during the common observation period, which is higher than that of denuded mountain slopes of weathered granitic rocks. We found mean daily rainfall as an effective rainfall intensity index to evaluate sediment movement tendencies. Sediment movement on the experimental slope occurs even after a little rainfall, which is not usually considered erosive. Most of the deposition was found in the winter season having little rainfall, whereas almost all of the erosion was found in the summer and rainy seasons. As for the preparation of the unstable sediment, the fall of smaller scale soil pillars was found to be the most important factor, and their fall prevails in the winter season.

View full abstract

The growth of stand stem volume and diameter at breast height (DBH) of individual trees in seven old man-made sugi (Cryptormeria japonica) stands (from 101 to 229 years old) in Kawakami Village, Nara Prefecture, were measured over a period of 2 to 3 years. When first measured, mean stand DBH and heights ranged from 46 to 106 cm and 29 to 50 m, respectively, and stand stem volumes ranged from 890 to 1, 690 m³ ha¹. In every stand, the periodic annual DBH increment of individual trees tended to increase with DBH. The periodic mean DBH increment ranged from 0.21 to 0.37 cm yr^-1 in the seven stands. At the sites suitable for sugi growth, it was confirmed that the trees, which were around 200 years old, could grow in DBH by 0.20.4 cm yr^-1. The periodic annual increments of stand stem volume were larger than 10 m³ ha^-1 yr^-1 in every stand. Four stands in particular had larger increments : 16-19 m³ ha^-1 yr^-1. In old sugi stands, stand stem volume and mean DBH estimated using the stand density control diagram were smaller than the measured values. It was suggested that the estimated stand stem volume can be calibrated using the measured DBH in the stand density control diagram.

View full abstract

Multi-temporal aerial photos were processed into digital orthophotos to examine temporal range shifts of bamboo stands in relation to adjacent landcover. In both study areas, in Sasaguri and Tachibana, in Fukuoka Prefecture, Japan, the area of bamboo stands increased 1.3 to 1.7 times over about 30 years. Broadleaved forest occupied at least 40% of the area into which bamboo expanded. Areas of reduction of bamboo stands were also identified; the major cause was land alteration by humans. The bamboo invasion ratio was calculated as the ratio of the length of the adjacent edge initially to that after expansion in both study areas. The highest value was for grassy sites, followed by broadleaved forest. The bamboo front moved at about 1.11.6 m annually, and no difference among landcover types was found.

View full abstract

On Mt. Iwate and the surrounding area, vegetation of the riparian management zone and impacts of its harvest restriction on forestry were examined by using Digital Topographical Map 25000, Digital Vegetation Map, and digital forest resources data. The riparian management zone (RMZ) was set up with buffering from permanent channels and lakes. RMZ shared 4% and 11% under buffer width of 15 m and 50 m respectively. In RMZ outside forest planning area, the riparian forest should be restored because a few forests currently existed there. In the RMZ inside forest planning area, the ratio of plantation forest was lower than in the whole area. However, non-national forests in RMZ needed to be preserved since in many forest stands their age was not high enough. Forest stands including RMZ were generally located near road and many of them had a high ratio of RMZ area to whole stand area. Present restriction to those stands is very inattentive. If the harvest in RMZ is prohibited, compensation for the restriction would become a higher value as the buffer width would be wider. On the other hand, RMZ was fragmented in cases where small stands would be exempted. Therefore, to introduce RMZ harvest restriction efficiently, a narrower RMZ width and moderate restriction would be appropriate for non-national forests.

View full abstract

Stand structure investigations of old-aged sugi stands were carried out at Aizu in Fukushima Prefecture. Current data between 80 and 100 years and previous data were examined in accordance with the average upper story stand height. Then they were analyzed and a minimum numerical value was assigned using the method of least squares to make a site index guide curve. As a result, height growth could be approximately confirmed using the Mitscherlich function. With this result, we could predict that an upward tendency is occurring compared with the usual height growth of the same age grade after 60 years. As years of the stand passed by, the differences between both guide curves also increased.

View full abstract

Genetic parameters of a control pollination family in Cryptomeria japonica in respect to fundamental indicators of wood quality (specific gravity at sapwood and heartwood, moisture content at sapwood and heartwood and Young's modulus) and diameter at breast height was evaluated by thinning a 17 year-old progeny test plantation (3 replica-tions, 21 combinations). Variance-covariance analysis was conducted as factorial mating and narrow sense heritability and phenotypic and genetic correlations were calculated. ANOVA showed that there were significant differences among female and male adults in most characteristics of wood quality but only in Young's modulus among replica-tion x combination and female x male adults. Narrow sense heritability showed around 0.2 on the specific gravity at sapwood and heartwood and Young's modulus but showed low values on moisture content. Genetic correlation was more closely related between almost all characteristics than phenotypic correlation. However, this fact did not always indicate that improvement of a single characteristic improved other characteristics. These results suggested that although each characteristic of wood quality could be improved, the selection method must be considered to improve wood quality comprehensively.

View full abstract

The author investigated the pattern of snow accretion damage in a dense plantation of old sugi (Cryptomeria japonica D. Don) in relation to slope inclination and tree size. For the analysis, I used data from tree censuses during 24 years, beginning when the stand was 134 years old. Almost all trees with snow damage were distributed on the slope site. The diameter at breast height (DBH) and the height of trees with snow damage were smaller than those of undamaged trees. In contrast, the height-DBH ratio of trees with snow damage was higher than that of undamaged trees. The height-DBH ratio of the trees with snow damage was generally >70. In conclusion, even in old sugi plantations that are generally constituted from large trees with DBH ≥ 30 cm, snow accretion damage will occur in trees with a height-DBH ratio >70.

View full abstract

Aboveground biomass and net production rates of a young Salix subfragilis community were studied in an abandoned paddy field at Shimagahara, Mie Prefecture. The estimated leaf biomass (3.18 t/ha) and LAI (4.75 ha/ha) coincided with the mean values for deciduous broadleaved forests in Japan. The stem and branch biomass increased from 44.10 t/ha to 56.82 t/ha during the growing season in 2003. The net production rate was estimated to be 20.32 t/ha/yr as the total of three components: the biomass increment calculated as the difference between the biomasses during the same 2003 period (12.72 t/ha/yr), the loss due to the death of trees and their parts (7.42 t/ha/yr), and the loss due to grazing by insects estimated from the fall rates of insect feces (0.18 t/ha/yr). This production rate was far larger than the mean value for deciduous broadleaved forests in Japan, although high production rates equivalent to that of the study community have been reported for young forests. The aboveground biomass density (dry weight divided by the 3-D space occupied by the plant community) calculated from the estimated maximum biomass in summer (60.0 t/ha) and the mean height of dominant trees (8.8 m) was 0.68 kg/m³, which is close to those of several communities of other shade-intolerant trees.

View full abstract

Wilt disease of Fagacea trees bored by Platypus quercivorus has increased in various districts in Japan. We collated information on the damage and discussed the damage factor. It is proved that Raffaelea quercivora isolated frequently from damaged trees is a pathogen, and P. quercivorus is the vector of the pathogen. Trees are killed by the spreading of discolored areas in sapwood where the tracheary function is lost. The loss of the tracheary function is caused by R. quercivora which is carried in large quantities by themass attack of P. quercivorus and spreads around the beetle's galleries. The mass attack of P. quercivorus is induced by aggregation pheromones emitted fromunmated male beetles, and this occurs easily when the population density of the beetles is high. P. quercivorus prefers large trees or fallen trees, because the former have large breeding capacity and high water content maintained for along time, and the latter discharge hardly any sap inhibiting the reproduction of the beetles. Such suitable hosts increase the population density of the beetles. Investigations of the damaged forests indicate that the damage beginsjust after trees are felled or blown down by wind in stands with many large trees. This information suggests that the increase of large trees caused by the neglect of fuel wood forests is occurring everywhere, and in this situation, thefirst damage was caused by the infestation of a large population of P. quercivorus that reproduced using windfall trees or felled trees.

View full abstract