| Co-Investigator(Kenkyū-buntansha) |
YOSHIMURA Takao Remote sensing and Image Research Center, Chiba University, Assistant, 映像隔測研究センター, 助手 (80111417)
ISHIKAWA Toshio Remote sensing and Image Research Center, Chiba University, Professor, 映像隔測研究センター, 教授 (70009231)
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| Research Abstract |
About 10 % of tree numbers of the ckimax forest dominated Castanopsis cuspidata and Machilus thunbergii, have replaced every year. The numbers of dead tree during two years from April 1990 to January 1991 were 252. Thirty one percent of those, were caused by fungi and the causes of death of remaining 69 % cannot specify. It will be caused mainly by very weak light intensity in the forest. However, it cannot confirm the true causes of death, so long as we don't obtain the light intensity striked against each individual growing in the foreat floor. So, we have measured that by the method of a simple measurement of integrated solar radiation originated with Dr. T. Ishikawa and Mr. T. Yoshimura(1987 ; 1990)on and after April 1990. It is the method of measurement using the properties of diazo color, ex. Pyridylazo-2-naphthol(the peak of absorbance at 468nm), which a diazo-radical is decomposed by light energy and fades. Daily mean amount of integrated light energy striked against surving in
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dividuals was 0.697 MJ/m^2/day(0.666 in 1990 ; 0.717 in 1991), that of dead individuals by fungi was 0.715(0.704 ; 0.775)and that of dead individuals from unknown cause was 0.565(0.575, ; 0.552). There was a significant difference in the amounts of integrated light enery striked between surving individuals and dead ones from unknown causes, and it suggests that a shortage of light energy will be one of the main causes of death. A mortality rate, such as Aucuba japonica(36% in 1990 ; 11% in 19 90) ; Machilus. thunbergii(27% ; 18%) ; Castanopsis cuspidata(23% ; 18%)and Pittosporum tobira(34% ; 8%), and the integrated light energy striked of dead individuals, such as C. cuspidata and M. thunbergii(0.5 MJ/m^2) ; Fatsia japonica(0.6)and A. japonica, Cinnamomum iaponicum and P. tobira(0.6 - 0.7), differed according to the species. More than 50 % of seedlings and saplings every species grew in height and diameter, but the growth rates of more than 90% of those were less than 20%. It suggests that the resistance against light stress depends on the species and the age, and the light energy striked is not the dominating cause for the growth of height and diameter under the weak light intensity. In the near future, we must measure the integrated light energy striked at other range of light wavelength range, and examine the relationship between the soil factor and the growth of height and diameter or the death of seedlings, saplings and young trees. Less
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