Continuous observations and environmental analysis of forest decline in sub-arctic coniferous forest

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1) Recently, decline of yezo spruce and todo fir in boreal forests in Hokkaido has been widely observed. In order to clarify the mechanism of the decline, water status of ezo spruce and todo fir trees were investigated at Tokyo University Forest in Hokkaido.The decline is occurring mainly in stands damaged by Typhoon XV in 1981 (D-stands), and not observed in undamaged stands (H-stands). Severity of decline in the sample trees was evaluated in the stands, and water relation parameters such as diurnal water potentials, water potential at turgor-loss point (PSIw (tlp)), osmotic potential at saturation point (PSIs (sat)), and cell wall elasticity (epsilon) were estimated by pressure chamber technique.The diurnal trends of the water potentials in sample trees were clearly different between D-stands and H-stands, that means water stress in trees was more severe in D-stands than in H-stands. An yezo spruce tree which died during the observation in a D-stand showed the most severe water stress of PSIw below -2.0MPa. PSIw (tlp) and PSIs (sat) of the declined trees were lower in D-stands than in H-stands.From these results, the major factor which cause decline of yezo spruce and todo fir is thought to be micro climate change in stand level by the typhoon damage, which resulted in water stress in the conifer trees. The measurement of water relation parameters should be useful for prediction of the decline.2) GPS positioning tests were conducted in the Tokyo University Forest in Hokkaido, to evaluate differential GPS (DGPS) accuracy in forested areas. The results indicate that the mean error was less than 1m by the carrier phase positioning method, and less than 10m by the translocation method, although operation efficiency reduced to 1/3 to 2/3 compared with point positioning.