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

1)近几年来，北海道北部针叶林中的云杉和杉木衰退现象普遍存在。为了阐明衰退的机理，在日本北海道的东京大学森林中，对Ezo云杉和Todo冷杉的水分状况进行了调查。衰退主要发生在1981年第15号台风损毁的林分(D林)，而未受台风破坏的林分(H林)则没有观察到衰退。用压力室技术测定了样木的日水势、水分亏损点水势(PSIw(TLP))、饱和点渗透势(PSIS(Sat))和细胞壁弹性(Epsilon)等水分关系参数，D林和H林的水势日变化趋势明显不同，说明D林的水分胁迫比H林严重。在D立地观察期间死亡的一棵Yazo云杉表现出最严重的PSIw低于-2.0 MPa的水分胁迫。D型林分衰退树的PSIw(TLp)和PSIs(Sat)均低于H型林分，由此认为台风破坏造成针叶树水分胁迫的小气候变化是造成Yazo云杉和TODO冷杉衰退的主要原因。2)在北海道东京大学森林进行了GPS定位试验，以评估森林地区差分GPS(DGPS)的精度。结果表明，载波相位定位法的平均误差小于1m，移位法的平均误差小于10m，但运算效率比单点定位降低了1/3~2/3。

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.