Estimation of stress history of trees in declined and deserted forests by carbon isotope analysis

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In Loess Plateau in China, Chinese pine (Pinus tabulaeformis) and black locast (Robinia pseudoacacia) are widely planted to prevent desertification. For these two species, carbon isotope ratios of early and late wood of tree rings were analyzed. Pine has more sensitive stomata than locust, and climate of previous October to current June was found to affect to the isotope ratio of the early wood, and those of current June to August to the late wood. Locust showed less sensitive reaction of stomata to the climate, and isotope ratio was lower than that of pine. These result suggested lower WUE (water use efficiency) of locust.In the stands planted with pine had higher soil water content and water permeability and richer floor vegetation, while locust showed lower water content than grassland. All of these results suggested that locust tend to transpire water than pine.Forest decline caused by pine wilt disease in Mt. Tsukuba was surveyed and damaged pine stand was detected by remote sensing data of IKONOS. The process of wilting in pine wilt disease was visualized by Magnetic Resonance Microscopy, and mechanism of wilting was suggested to be a runaway embolism. In declined beech (Fagus crenata) forest in Tanzawa Mountains, decline was suggested to affect ectomycorrhizal diversity. In subalpine fir-wave forest of Abies spp., process of stand development and decline was studied, and mechanism of coexistence of two fir species was clarified.