We reviewed the applicability of a strain gauge for monitoring the diurnal diameter changes in tree stems and branches and the relationships between water status of trees and diurnal diameter changes. We summarized differences of diurnal changes in stem diameters between healthy and declining trees of hinoki cypress. The diurnal changes in xylem diameters (ε) are more closely related than the changes in phloem diameters to the changes in leaf water potential, because the diurnal change rates (Rε) in xylem diameters match the diurnal changes in water balance (sap flow velocity-transpiration rate). The diurnal patterns of Re can be divided into seven types (from type I to type VII) in relation to the soil water condition and water status of a tree. In declining trees, diurnal patterns of Re shift from the type I to VI rapidly as dry condition is continued. Therefore, the maximums and minimums of ε in declining trees tend to decrease more rapidly than those of healthy trees during the long dry period. Last, we discussed wide range of application of measurement of diameter change by strain gauges.

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Bark gnawing by Formosan squirrels has been observed in forests around Yokohama City, Kanagawa Prefecture. Chemical components may be key features for squirrels in choosing target trees. In the present study, the amounts of polyphenols, resins, and flavanols, which are assumed to act as repellent to Formosan squirrels, were compared among nine tree species dominated in this area. The samples were collected and analyzed individually through four different seasons. The results suggested that the amounts of these three components were constant to each species and did not show apparent seasonal variations in most species. Trees of hurt species (e.g., Machilus thunbergii and Neolitsea sericea) included lower percentage of three components, while those of non-hurt species (e.g., Quercus serrata and Prunus jamasakura) showed higher concentration in some of them.

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In order to evaluate the influence of tread pressure on the growth of trees, the physical properties of soil were measured in the arboretum of the Experimental Station at Tanashi, The University of Tokyo. In three different sites, i.e., the roadway of working vehicles (A), the woods trodden by visitors (B1, B2) and the woods without any tread pressure (C). The measurements of soil penetration expressed that the soils of the roadway were more compacted to the depth of 40 cm than those of the woods to the depth of 30cm. The surface layer of compacted soil was characterized by small amount of macro-pore and low water permeability. These characteristics were most distinct for the roadway. Only the roadway expressed decrease of oxygen concentration in the surface layer of soil after rainfalls. This means that the surface layer of soil of the roadway may easily lose soil aeration under wet conditions. On the other hand, the influence of tread pressure of visitors to the growth of trees seems not so severe.

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Effects of aluminum in hydroponic culture media on the growth rate and biomass allocation of woody plants were studied. The seedlings of Quercus acutissima Carr., Cinnamomum camphora (L.) Sieb. and Eucalyptus viminalis Labill. were cultured in five different hydroponic culture media containing 0, 0.027, 0.27, 2.7 and 27 mM aluminum, respectively for 5 weeks. The application of 2.7 mM aluminum significantly promoted root development in Q. actissima. The root elongation stimulated by aluminum treatment was observed in other two species, too. These results suggest that root biomass increment in woody species has an important role in aluminum tolerance.

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Revegetation works on roadside slope with compounded eeds matched to surrounding were tried in Mae-Nikko highland line in Tochigi Prefecture in June, 1999. When we investigated this slope in September, 2000, the growth from compound seeds was very poor. In contrast, the roadside slope was completely covered with moss communities of Funaria hygrometrica and/or Conocepharum japonicum. Since the covering with mosses is considered as the begining of succession of vegetation, it may become a new way of revegetating roadside slopes.

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