A new sensitive dendrometer system was invented by using a potentiometer and datalogger and applied to the stem of some canopy trees of a stand of deciduous broad-leaf tree species native to Hokkaido, northern Japan. Different types of diameter/age growth curves were observed at the fine level for different species: (1) an ordinary type with smooth and gradual growth; and (2) a slow growth curve mixed with intermittent stair-like periods of rapid growth. Possible reasons for the presence of stair-like rapid growth were examined, including the significance of water availability condition.