Long-term canopy dynamics analysed by aerial photographs in a temperate old-growth evergreen broad-leaved forest

1 We used aerial photographs to analyse canopy dynamics over 32 years in a 4-ha permanent plot of an old-growth evergreen broad-leaved forest in the Tatera Forest Reserve, south-western Japan. 2 We used aerial photographs taken in 1966, 1983, 1993 and 1998 to create digital elevation models (on a 2.5-m grid) of the canopy surface in a 10-ha area that included the 4-ha plot. A topographic map of the ground surface of the 4-ha plot was also created from ground measurements taken in 1990. The canopy height at each location was calculated and the 'vegetation height profile technique' was applied to quantify canopy dynamics. 3 The size distributions of gaps at each observation time showed peaks at both small and intermediate sizes. The total number of gaps and gap density increased over the study period, while total gap area, mean gap size and maximum gap size fluctuated. While the overall mean rates of gap formation and closure (0.58 vs. 0.50% year(-1) ) were nearly balanced, we found large temporal variation. 4 Of the 6400 of 2.5 x 2.5-m quadrats, 3.4% remained as gaps throughout the 32-year period. These tended to be in the centres of large, old gaps, whereas those that experienced re-disturbance (2.5%) were distributed along the edges of old gaps. A large proportion (74.5%) maintained a closed canopy state. 5 Meteorological data suggested that the variation in gap formation and gap closure rates may be related to year-to-year variations in the number and severity of typhoons. 6 This study suggests that long-term and large openings are essential for the establishment of deciduous broad-leaved and shade intolerant pioneer species in predominantly evergreen broad-leaved forests.