Long-term canopy dynamics in a large area of temperate old-growth beech (Fagus crenata) forest:: analysis by aerial photographs and digital elevation models

1. Long-term canopy dynamics in a large area of temperate old-growth beech forest in the Daisen Forest Reserve, south-western Japan (11.56 ha studied over 43 years), were investigated using digital elevation models (DEMs) of the canopy surface, constructed from aerial photographs taken in the growing season (i.e. with foliage) in 1958, 1978, 1992 and 2001. A ground surface DEM at the same resolution (a 2.5 x 2.5 m grid) was constructed using aerial photographs taken when foliage was absent (winter 2002). Canopy height data were obtained by calculating differences in elevation between the canopy and the ground surface, and a canopy height profile was constructed. 2. Topographic data for a 4-ha plot, located within the 11.56-ha area, were obtained via a ground survey and used to validate the ground surface DEM derived from aerial photographs. 3. Canopy height class distributions changed significantly over the 43 years. The total number of gaps, defined as areas where canopy height was less than or equal to 15 m, decreased but total gap area increased over time. Total gap area in 2001 was twice that of 1958. The density of gaps decreased as gap size increased. 4. Gap formation rates increased from 0.47% year(-1) (1958-78) to 1.30% year(-1) (1992-2001), with a mean of 0.77% year(-1), and substantially exceeded closure rates, which fluctuated from 0.28% year(-1) (1958-78) to 0.54% year(-1) (1978-92), with a mean of 0.39% year(-1). Gaps generally expanded and became connected to each other. 5. Temporal variation in gap formation and closure might be correlated with the frequency and severity of typhoon disturbances but, if the observed trends continue, this old-growth beech stand may become an open stand. The long-term dynamics of this forest type appear to be far from equilibrium.