Landforms and distribution patterns of giant Castanopsis sieboldii trees in urban areas and western suburbs of Tokyo, Japan

Combining both biological diversity and cultural significance, populations of big trees in Japan are considered important. Furthermore, individual specimens, often with broken and unusual tree form, are highly striking and create a ‘sense of place’ in a locale. The giant Castanopsis sieboldii trees belonging to the family Fagaceae have a trunk circumference of over 3 m. These trees are distributed on various landforms in Tokyo and its western suburbs. In this study, we conducted field surveys to determine the distribution pattern and geographical conditions of giant C. sieboldii trees growing in urban areas and western suburbs of Tokyo. The topography of Tokyo is variable, comprising mountainous areas, hills, plateaux, lowlands, and reclaimed lands with large rivers or streams. The places where giant C. sieboldii trees grew were classified into 13 categories using cluster analysis of geomorphic landscape sections. The lowest point of the area within a 2-km radius surrounding the giant trees was determined through field surveys and based on geomorphic sections in four directions. Trees growing on slopes, plateaux, and hilltops or mountain tops, or along the edges of plateaux represented 80 % of the total recorded trees. Two categories were an exception to this, where the height difference between the lowest and highest altitude was less than 10 m. Giant trees were mostly distributed above the 10-m contour line, on plateaux or hills and especially on slopes along the edges of 10, 30, 120, 170, and 210-m contour lines on flat uplands. Altitude appeared to be a significant factor for giant tree distribution, with only a few giant trees located below the 10-m contour line in low lying or reclaimed lands. Finally, we discuss the reasons underlying this unique distribution of C. sieboldii in the light of the physical characteristics of different landforms.