Historical transition of Crown Size Index on Amami Oshima Island after the 1960s: correspondence to important forest areas

Abstract

We drew 1-ha mesh maps of the Crown Size Index of globally rare subtropical lucidophyllous forests on Amami Oshima Island (712 km2), Japan, using morphological analysis of aerial photographs taken in the fiscal years 1965, 1984, and 2008. The Crown Size Index corresponded to the vegetation map and the history of human intervention on the island. We roughly categorised forests into three types based on Crown Size Index transitions: mature lucidophyllous forests with consistently large Crown Size Indices since the 1960s; secondary lucidophyllous forests with small Crown Size Indices, which were established after clear-cuts during the 1960s.1980s; and stands of pioneer trees, which grew to form large crowns by the 2000s. Large mature lucidophyllous forest patches are distributed in the designated protected areas of Amami Gunto National Park, and the average Crown Size Index in special protection areas has been consistently maintained at a large value. The species diversity of sub-large trees was higher in areas with larger Crown Size Indices. These results imply that our method may be useful in prioritising forest areas with high conservation values, and that the zoning of Amami Gunto National Park is appropriate for the conservation of subtropical lucidophyllous forests of important biodiversity.