Miyawaki gradually formed a large seed bank (more than 10 million seeds have been identified and classified, according to their geographical origin and soil). They are mostly remnants of natural forests preserved for generations around temples and cemeteries because of the traditional belief in Chinju-no-mori (literally "forests where the gods dwell"; it was considered unlucky to interfere with these forests). These places have allowed the preservation of thousands of small reserves of native species and tree genes descending from prehistoric forests.