Study on histories of old-growth forests and disturbances to them by fine scale pollen analysis of small hollows.

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Pollen and charcoal fragment data from small hollows made clear histories of forests and disturbances to them in the two old-growth forests, Odaigahara, Nara Prefecture and Ashiu, Kyoto Prefecture, western Japan. This study indicates that pollen analysis is useful for the study of the forest dynamics.1. Linear regression analysis was used to analyze a relationship between pollen percentage from surface layr of soil under a canopy and tree percentage in the two old-growth forests. These results were used to interpret fossil pollen assemblages from small hollows as a record of stand-scale forest changes.2. Comparison of pollen data from three forest hollows in a beech-fir forest at Nanatsuike in Odaigahara indicated forest dynamics for the last 1300 years. In the early stage, Chamaecyparis obtusa percentage in the forest was higher than that at present. A gap formation at about 300 years ago was recognized near one hollow in this beech-fir forest. Deciduous oak trees invaded into this gap. Also, a tree of deciduous oaks near the hollow was 300 years old based on its tree ring. Charcoal fragments that increased at same time indicated that the cause of the formation of the gap was possibly a small fire by lightning.3.A spruce forest at Masakigahara in Odaigahara has maintained for about 1000 years. Before then, spruce was rare in the forest that was dominated by deciduous oak.4.Pollen analysis of a core from the Chojidani Moor in Ashiu made clear that Crytomeria japonica was a forest dominant from 1000 yr.BP.to 500 yr.BP.Pollen accumulation rate of Cryptomeria in this period was almost equal to that of Cryptomeria forests at present. Since about 500 years ago, trees of secondary forest elements such as deciduous oak and charcoal fragments increased. These are associated with man-induced disturbances.