The relationship between past vegetation type and fire frequency in western Japan inferred from phytolith and charcoal records in cumulative soils

Abstract

Phytolith and macrocharcoal records in cumulative soils were compared in five areas in western Japan, including two sites on the Tonomine Plateau where we examined those records. Past vegetation types, as represented by the compositions of phytolith assemblages, are closely related to macrocharcoal fluxes, regardless of age, suggesting that in Japan, fluxes in cumulative soils could be an indicator of fire frequency. On the Tonomine Plateau, phytolith and charcoal records indicate that, in the middle and late Holocene (at least 5000 to ∼1000 years ago), Sasa and Panicoideae species in a temperate climate. At least for approximately the last 600 years the Japanese pampas (Miscanthus sinensis) grassland has undergone annual burning. The results from the Tonomine Plateau site of this study and from four other sites suggest that macrocharcoal fluxes in cumulative soils of >10 particles·cm−2 y−1 indicate a high frequency of fires, resulting in the dominance of Andropogoneae species. Dominance of Pleioblastus species under the influence of fire was observed in soils with a charcoal flux of 2–10 particles·cm−2 y−1, suggesting that the species flourished under a moderate frequency of fire (possibly every several years or more). In soils with a charcoal flux of less than ∼1 particles·cm−2 y−1, there was no influence of fire on vegetation, and Sasa and Pleioblastus species flourished where the vegetation type was determined primarily by the climatic conditions. These findings indicate that macrocharcoal fluxes and phytolith assemblages exhibit a consistent relationship that is independent of age, and that macrocharcoal fluxes are linked to fire frequency, thus suggesting that the frequency of fire has determined the vegetation type in these areas. Therefore, phytolith and charcoal records in cumulative soils provide a context for quantitatively understanding the influence of fire on vegetation patterns in the past.