Pollen-vegetation relationship of surface pollen assemblages and objective vegetation reconstruction in the Hakkoda Mountains, northeastern Japan

Abstract

To investigate the pollen-tree relationship of surface pollen sample from under canopy sites, surface pollen samples were analysed from 56 sites collected in the montane zone to the subalpine zone of the Hakkoda Mountains, northeastern Japan. The characteristic pollen assemblage was observed in each vegetation type. High percentages of Pinus Haploxylon type pollen were recognized in the Pinus pumila thicket. Abies pollen was characterized in the Abies mariesii forests and the Fagus-Abies mixed forests although it was strongly under-represented. Betula pollen increased in the upper part of Fagus-Abies mixed forest and reached the highest values in the Betula ermanii stands, which corresponded to the vegetation composition. Fagus pollen was abundant not only in the Fagus crenata forests and the Fagus-Abies mixed forests but also in the P. pumila thickets and the A. mariesii forests. Cryptomeria pollen, derived from Cryptomeria japonica plantations in the lower montane area, varied from 4 to 126% (average 52%) in all vegetation types. The scatter plot of pollen percentages and coverages indicated taxa-specific representation. Pinus Haploxylon type and Abies pollen were under-represented because of low plant height, low plant density and small dispersal ability of pollen, respectively. Fagus and Betula showed relatively good linearity. Quercus was over-represented although its coefficient of correlation was the worst, which may be caused by different distributions pattern of two Quercus species, Quercus crispula in the montane zone and dwarf oak Q. crispula var. horikawae in the subalpine zone. The pollen assemblage of the P. pumila thicket, the A. mariesii forest, the Fagus-Abies mixed forest and the F. crenata forest can be distinguished by Canonical Variate Analysis (CVA). CVA results allow clear assessment of former vegetation changes by objective interpretation of fossil pollen data from two forest hollow sites (KS-3 and KS-4 sites) in the Hakkoda Mountains. The vegetation at KS-3 prior to the To-a tephra layer (A.D.915) was a F. crenata forest, shifting to Fagus-Abies mixed forest after A.D.915. The low elevation site of KS-4 was continuously dominated by F. crenata forest, although a temporal change to Fagus-Abies mixed forest was observed. © 2011 Elsevier Ltd and INQUA.