Larix-Picea forests of the Last Glacial Age on the eastern slope of Towada Volcano in northern Japan

Abstract

Larix is an under-represented taxon in pollen assemblages, and its contribution to past forest composition is difficult to estimate from macrofossil assemblages only. Buried forests reflect the past forest composition directly, and the dimension of the component individuals and the distribution of forest stands can also be studied. Forests buried by the Towada Hachinohe pyroclastic fall deposits (To-HP) occur extensively on the eastern slope of Towada Volcano in northern Japan. Fossil woods composing these buried forests and those from lower peat-bearing deposits, named the Upper Ofudo Formation, show the formation of Larix-Picea forests, accompanied by Abies, during the period 18,600 to 12,900 yr B.P. These forests established themselves after the destruction of Picea-Larix forests at ca. 31,800 yr B.P. by the Towada Ofudo pyroclastic fall deposits (To-BP1). Throughout the Upper Ofudo Formation, Larix and Picea are dominant, and Abies is a sporadic secondary element of these Larix-Picea forests. All the trees are less than 30 cm in diameter in the lower part of the Upper Ofudo Formation, and larger individuals, up to 70 cm in diameter, are detected in the upper part and the forests buried by the To-HP. Coexistence of Larix, Picea and Abies, and the existence of a peat layer in the probable soil surface indicate that the buried forests were very similar to present-day Larix gmelinii var. japonica forests on transitional or low moors on Sakhalin. Among the large individuals of the To-HP buried forests, the growth rate of Larix was slightly higher than that of Picea or Abies which have a similar growth rate.