Disturbed vegetation reconstruction using the biomization method from Japanese pollen data: Modern and Late Quaternary samples

摘要

Arboreal and herbaceous pollen taxa are assigned to plant functional types (PFTs), and classified into forest biomes and non-forest biomes in Japan at present. Eight sites were found to belong to non-arboreal biomes, which do not exist in Japan. This shows that the herbaceous pollen plays a critical role in the reconstruction of forest biomes because Japan is mostly covered with disturbed vegetation. Disturbed vegetation was reconstructed using a modified biomization scheme. Four herbaceous taxa and characteristic arboreal taxa in disturbed vegetation were assigned to the newly defined disturbed vegetation biome (DISV). When applied to surface pollen spectra, the method assigns 71% of the samples to the correct biomes. The biomization method was applied to the Late Quaternary pollen record from Lake Mikata to reconstruct the vegetation changes, including DISV. Reconstructed DISV appeared in two phases, the Late Holocene and Last Glacial. The appearance during the Late Holocene was caused by human impacts, such as deforestation and agriculture. During the Last Glacial, it was caused by an abrupt climate change, such as the Dansgaard-Oeschger cycle. The vegetation was not able to keep pace with the abrupt climate change, and temporarily shifted from climax forest to disturbed vegetation around the lake.