Characteristics of temporal variations in ecosystem CO₂ exchange in a temperate deciduous needle-leaf forest in the foothills of a high mountain

Abstract

　We report the four-year (2006-2009) measurements of the net ecosystem CO₂ exchange flux (NEE) over a deciduous needle-leaf plantation forest in the foothills of Japan's highest mountain, Mt. Fuji. We focus on the characteristics of temporal variations in NEE and their relationships to environmental factors and phenology in a forest stand. We evaluate year-to-year variations in the seasonal patterns of flux components and investigate factors controlling the NEE. During the growing season, light availability is likely to affect the photosynthetic uptake of CO₂ at the site. We found significant differences in the length of the growing season for the four years; these are due mainly to variations in the timing of the progress of the autumnal coloring of leaves. The timing for the start of the autumnal coloring of leaves is highly dependent on when the daily lowest air temperature drops below 10°C. Secondly, we investigate the characteristics of short-term and long-term variations in the structure of CO₂ storage in the forest stand using a newly developed profiling system. We demonstrate the characteristics of temporal variations in the vertical distribution of CO₂.