Three years of carbon and energy fluxes from Japanese evergreen broad-leaved forest

Abstract

Carbon dioxide and sensible and latent heat fluxes over a warm-temperate evergreen broad-leaved forest in central Japan observed for 3.5 years using the eddy covariance method were analysed with an extended big-leaf model. Net ecosystem production (NEP) was estimated after correcting for night-time efflux by using chamber observations of soil and leaf respiration and for day-time CO 2 flux by using the light–response curve. Peak CO 2 uptake occurred during early summer and autumn; a summer depression and winter uptake were also characteristic of this forest. The estimated NEP showed differences among the years, depending on drought and radiation conditions. The mid-day average of surface conductance was fluctuated between 5 and 10 mm s −1 during normal years and sometimes decreasing in dry summers. In the wet summer, it increased up to 20 mm s −1. During the severe and long-term drought, the surface conductance was clearly depressed, suggesting that the surface conductance was strongly influenced by drought. The canopy maximum carboxylation rate (big-leaf V CMAX) was derived from 30 min fluxes using the same inversion procedure as used in leaf-level analysis. V CMAX at the normal period was generally explained with one temperature-dependence curve ( V CMAX25: 58.4 μmol m −2 s −1, Δ H a: 32,200 J mol −1) at this warm-temperate evergreen broad-leaved forest. The decline of the normalised V CMAX ( V CMAX25) was detected during the severe drought and the expanding period. V CMAX25 did not recover after rain during winter of the year of the severe drought, which suggests that leaf function had suffered severe damage.