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

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 CO2 flux by using the light-response curve. Peak CO2 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 VCMAX) was derived from 30 min fluxes using the same inversion procedure as used in leaf-level analysis. VCMAX at the normal period was generally explained with one temperature-dependence curve (VCMAX25: 58.4 μmol m−2 s−1, ΔHa: 32,200 J mol−1) at this warm-temperate evergreen broad-leaved forest. The decline of the normalised VCMAX (VCMAX25) was detected during the severe drought and the expanding period. VCMAX25 did not recover after rain during winter of the year of the severe drought, which suggests that leaf function had suffered severe damage.