Photosynthetic recovery of foliage after wind disturbance activates ecosystem CO2 uptake in cool temperate forests of northern Japan

The effects of wind disturbance on forest dynamics and ecosystem CO2 exchange were examined in cool temperate forests of northern Japan during 2004-2008 using eddy covariance (EC) measurements. One site was a young, even-aged, monoculture, deciduous forest; the other was an uneven-aged mixed forest of evergreen and deciduous overstory tree species, including some over 200 years old. On 8 September 2004, a strong typhoon struck the forests, after which leaf and branch amounts decreased in young growth forest, but foliage showed little change in old growth forest. By 2006, foliage at the young-growth forest had recovered to the 2004 pretyphoon state. Average daily accumulated gross primary production (GPP(d)), terrestrial ecosystem respiration (TERd), and net ecosystem exchange (NEEd) were assessed for six growth stages annually. After the typhoon, large increases in GPP(d) were found during the growing stage of overstory tree species with high photosynthetic rates compared to that before the typhoon. Pronounced increases in GPP(d) and corresponding large reductions in NEEd were detected at the young-growth forest, indicating that NEEd was largely regulated by GPP(d) throughout the growing stages. Although EC measurements contain uncertainty, our continuous EC measurements revealed that interannual variability in meteorological variables and structural changes in foliage have only small impacts on GPP and NEE, while photosynthetic recovery of foliage from typhoon damage has high potential to increase GPP and enhance NEE as compared with those under nondamage conditions.