5:15 PM - 6:30 PM
[ACG22-P10] Phenological changes for 10 years and the influence on ecosystem productivity in a larch forest at the foot of Mt. Fuji
Keywords:Phenology, Growing season, Climate change, Carbon cycle, GPP
Our study was conducted in a larch plantation at Fuji-hokuroku flux observation site (Fujiyoshida city, Yamanashi). About 87 % of the canopy is dominated by 60-year-old Japanese larch (Larix kaempferi) and the maximum LAI of the canopy was 3.2 m2 m-2 in 2012. CO2 flux and micro meteorological factors have been measured by eddy covariance method for ten years since 2006. For phenological observation, reflectance from the canopy has been continuously observed on the observation tower by using two spectral radiometers (upward and downward) and digital cameras. The vegetation index to detect seasonal changes of the canopy greenness was calculated as Green Ratio: GR=G/(R+G+B). The start and end dates of the growing season were determined from the days when the time series of GR indicated the maximum rate of increase and decrease. Then relationships of the yearly variations of phenology, temperature, net ecosystem exchange (NEE) and gross primary production (GPP) were analyzed.
As results, the mean dates of start and end of growing season were Apr. 23 and Nov. 8, with large amplitudes of 12 and 8 days respectively. Significant earlier or later phenological trend was not found across these ten years from 2006 to 2015. The mean annual growing season length was 198.5±4.1 days. The start and end dates were significantly related to the mean temperature respectively during Mar.-Apr. and during Sep.-Oct. The phenological responses to temperature were −4.5 day/ºC (R2 = 0.88) in spring and 2.3 day/ºC (R2 = 0.74) in autumn. In addition, the influences of phenology on GPP and NEE during spring (Apr. and May) and autumn (Oct. and Nov) were indicated. Meanwhile, yearly variations in annual GPP and NEE were more influenced by the decrease of summer productivities due to thinning and typhoon than phenological factors.