Interannual Variation and Trend of Carbon Budget Observed Over a 28-year
Period at Takayama in a Cool-Temperate Deciduous Forest in Central Japan
Long-term carbon dioxide (CO2) flux measurements between the atmosphere
and the ecosystem have been made since 1993 at a cool-temperate
deciduous forest site (Takayama) in Japan influenced by Asian Monsoon,
constituting the longest dataset among all the AsiaFlux sites.
Interannual variations (IAVs) and trends of the annual carbon budget
components and their environmental factors were examined. Annual net
ecosystem production (NEP) (mean ± 1σ) during the period of eddy
covariance measurement in 1999-2021 was 265 ± 86 gC m-2 yr-1, and its
IAV was dependent more on gross primary production (GPP) than on
ecosystem respiration. IAVs in annual NEP and GPP were correlated with
the IAVs of the monthly mean NEP, GPP and leaf area index (LAI) from
June to September, as well as with that of the length of the net carbon
uptake period. Significant increasing and decreasing trends in the
annual NEP and GPP were detected during 2004-2013 and 2013-2021,
respectively; the increasing trends were mainly caused by the vegetation
recovery from typhoon disturbances while the decreasing trends were
partly influenced by recent extreme weather events. Significant positive
correlations of the IAVs between the start and the end of the net carbon
uptake period, and between the leaf expansion and leaf fall were found.
These may be attributed to biological functions and interseasonal
relationship of meteorological parameters associated with ENSO events
that can also influence IAVs in annual NEP and GPP.