Members’ Publications

Temporal changes in the relationship between tree-ring growth and net primary production in northern Japan: a novel approach to the estimation of seasonal photosynthate allocation to the stem

Koide D., Ito A.
Ecol. Res., 33: 1275–1287

Tree-ring (TR) observations provide important data on long-term forest dynamics and their underlying ecophysiological mechanisms. To elucidate the seasonal link between photosynthetic carbon acquisition and TR growth, we analyzed the correlation between observed TR data (carbon sink) and model-estimated net primary production (NPP; carbon source). Temporal trends of the TR–NPP correlation over the last century were also analyzed to identify influences of past climate changes.

We used TR data from Picea glehnii at seven sites on Hokkaido Island, Japan, which were obtained from the International Tree-Ring Data Bank. At each site, NPP was estimated using the Vegetation Integrative Simulator for Trace gases model, which was driven by longterm (1900–2010) meteorological data. Site-mean treering width index (TRWI) chronologies were analyzed to reveal any relationship with the current or previous year’s annual or monthly NPP. We found moderate to strong correlations between TRWIs and model-estimated monthly NPP from April to June, especially in June of the current year, but no clear spatial trend was observed. During the twentieth century, the TRWI–NPP correlation increased for February, March, April, and July NPP of the current year and for October NPP of the previous year. Ecophysiologically, the period from April to June corresponds to the season when tree cambial cells are formed in the study area. Our findings suggest that photosynthate produced during this cambial growth season is allocated to stem growth and that this source allocation season has become longer due to past environmental changes.