Comparison of inter-annual variation in net primary production among three forest types in the same region over 7 years

Differences in dominant tree species affect ecosystem carbon budgets in forests, but their independent impacts have not been fully recognized. We aimed to clarify the interannual variation in net primary production (NPP) in three different forest types and the effects of dominant tree species on this. We calculated NPP excluding belowground litter fall using a biometric-based approach for 7 years (2012 − 2018) in three different forests in the same region dominated by deciduous oak (Quercus serrata), Japanese larch (Larix kaempferi) and Japanese red pine (Pinus densiflora). Aboveground litter fall (LF) and stand biomass increment (SI) were determined using the litter trap method and allometric relationships of tree biomass with diameter, respectively. Although inter-annual variation in LF seemed to be affected by the strong typhoons that passed through the study area, the sensitivity to the typhoons differed among the forest types: L. kaempferi and P. densiflora forests were more susceptible than the Q. serrata forest. Inter-annual variation in NPP (LF + SI) differed greatly among the three forests; this was primarily explained by the inter-annual variation in SI. Mean NPP excluding belowground litter fall for 7 years was 6.0 ± 0.50, 5.2 ± 0.44, and 6.7 ± 0.40 MgC ha⁻¹ year⁻¹ in Q. serrata, L. kaempferi, and P. densiflora forests, respectively. Our results suggest that differences in dominant tree species have non-negligible effects on inter-annual variations in NPP and its components (SI and LF), even in the same region.