Effects of canopy phenology on deciduous overstory and evergreen understory carbon budgets in a cool-temperate forest ecosystem under ongoing climate change
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- Saitoh, T.M., Nagai, S., Yoshino, J. et al. Ecol Res (2015) 30: 267. doi:10.1007/s11284-014-1229-z
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Canopy phenology is a key regulator of carbon cycling in forest ecosystems. To clarify its possible effects on carbon budgets of forest ecosystems under ongoing climate change, we developed a canopy-phenology model for a forest with deciduous overstory and evergreen understory based on in situ observations, and used it to improve an ecosystem carbon budget model. Under future conditions (2068–2073) based on the IPCC SRES A1B scenario, leaf expansion began 12.5 ± 1.9 days earlier and leaf-fall ended 11.3 ± 2.7 days later than under current conditions (2002–2007). We also estimated the possible influence of altered light availability on understory vegetation. Even though the photosynthetically active period in the understory (i.e., from the end of spring snowmelt to the beginning of late-autumn snow cover) expanded by 15.7 ± 15.7 days, the total downward photosynthetic photon flux density above this vegetation during the snow-free period decreased by 11.8 % because of changing overstory canopy phenology. The net effect of these changes increased ecosystem-level annual gross primary production (GPP) by 12.5 %, net primary production (NPP) by 12.0 %, and net ecosystem production by 12.1 %, especially in late spring (when the highest solar radiation occurred). The increased GPP and NPP were mostly attributable to changes in overstory vegetation. Our analysis indicates that understanding the temporal variation of canopy phenology dynamics and snow cover is important and that the effects of vegetation phenology on the carbon cycle should be evaluated in future climate change studies.