Comment on “Late 20th century growth acceleration in Greek firs ( Abies cephalonica) from Cephalonica Island, Greece: A CO 2 fertilization effect?”

Abstract

In the recent article ‘‘Late 20th century growth acceleration in Greek firs (Abies cephalonica) from Cephalonia Island, Greece: A CO2 fertilization effect?’’ (Dendrochronologia 26(2008) 13–19) by Koutavas, a dataset of radial stem growth increment was presented. Eight individual trees, after detrending to remove the biological age trend, show a growth increase that is hypothesized to be related to CO2 fertilization. Such a conclusion, if correct, would be of great relevance towards understanding the impact of anthropogenic emissions on forest productivity, with consequences on the global carbon cycle, ecosystem functioning, land– atmosphere interactions, and climate model experiments. However, as suggested by the author, these results reflect a preliminary assessment of CO2 fertilization effects on tree growth. Here in, we expand upon known challenges in growth attribution, and bring attention to subtle though important methodological considerations, in using such tree-ring data to make conclusions about CO2 impacts on radial tree growth. These issues are: (i) few data, (ii) non-systematic consideration of environmental forcing factors and, (iii) end-effects in detrending. We suggest that these three factors reduce support for the conclusion that the