The effect of nutrient availability on global forest carbon balance is uncertain

To the Editor — Fernández-Martínez et al. 1 show a chief determinant of nutrient availability on net ecosystem production (NEP) and ecosystem carbon-use efficiency (CUEe, the ratio of NEP to gross primary production i.e. GPP) in global forests. However, their conclusions depend on an improper treatment of differences in the GPP range of nutrient-rich and nutrient-poor forests (uneven sampling effect) and outliers. A statistical re-analysis of their datasets, while simultaneously excluding the uneven sampling effect and outliers, indicates no significant control of nutrient availability on carbon (C) balance.