From their 15N tracer results1 and an estimated deposition rate to forests of 5.1×1012 g nitrogen per year2,3, Nadelhoffer et al.conclude that about 0.25×1015 g carbon per year is sequestered by northern temperate forests. Their 15N-tracer measurements are robust but there is a problem with their assumption that they have simulated atmospheric nitrogen deposition at forests by adding 15N tracers systematically to forest floors “in all cases”. Atmospheric nitrogen deposition is actually intercepted by the forest canopy, particularly at the nine closed-canopy forests studied.