NITREX is a consortium of European experiments in which nitrogen depos
ition is drastically changed for whole catchments or large forest stan
ds at eight sites spanning the present-day gradient of nitrogen deposi
tion across Europe. NITREX focuses on the impact of nitrogen depositio
n on forest ecosystems, in particular the factors and processes affect
ing 'nitrogen saturation'. A large number of ecosystem processes and c
omponents are investigated as part of NITREX to identify and quantify
the factors which lead to changes in nitrogen cycling and outputs due
to experimental changes in nitrogen inputs. The data are used to devel
op and test several types of nitrogen models. NITREX is linked to seve
ral other European research projects, as well as to similar large-scal
e ecosystem experiments in North America.