Reactive nitrogen deposits to woodland/forest at a higher rate than to shorter vegetation types. This is because forests and woodland habitats have a higher aerodynamic roughness (e.g. leaves, branches etc) as opposed to a shorter type of vegetation habitat types and deposition to woodland habitats can be twice as that for short vegetation. So even at the same location different habitats can receive different depositions of pollutant.
APIS provides the appropriate deposition values for each of the main habitats using either short vegetation (labelled moorland) or tree (woodland) deposition velocities.