Why are there multiple critical load graphs for the same interest features at a particular site especially for dune habitats?

Some habitats have been linked/matched to more than one nitrogen critical load and local site knowledge should be used to set the right one. For (most) sand dune habitats they can have a critical load associated with acid or calcareous soils, hence they have different critical loads.

Site specific advice should be sought from the relevant authority where there is doubt in which critical load to use.