When expressing degree and followed by a plural, it is predominantly construed like an adverb, meaning that the following phrase is not necessarily dative, but takes its construction from its syntactic function. Thus:Bis zu zwei Drittel der Insel sind bewaldet(“Up to two thirds of the island are made up of forest”), wherezwei Drittel is treated as the subject, rather thanBis zu zwei Dritteln der Inselist bewaldet, where the prepositional phrase as a whole serves as subject.
When followed by a singular, the dative construction is usually maintained:Es fiel bis zu einem Meter Schnee(“There fell up to a metre of snow”), but at least informallybis zu ein Meter is also possible.
