heathland vs muskeg

heathland

noun
  • A tract of scrubland habitats characterised by open, low growing woody vegetation, found on mainly infertile acidic soils. Similar to moorland but with warmer and drier climate. 

muskeg

noun
  • A terrain composed of peat bog with tussocky meadow and woody vegetation including spruce. 

How often have the words heathland and muskeg occurred in a corpus of books? (source: Google Ngram Viewer )