boscage vs underbrush

boscage

noun
  • A place set with trees or mass of shrubbery, a grove or thicket. 

  • Among painters, a picture depicting a wooded scene. 

  • Mast-nuts of forest trees, used as food for pigs, or any such sustenance as wood and trees yield to cattle. 

  • A tax on wood. 

underbrush

noun
  • The small trees and other plants that clutter the floor of a forest. 

verb
  • To clear (an area) of underbrush. 

  • To work among the underbrush. 

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