scrubland vs undergrowth

scrubland

noun
  • A plant community characterized by scrub vegetation, consisting of low shrubs, mixed with grasses, herbs, and geophytes. 

undergrowth

noun
  • The plants in a forest which only reach a relatively low height (such as shrubs and bushes). 

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