leaf litter vs midden

leaf litter

noun
  • Dead plant material, such as fallen leaves, bark, and twigs, that has fallen to the ground and may be used by animals as habitat or for nest-building, eventually decomposing and releasing nutrients into the soil. 

midden

noun
  • A shelter made of vegetation and other materials by packrats. 

  • An accumulation of dried urine and fecal deposits made by hyraxes. 

  • A refuse heap usually near a dwelling. 

  • A prehistoric pile of bones and shells. 

  • A dungheap. 

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