fir vs pine tree

fir

noun

  • Any pinaceous conifer of related genera, especially a Douglas fir (Pseudotsuga) or a Scots pine (Pinus sylvestris). 

  • A conifer of the genus Abies. 

  • Wood of such trees. 

pine tree

noun

  • Any coniferous tree in the genus Pinus 

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