alder vs black alder

alder

noun
  • Any of several trees or shrubs of the genus Alnus, belonging to the birch family. 

  • An alderman or alderwoman. 

black alder

noun
  • Wood or other product of the tree. 

  • A tree (Alnus glutinosa), of many practical uses, growing in moist conditions in Europe. 

  • American winterberry, Ilex verticillata. 

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