The Collaborative International Dictionary of English v.0.48:

Riga fir \Ri"ga fir`\, [So called from Riga, a city in Russia.]
   (Bot.)
   A species of pine (Pinus sylvestris), and its wood, which
   affords a valuable timber; -- called also Scotch pine, and
   red deal or yellow deal. It grows in all parts of Europe,
   in the Caucasus, and in Siberia.
   [1913 Webster]