Looking out at the snow-covered garden this morning, I noticed that the snow beneath all the Garry Oaks is yellow and getting darker as the snow melts. There are no animal foot prints nearby that would lead me to think animals are responsible. Garry Oak leaves leave brown stains where they land on sidewalks, etc. in the fall so I'm wondering if the yellow colour is also caused by tannins or if it might come from lichen in the branches. Any guesses?