This plant is Berberis thibetica and this is the most colorful natural sawdust I have ever seen! Barberries, mahonias, nandinas (all members of the Berberidaceae) are yellow when you prune them but wow! The intensity of this plant is remarkable. I don't know whether it is a result of genetics or situation but against the brown and gray of a dreary winter day this is some color. It results from the presence of the complex organic ammonium salt, berberine. The native perennial Goldenseal, or Hydrastis, though not in the Berberidaceae is in the related Buttercup Family, Ranunculaceae, contains the same chemical, and exhibits the same yellow coloring.
Berberine has been researched for use as an anticancer drug. Results are not final but the compound is used in a variety of treatments. Traditionally it has been used (and still is to a limited extent) as a fabric dye. Hey, it's just one of those remarkable chemical products of plant metabolism. I wish I had brought a piece of wood home because the literature tells me that it fluoresces strongly. I will cut a piece tomorrow and see for myself! What a curious and wonderful world we live in.