The Collaborative International Dictionary of English v.0.48:

Stumpage \Stump"age\, n.
   1. Timber in standing trees, -- often sold without the land
      at a fixed price per tree or per stump, the stumps being
      counted when the land is cleared. [Local, U.S.]
      [1913 Webster]

            Only trees above a certain size are allowed to be
            cut by loggers buying stumpage from the owners of
            land.                                 --C. S.
                                                  Sargent.
      [1913 Webster]

   2. A tax on the amount of timber cut, regulated by the price
      of lumber. [Local, U.S.] --The Nation.
      [1913 Webster]