I have 50 trees that I have tapped for 5years. 5 Red Maples and 45 Sugar Maples. Last season I collected about 900 gallon of sap in all. However, the 5 Reds (16"to24"dia.) have consistently given me less than a gallon of sap each per year.
The trees are odd in that although they have the distinctive canker target, they have the smooth gray bark of a beech tree. Not what I would expect from an older Red Maple.
I have spoken with a local forester, experienced people at our supply store, and folks at MSU (Michigan) forestry department. No answers.
Any incite would be appreciated.