Potential yield is one of the first things one must know about a species to be planted.  It is difficult to handle in a general handbook for a state as large and varied as Montana.  Smooth bromegrass, for example, produces more than crested wheatgrass in areas receiving 16 inches or more precipitation annually, but less in areas that receive little precipitation. 
These ratings compare species on the basis of production under optimum conditions for each individual species.  The user must know moisture and fertility requirements of each for optimum production to interpret this rating.  Species are placed in one of three groups as follows: 
1 = High.
2 = Medium. 
3 = Low.