For example, in the Black Hills it is easy to correctly predict associated species and habitat characteristics for stands of paper birch and beaked hazel. In other cases, it can be very difficult to subdivide vegetation into consistent, repeating assemblages of species. Much of the ponderosa pine vegetation in the Black Hills presents this problem to some degree. Understory composition often is too variable or varies over too fine a scale to easily define discrete communities, especially using remotely sensed data. Boundaries are not easily recognized.
Types grade into other types.
The extensive disturbance history of ponderosa pine stands in the Black Hills makes this picture even more difficult to interpret. In the Black Hills, many investigators have reported difficulties in classifying ponderosa pine vegetation. In our study, we encountered the same problems. In contrast, stands found on intermediate sites were often problematic due to variable understory composition. The classification of Mount Rushmore NM follows.