Jerry Nicholls, timber contracting officer (trainee) for the Tonto National Forest forestry department, studied a patch of trees through a No. 10BAF (Basal Area Factor) prism — counting on how the prism bends the light to determine how much basal area was present to then remove the prescribed amount. Basal Area is a common way for foresters to describe tree stand density. …This process is called horizontal point sampling and foresters use the prism and calculations to determine the number of trees to be removed, based on the silviculturalist prescription. That prescription “could favor leaving larger healthier trees, (or have) a preference on species, such as ponderosa pine versus Douglas fir, for their health, or a preference” for a certain size of tree because that is missing from the mix of tree sizes. …He explained that the Basal Area Factor will change based on the prism size a forester picks, either a five, eight, or 10.