Clifford A. Myers conceived the ponderosa pine growing stock levels (GSL) study in 1961 and completed installation of the study in 1963 in western South Dakota on the Black Hills Experimental Forest (BHEF). The GSL concept was intended to help plan, implement, and illustrate tree thinning strategies (from below) in even-aged stands. A GSL is the suggested tree density (i.e., trees and basal area per acre) based on d.b.h. that can be tended to produce a desired basal area per acre (e.g., 80, 100, 120 square feet) when the mean d.b.h. is 10 inches. Plots representing GSLs 20, 40, 60, 80, 100, and 120 were thinned and measured through 2014. The thinnings that occurred in the GSL 80 plots showed the most promise for producing commercially sized trees and volumes through 2010. Unfortunately, by 2014, mountain pine beetles killed trees in all of the plots and ended the study.