The spatial pattern of trees and open spaces influences many ecological processes in dry conifer forests. Understanding and replicating historical spatial patterns is important to create forests that are resilient to fire and other disturbances. USDA Forest Service scientists stem-mapped all ponderosa pine trees that were greater than 40-centimeters (about 16 inches) diameter breast height within two large old growth ponderosa pine study sites (Long Valley: 73 hectares, about 180 acres; and Fort Valley: 32 hectares, or about 79 acres) with different soils and tree densities in northern Arizona. Trees were clumped into different sized groups. Most tree groups were small, two-to-four trees, with a few large groups of up to 113 trees. When tree densities were equal, the spatial patterns were very similar between the two sites, suggesting that tree spatial pattern variability is a function of tree densities and only indirectly related to site productivity. Although both sites were dominated by small openings, most of the open area was found within a few large openings. The large plots allowed the scientists to capture a larger range of tree and opening spatial patterns compared to previous studies to provide new insights on spatial heterogeneity that can inform management of this important forest type.