Native Ponderosa Pine at Joint Base Lewis–McChord, Washington

Joint Base Lewis–McChord, Washington, has the largest population of ponderosa pine (Pinus ponderosa) west of the Cascade Range in the Pacific Northwest. Field mapping showed a modern geographic range of approximately 13,270 ha. The ages and locations of the largest, oldest pines indicated that at the time of Euro-American settlement in the mid-1800s, most pines grew in a single area of approximately 1,730 ha within a landscape of woodland, savanna, and grassland maintained by Native American fire. After settlement ended burning, conifer forest replaced much of the original vegetation and the range of pine expanded. I repeatedly measured permanent plots over an 11-year period (2007–2018) within the two forest types with pine: Closed Forest (mean canopy cover ≥ 60%) dominated by Douglas-fir (Pseudotsuga menziesii), and Woodland/Savanna (mean cover 5–59%) often mixed with Douglas-fir and Oregon white oak (Quercus garryana). Pine basal area and density were similar between forest types. Overstory pines in Woodland/Savanna had a larger diameter growth and crown ratio, lower height and height:diameter ratio, and averaged 40 years younger than those in Closed Forest. Pine regeneration was scarce or absent in Closed Forest, except for a pulse in 2018. The only notable temporal trend was log accumulation in Woodland/Savanna following a wildfire. Pine diameter and age distributions showed an increasing deficit of young pines over time. Major impediments to pine regeneration are competition from Douglas-fir in Closed Forest, competition from a non-native shrub Scotch broom (Cytisus scoparius) in Woodland/Savanna, and fires that burn hotter than historic fires. Active management will be necessary to perpetuate this pine population long-term in Woodland/Savanna; it may not be possible to do so in Closed Forest. Key Points Joint Base Lewis–McChord has the largest population of ponderosa pine west of the Cascade Range in the Pacific Northwest. Pine is much more abundant, grows faster, and has proportionally bigger crowns in woodlands and savannas than in dense conifer forests. Scarce pine regeneration in dense conifer forests means that pine will gradually disappear from the overstory, while in woodlands and savannas, full replacement by pine regeneration of existing overstory pine mortality is unlikely. Active management is necessary to temporarily retain mature pines in dense forest overstories and maintain pine of all sizes long-term in woodlands and savannas.