The extent and significance of old-growth ponderosa pine forest at Mount Rushmore National Memorial

Symstad, Amy; Bynum, Michael

Mount Rushmore National Memorial (MORU) is a small portion – 517 ha (1,278 acres) – of the 1.5 million ha (3.8 million acres) that comprise the Black Hills. However, because it has been protected from logging and other extractive activities since the late 1930’s, it may serve as an important part of the Black Hills forest as a whole. To understand this role, we determined the extent and location of unlogged and old-growth forest stands in the park using historical documents and field investigations. Our results suggest that approximately 29% of the park has had no tree harvesting activity, and 18% of the park has had selective cutting of larger trees. Some of these unharvested areas have had recent thinning of small trees. When “old-growth” forest is defined according to the only published description of “old-growth” Black Hills ponderosa pine forest (Mehl 1992), 344 ha (849 acres) of old-growth ponderosa pine forest occur in the Memorial; this is 78% of the area we surveyed and 66% of the Memorial as a whole. All of the forest in the undeveloped portions of the Memorial is in a “mature” structural stage. Based on current estimates of similar forest in the Black Hills National Forest and Custer State Park, the forest at MORU constitutes the second-largest area of old-growth ponderosa pine forest in the Black Hills (the largest being at Custer State Park). This forest provides habitat for species dependent upon mature forest that is rare elsewhere in the Black Hills. For example, Redbreasted Nuthatch densities are greater at MORU than in forest typical of the Black Hills National Forest. The close proximity of MORU’s old forest to other old, relatively undisturbed ponderosa pine forest in the Black Hills in the National Forest and Custer State Park is also significant. The forest is not pristine, however, even in apparently unharvested areas. More than a century of fire suppression has increased the density of trees, particularly younger ones, as well as standing and downed dead wood, beyond that of pre-settlement times. These increased densities put the MORU forest in danger of intense, perhaps stand-replacing fires, that would likely be more intense than in pre-settlement times. Ongoing research will provide a clearer picture of management and restoration targets for the Memorial’s forests.