The National Forest Management Act of 1976 mandates that a site’s productive capacity must be protected on federally managed lands. Monitoring the effects of management on a site’s productive capacity is not easy, and in 1989 a national program of Long-Term Soil Productivity (LTSP) research was established to assist National Forests toward this end. The LTSP program focuses on disturbances associated with timber harvest, but findings apply to any activities altering vegetation or soil. LTSP centers on core experiments that manipulate site organic matter, soil porosity, and the complexity of the plant community. Results from a dozen decade-old LTSP installations in the Sierra Nevada and the Southern Coastal Plain do not indicate that site productivity has been impaired despite substantive soil compaction and massive removals of surface organic matter. The strongest effect of treatment on planted tree growth on sites governed by temperate and subtropical climates was the control of competing vegetation. With only one-fifth of the LTSP installations reporting, findings should not be generalized to other sites and climates.