Lessons learned from a 15-year experiment on the efficacy of mechanical harvest and prescribed fire to restore Pinus albicaulis forests

Introduction: Forest restoration is growing rapidly, increasing demand for reliable and generalizable information on management impacts. However, evidence on the efficacy and adverse effects of treatments, particularly in high-elevation ecosystems, remains limited. Objectives: We monitored the efficacy and ecological effects of mechanical cutting and prescribed burning to restore Pinus albicaulis forests and evaluated the effectiveness of the monitoring design. Methods: We used data from a 15-year, replicated before-after-control-impact study to evaluate treatment effects on adult P. albicaulis tree mortality, basal area of competing conifers, and P. albicaulis seedling density. We also quantified the precision of estimation associated with the monitoring design. Results: Tree mortality was high (77–100%) within all units, likely reflecting pre-existing Cronartium ribicola infection and a region-wide Dendroctonus ponderosae outbreak rather than treatment effects. Mortality of small-diameter P. albicaulis trees declined with greater basal area removal. Treatments reduced basal area for only one competing conifer, P. contorta. Pinus albicaulis seedling density declined across treatments, with significant effects at only one of 2 units. Despite using widely accepted sampling protocols, the relative margin of error for study variables was high (19, 48 and 73%, respectively, for P. albicaulis basal area, tree mortality, and seedling density). Conclusions: Treatments did not fulfill most restoration objectives for P. albicaulis, and widespread disease and insect outbreak impact likely masked treatment effects. Given the likelihood of forest disturbances and that data needs for inference may exceed the scope of individual projects, a coordinated, large-scale, long-term monitoring network is recommended.