Centerpiece of research on the Penobscot Experimental Forest: the US Forest Service long-term silvicultural study

Established between 1952 and 1957, the U.S. Department of Agriculture, Forest Service experiment comparing several silvicultural treatments is not only the centerpiece of research on the Penobscot Experimental Forest in Maine, it is also one of the longest-running, replicated studies of how management techniques influence forest dynamics in North America. Ten treatments representing even- and uneven-aged silvicultural systems and exploitative cutting are replicated twice on operational-scale experimental units averaging 21 acres in size. Treatments are applied uniformly to experimental units in accordance with prescriptions designed to direct both stand structure and composition. In some treatments harvests are scheduled at intervals (e.g., 5, 10, or 20 years); in others, harvests are triggered by stand conditions. Each experimental unit, or compartment (most recently termed management unit), has an average of 18 permanent sample plots (PSPs) for measuring attributes of trees =0.5 inches in diameter at breast height. Tree regeneration and other vegetation are measured on multiple subplots within each PSP. Measurements are taken before and after harvests and, in many treatments, at intervals between harvests. Over the past 60 years, this long-term experiment and associated short-term studies have generated fundamental knowledge about forest ecosystems and silvicultural guidelines for the northern conifer forest type, and, in a more general sense, have contributed to our understanding of mixed-species forest science and management.