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Penobscot Experimental Forest

Research Insights

[photo:]  Uneven-aged stand in the U.S. Forest Service experiment on the PEF.Principal findings of Forest Service research on the PEF can be summed up in two words: silviculture matters. If managers wish to manage stands dominated by shade-tolerant conifers in a way that maintains species composition and productivity, they must focus on retaining desirable species and establishing regeneration in the partial shade of the overstory.

[photo:] Poorly stocked, poor-quality stand resulting from experimental exploitative cutting on the PEF.If instead, trees are harvested opportunistically without consideration of the residual stand or new cohort, stands are likely to be converted to shade-intolerant and low-quality trees. This distinction is well-illustrated by comparing diameter-limit and unregulated harvest treatments to selection and shelterwood. The former have resulted in undesirable shifts in composition, quality, and structure, while the latter are well-stocked with vigorous conifers. The outcomes of this work have motivated changes in forestry practice and policy throughout the region.

[image:] Diameter distribution of the 20-year selection treatment on the Penobscot Experimental Forest; observed structure was closer to the target in year 20 of the study than in year 40.A second important finding from Forest Service research on the PEF is results change over time, particularly when harvests occur multiple times in the same stand (as they often do in managed forests). Effects of individual treatments on ecosystem components, and similarities and dissimilarities between treatments, rarely remain constant over time. Findings reported for selection cutting after 20 years of study, for example, suggested long-term sustainability of structure and composition. Yet, recent data reveal that the stands have not developed as expected .

Though the PEF studies are long-term from a human perspective, they cover a small fraction of the lifespan of dominant tree species. We already know that some treatments have undesirable results, but the verdict is still out on which are most productive or sustainable over the long-term.