The recurring role of site challenges assumptions about regeneration under selection systems in northern hardwoods

In naturally regenerated managed forests, silvicultural methods leverage timing and intensity of harvesting activities to align with species-specific reproduction mechanisms. With contemporary emphasis on complex stand structure and diverse composition, there is uncertainty in the continued use of timber-oriented management practices in meeting evolving objectives. In the northern hardwood region of North America, selection regeneration systems are assumed to result in homogenization of structure and composition through increasing dominance of Acer saccharum Marsh. Given the coupling of soils and vegetation in northern hardwoods, trends in site conditions that may be more resilient/facilitative to community diversity may be of value to silviculturists. Remote sensing products and inventory records were integrated to assess tree communities across site variables in northern Michigan, USA. Results reveal that composition is stabilized by local landforms and diversity increases with hydrologic catchment area. Time since treatment (0-54 years) appeared negatively correlated with catchment area, suggesting lowlands with high diversity are not managed or harvested infrequently, reflecting equipment access and operational logistics. Broad interpretations of selection regeneration systems may be invalidated by the influence of site conditions not previously accounted for, and results highlight a novel technique to capture the effect of topography on species assemblages.

Six Decades of Growth and Yield and Financial Return in a Silviculture Experiment in Northern Hardwoods

The Cutting Methods Study at the Ford Forest in the Upper Peninsula of Michigan, USA, was established in 1956 and has been maintained continuously on a 10 year cycle. Methods consist of three diameter limits (DL; 13, 30, and 41 cm), single-tree selection to three residual basal area limits (STS; 11, 16, and 21 m2ha−1), and light improvement (LI) focused on improving tree grade. Long-term results show that the 41 cm DL produced the greatest managed forest value and cumulative sawlog production, followed by the STS to 11 m2ha−1 residual basal area. STS treatments and LI were uniformly superior at improving standing tree grade. In contrast, treatments that emphasize removal of large diameter trees while retaining moderate residual basal area (the 41 cm DL and 11 m2ha−1 STS) produced the largest harvest volumes of high-grade sawlogs, driving financial performance. Stand density has declined in all treatments except the 30 and 41 cm DL, where it has increased, and these two treatments have larger abundance of saplings and poles. Alternative partial cutting methods such as selection to lower residual basal areas and medium-intensity diameter-limit cuts thus may provide greater financial returns and higher average quality, and could have implications on regeneration and long-term sustainability. Study Implications: Long-term comparison of alternative partial cutting practices in northern hardwoods in the Upper Peninsula of Michigan over 60 years reveals that Arbogast-based single-tree selection is inferior using financial and volume yield criteria. Alternatives that remove more of the larger trees appear over time to increase regeneration and harvested tree quality, which in turn drives financial performance. However, treatments with extremely high volume removals perform poorly against all others, and have few, if any, redeeming financial, silvicultural, or ecological qualities.

Sugar Maple, Red Maple, and Yellow Birch Growth and Mortality in Even-Aged Adirondack Northern Hardwoods

Tree diameter growth models for northern hardwoods commonly used large data sets representing a composite of stands with varying management histories, structural characteristics, and age distributions. Yet common predictor variables like diameter can show differences in growth patterns for stands with different age structures and management histories. To address that, we modeled growth and mortality for sugar maple, red maple, and yellow birch in thinned even-aged Adirondack northern hardwoods. Findings indicate that change in diameter depends on initial diameter for sugar maple, with the rate decreasing exponentially from the largest size class to the smallest. Initial diameter did not prove significant with red maple and yellow birch in these thinned stands, perhaps because of the limited sample of trees of small diameter. Stand relative density and time since treatment affected growth for all three species. Those variables also proved significant for predicting mortality of sugar maple. Analyses revealed fewer losses of sugar and red maples among the larger diameter classes, but no relationship with diameter for yellow birch. Plot relative density did not affect mortality with red maple, but time after thinning had a significant effect on survival of all species. Study Implications Crown thinning and other methods that release upper canopy trees within even-aged stands should result in favorable postthinning growth of sugar maple, red maple, and yellow birch. Yet, the small trees of sugar maple will grow slower than larger ones after release by thinning, and small sugar and red maple have greater probability of dying. Residual stand density will temper the growth of all three species and the survival of sugar maple and yellow birch. Findings suggest that management strategies favoring removal of the large-diameter sugar maple trees of upper canopy positions from an even-aged stand (e.g., diameter-limit cutting) will result in lower rates of diameter increment within the residual stand. That should negatively affect stand dynamics and volume production and result in greater mortality among the remaining sugar and red maple. By contrast, crown thinning will enhance residual tree growth and survival, as well as stand development.