LONG-TERM STRUCTURAL STABILITY IN NORTHERN HARDWOOD STANDS TREATED WITH DIFFERENT ALTERNATIVES OF PARTIAL CUTTING
Selection cutting should result in and sustain consistent production, a stable structure, and stable conditions within uneven-aged northern hardwood stands. Some reports suggest using it in second-growth even-aged stands as well. This study investigated the structural stability of uneven-aged northern hardwood stands treated with various alternatives of single-tree selection system over extended time frames (20 to 80 years), and the effect in even-aged stands treated with selection-like cuttings. Data from stands in New York, the Upper Peninsula of Michigan, and Wisconsin were analyzed to determine changes through time in the number of trees across 1-inch diameter classes, the shape and scale of the 3-parameter Weibull function used to describe the diameter distribution, and other stand structural attributes. Findings showed that single-tree selection created and sustained a stable structure in uneven-aged stands, while structural characteristics varied through time after selection-like cutting in even-aged northern hardwoods. Findings showed similar tendencies for the uniformity of different stand attributes over time, and the tendency of the Weibull shape and scale to migrate towards those of the recommended selection system target distribution with consecutive entries into uneven-aged stands. By contrast, these features fluctuated over time after use of selection-like cuttings in even-aged stands. Sustaining a stable structure depended on consistent recruitment into the 5-inch diameter class, and good survivor growth across all diameter classes. Length of the cutting cycle and the residual basal area had insignificant effects on the parameters over time. Also, effects from a variation in the proportions of American beech (Fagus grandifolia) and sugar maple (Acer saccharum) were not significant. The random effect of site influenced the scale parameter, but was irrelevant for the shape parameter.