Long-Term Structural Change in Uneven-Aged Northern Hardwoods

Abstract

Abstract The diameter distributions of 10 previously unmanaged northern hardwood stands on the Bartlett Experimental Forest in New Hampshire were analyzed to determine changes over a 35 yr period since a single cutting by the diameter-limit or single-tree selection methods. The diameter distribution of an uncut old-growth stand (the Bowl) provided a comparison. The cuttings left residual basal areas of 25 to 96 ft² of basal area per acre (5.7 to 22.0 m²/ha), as well as a wide range in diameter distribution. Basal area of the old-growth stand was 123 ft²/ac (28.2 m²/ha), and the diameter distribution was reverse J-shaped (negative exponential) as evidenced by a close fit (adjusted r² = 0.97) of log (no. of trees) over dbh class; the q (ratio between numbers of trees in successive 2 in. dbh classes) equaled 1.39. Under all cutting methods, the diameter distributions after 35 yr fit the reverse J-shaped form only moderately well with adjusted r²'s of 0.81 to 0.95. An equal or better fit in most cases (adjusted r²'s of 0.91 to 0.98) was provided by log (no. of trees) over dbh², which reflects the tendency of the quotients between numbers of trees per dbh class to increase with dbh. None of the initial diameter distributions of the cut stands had rotated sigmoid characteristics, but five of the final diameter distributions had significant rotated sigmoid characteristics, and at least two others showed graphical sigmoid tendencies. Apparently, rotated sigmoid characteristics are caused by disturbance, perhaps coupled with successional trends toward increased tolerant softwoods. For. Sci. 42(2):160-165.