Structural Characteristics of Old-Growth, Maturing, and Partially Cut Northern Hardwood Forests

Live tree diameter distributions, and abundance and quality of standing and downed coarse woody debris (CWD), were compared among three northern hardwood stand types in the Adirondack Mountains of New York, USA: old growth; partially cut, uneven-aged with 40–50 cm maximum residual diameters; and maturing, even-aged, 90–100 yr old, postfire. Downed CWD (stumps ≤1 m tall and logs) volumes in the old-growth, partially cut, and maturing stands were 139, 69, and 61 m3/ha, respectively. Large (≥50 cm diameter) CWD comprised 17%, 13%, and 4% of the total downed CWD volume in the old-growth, partially cut, and maturing stands respectively. Approximately one-half the large CWD in the partially cut stands was in the form of cut stumps. Standing CWD (stumps >1 m tall and standing dead trees) basal areas averaged 8.6, 1.2, and 4.1 m2/ha in the old-growth, partially cut, and maturing stands, respectively. Basal area of large (≥50 cm diameter) standing CWD averaged 70%, 0%, and 5% of the total in the old-growth, partially cut, and maturing stands. Both downed and standing CWD loads were influenced by mortality due to beech bark disease. Decay distributions of downed CWD were similar in all stand types. The old-growth stands averaged 55 live trees ≥50 cm dbh/ha, including 14 trees ≥70 cm dbh/ha. The partially cut stands contained 5 trees ≥50 cm dbh/ha, with none >55 cm dbh. The maturing, even-aged, stands averaged 1.3 stems ≥50 cm dbh/ha in the postdisturbance cohort but also had ∼8 postfire residuals/ha with diameters up to 70 cm dbh. Implementing forest ecosystem management guidelines to emulate the structural characteristics of old-growth northern hardwoods should retain at least 16 live trees/ha ≥50 cm dbh including 6 trees/ha ≥70 cm dbh. Target levels for downed CWD volume would be less (perhaps 25% less) than the 139 m3/ha reported here, considering the influence of beech bark disease on the stands we studied. These goals can be accomplished by increasing diameter limits in selection systems, by extending even-aged rotations beyond 100 yr, and implementing “reserve shelterwood” cuts that retain large trees in regenerated, even-aged stands. Retaining large trees will provide more future options to increase the proportion of large standing and downed CWD in managed stands.