Mass of downed wood in northern hardwood forests in New Hampshire: potential effects of forest management

Abstract

Downed (i.e., fallen, dead) wood was sampled in 1-, 15-, 50-, and 100-year-old managed stands, an uneven-aged, managed stand, and an uncut stand of northern hardwoods in New Hampshire. Mass of downed wood ranged from a mean of 32 t/ha in the 15- and 50-year-old stands to 86 t/ha in the recently cut stand. Mean estimates varied significantly among stands, although most of the variation was due to the large amount of downed wood in the recently cut stand. The range of downed-stem diameters was greatest in the 100-year-old and uncut stands. Large (> 38 cm) logs were notably absent from the uneven-aged, managed stand, indicating that selective cutting utilizes mature stems efficiently. Comparison of our data with other estimates shows that the amount of downed wood in northern hardwood stands declines to about 20 t/ha within 20-30 years after logging. Quantities remain relatively stable for up to an additional 30 years and then begin to increase. They stabilize at 35-40 t/ha after approximately 100 years. Large-diameter logs become an increasingly important component of downed wood as stands mature beyond 50 years of age. Rapid decomposition of even the largest logs precludes continued accumulation of downed wood in uncut, old-growth stands. The data suggest that less downed wood and fewer large-diameter logs are likely to accumulate under short-rotation (< 50 years) harvest, whole-tree harvests, and selection cuts than under long rotations or in uncut forests.