Abstract
The downed woody debris in a stand is driven by inputs from overstory trees and outputs via decomposition throughout the stand’s development. The development of an individual stand, however, takes place over long periods of time and thus is difficult to study directly. We re- sampled a chronosequence of sixteen northern hardwood stands in the White Mountains of New Hampshire to describe how volume, species composition, and decay class of downed woody debris vary with stand development. As expected, the species composition of downed woody debris was different in forests at different stages of overstory succession and total downed woody debris increased with stand age and the production of larger downed wood. Re-sampling the chronosequence revealed a decrease in downed woody debris volume from ~80 to 40 m3/ha in a 70-year-old stand and an increase from ~50 to 120 m3/ha in a 145-year-old stand, resulting from infrequent disturbances. Fine woody debris peaked at 30-50 years during the self-thinning of early-successional species, especially pin cherry. The 145-year-old second-growth stands were unlike true old-growth stands due to a lack of live (p = 0.09) and downed trees (p = 0.06) > 40 cm. The live aboveground biomass throughout this chronosequence was highest in one of the old growth stands at about 450 Mg/ha, while the second-growth stands appeared to level off at about 350 Mg/ha after 145 years. These results suggest that tree biomass has the potential to surpass 300 Mg/ha in stands less than 200 years old. Steady state conditions for live trees may not be reached within 150 years in this forest type, while downed woody debris biomass may fluctuate around 15 Mg/ha after 150 years depending on disturbances.