Dead wood dynamics in declining balsam fir and spruce stands in New Brunswick, Canada

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Abstract
Forest management prescriptions increasingly incorporate snag and downed dead wood (DDW) guidelines. This study utilizes permanent inventory plots to determine dead wood dynamics in 33 balsam fir (Abies balsamea (L.) Mill.) – spruce (Picea spp.) (BFSP) and 17 spruce – balsam fir (SPBF) stands in New Brunswick, Canada. Stands were declining, unmanaged, and had a history of recurrent spruce budworm (Choristoneura fumiferana (Clem.)) outbreaks and aerial insecticide spraying. Fixed-area sampling matched remnants of 1165 dead trees and 864 corresponding pieces of DDW to plot trees that died over the last 15–18 years with known year and cause of death. Declining BFSP stands had the highest accumulation of dead wood (196 m3/ha) compared with SPBF and nondeclining BFSP (122 m3/ha and 77 m3/ha, respectively). Dead wood dynamics were influenced by cause of death, as a function of differences in tree height at death affecting snag decay, fragmentation, and fall. One-half of all dead trees never made a significant contribution to the snag population (25% uprooted and 25% stem breakage), and attrition resulted in only 50% of snags standing with a mean height of 6 m 15–20 years after death. This study will be of direct value to those managing or modeling dead wood dynamics in similar forests.