Both volume and diversity of coarse woody debris (CWD) are vital attributes of forest ecosystems. However, despite their importance, their long-term dynamics associated with fire- or logging-origin and overstory type have not been examined in boreal forest. We hypothesized that, with stand development, (i) CWD diversity increases while its volume follows a U-shaped pattern, (ii) CWD volume and diversity for postlogged and postfire stands converge shortly after disturbance, and (iii) mixedwoods have more CWD volume and greater diversity than conifer or broadleaf overstory types. We sampled 72 stands ranging in age from 7 to 201 yrs in fire-origin stands and 7 to 31 yrs in managed stands with conifer, mixedwood, and broadleaf overstory types in central boreal Canada.
Results/Conclusions

CWD volume followed a U-shaped pattern in postfire stands from 7 to 201 yrs; CWD diversity increased from 25 to 124-139 yrs-old and plateaued, but in 7 yr-old stands, CWD diversity was as high as that in the 124 and up yr-old age classes. Logging resulted in a smaller amount and less size variability of CWD in 7 yr-old stands, with a larger portion being fast-decomposing Betula papyrifera, but CWD characteristics converged by approximately 30 yrs since disturbance between the two stand origins except for downed woody debris volume, which was estimated to converge by approximately 60 yrs since disturbance. Overstory type had a significant effect on most CWD characteristics. CWD in mixedwoods were generally more diverse than the other two overstory types, but conifer stands contained the greatest CWD volume except in 7 yr-old postfire stands, where higher snag volume in mixedwoods was attributed to higher stand volume in the predisturbed stands. This study demonstrates that CWD volume and diversity in boreal forest are largely determined by time since stand-replacing disturbance. Logging reduced CWD volume and diversity; leaving both fast-decomposing broadleaf and slow-decomposing conifer trees as snags will more likely mitigate its negative impact on CWD characteristics in managed forests. Managing diverse overstory types including mixedwoods is an important means of maintaining diverse CWD in boreal forest.