Spruce budworm, windthrow and partial cutting: Do different partial disturbances produce different forest structures?

Forest management that incorporates the emulation of natural disturbances is promoted as a coarse filter approach to maintaining natural ecosystem functions, yet the initial outcomes of different natural and anthropogenic disturbances of similar severity may be quite different. We question whether a variant of diameter-limit partial harvesting effectively generates structural and compositional patterns similar to those found after spruce budworm outbreaks or windthrow, and whether stands issued from these two partial natural disturbances are more similar to each other or to those resulting from the studied partial harvests. We conducted our study 20-25 years after these partial disturbances occurred to determine whether the patterns converged or diverged over time. Results showed that post-disturbance vegetation distribution and abundance were similar after all partial disturbance types. Tree diameter distribution followed a reverse-J pattern and mean densities of mature trees were similar, although a higher proportion of deciduous species was observed in the partial harvest sites. Snag densities converged among the three partial disturbance types, despite initial differences that likely occurred in snag abundance and differences in the type of mortality (selective tree removal in partial cuts, uprooting/snapping in windthrow and standing mortality after insect outbreaks). The density of moderately decomposed coarse woody debris was significantly lower after partial harvesting relative to after windthrow and spruce budworm disturbances. Although a higher total number of canopy gaps was observed in the sites disturbed by spruce budworm, the percentage of canopy openness was similar among the three partial disturbances. Our results suggest that convergence of structural and compositional components occurred over the 25 year period since the disturbance. Thus after one entry, the studied partial harvests may be reasonable analogs to both of the studied natural disturbances in terms of medium-term post-disturbance species composition and structural complexity. (C) 2011 Elsevier B.V. All rights reserved.