Effects of post-windthrow salvage logging on microsites, plant composition and regeneration

Questions How does windthrow influence plant diversity and composition as well as regeneration and microsite characteristics? What are the consequences of post-windthrow salvage logging on these key attributes? Location Eastern black spruce-moss forest, Quebec, Canada. Methods A total of 92 plots were sampled, each with a radius of 11.28m; 49 of these plots were salvaged while 43 were unsalvaged. Regeneration density, plant diversity and seedbeds were characterized. We tested the effect of microtopography and windthrow severity on species richness and Shannon diversity index for salvaged and unsalvaged windthrows using a mixed model. Partial redundancy analysis (RDA) determined which environmental and stand characteristics were most important in explaining differences in plant species and forest floor types among the treatments. The effects of treatments (salvaged and unsalvaged windthrows), microtopography attributes, windthrow severity and regeneration species on seedling and sapling abundance were tested using a linear mixed model. Results Salvaged windthrow, with a large proportion of skid trails, dead mosses and Sphagnum, had a lower degree of seedbed heterogeneity. Also, some understorey species present in the unsalvaged ecosystem were absent from the salvaged windthrow. Sphagnum and other moss species were clearly associated with the unsalvaged treatment. White birches were positively associated with mound microtopography in the unsalvaged windthrow. Conclusion From an ecosystem-based forest management perspective, natural post-windthrow understorey conditions and microsite heterogeneity can be in part maintained in salvaged cut blocks by incorporating retention patches that include downed and standing dead wood and living trees of diverse sizes. These steps should favour plant regeneration and augment diversity for salvage logging after wind disturbance.