Comparison of small mammal and herpetofauna community composition in naturally regenerated clear-cuts, pre-commercially thinned, and soft-wood plantation forests, at two developmental stages

Abstract

A viable softwood forestry industry relies on intensive forest management practices to optimize yield, and reduce rotation time. In New Brunswick, Canada, the primary management strategies are plantations followed by herbicide spraying, or naturally regenerated stands that are selectively pre-commercially thinned. Forest managers have both economic and conservation targets so it is critical to understand (1) how managed stands provide habitat value to native biodiversity relative to natural Acadian mixed-wood forest and (2) how the succession since the management intervention (i.e. time since clear-cutting, planting, thinning, etc.) affects habitat quality. This thesis addresses these questions by estimating and comparing small mammal and herpetofauna abundance and taxonomic richness in plantations, thinned, and naturally regenerated stands at two different developmental stages following clear-cutting. Stand characteristics within these treatment and stage categories were surveyed, in order to develop hypotheses about the mechanisms underlying relationships between stand treatment and development stage, and taxonomic richness or individual species abundances. Abundance and taxonomic richness of small mammals, and forest dependent amphibians (wood frog and red-backed salamander), were negatively affected by intensive forest management practices, with plantations having a greater effect than pre-commercially thinned stands. Small mammal richness and abundance, and specifically abundances of Sorex, red-backed voles (Myodes gapperi), wood frogs (Lithobates sylvatica), and red-backed salamanders (Plethodon cinerus), were greater in naturally regenerated mixed-wood stands than in pre-commercially thinned and planted stands. Associations with stand characteristics were species specific, but deciduous components (i.e. canopy cover, leaf litter, percentage of hardwood) were important for species negatively affected by management practices. This is particularly true of canopy cover, which was greatest in naturally regenerated mixed-woods, and lowest in plantations. The relationship between thinning and native small mammal and herpetofauna species was relatively subtle and should be further studied to address the question of whether there are critical thresholds. Contrary to previous studies, no overall effect of forest management was found for herpetofauna taxonomic richness, woodland jumping mouse (Napeozapus insignis), short-tailed shrew (Blarina brevicauda), or deer mouse (Peromyscus maniculatus) abundances, however, this study may not have had the power to detect small effects. Both small mammals and herpetofauna were more abundant in the earlier development stage than the later, but taxonomic richness was similar between stand stages. This highlights the importance of measuring abundance and taxonomic richness, as particular species may be present but reduced in abundance in managed stands. Wood frog and red-backed salamander, two species that are more dependent on a terrestrial life stage than other amphibian species in the region, were positively associated with stand stage. This is likely due to increased canopy closure and resulting higher moisture microclimate levels at later developmental stages. Effective management for small mammal and herpetofauna habitat will require the conservation of mixed-wood stands with a high amount of closed canopy cover.