Vulnerability of boreal indicators (ground-dwelling beetles, understory plants and ectomycorrhizal fungi) to severe forest soil disturbance

Abstract

Forest ecosystems can be greatly affected by multiple interacting disturbances, with outcomes that may range from degraded and poorly-functioning to novel but productive ecosystems. We assessed the vulnerability of boreal biotic indicators (epigeic beetles, understory plants, ectomycorrhizal fungi) to compound soil disturbances at 20years post-logging in northcentral British Columbia (Canada) to examine these issues of ecological integrity. The study was a full factorial experiment with 3 levels of organic matter removal (tree boles only; tree boles+logging slash; tree boles+logging slash+forest floors) and 3 levels of soil compaction (0, 2, 4cm impression), with a tree species split-plot of lodgepole pine (Pinus contorta) and hybrid white spruce (Picea glauca×engelmannii). There was little effect of soil disturbance on ground-dwelling beetles, particularly beneath pine. Removal of forest floors and, to a lesser degree, compaction significantly altered plant and fungal communities. There was no effect of retaining logging slash but a consistent influence of tree species on biotic communities likely due to initial differences in conifer growth rates. Average community dissimilarity of the 3 guilds from a least disturbed baseline (tree bole removal, no compaction) increased linearly by a small amount (4–6%) with each level of disturbance severity. Some degree of soil disturbance across landscapes can be acceptable in creating regeneration niches for rare and functionally important pioneer species, but we also see losses in ecological integrity, such as the spread of invasive plants, that merit concern in managing these ecosystems.