| Summary: | Spiders are known for their direct (consumptive) and indirect (non-consumptive) impacts on herbivorous insects. It is unclear to what degree these effects occur in structurally complex habitats like boreal forest canopies. It is reasonable to expect that the relationship between vegetative structure and spider populations would manifest at the stand level; however, few studies have explored these relationships at this scale. I conducted two studies to examine the direct and indirect effects of spiders on a common forest insect pest and to compare the spider community in differing forest stands in the boreal forest. Using a microcosm experiment, I established a study to determine both the consumptive and non-consumptive effects of spiders on spruce budworm. I found that spiders did not significantly affect the survival, mass or defoliation caused by spruce budworm. Instead, bottom-up control from the number of available shoots appeared to be a more important factor. Even though this study suggests spiders are less effective as natural enemies in controlling spruce budworm populations than predicted, much remains to be learned about their role in forest pest control. I also examined spider community assemblages in three different forest stands. Deciduous stands had greater spider abundance and species richness than coniferous and mixedwood stands, but diversity indices were similar among the three stand types. My studies provide insights into the relationship between spiders and forest ecosystems and spiders as natural enemies of a common forest pest. These findings highlight the importance of considering diversity and complexity in biodiversity management and contribute to understanding how biodiversity responds to environmental conditions and forest management practices.
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