Out on a limb: microarthropod and microclimate variation in coastal temperate rainforest canopies

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Abstract Species richness of microarthropods in coastal temperate rainforests of western North America is enhanced by the presence of heterogeneous arboreal habitats (moss mats). We studied the relationship between species traits and microclimate as a structuring mechanism for understanding this high diversity. To examine whether community composition is associated with distinct microclimate zones we used Non‐metric Multidimensional Scaling ordination of environmental and community data. To link the traits of arboreal microarthropod species with observed environmental variables we used a trait‐based approach of RLQ and fourth‐corner analysis. Distinct microclimatic zones were observed in the canopy ecosystem stemming from gradients of moisture, temperature, and climatic stability associated with height in canopy and distance from trunk. Associated with these gradients is the growth and development of epiphytic bryophytes such as moss mats and suspended soils, which in turn, influence canopy microclimates. Microarthropod fauna displayed a community‐level response to microclimate gradients which was mediated and partially explained by a trait‐based analysis. A general decline in species richness was associated with harsher microclimate conditions. While many species possessed desiccation resistance traits under low‐moisture conditions, we posit that other species were able to persist by compensatory movements at very small spatial scales. In conclusion this study highlights the importance of environmental buffering associated with greater epiphytic biomass for preserving canopy microarthropod biodiversity, but also how developing an understanding of the species trait distributional shifts can enhance our understanding of communities under different environmental conditions, and for predicting future communities under global environmental change.