Conservation of biodiversity is a major issue in ancient temperate rainforests of British Columbia. While significant efforts have been made to document species of birds and mammals, little is known about canopy arthropod communities in British Columbia. Microhabitats (suspended soils) within canopy systems of temperate rainforests support diverse microarthropod communities, dominated by mites of the suborder Oribatida. These oribatid mite communities are distinct from forest floor communities, contribute significantly to overall forest biodiversity, and are functionally important components of forest ecosystems.
I used the suspended soil system in western redcedar trees in the Walbran Valley to study the relative importance of local environmental factors versus regional spatial factors contributing to the community structure of arboreal oribatid mite communities, and compare these patterns to forest floor oribatid mite communities at the same study location. An array of sampling methods was used to complete these objectives: substrate core samples, bark scrapings, colonisation of litterbags, litterfall trap collection, and colonisation of artificial canopy habitats.
This study identified 138 species of oribatid mites associated with ancient western redcedar trees of the Walbran Valley on Vancouver Island. The documented patterns of oribatid mite diversity in this rainforest demonstrated higher local species richness (alpha diversity) in terrestrial (forest floor) habitats, and greater beta diversity in arboreal (suspended soil) habitats. The oribatid mite community within suspended soils are formed primarily by dispersal patterns and colonisation within the canopy system, with limited colonisation from the forest floor.
The factors, which shape canopy oribatid mite communities within suspended soils, are related to habitat availability, moisture limitation and random dispersal events of individual species. My results suggest the arboreal oribatid mite community experiences regional dispersal limitation associated with physical tree-to-tree dispersal barriers. However, factors other than physical dispersal barriers, such as aggregation and niche partitioning, likely also limit the local distribution of species in both arboreal and terrestrial habitats. I conclude that stochastic dispersal dynamics within the canopy are crucial to understanding oribatid mite community structure in suspended soils, but that the relative importance of stochastic dispersal assembly is dependent on a strong deterministic element to the environmental tolerances of individual species, which drives non-random patterns of community assembly.