Cross-ecosystem effects of a large terrestrial herbivore on stream ecosystem functioning

Large terrestrial consumers have direct and indirect effects on forest ecosystem function, but few studies have investigated the impacts of terrestrial consumers on freshwater ecosystems. In the Cape Breton Highlands of Nova Scotia, browsing by hyper-abundant moose has transformed boreal forest into grasslands. We investigated the potential for cross-ecosystem effects of hyper-abundant moose on small boreal stream ecosystem structure and function. We predicted that watersheds with higher levels of moose-mediated grasslands in their sub-basins would have higher stream temperatures, total nitrogen, electrical conductivity, periphyton biomass, and macroinvertebrate abundances. We found evidence of higher stream temperature range, total nitrogen, electrical conductivity and relative abundance of predatory inverts in streams with high moose impacts in their watersheds. However, we found little evidence of moose impacts on average daily maximum, average, maximum and minimum stream temperatures, periphyton biomass and the abundance of shredders, filterers, gatherers, and grazers. This empirical study fills a key gap in our understanding of meta-ecosystem ecology by providing insight into the effects of large terrestrial consumers across ecosystem boundaries with potential implications for landscape-scale management of hyper-abundant ungulates.