Macroinvertebrate community response to riparian red alder within headwater streams of second-growth forests in southeast Alaska

Recent declines in Pacific Northwest salmon returns and the subsequent loss of in-stream nutrients have increased consideration for watershed restoration practices to include Red alder (Alnus rubra Bong.). Red alder is an aggressive pioneer species that colonizes disturbed soils, particularly within riparian corridors of young-growth forests following clearcut timber harvesting. Although riparian red alder appears to add nutrients to aquatic ecosystems, the thinning and removal of alder within regenerating forests is still practiced. In an effort to improve scientific knowledge about the ecological role of red alder on aquatic ecosystems, we compared benthic macroinvertebrate colonization of wood substrates among 13 headwater streams with a range riparian alder (0--53%). Research was conducted within the Maybeso Creek and Harris drainages on eastern Prince Of Wales Island, southeast Alaska. Alder wood, especially pieces in more advanced decay, generally supported greater density and diversity of macroinvertebrates than did conifer wood. Collectors and shredders responded to the presence of riparian alder, and streams with more alder in riparian habitats produced greater mean macroinvertebrate density and biomass. Results from this study suggested that the presence of alder along headwater corridors enhances macroinvertebrate productivity and may subsidize lost nutrients within Pacific Northwest watersheds, thus managing forested uplands to include red alder should be considered as a management tool to improve salmonid production.