Influence of disturbance on insect communities in Pacific Northwest streams

Abstract

Coniferous forests of the Pacific Northwest provide a unique setting for stream ecology research because of the great age of the forests and the important role of wood debris in structuring aquatic systems. The composition and diversity of the insect community in Mack Creek, a stream in a 450 yr conifer forest, was compared with that in Grasshopper Creek where it flowed through a recent cleat-cut, and at Quartz Creek, which had a 40 yr deciduous canopy. Of the 256 taxa identified, Mack Creek had the highest species richness (196) and evenness. The open site had 191 taxa but high dominance of a few grazer taxa. The deciduous-canopy site had 165 taxa with abundant detritivores. Despite differences in density, the biomass of emergence was similar at the three sites, ranging from 1.53 to 1.65 g rnp2 yr-'.The importance of disturbance in structuring stream communities was demonstrated in phenomenological studies after a debris torrent at Quartz Creek, and by monitoring stream recovery following the eruption of Mt. St. Helens in 1980. At Quartz Creek, the debris torrent eliminated the fauna from a 300 m reach, but there was rapid recovery. Emergence density in the same year was similar to that of the control site. The major shift in populations was a decrease in detritivores and moss associates and an increase in grazers, especially Baetis mayflies.At Ape Creek on Mt. St. Helens, over 200 taxa were recorded by 1987 but most occurred in very low densities. This site is reset by winter freshets and by infilling with glacial fines in the summer so the fauna continues to be dominated by weedy, or early successional species. At Clearwater Creek, the presence of wood debris as a stable substrate and limited inputs of fine sediment after 1980 have hastened population recovery. A decade after the eruption this site can be characterized as being in the mid-stages of succession with high insect productivity from an algal-based food web. With further growth of the riparian vegetation I predict a shift towards a detritus-based food web and fauna more similar to Mack Creek than it is at present. IntroductionTeam) developed as a group of researchers studying factors affecting the structure and function of Interdisciplinary ecological research in the Conifstream ecosystems. With biologists, hydrologists, erous Forest biome received a major boost from geomorphologists, and foresters involved, there the IBP funding in the early 1970's. The Stream was a broad perspective on the watershed level, Team at Oregon State University (OSU Stream echoing the approach advocated by Hynes (1975)

Biological traits and community patterns of Trichoptera at two Patagonian headwater streams affected by volcanic ash deposition

“…This also has been reported for other volcanically impaired streams (Anderson and Wisseman 1987;Anderson 1992;Dorava and Milner 1999;Collier et al 2002). Moreover, significant changes in Trichoptera richness and density of some functional feeding groups were associated with the ashfall event.…”

“…Anderson (1992) also observed that the increases in density, biomass, and diversity after a volcanic episode (Mt. Saint Helen) were related with the stabilization of stream bed.…”

“…Despite that many studies having attempted to describe the effects of volcanic ash deposition on aquatic environments, few of them support their comparisons with pre-eruption data (Anderson 1992;Antos and Zobel 2005). During 2007 to 2008, we were conducting a research on the life history of Trichoptera species inhabiting Nant y Fall and Chiquito Streams when the eruption of the Chaitén volcano occurred (May 2008).…”

Natural and Anthropogenic Disturbance Influences on Aquatic Biological Diversity in the Pacific Northwest

“…Interestingly, eight years after disturbance related to the Mt. St. Helens volcanic eruption richness was high (200 species) but most taxa were uncommon [23]. Rare taxa may be the main biological basis of disturbance responses.…”

Archaic black flies and ancient forests: Conservation of Parasimulium habitats in the Pacific Northwest

“…The topography and climate of the CRG is strikingly varied, which presumably has contributed to the diverse and distinct biota. The geological history of the CRG is equally complex, including Miocene and younger lava flows and massive post-glacial landslides and catastrophic floods (Allen, 1984;Baker and Bunker, 1985;Allen and Burns, 1986;Orr et al, 1992). These and more recent hydrological and climatic events have played a significant role in the formation and structure of the CRG's Parasimulium habitats.…”