|Abstract or Summary
- Recent studies of headwater streams have demonstrated their importance to overall watershed biodiversity, nutrient cycling, and energy flux. However, little attention has been paid to long-term effects of forest harvest on macroinvertebrate communities in headwater streams. This study investigated headwater stream macroinvertebrate communities in the H.J. Andrews Experimental Forest, Oregon, U.S.A and used a paired-stream study design to examine the effect of prior forest harvest on stream macroinvertebrates. Concomitantly, this study examined how macroinvertebrate life-history traits were related to stream size, substrates, discharge, or water temperature.
Results from this study suggest that neither richness nor densities differed between streams flowing through young growth versus old growth forests. Despite similarities among these metrics, multivariate ordination techniques helped elucidate differences in benthic community composition between paired streams when red alder was present in riparian zones of previously harvested basins. Indicator Species Analysis of community composition and abundance revealed that no taxa were exclusively indicative of either forest type.
Macroinvertebrate life-history traits among headwater streams were related to stream size, stream substrates, or stream discharge. As predicted, macroinvertebrates that ingest leaf litter (shredders) decreased proportionally with increasing stream width, while macroinvertebrates that scrape off algae and biofilms from instream substrates (scrapers) increased with increasing stream width. Differences in macroinvertebrate habit-trait groups were related to differences in stream substrates or stream discharge between very small headwater streams (< 20ha basin area) and larger headwater streams (50-100ha basin size). Seasonal variation in stream discharge also influenced macroinvertebrate communities.
Patterns in adult insect emergence in these streams displayed pulses of activity that varied among streams. During summer 2003, total emergence was greatest in one high elevation stream in this study. During spring 2004, total emergence began earlier in one low elevation and one mid elevation stream, but linkages with stream water temperature were tenuous; cumulative emergence remained higher in these streams than all others through early summer 2004.
Though forest harvest often has immediate effects on macroinvertebrate communities, shifts in community composition may persist long-term if regrowth of riparian vegetation includes red alder (Alnus rubra). Analyses of macroinvertebrate life-history traits provided insight regarding species adaptations to environmental conditions. Among six headwater streams within a relatively small landscape (6400ha), proportions of stream macroinvertebrate communities with specific traits differed among streams relative to variability in physical stream attributes.