College of Forestry
Harvest
Long-term Studies of Macroinvertebrate Responses to Harvest
Apr-18-2013
Our studies of stream invertebrate responses to contemporary timber practices compared treated to control sites prior to and following harvest at Hinkle, Alsea and upper Trask watersheds. In each watershed the BACI study design and robust replication has been crucial in accounting for natural variations in macroinvertebrate distributions while examining patterns of change in response to harvest. As these basins vary physically in association with regional and geologic differences, initially we observed distinctive invertebrate assemblage composition for each watershed. In addition the proportion of chironomid midges and total benthic densities were higher at Alsea and Trask headwaters than at Hinkle. Our ability to detect responses to harvest within basins was enhanced when we found no pre-harvest differences in macroinvertebrate densities, percent chironomids, or taxa richness between control and treatment reaches of similar size at Hinkle and Trask watersheds. However significant invertebrate community differences were observed between the two Alsea tributaries, likely due to differences in tributary sizes or other physical and chemical differences. Though benthic invertebrate densities increased at headwater sites post-harvest, there were no detectable density differences at mainstem sites. Prey consumption by trout, whose densities at mainstem sites increased following harvest, possibly explained the lack of change observed for invertebrate densities.
Setting the Landscape Context for Paired Watershed Studies in Western Oregon
Apr-01-2008
Paired watershed studies provide valuable scientific understanding of the effects of disturbance on aquatic resources. Geographic information system (GIS) tools, combined with principal components and cluster analyses, were used to develop a landscape classification of forested headwater basins in order to support these paired watershed studies. Spatial and statistical analyses were applied to landform, geologic texture, forest cover, and climate variables that describe the biophysical and climatic setting of forested headwater catchments (300 – 58,000 km2) in western Oregon. Cluster analysis isolated 5 groups that account for major differences in environmental conditions across the landscape, but have a large ratio of among to within group dissimilarity. The first and second principal component axes correlate most strongly to differences in slope and elevation, and the percent coniferous tree cover and past harvest, respectively.
Short-Term Response of Dicamptodon tenebrosus Larvae to Timber Management in Southwestern Oregon
Apr-17-2011
In the Pacific Northwest, previous studies have found a negative effect of timber management on the abundance of stream amphibians, but results have been variable and region specific. These studies have generally used survey methods that did not account for differences in capture probability and focused on stands that were harvested under older management practices. We examined the influences of contemporary forest practices on larval Dicamptodon tenebrosus as part of the Hinkle Creek paired watershed study. We used a mark–recapture analysis to estimate D. tenebrosus density at 100 1-m sites spread throughout the basin and used extended linear models that accounted for correlation resulting from the repeated surveys at sites across years. Density was associated with substrate, but we found no evidence of an effect of harvest. While holding other factors constant, the model-averaged estimates indicated; 1) each 10% increase in small cobble or larger substrate increased median density of D. tenebrosus 1.05 times, 2) each 100-ha increase in the upstream area drained decreased median density of D. tenebrosus 0.96 times, and 3) increasing the fish density in the 40 m around a site by 0.01 increased median salamander density 1.01 times. Although this study took place in a single basin, it suggests that timber management in similar third-order basins of the southwestern Oregon Cascade foothills is unlikely to have short-term effects of D. tenebrosus larvae.
