The importance of multiple processes and instream factors to aquatic biota has been explored extensively, but questions remain about how local spatiotemporal variability of aquatic biota is tied to environmental regimes and the geophysical template of streams. We used an individual-based trout model to explore the relative role of the geophysical template versus environmental regimes on biomass of trout (Oncorhynchus clarkii clarkii). We parameterized the model with observed data from each of the four headwater streams (their local geophysical template and environmental regime) and then ran 12 simulations where we replaced environmental regimes (stream temperature, flow, turbidity) of a given stream with values from each neighboring stream while keeping the geophysical template fixed. We also performed single-parameter sensitivity analyses on the model results from each of the four streams. Although our modeled findings show that trout biomass is most responsive to changes in the geophysical template of streams, they also reveal that biomass is restricted by available habitat during seasonal low flow, which is a product of both the stream’s geophysical template and flow regime. Our modeled results suggest that differences in the geophysical template among streams render trout more or less sensitive to environmental change, emphasizing the importance of local fish–habitat relationships in streams.

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.

Little is known on the importance of riparian areas to birds near small headwater streams in mesic forests. Progress towards understanding limiting factors that affect bird populations has been difficult because of lack of information beyond the breeding period. I compared bird assemblages between headwater riparian and upland areas throughout the post-breeding period by capturing birds using mist-nets in six paired riparian and upland locations along six headwater streams of the Trask River in northwestern Oregon. In order to assess whether birds prefer headwater riparian areas, I also examined factors affecting habitat selection by juvenile Swainson's thrushes (n=37) using radio telemetry. While riparian and upland locations had similar coarse wood volume and fruiting and tall (> 1.3 m tall) shrub cover, riparian locations had less shrub cover (< 1.3 m tall) and different shrub composition than upland locations. Total capture rate was double that of upland in riparian locations, while bird species richness was similar. Similar numbers of birds were captured in mist-nets oriented perpendicular and parallel to the stream suggesting that birds were not using riparian areas as movement corridors. Adult capture rate was greater in riparian locations than adjacent uplands while results of juvenile capture rates were ambiguous. Riparian locations supported higher capture rates of Swainson's thrushes and winter wrens than adjacent uplands.

This document presents brief portraits of various aspects of the Trask River study area. For each portrait, there is more information that can be derived from it however, in an effort to at least provide an initial look at the watershed the narrative was kept brief. For example, the section on geomorphology is evolving with the linkage of the terrain map with the channel gradient map to help us predict where we would expect to find more sediment accumulation. This contextual analysis is meant to help bound expected responses to management given the physical and biological template of the watershed. In the next installment I will look in more detail at the small catchments and how they vary. Some of the salient features of the physical and biological Trask Study landscape are summarized below with the more detailed sections following.