Intermittent, headwater streams recently have been recognized as important
components of forest ecosystems and have been provided increased protection by the
Northwest Forest Plan. However, few studies have examined their distribution,
dynamics, and ecological roles, such as habitat for wildlife. My goal was to provide
additional information on the ecology of intermittent streams in the Pacific Northwest. I
examined and compared hydrologic, water quality, and physical characteristics of 16
intermittent streams in old-growth and young forest stands in the central Cascade Range
in western Oregon. I documented amphibian communities and habitat associations in
these streams during spring and summer. I used comparisons of current habitat
conditions and amphibian communities between stand types to gain insight into potential
impacts of timber harvesting on these stream systems.
Of the streams surveyed in old-growth and young forest stands, relatively few
(23%) were designated as intermittent based on my definition which included presence of
a definable channel, evidence of annual scour and deposition, and lack of surface flow
along at least 90% of the stream length. Intermittent streams in old-growth stands
exhibited the following characteristics: (1) annual flow pattern in which streams started
to dry in May and June and were mostly dry by July; (2) lengthy annual flow durations
(range 6-11 months); (3) cool and stable daily stream temperatures; (4) primarily coarse
substrates, such as cobbles and pebbles; (5) streamside vegetation comprised of
predominantly coniferous overstories, and plant species associated with uplands or dry
site conditions, such as Oregon-grape and salal, as well as riparian areas or wet site
site conditions, such as Oregon-grape and salal, as well as riparian areas or wet site
conditions, such as red alder, oxalis, red huckleberry, and vine maple (Steinblums et al.
1984, Bilby 1988); and (6) low to moderate densities of large wood, mostly moderately- and
well-decayed. Study streams in young forest appeared to dry about one to two
months later than the streams in old growth but had similar annual flow durations. They
also were characterized by higher daily stream temperatures, similar diel fluctuations,
finer substrates, more deciduous overstory and herbaceous understory cover, and lower
densities of moderately-decayed large wood. Differences in habitat conditions between
stand types may be attributed to timber harvesting as well as discrepancies in
physiographic and geological factors, such as elevationgradient, and soil type.
Amphibian communities in spring and summer were comprised primarily of the
Cascade torrent salamander (Rhyacotriton cascadae), Dunn's salamander (Plethodon
dunni), and Pacific giant salamander (Dicamptodon tenebrosus). Amphibian
communities in streams in young forest stands exhibited different species composition
and seasonal patterns in total density from those in old growth. Cascade torrent
salamanders and Dunn's salamanders maintained similar densities and biomass between
spring and summer by potentially adopting drought avoidance strategies. Species
differed in their use of habitat types and associations with habitat features. In general,
amphibian species were positively correlated with percent surface flow, water
depth, intermediate-sized substrates and negatively associated with overstory canopy
cover, elevation, and wood cover.
Results of my study suggest that intermittent streams may warrant protection for
their potential effects on downstream habitat and water quality and for their role as
habitat for aquatic species, such as amphibians. Streamside vegetation should be
maintained along intermittent channels to provide shade protection for water temperature
regulation and sources of large woody debris and other allochthonous energy input, to
help stabilize slopes, and to minimize erosion and sedimentation. At a minimum,
intermittent stream channels should receive protection from physical disturbance during
timber harvesting operations. However, since intermittent stream systems are highly
variable, management should address individual site conditions and vary accordingly. / Graduation date: 1997
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/34085 |
| Date | 03 February 1997 |
| Creators | Lee, Yu Man |
| Contributors | Collopy, Michael W. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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