| dc.description |
Thirteen different habitat parameters were measured either quantitatively or
qualitatively around seven different Salix (willow) species on a defined reach of stream
on the southwestern slope of Steens Mountain in southeastern Oregon in order to both
broaden the current information base of riparian ecology and inform future willow
plantings aimed at improving riparian habitat. Willow species included in the research
were: S. lemmonii (Lemmon willow), S. scouleriana (Scouler willow), S. boothii (Booth
willow), S. geyeriana (Geyer willow), S. exigua (coyote willow), S. lasiandra (whiplash
willow), and S. lutea (yellow willow). The habitat parameters measured were: height and
distance of willow individual from stream channel bankfull elevation, stream channel
slope, entrenchment ratio, width-to-depth ratio, watershed elevation, valley azimuth,
valley width, soil rock size distribution, soil texture, and winter air temperature. Logistic
regression models were built to describe probabilities of occurrence for five out of the
seven willow species based on the habitat data collected. Multi-response permutation
procedures were performed to describe differences between respective willow habitats.
Booth and Geyer willow habitats were best described by watershed elevation as these
species dominated the research stream channel’s upper reaches. Whiplash willow habitat
was best described by stream channel entrenchment and width-to-depth ratio as this
species occurred, on average, in habitats with high stream channel entrenchment and
width-to-depth ratios. Specifically, the odds of whiplash willow occurrence are expected
to increase by 17% with a unit increase in width-to-depth ratio. Yellow willow habitat
was best described by watershed elevation and stream channel width-to-depth ratio as this
species occurred only on the lower reaches of the research stream channel. Lemmon
willow habitat was best described by interactions between watershed elevation and valley
azimuth and between stream channel slope and width-to-depth ratio as the first of these
interactions worked to create air temperatures favorable for species occurrence. Coyote
willow habitat was best described by stream channel slope, entrenchment, and width-todepth
ratio as this species occurred, on average, in habitats with combinations of stream
channel slopes, entrenchment, and width-to-depth ratios able to promote frequent
streambank rejuvenation. Scouler willow habitat was best described by stream channel
entrenchment ratio, as well as interactions between watershed elevation and valley
azimuth and between stream channel slope and width-to-depth ratio. Specifically, the
odds of Scouler willow occurrence are expected to decrease by 89% with a unit increase
in entrenchment ratio. Scouler willow, on average, occurs in habitats with air
temperature dynamics similar to those described above for Lemmon willow, and on
hydraulically efficient stream channels with low entrenchment and width-to-depth ratios. |
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