| Abstract: | In semiarid regions such as the Great Basin, riparian areas function as oases of cooler and more stable microclimates, greater relative humidity, greater structural complexity, and a steady flow of water and nutrients relative to upland areas. These qualities make riparian area‘s attractive not only to resident and migratory wildlife, but also to visitors in recreation
areas such as Great Basin National Park in the Snake Range, east-central Nevada. To expand upon the system of ten permanent plots sampled in 1992 (Smith et al. 1994) and 2001 (Beever et al. in press), we established a collection of 31 cross-sectional transects of 50-m width across the mainstems of Strawberry, Lehman, Baker, and Snake creeks. Our aims in this research were threefold: a) map riparian vegetative communities
in greater detail than had been done by past efforts; b) provide a monitoring baseline of hydrogeomorphology; structure, composition, and function of upland- and riparian-associated vegetation; and edaphic properties potentially sensitive
to management; and c) test whether instream conditions or physiographic variables predicted vegetation patterns across the four target streams. In each of the four watersheds, we performed walking transects from the lower-elevation boundary of the park along creek mainstems to a point well above the point at which vehicle
access stopped. In these transects, we ranked, by cover, the riparian and upland woody species on each side of the creek, in 0.32-km segments. These walking transects also facilitated selection of a suite of cross-sectional transects that might serve as an early-warning signal of change for natural (e.g., aggradative)
and anthropogenic changes (e.g., due to visitor impacts or climate change). At each cross-sectional transect, we used several methods: a) measurement of the number, approximate
volume, and total length of instream logs greater than 10 cm in diameter that were within 5 m up- or downstream of the transect; b) counts of pebbles by size class, following
Wolman (1954); c) line-point intercepts, which provided various measures of percent cover; d) gap-intercept transects, following Herrick et al. (in press), to measure susceptibility of uplands to erosion by wind or water; e) 1-m2 quadrats, to obtain frequency of woody species; f) nested-frequency plots, to measure frequency of all plant species in quadrats of varying
size; g) a field-based soil aggregate stability test following
Herrick et al. (2001); and h) an impact penetrometer, to measure penetration resistance of soil horizons. We used species-accumulation curves to assess the ability of our methods to detect the majority of plant species at sites, using the most species-rich and species-poor sites as illustrations.
We compared characteristics of hydrogeomorphic valley types (designated by Frissell and Liss 1993), vegetation types, and creeks individually and, using multivariate analyses for the first two >types,‘ simultaneously. For the latter, using both the nested-frequency and 1-m2 frequency data, we first used nonmetric multidimensional scaling (NMS) to assess relationships
of plant communities among sites. Secondly, we used multi-response permutation procedures (MRPP) to test whether plant-community differences existed among either hydrogeomophic valley types or vegetation types. To increase the value of these comparisons for management, we used indicator
species analyses to quantify the indicator value of each individual plant species for separating groups. In contrast to the more incised riparian channels of central
Nevada, we observed knickzones, downcutting, and incision
only rarely and usually with limited extent in the walking surveys. Downcutting occurred most frequently and extensively
in Strawberry and Snake creeks, due in part to their more erodible soils. According to a hydrogeomorphologist with extensive experience in Great Basin riparian systems, the sediment-delivery and hydrologic systems appea |
| Citation Search Results Text: | Integrated monitoring of hydrogeomorphic, vegetative, and edaphic conditions in riparian ecosystems of Great Basin National Park, Nevada; 2004; SIR; 2004-5185; Beever, Erik A.; Pyke, D. A. |
