Changes in riparian vegetation along the Colorado River and Rio Grande, Colorado

Changes in vegetation including area occupied, canopy cover, and maturity class of cottonwoods ( Populus spp.) within lower-elevation zones of the Colorado River and Rio Grande in Colorado were monitored over 25- and 27-year intervals, respectively, using photo-interpretative methods. Estimated loss of cottonwoods along the Colorado River was 2ha/km (-17.5%), and remaining stands had become more open and older. Cottonwoods along the Rio Grande increased 1.6 ha/km (9.3%) with minor canopy cover and maturity class changes. Area occupied by shrubs and river channel changed little along the Colorado River, but declined along the Rio Grande. Loss of hay meadow occurred along both rivers, whereas developed land increased along the Colorado River and farmland increased along the Rio Grande. Wildlife habitats along the Colorado deteriorated much more rapidly than those along the Rio Grande during monitored intervals.     

Classification of the riparian vegetation along a 6-km reach of the Animas River, southwestern Colorado

Riparian ecosystems are important components of landscapes, particularly because of their role in biodiversity. A first step in using a ""coarse-filter"" approach to riparian biodiversity conservation is to determine the kinds of riparian ecosystems. These ecosystems vary substantially in plant species composition along a single river reach, as well as between rivers, and yet the river-reach scale has received little attention. We sampled the vascular plant composition of 67 contiguous patches of riparian vegetation along the reach of the Animas River, in southwestern Colorado's San Juan Mountains, that is relatively undisturbed by human land uses. Using cluster analysis and detrended correspondence analysis, we identified eight riparian community types along the reach. Using a new technique, we combined overstory size-class data and understory cover data to identify community types. The eight community types, which are in part the products of past floods, are spatially arranged along the reach in relation to variation in valley morphology, tributary location, and geomorphic landforms. These eight community types do not necessarily represent successional stages of a single potential vegetation type. This study at the river-reach scale suggests that sampling and analysis, as well as conservation, may need to be turned to the scale of patchiness produced by flood disturbances in the riverine landscape, since vegetation varies significantly at this scale.     

Transverse and longitudinal variation in woody riparian vegetation along a montane river

This study explores how the relationship between flow and riparian vegetation varies along a montane river. We mapped occurrence of woody riparian plant communities along 58 km of the San Miguel River in southwestern Colorado. We determined the recurrence interval of inundation for each plant community by combining step-backwater hydraulic modeling at 4 representative reaches with Log-Pearson analysis of 4 stream gaging stations. Finally, we mapped bottomland surficial geology and used a Geographic Information System to overlay the coverages of geology and vegetation. Plant communities were distinctly arrayed along the hydrologic gradient. The Salix exigua Nuttall (sandbar willow) community occurred mostly on surfaces with a recurrence interval of inundation shorter than 2.2 years; the Betula occidentalis Hooker (river birch) community peaked on sites with recurrence intervals of inundation between 2.2 and 4.6 years. The hydrologic position occupied by communities dominated by Populus angustifolia James (narrowleaf cottonwood) was strongly related to age of trees and species composition of understory shrubs. The fraction of riparian vegetation on surfaces historically inundated by the river decreased in the upstream direction from almost 100% near Uravan to <50% along the South Fork of the San Miguel River. In upstream reaches much of the physical disturbance necessary to maintain riparian vegetation is provided by valley-side processes including debris flows, floods from minor tributaries, landslides, and beaver activity. Where valley-side processes are important, prediction of riparian vegetation change based on alterations of river flow will be incomplete.     

Factors controlling structural and floristic variation of riparian zones in a mountainous landscape of the western United States

We examined landscape patterns in the physical conditions and vegetative composition of montane riparian zones to identify their most important sources of variation. Information on plant species cover and on physical characteristics that occur at coarse, medium, and fine scales was collected for 144 riparian plots located throughout the Lake Tahoe Basin, which straddles the California-Nevada border in the western United States. Constrained and unconstrained ordination analyses were used to identify the most important correlates of physical form and plant species composition. Through multivariate analysis of environmental variables (principal components analysis), vegetation data (detrended correspondence analysis), and the combined relationship between the environmental and vegetation data (canonical correspondence analysis), we consistently found that the greatest variation occurred along a gradient of decreasing valley width, decreasing stream sinuosity, and increasing stream slope. Although surface characteristics reflected a 2nd important source of variation in physical conditions, plant species distribution was not strongly correlated with riparian surface conditions. Strong correlations among physical variables that occur at different scales, such as between valley form and geofluvial surface and between geofluvial surface and surface conditions, support the use of a physically based hierarchical framework for organizing riparian zones within the landscape. Such a hierarchical framework would be useful for interpreting patterns in riparian structure and process at different scales and could be applied to riparian zones in other mountain landscapes of the western United States and elsewhere. Moreover, our finding that riparian plant species composition is most strongly correlated with environmental variables that occur at coarse to moderate scales, most of which can be derived from existing data, supports the idea that modeling montane riparian community distribution using topographic and remotely sensed data could be useful; however, a large degree of species variation, unexplained by the variables we collected, indicates that other variables, perhaps disturbance regime, should be included in such a venture. Nomenclature: Hickman (1993).     

Persistence of subalpine forest--meadow ecotones in the Gunnison Basin, Colorado

Forests of the southern Rocky Mountains are punctuated by persistent meadows called parks that are dominated by grasses and forbs. In an attempt to elucidate the maintenance of subalpine parks in the Gunnison Basin, Colorado, soil texture and tree morphology differences along 60-m transects spanning the forest-park ecotone were studied in 6 representative parks. Seedling survivorship, percent seed germination, and soil moisture available to plants were also studied along one of the transects in Willow Park. Soil analyses revealed 40% more silt and significantly less sand and clay in all 6 parks ( P P = 0.011), with 54% more water in forest than in park soils. Measures of growth rate obtained from tree height, dbh, and age were significantly higher nearer the ecotone ( P P = 0.002). These results suggest that stress of mature Engelmann spruce ( Picea engelmannii ) and lodgepole pine ( Pinus contorta ) is an unlikely explanation of park maintenance. P. engelmanii percent seed germination and seedling survivorship were significantly higher in the forest than in the park ( P < 0.001). This may be largely due to the more severe seedling microclimate observed in the park. Results indicate that limited seedling establishment is primarily responsible for maintenance of subalpine parks in the Gunnison Basin.     

A preliminary classification of the natural vegetation of Colorado

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} A classification of the natural vegetation of Colorado is presented. This classification, which uses the Plant Association as the basic unit, was developed by sorting data in the scientific literature, supplemented by field research. The classification uses a standardized nomenclature. Citations are given for the literature from Colorado and adjoining states for each Association. The classification includes a total of 403 Plant Associations, with 28 Angiosperm Forests/Woodlands, 2 Mixed Angiosperm&ndash;Gymnosperm Forests/Woodlands, 114 Gymnosperm Forests/Woodlands, 100 Shrub Associations, 74 Grassland Associations, 38 Graminoid Associations, and 47 Herb Associations.     

Monitoring temporal change in riparian vegetation of Great Basin National Park

Disturbance in riparian areas of semiarid ecosystems involves complex interactions of pulsed hydrologic flows, herbivory, fire, climatic effects, and anthropogenic influences. We resampled riparian vegetation within ten 10-m × 100-m plots that were initially sampled in 1992 in 4 watersheds of the Snake Range, east central Nevada. Our finding of significantly lower coverage of grasses, forbs, and shrubs within plots in 2001 compared with 1992 was not consistent with the management decision to remove livestock grazing from the watersheds in 1999. Change over time in cover of life-forms or bare ground was not predicted by scat counts within plots in 2001. Cover results were also not well explained by variability between the 2 sampling periods in either density of native herbivores or annual precipitation. In contrast, Engelmann spruce ( Picea engelmannii ) exhibited reduced abundance at all but the highest-elevation plot in which it occurred in 1992, and the magnitude of change in abundance was strongly predicted by plot elevation. Abundance of white fir ( Abies concolor ) individuals increased while aspen ( Populus tremuloides ) individuals decreased at 4 of 5 sites where they were sympatric, and changes in abundance in the 2 species were negatively correlated across those sites. Utility of monitoring data to detect change over time and contribute to adaptive management will vary with sample size, observer bias, use of repeatable or published methods, and precision of measurements, among other factors.     

Bird use of riparian vegetation along the Truckee River, Califonia and Nevada

The Truckee River in California and Nevada is subject to diverse water regimes and a corresponding variety of flow rates. Original riparian vegetation has been altered by these variable flow rates and by a variety of human uses resulting in loss of native riparian vegetation from its historic extent. We conducted bird surveys along the Truckee River during spring 193 to (1) determine relationships between birds and the present vegetation; (2) determine the importance of different vegetation types to sensitive bird species that have declined recently in the western United States due to competition from exotic plant species, cowbird ( Molothrus ater ) parasitism, reduction in nesting habitat, or other unidentified reasons; and (3) establish a monitoring program and collect baseline data for future comparisons. The most frequently detected bird species throughout the study was the Brown-headed Cowbird. The greatest number of bird species (98 of 116) was found in the native mixed willow ( Salix spp.) riparian scrub vegetation type. We recommend protecting the remaining native riparian vegetation types for bird habitat along the Truckee River.     

Soil and vegetation development in an abandoned sheep corral on degraded subalpine rangeland

Vegetation and soils inside and outside an abandoned sheep corral on degraded subalpine range of the Wasatch Plateau were studied to determine the influence of approximately 37 years' use of the corral on soil and plant development. Vegetal and surface cover were estimated. Herbage, litter, and soils were sampled inside and outside the corral and analyzed for C org , N, P, and S. Soil pH, bulk density, and C0 3 -C also were measured. Storage (mass/unit area) of C org , N, P, and S was determined for each component. Yield and vegetal composition were significantly affected inside the corral boundary. Herbage yield was 2.2 times greater, litter mass 16 times greater, foliar cover of grasses 2 times greater, and forb cover 70% lower inside than outside the corral. Cover of meadow barley ( Hordeum brachyantherum ), a component of the predisturbance vegetation of the Wasatch Plateau, was nearly 12 times greater inside than outside the corral. These and other vegetal and cover differences reflect inside-outside differences in concentration, storage, and availability of soil C org , N, P, and S. Concentrations of C org and total and available N, P, and S were greater in the surface 5 cm of soil inside the corral. Available P inside the corral was much higher in all soil layers. Because of bulk density differences, storage was greater inside the corral only for C org and N at 0-5 cm and for P at 5-15 cm. Lower soil pH inside the corral appears related to soil P distribution and C0 3 -C storage. Results suggest a need to reexamine earlier conclusions that tall forbs are the climax dominants of the Wasatch summer range.     

Late Quaternary vegetation and climate in the Escalante River Basin on the central Colorado Plateau

Five alcoves (rock shelters) in the Forty-Mile Canyon—Willow Gulch area of the Escalante River Basin in southeastern Utah yielded rich deposits of late Quaternary macrobotanical remains. The deposits were sampled and the contents identified in order to construct a chronology of vegetational change. Fourteen radiocarbon dates indicate that the fossils were deposited between 12,690 and 7510 yr B.P. (years before present). Ninety-one plant taxa were identified, 62 to species. Six species were common to all alcoves: Gambel oak ( Quercus gambelii ), box-elder ( Acer negundo ), prickly pear ( Opuntia subgenus Platyopuntia), skunkbush ( Rhus aromatica var. trilobata ), serviceberry ( Amelanchier utahensis ), and Indian ricegrass ( Oryzopsis hymenoides ). Late Pleistocene samples (>11,000 yr B.P.) contain extralocal, elevationally depressed species such as Douglas fir ( Pseudotsuga menziesii ), spruce ( Picea sp.), and mountain mahogany ( Cercocarpus ledifolius ), and mesophytic species such as rose ( Rosa woodsii ) and water birch ( Betula occidentalis ). Early Holocene samples (11,000-8000 yr B.P.) contain no elevationally depressed conifers, and the remaining mesophytic species decrease in relative abundance. Reticulated hackberry ( Celtis reticulata ) becomes common. The terminal Early Holocene sample (8000-7000 yr B.P.) contains abundant Gambel oak and prickly pear, but little else. Paleoclimatic interpretations for the Late Pleistocene correspond well to those of most other workers on the Colorado Plateau. Climates that were wetter and at least seasonally cooler than they are today are inferred from the macrobotanical assemblage. However, the increased moisture is attributed to higher stream base levels and increased groundwater rather than directly to increased precipitation. Early Holocene climates are interpreted as warmer and drier than those of the Late Pleistocene but still wetter than the present climate. Groundwater levels appear to be decreasing due to stream entrenchment. Terminal Early Holocene climates were much warmer and at least seasonally drier. By the end of the period, groundwater levels had decreased so much that the alcoves were unable to sustain plant communities; stream base level was probably near the present level.     

Tundra vegetation of three cirque basins in the northern San Juan Mountains, Colorado

The vegetation of three alpine cirque basins in the northern San Juan Mountains of southwestern Colorado was inventoried and analyzed for the degree of specificity shown by vascular plant communities for certain types of habitats identified as representative of the basins. A total of 197 vascular plant species representing 31 families was inventoried. Growth forms of all species were noted and a growth form spectrum for all of the communities was derived. The caespitose monocot and erect dicot growth forms are the most important growth forms among the community dominants. The most common growth form among all species is the rosette dicot. &nbsp;&nbsp; &nbsp;&nbsp;     

Long-term vegetation dynamics in a cut western juniper woodland

Western juniper ( Juniperus occidentalis spp. occidentalis Hook.) expansion in the northern Great Basin has reduced shrubsteppe productivity and diversity. Chainsaw cutting of western juniper woodlands is commonly applied to remove tree interference and restore sagebrush plant communities. Studies assessing understory response following cutting have been limited to early successional stages and have not evaluated the effects of western juniper debris on plant succession. Cutting western juniper produces a large amount of debris which is commonly left on site, occupying a significant portion of treated areas. This study evaluated successional dynamics spanning 13 years after western juniper cutting. Four 0.45-ha blocks were selected on Steens Mountain in southeastern Oregon. Western juniper cover averaged 26% and mature tree density averaged 250 trees ? ha –1 . Blocks were cut in late summer 1991. Understory standing crop, cover, and density were compared among 3 locations: old canopy litter mats (canopy), interspace, and area underneath cut western juniper (debris). In the interspace, perennial grasses increased in cover and in standing crop relative to other functional groups. In canopy and debris locations, species composition shifted in the 6th year after cutting as annual grass cover, density, and standing crop increased. However, by 2003, perennial grass biomass was 2 times greater than annual grass biomass in canopy and debris locations. Because annual grasses increased in areas of debris accumulation, managers need to be cognizant of western juniper treatments that create safe sites that are favorable to the establishment of weedy species. Retaining western juniper debris on this site did not increase establishment and growth of perennial grasses compared to the interspace. A shift in perennial grass dominance from Thurber's needlegrass ( Achnatherum thurberianum [Piper] Barkworth) to bottlebrush squirreltail ( Elymus hystrix [Nutt.] Smith) occurred in areas of debris accumulation. Our results demonstrated that long-term vegetation evaluations are necessary to properly assess management activities and disturbance.     

Establishment, growth, and early survival of woody riparian apecies at a Colorado gravel pit

Presence of a wetted edge during the period of seedfall was an effective predictor of suitable establishment (defined as germination and survival to the 1st autumn) locations for Populus deltoides subsp. monilifera, Salix amygdaloides, S. exigua, and Tamarix ramosissima seedlings during 3 successive years of a gravel pit revegetation project in Fort Collins, Colorado. At locations predicted to be suitable for establishment, position within the pit (possibly reflecting additional moisture provided by seepage) was a significant factor in determining whether establishment actually occurred. Cover of herbaceous species, which became established at the same time as, or after, woody seedlings, was positively related to probability of establishment for 8 of 11 species-year combinations, probably reflecting more favorable moisture conditions at certain locations. Herbaceous cover also was positively related to seedling height at the end of the 1st summer of growth for 9 of 11 species-year combinations. Neither establishment nor 1st-summer growth was consistently related to overall decline in the water table as estimated by the drop in surface-water level during the growing season. Flooding in the 1st spring after establishment was negatively related to subsequent survival for 5 of 8 species-year combinations. The 4 species established at different elevations in the pit, depending on location of the wetted edge during the period of seedfall, and there was no evidence that differential mortality subsequently altered their distribution along the elevation gradient. However, the primary objective in this study was to restore native woody species, and we attempted to maintain conditions conducive to meeting this objective. Differential postestablishment mortality may be more important in structuring the riparian community in more rigorous riverine environments.     

Microhabitat partitioning by two chipmunk species ( Tamias ) in western Colorado

We examined microhabitat use of sympatrically occurring Tamias minimus (least chipmunk) and T. rufus (Hopi chipmunk) in a pi?on-juniper/sagebrush vegetative community near Molina, western Colorado, from October 1994 to June 1999. This community is dominated by 2 major microhabitat types: shrub (sage; Artemisia spp.) and tree (pine and juniper; Pinus edulis and Juniperus scopulorum ). Small mammals were live-trapped, marked, and released throughout this study. When it was the most abundant Tamias species on the study plots (1994-1997), Tamias minimus captures were associated with trees. Tamias rufus also exhibited this association but was captured at very low abundances during this period. Tamias rufus abundance was much greater, on average, than that of T. minimus between 1998 and 1999. During this time T. minimus captures were not associated with trees, but T. rufus captures remained associated with trees. As has been previously reported for other Tamias species, the greater abundance of 1 of 2 coexisting congeners in select areas may play a role in the microhabitat use of these 2 chipmunk species.     

Home range of the western jumping mouse, Zapus princeps, in the Colorado Rocky Mountains

Western jumping mice, Zapus princeps, were live - trapped during the summer of 1975 in an aspen forest in the Front Range of the Colorado Rocky Mountains. Home range sizes were calculated using the exclusive boundary strip method, and it was discovered that males had larger home ranges (298 &ndash; 3315 m 2 , x = 1743 m 2 ) than females (680 &ndash; 1275 m 2 , x = 1041 m 2 ). Mean range length was 96.5 m for males and 78.5 m for females. Spatial relationships showed that females tended to be more territorial than males, based on the females' higher percentage of exclusive home ranges, greater distance between centers of activity, and more uniform spacing.     

Presettlement vegetation of part of northwestern Moffat County, Colorado, described from remnants

A general botanical inventory of a part of northwestern Moffat County, Colorado, resulted in the location of &ldquo; remnants &rdquo; of the presettlement vegetation spectrum that are largely unaltered by grazing, logging, or other recent human - related land uses. The 69 samples taken from these remnants were classified into 22 plant associations. Composition, structure, environmental location, geographical range, and response to disturbance are discussed for each association, and a photograph of each is presented. Seven of the 22 associations are apparently restricted to the study area. Restricted associations occur in the more extreme environments of the study area, such as on calcareous substrata or very xeric sites. More mesic sites along ephemeral creeks, on north - facing slopes, or on sandstones support plant associations that have much wider ranges, many of them extending across the northern Great Basin. &nbsp;&nbsp;     

New species of oribatids from western Colorado (Acarina: Cryptostigmata, Suctobelbidae)

A new species of Suctobelba, S. tumulata, and a new genus and species, Parisuctobelba septenia, are described from collections of oribatids taken in coal strip-mining spoil banks near Hayden, Colorado. The new species are compared with members of the family from North America and Europe. The new genus is differentiated by a smooth, narrowed sensillum and seven pairs of genital setae. Taxonomic and ecological data are also discussed.     

Incidence of the leech Helobdella stagnalis on the Colorado River in west central Colorado

Fifty-seven fish of three genera were taken from the Colorado River in west central Colorado and examined for external parasites. No external parasites were found on Ictalurus. Seven percent of the Hybognathus and 100 percent of the Catastomus were infected with a Hirudinean of the species Helobdella stagnalis. &nbsp;&nbsp;