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Summary of information on the affects of seasonal movement, diel movement, winter feeding programs, and winter concentrations by wildlife on water quality (Objective 3). Foraging behavior of wildlife in different riparian habitats and the influence on water quality (Objective 4).
Objectives 3 and 4 have been addresses in a single section because of the overlapping nature of the two objectives. Wildlife foraging behavior, seasonal movement, diel movement, and winter concentrations of most of the species in Wyoming involve riparian habitats. Combining the two objectives avoids substantial redundancy in the presentation.
Activities of large ungulates grazing in both upland areas and in the riparian area influence the quantities of sediment, bacteria, and nutrients in streams (Skovlin et al. 1977). Grazing animals impact the landscape by three mechanisms: consumption of forage, trampling, and deposition of excreta (Smeins 1975).
Consumption and trampling by large ungulates reduces plant vigor and vegetative production (Winegar 1977). Decreasing vegetation negates the functions that vegetation preforms in preventing soil loss (Packer 1953). The ability of vegetation to binding soil, reduce rainsplash, and trap sediment is reduced by large ungulates.
Soil structure is changed by trampling of large ungulates (Bohn and Buckhouse 1985b). The weight of ungulates causes soil compaction which increases the bulk density of the soil and reduces infiltration rates (Rauzi and Hanson 1966). Run-off rates are altered by these changes to soil. The combination of trampling and vegetation removal by grazing ungulates changes the amount of bare soil exposed to precipitation (Packer 1953). This can result in increased amounts of soil loss to erosion (Toy and Hadley 1987).
The riparian zone impacts from ungulate activities are more profound than in the uplands because it is the last terrestrial area that run-off crosses before entering the stream (Bohn and Buckhouse 1985a). Trampling and vegetation consumption reduces the effectiveness of the riparian vegetation's ability to trap sediment from upland runoff.
When activities of ungulates make soil available for transport in the riparian zone, the soil particles have a shorter physical distance before they reach the stream, thus they are more likely to enter the stream. As in the upland, trampling in the riparian zone compacts soil, reducing infiltration rates. But because riparian soils tend to be moister due to the high water table, flatness of the floodplain, and water received from the upland, they are more prone to compaction (Bohn and Buckhouse 1985b). Soil compaction can interfere with the water storage function of riparian zones (Lowrance et al. 1985).
As with sediment delivery, dung deposition in the riparian zones means a short physical distance that it must be mobilized. Thus increasing the likelihood that it will contribute to bacteria and nutrient levels of the stream. During periods of high run-off, streams that have exceeded bank full conditions wash dung from the riparian zone, increasing the amount of bacteria (Skinner et al. 1984) and nutrients delivered to the stream.
Information regarding water quality impacts and related degradation processes caused by large ungulates (livestock and wildlife) was presented in general terms as both may cause similar impacts in upland and riparian areas and subsequently affect water quality (Claire and Storh 1977). The level of impact and processes by which impacts occur do vary depending on the type of ungulate. Specific information available on each of the major large ungulates in Wyoming is presented.
Impacts of Livestock
Studies that assess the impacts of large ungulates on water quality are more numerous for livestock than for wildlife species. In Wyoming, livestock of greatest concern regarding impacts to water quality are cattle (Bos taurus), sheep (Ovis aries) and horses (Equus caballus). Most studies are concerned with impacts caused by cattle. The terrain and diet that cattle prefer and other behavioral characteristics influence the magnitude of their impacts on water quality.
Cattle
Cattle prefer flat or gently sloping terrain (Mueggler 1965, Stevens 1966, Mclean and Williams 1982). Bryant (1982) reported that cattle prefer slopes of less than 35%, and as slope increases cattle use decreases. In a study in north-central Montana, Allen (1968) reported that cattle utilized bottomlands in all seasons.
Cattle primarily graze on graminoid species when available (Hansen and Reid 1975, Hubbard and Hansen 1976). Hurd and Pond (1958) identified Idaho fescue (Festuca idahoensis), bluegrasses (Poa spp.), and sedges (Carex spp.) as the important species in the diets of cattle in the Big Horn Mountains, Wyoming. In a study in the Piceance Basin, Colorado, Hubbard and Hansen (1976) identified seven graminoids and one shrub species as the principle forage species of cattle. A study in Douglas Mountain, Colorado (Hansen et al. 1977) rated needlegrasses (Stipa spp.), wheatgrasses (Agropyron spp.) , and brome (Bromus spp.) as the major forage species of cattle.
Shrub species are also important in cattle diets. As the palatability of herbaceous species decreases through the season, use of shrub species increases (Roath and Krueger 1982). Allen (1968) found that browse species were more prevalent in cattle diets during the winter, probably because snow cover decreased availability of preferred grasses.
In general, cattle prefer riparian areas because of the topography, variety of forage, and availability of shade, water, and thermal cover (Ames 1977, Gillen et al. 1985). The combination of cattle preference for riparian areas and the importance of these areas for maintaining water quality accentuates the problems caused to water quality.
The affinity of cattle for flat or gently sloping terrain corresponds to their disproportional occupation of riparian zones (Severson and Boldt 1978, Platts and Nelson 1985b). Gary et al. (1983) determined that cattle spent 65% of their time within 100 m of the stream in a study in the Front Range of Colorado. Roath and Krueger (1982) noted that cattle utilized the riparian zone rather than slopes through the grazing season even though forage became progressively reduced. Goodman et al. (1989) noted heavy use of riparian areas by cattle, but determined that riparian use never exceeded 45% of the available grazing area.
Cattle prefer riparian vegetation to upland vegetation (Ames 1977, Dwyer et al. 1984). Riparian zones have greater plant biomass and species diversity (Bedell 1984). Also, the vegetation stays green longer and has a higher water content, making it more palatable for a greater period of time (Ames 1977, Schmidly and Ditton 1978, Bedell 1984). Platts and Nelson (1985b) found that (92 % of observations) streamside vegetation use by cattle was twice as heavy as that of the adjacent range.
Cattle usage of riparian zones differs by season (Kinch 1989, Clary and Webster 1989). The summer growing season is the time of greatest use of the riparian zone because forage palatability and variety are at their peak (Goodman et al. 1989). Shade and water are most critical to cattle during the warmest part of the season. In southwestern Montana, Marlow and Pogacnik (1985, 1986) found that riparian zone use by cattle increased over upland use from late June to August with the last half of the season being equal between the two areas.
Cool season grass species in the uplands are more palatable in the fall, thus, cattle may shift usage to the upland in this season (Kinch 1989). Also shade and water are less important in the fall than in the summer. In a study in southwestern New Mexico, Goodman et al. (1989) determined that cattle moved from the riparian zone after the vegetation became dormant and the only green vegetation was upland evergreen species.
Winter usage of riparian zones by cattle often is decreased because of deep snow that cattle avoid (Platts and Raleigh 1984, Knopf and Cannon 1982). Also, the micro-climate of the riparian zone may be colder in winter. Conversely, Allen (1968) found that cattle used the bottomland most in the winter. An explanation would be that vegetation is dormant in the winter, but there may still be available browse species in the riparian zone. Thus, winter usage is dependent on snow depth, temperature, and plant communities.
Spring usage of riparian zones by cattle may be highly variable. Cattle may be distributed between the riparian zone and the upland because of forage availability in the uplands and spring flooding may preclude usage of the riparian zone (Kinch 1989). Other parameters that dictate cattle usage of the riparian zone are their need for water and shade, and their general lack of dispersal behavior (Bryant 1982). This causes cattle to congregate in riparian zones, increasing the likelihood of impacting water quality.
Many authors state that over-utilization of riparian zones by cattle results in damage to the riparian habitat and to water quality (Platts 1981a, Platts and Nelson 1985a, Mizell and Skinner 1986, Thomas 1986). Many of the statements that attribute cattle grazing to riparian degradation and water quality degradation are based on comparison studies of grazed versus non-grazed areas. Observations of recovery of areas from which cattle have been removed have been used to make inferences regarding damage caused by cattle.
Livestock grazing is related to run-off, erosion, and sediment (Packer 1953, Van Haveren et al. 1985, Platts and Meehan 1977). The parameters that influence run-off, including soil bulk density, infiltration rates, and ground cover are also affected by cattle grazing and trampling (Rauzi and Hanson 1966). In a northern Colorado riparian zone, Leininger and Trlica (1986) found that bulk densities averaged 21% higher in areas grazed by livestock versus protected areas. Buckhouse et al. (1977) and Sartz and Tolsted (1974) noted improved infiltration rates.
A study by Rauzi and Hanson (1966) evaluated the influences of grazing levels and vegetation cover on water run-off in mixed prairie in South Dakota. They found that water intake rate decreased as grazing intensity increased and that annual run-off was greatest from heavily grazed watersheds and least from lightly grazed watersheds. Differences in soil bulk density and soil pore space between the grazing levels were significant. The authors concluded that heavy grazing can change soil properties including decreasing the pore spaces and increasing bulk density.
Because of alteration of soil properties by cattle grazing, runoff levels and soil erosion are affected. In a study of different grazing levels in a Colorado pine-bunchgrass range, Dunford (1949) noted an increase of 210 and 325% in moderate and heavy grazing areas, respectively, compared to a control area. The amount of soil eroded from control areas was approximately half the amount yielded from the heavily grazed area, but no change from the control area was noted in the moderately grazed area.
In the Badger Wash Basin of western Colorado, Lusby (1970) found that run-off was directly related to the amount of bare soil. Grazed watersheds were compared to watersheds where cattle and sheep were removed. After 2 years, the grazed watersheds averaged 30% more run-off than the ungrazed. Also the ungrazed watersheds yielded 45% less sediment. The greatest differences in sediment were noted after 3 yr of cattle exclusion, with the grazed watersheds averaging 51% more run-off than the ungrazed watersheds (Lusby et al. 1971). In a southwestern Wisconsin study, Sartz and Tolsted (1974) also reported reduced run-off levels following 3 years of cattle exclosure.
Duff (1977) documented differences between stream sections within an area exclosed from livestock and two grazed areas in northeastern Utah. Both grazed stream sections had increased sediment loads possibly because of grazing in upstream areas. In a canyon section of Buffalo Creek, Wyoming, Rockett (1974) observed that the number of silt bars increased, and silt covered riffle gravel and filled in pools, in an area grazed by cattle. Streambanks were in poor condition due to overgrazing and trampling by cattle.
Impacts to stream channels and streambanks can result from cattle grazing in the riparian zones (Kauffman et al. 1983b, Marlow et al. 1987). In a comparison study in Rock Creek, Montana, Marcuson (1977a) reported 80% more stream channel instability in an area grazed by cattle at 0.27 acres/AUM than an ungrazed area. The general channel morphology of the ungrazed area was unchanged, while the grazed area was unstable and constantly shifting.
Duff (1977) reported alteration of stream width, stream depth, and pool depth due to cattle and sheep grazing in Big Creek, northeastern Utah. While average stream depth within the areas exclosed to cattle and sheep decreased, the stream width within the grazed area increased in each year of the 2 yr study. The exclosed area had mean a depth of 33 cm in the four years of the study as compared to 8 cm in the grazed areas. Likewise, pools within exclosed area had decreased depth because of channel movement and siltation caused by livestock grazing and trampling.
Van Velson (1979) reported the results of a recovery study in which changes to the stream were noted after cattle were removed from Otter Creek, Nebraska. Decreases in stream width were noted as well as increased velocity which helped to flush accumulated sediment from spawning gravel. The stream channel became more variable with more riffle/pool sequences. Similar results were reported by Smith (1982).
In a study by Platts et al. (1983), differences between cattle grazed and ungrazed stream sections in western Nevada were compared. In the ungrazed areas the channel width was narrower and the water depth was greater than in the grazed area. Also bank undercuts were more abundant in the ungrazed areas, indicating a greater degree of bank stabilization. Similar results were noted in a study on Big Creek, Utah (Platts and Nelson 1985c).
Cattle also impact riparian vegetation, reducing its effectiveness in maintaining water quality. In a study of western streams, Platts and Nelson (1985c) found that cattle consistently used forage in the riparian areas more than the upland and that this use was frequently heavy (76 to 100% forage removal). Although sheep were also present in the study area, cattle were the primary users of the riparian zone. Similar results were reported by Platts et al. (1983) in Tabor Creek, Nevada.
In a Colorado riparian willow community, cattle were observed to find shade under the willows causing breakage of lower branches (Knopf and Cannon 1982). Lower branches are also removed by grazing. Rickard and Cushing (1982) noted negative grazing impacts on the riparian willows in south central Washington from cattle, sheep and horses. Young willow shoots were persistently grazed, leading to a generally sparse and discontinuous vegetation in the riparian corridor.
Duff (1977) described the riparian vegetation as almost completely eliminated by cattle along Big Creek, Utah. No instream shade or cover was provided and bank stability was poor. In another Big Creek study, Platts and Nelson (1985a) indicated that bank stability and riparian vegetation and overhanging vegetation were rated significantly higher in the ungrazed area than the grazed section. Others have reported improvements to riparian vegetation after cattle have been removed (Van Velson 1979, Rinne 1988).
Cattle grazing alters stream habitat characteristics including width, depth, pools, and substrate size (Hubert et al. 1985). Impacts to stream habitat from cattle grazing will ultimately impact fish populations. Keller and Burnham (1982) reported trout species preferred the habitat in ungrazed areas compared to grazed areas in all habitat types sampled.
A study of Rock Creek, Montana showed that a grazed area had an inferior fishery compared to an ungrazed area (Marcuson 1977b). In estimates of trout biomass, the ungrazed area yielded 317% the trout biomass per acre than the grazed area. The grazed areas actually supported greater numbers and more biomass because of the large numbers of whitefish and suckers present.
Prior to exclusion of cattle, rough fish composed 88% of the fish population of Otter Creek, Nebraska (Van Velson 1979). After exclusion, rainbow trout composed 97% of the population. Similarly, ratios of brown trout to rough fish steadily improved by the removal of grazing animals and streambank improvements in Blue Creek, Montana (Marcuson 1969).
Cattle grazing on rangeland generally does not cause high enough levels of fecal inputs into streams to affect water quality degradation. Levels of contamination are dependent on the intensity and duration of cattle grazing. Grazing at low to moderate levels did not result in high bacteria levels in streams (Buckhouse and Gifford 1976, Buckhouse et al. 1977, Gary et al. 1983).
Also, proximity of cattle to the stream determines the level of impacts to water quality. Cattle grazing adjacent to streams causes greater impacts to water quality (Buckhouse and Gifford 1976, Milne 1976). Unless animals are defecating directly into the stream or adjacent to the streambed, bacterial contamination is unlikely (Buckhouse and Gifford 1976). A study of a western Montana stream concluded that in a cattle and sheep winter grazing situation little bacterial impact existed on stream sections that were unaccessible to the livestock (Milne 1976).
Run-off affects delivery of animal wastes to streams (Jawson et al. 1982). In a study by Saxton et al. (1983), fecal coliform and fecal streptococcal bacteria increased from a cattle grazed area with run-off levels in the spring after animals were removed. In Big Creek, Utah, Duff (1977) noted that bacteria levels from grazed stream reaches were generally low except during a period of heavy rains which increased run-off levels.
Nutrients levels in streams are not increased significantly within rangelands where cattle grazing occurs (Milne 1976, Gary et al. 1983). As with bacteria, Duff (1977) found nitrate and phosphate levels associated with cattle grazing in the bottomlands to increase with run-off, but water quality remained acceptable.
In the studies reviewed, it is clear that levels and intensity of cattle grazing influence water quality degradation (Rauzi and Hanson 1966, Buckhouse et al. 1981, Buckhouse 1984a). Definitions of grazing level are variable because of climatic and vegetative factors. A general rating for cattle grazing levels defines light grazing as 67% of the previous years growth remaining (1 AUM/6 acres), moderate 33% to 66% of the previous year's growth remaining (AUM/1.35 acres), and heavy as > 33% of the previous year's growth remaining (1 AUM/fraction of an acre) (Kirsch 1969).
Heavy grazing can severely impact riparian areas (Dahlem 1979, Rodgers 1981, Wood and Blackburn 1981), but the impacts of moderate and light grazing are poorly defined. Several authors have noted impacts caused at light and moderate grazing levels are not significantly different (Gary et al. 1983), and only heavy grazing causes detrimental impacts to riparian zones and water quality (Platts 1981a).
To control livestock use of the landscape and reduce over use of forage, different types of grazing strategies have been developed, but primarily for upland areas (Platts and Nelson 1985d, Platts 1989). The usefulness of different strategies in reducing the impacts to riparian zones is variable (Platts 1984, Clary and Webster 1989). Literature on the major types of grazing strategies and the level of protection from impacts has been extensively reviewed by Bryant et al. (1982), Gifford and Hawkins (1976) Meehan and Platts (1978), and Platts (1981a). If designed without consideration of cattle affinity for riparian areas, grazing strategies do not enhance protection of riparian zones and water quality (Platts 1986).
Sheep
The second class of livestock of concern to riparian integrity and water quality are sheep. Because of their behavior, size, and management, sheep do not cause the same degree of impacts to riparian zones and water quality as cattle (May and Somes 1982). Sheep do not have as great a preference for riparian areas as cattle. They prefer steeper slopes and tend to spend more time in upland areas (May and Somes 1982). This behavior causes them to be less intrusive to the riparian zone.
Like cattle, sheep diets consist primarily of graminoid species, but forbs are also important food items (McMahan 1964, MacCracken and Hansen 1981). Sheep also utilize browse species. Olsen and Hansen (1977) report that saltbush was the most important species to sheep in all seasons except summer in the Red Desert, Wyoming. Sheep will browse on the new willow growth in riparian areas when forage in the upland is less palatable (Kinch 1989).
Because of their small size, sheep cause less trampling damage to soil and ground cover. The way they forage, by nibbling, prevents pulling and dislodging of entire plants as cattle and horses tend to do. Sheep also are not prone to breaking down willow as cattle (Kinch 1989). Sheep are managed differently than cattle. When properly herded, sheep do not have the opportunity to spend great amounts of time in the riparian zone. Thus, the likelihood of damage to the riparian zone is limited (Platts 1981a, May and Somes 1982, Kinch 1989).
Sheep have not been addressed as thoroughly in the literature regarding riparian zone and water quality impacts as cattle. In a study by Platts (1981a) an Idaho riparian area heavily grazed by sheep resulted in impacts similar to those caused by heavy riparian cattle grazing. Significant changes to streambanks, channel, and riparian habitat were reported. Fish density and biomass also declined. In the same study, sheep under herding had only periodic and limited access to the riparian zone. No significant changes to the stream ecosystem were reported.
Horses
Little information on the impacts of either domestic or wild horses to riparian areas and water quality is available. Perhaps horse grazing has not been noticed as a problem because they do not congregate as cattle and sheep do (Kinch 1989). Also, large horse operations are not as common as cattle and sheep ranching. In a study in central Wyoming, Hubert et al. (1985) noted the good condition of the riparian zone and the stream in a pasture grazed by horses and wildlife.
Impacts of Wildlife
Because the riparian zone is important to large wild ungulates (Gerhart and Olsen 1982, Thomas et al. 1979), concern has arisen that these animals may also impact riparian zones and water quality. If large wild ungulates use the landscape in a manner similar to livestock, impacts to riparian zones and water quality would be likely. For instance, trails caused by wildlife would be as susceptible to erosion as livestock trails (Clark 1980). Presently, literature which substantiates damage to riparian zones and water quality caused by large wild ungulates is limited.
Generalized comments that wild ungulates impact riparian zones and water quality have been made. Mizell and Skinner (1986) stated that wildlife grazing and browsing can accelerate erosion and streambank loss. Skinner (1986) suggested that livestock have merely replaced wildlife. He also stated that prior to settlement of the West by europeans, herds of wild grazing ungulates were impacting streams and that riparian systems of today are more vast than at that time. Bedell (1984) commented that the impacts caused to riparian areas are similar between livestock and wild ungulates, but information pertaining to wildlife was not presented. Buckhouse (1984b) noted that riparian areas receive heavy browsing and grazing pressure from both wild and domestic ungulates, especially in semiarid and arid regions.
General statements that wildlife do not cause impacts to riparian zones or water quality have also been made. Meehan et al. (1977) stated, "Wild ungulates also use the riparian zone, but their presence is much less noticeable than that of cattle and sheep." While livestock were reported as removing 29 - 40% more vegetation from the riparian zone that from uplands, Platts and Nelson (1985d) reported that "wildlife use was trivial".
Limited information is available on the impacts caused by large wild ungulates. Wildlife are typically addressed in antidotal comments made during livestock impact studies, where the intent was not to quantify wildlife impacts.
In a study to assess the impacts of cattle grazing on riparian plant communities, Kauffman et al. (1983a) stated that use of willow-dominated gravel bars by cattle ranged from 27-48% removal and succession appeared to be retarded. In the same area, wild ungulates utilization was always < 5%.
During a study of the influence of different grazing levels on trout streams, Hubert et al. (1985) observed that a study area accessible to wild ungulates and horses had a heavily vegetated riparian zone with stable, vegetated banks. Likewise, Van Velson (1979) found that recovery of riparian vegetation, after enclosure of livestock, made the area more attractive to wildlife. The increased use of the riparian area by large wild ungulates, did not result in observable degradation of the riparian area.
While trying to locate undisturbed sites within Wyoming to study riparian habitat, Olsen and Gerhart (1982) noted wildlife concentrations had effected the pristine nature of some sites, but evidence of livestock grazing was present in almost all of the sites.
Several studies have attempted to assess impacts caused by large wild ungulates. In a study of bank retreat from grazing of livestock and big game, Bohn and Buckhouse (1986) found that livestock grazing areas accessible to big game had significantly greater bank retreat than areas where big game was exclosed. They stated numerous limitations of the study including the lack of quantitative data on big game animal numbers and small experimental areas.
Another study by Bohn and Buckhouse (1985b) attempted to assess impacts of cattle and big game on riparian soils. Soil compaction increased significantly in the areas that were accessible to big game. The study design was problematic because pastures accessible to big game had less riparian area for use by livestock than the pasture from which big game were exclosed. They stated that comparisons based on big game may not be valid because the pasture sizes were not equivalent in terms of the amount of riparian area available. Also, big game numbers were not measured.
Several studies have attempted to measure changes in bacteria levels caused by large wild ungulates using ratios of fecal coliform to fecal streptococci. Although the ratios can distinguish between livestock, human recreation, and wildlife contributions, the technique is of questionable value as these indicator bacteria may not reflect behavior of the pathenogenic bacteria (Bohn and Buckhouse 1985a). While increased levels of indicator bacteria have been attributed to wildlife (Skinner et al. 1974, Doran et al. 1981), it is not possible to determine the contribution of large wild ungulates because the ratio includes the contributions of all wildlife including small mammals and birds.
Habitat use, diet, and behavior influence the degree of impact wild ungulates have on water quality and riparian zones. The degree of competition between large wild ungulates and livestock, both dietary and behavioral (Julander 1958), may affect impacts that wildlife may have on water quality and riparian zones. In Wyoming, large wild ungulates that may cause impacts to water quality and riparian zones are: elk (Cervus elaphus), mule deer (Odocoileus hemionus), white-tail deer (Odocoileus virginianus), and pronghorn antelope (Antilocapra americana). Of lesser concern are bison (Bison bison), moose (Alces alces), and bighorn sheep (Ovis canadensis).
Elk
Elk occur throughout Wyoming (Clark and Stromberg 1987). They are most typical of mountain meadows and prefer coniferous forests for cover (Nelson and Burnell 1975). Generally, elk are gregarious (Mackie 1970). In the winter they form herds, while in the summer they travel either singly or in small groups. Elk are migratory animals with winter being the time of greatest movement and summer being the least. Thus their use of the landscape varies with the seasonal pattern of their movements.
In general, the seasonal physiographic areas used by elk are upland summer range, mid-level transitional range during spring and fall, and lowlands in the winter (Skovlin 1975). In summer, elk use ridges and plateaus, but as summer progresses and vegetation becomes increasingly dry and temperatures increase, elk will use forest understory and moist meadows. Wet meadows and riparian habitats are preferred in summer (Campbell and Knowles 1978, Roberts and Becker 1982). The use of forests increases through the fall. In winter, elk congregate into larger herds and their use of cover diminishes.
Elk prefer slopes of > 10° with use of slopes up to 30 to 40 ° (Skovlin 1975, Mackie 1970). Although elk prefer slopes regardless of season (Skovlin 1975), they also use riparian habitat in late summer because of forage availability. Riparian areas are important as travel routes. Gerhart and Olsen (1982) state that elk use a variety of riparian habitats and that they commonly forage in riparian zones. In a study of tame elk in northern Utah, Collins et al. (1978) stated the preference that elk had for riparian areas. Riparian wet meadow areas within a lodgepole pine (Pinus contorta) habitat were used by elk for foraging and resting.
Another behavior that may influence seasonal use of riparian zones is wallowing, a rutting-season behavior of bulls (Lyon and Ward 1982). This behavior could be damaging to streambeds, but because this event is limited to a few animals within a herd and only in the fall it is doubtful that a sustained impact occurs. Skovlin (1975) reviewed literature on the proximity of elk to water. Although most studies show that distribution is under 1.2 km, the relationship of elk proximity to water and use of riparian zone is unknown.
Elk diets are variable; consuming grasses, forbs, and shrubs depending on availability. Spring diets are primarily grasses, while summer diets consist of both grasses and forbs. Shrubs are used in all seasons, particularly in winter when grass availability is low (Clark and Stromberg 1987).
Elk are grazers at most times of the year (Kufeld 1973). In winter, grasses or shrubs are used most depending on availability. Spring diets consist mainly of grasses. Forbs gain importance in the summer. In the fall, grass regains primary importance and shrub use becomes more frequent (Kufeld 1973, Miller and Vavra 1982). A survey of elk diet studies (Kufeld 1973) ranked the most used summer forbs as Agoseris glauca and Geranium viscossimum. The most valuable grasses were Agropyron spicatum, Carex geyeri, Festuca idahoensis, Festuca scabrella, and Poa sp.
Elk browsed more frequently in the aspen, willow, and wet meadow communities than in other vegetation types (Hobbs et al. 1981). Browse species of greatest importance to elk include Amelanchier alnifolia, Ceanothus sanquineus, and Ceanothus velutinus, Populus Tremuloides, Prunus virginiana, Purshia tridentata, Quercus gambellii and Salix spp. (Kufeld 1973).
Several studies have described the impacts to vegetation caused by elk. The Gros Ventre drainage in western Wyoming is used by elk as a winter feeding ground, where elk diets are artificial supplemented to reduce elk mortality. Riparian vegetation is absent along Flat Creek within the refuge because of grazing by wintering elk (Skates 1988). The elk heavily impact the aspen ecosystem by browsing and removing bark in early and late winter (Debyle 1979, Gruell 1979). Aspen regeneration and community successional processes are being hindered. Similar damage to aspen stands were reported by Weinstein (1979) along Pacific Creek in Grand Teton National Park, Wyoming, in an area relatively far from the winter feeding grounds. In the upper Gallatin River drainage, Montana, Patten (1988) used photo documentation to demonstrate changes to riparian vegetation caused by elk browsing during winter. Damage to streams or water quality has not been measured in any of these studies.
Skovlin (1984) stated that of the large wild ungulates elk cause the most problems to riparian habitats by their grazing and trampling activities. No data or references were given to describe the damages they cause. Platts and Raleigh (1984) noted that while elk were in riparian meadows in Idaho, riparian damage was not noticeable. They contend that trampling impacts from elk would be minimal in the riparian zone because elk tend to use the riparian zone in winter when snow depth precludes their use of shorter vegetation. Frozen soil is not as susceptible to compaction, thus, impacts are minimized. Although, usage of the riparian shrubs may be significant in spring and early summer, because the animals are dispersed by that time impacts are minimal.
Another reason that impacts from normal (not human induced) concentrations of elk may be minimal is their high mobility. Ward (1973) noted that elk seemed to have a "natural rotation pattern" of grazing through their summer range. They never stay in a particular area for more than a day or two at a time. Eng and Mackie (1982) also commented on the high mobility of elk allowing them to use preferred areas. Little evidence was found that elk are impacting water quality and riparian zones. The most substantiated reports were in situations where human-induced populations were present. Situations may exist where elk and livestock compete by using the same areas. Overlap of diets and behavioral interactions may be influencing how the animals partition resources. These interactions could influence the degree to which wild large ungulates have access to and impact riparian zones.
Dietary overlap of elk with livestock may indicate a source of resource competition (Skovlin et al. 1968, Lyon 1985). Cattle and elk, as well as sheep and elk, have been found to have similar diets (Cooperrider 1982, Berg and Hudson 1982).
Several studies have found high degrees of dietary overlap between elk and cattle. In northwestern Colorado, Hansen et al. (1977) found that elk and cattle diets overlapped 47%. In southern Colorado, Hansen and Reid (1975) reported cattle and elk dietary overlap varied from 30 to 51% in the summer. In the Red Desert, Wyoming, Olsen and Hansen (1977) found dietary overlap between elk and cattle to be greatest in the winter at 46%. Gordon (1968) identified the potential for competition between cattle and elk in elk winter range in the Crow Creek drainage, Elkhorn Mountains, Montana. Both cattle and elk used Agropyron spicatum which is the critical winter forage species for elk in this area.
Pickford and Reid (1943) stated that elk and sheep were using the same forage in eastern Oregon. MacCracken and Hansen (1981) found that elk diets were similar to sheep in a study of winter range in south-central Colorado, with mean dietary overlap of 30%. In the Red Desert, Wyoming, Olsen and Hansen (1977) found overlap between sheep and elk was also greatest in the winter at 53%. The idea that forage overlap is indicative of interspecific competition is questionable (Mackie 1978, Lyon 1985). Because unless forage becomes limiting, direct competition is not likely.
Another factor that influences the degree of interspecific competition between large wild ungulates and livestock is how animals behaviorially partition themselves through the landscape. Berg and Hudson (1982) reported that although dietary overlap between elk and cattle was significant, little spatial and temporal overlap existed in southwestern Alberta, because cattle tended to concentrate in lowlands while elk selected uplands. Allen (1968) stated that the potential for cattle and elk interactions was small in northwestern Montana because elk use the bottomland very little, especially in winter and spring. However, cattle used bottomland most during the winter, but usage was also high for the other seasons.
Komberec (1976) stated that both cattle and elk used areas with slopes of 0 - 10 ° in the spring and winter in eastern Montana. Skovlin et al. (1968) found that elk used steeper, rockier areas, while the cattle grazed the flatter areas. Drainage bottoms were not of as great importance to elk as they were to cattle (Stevens 1966, Knowles 1975).
As with dietary overlap, it is likely that behavioral interactions between livestock and wildlife modify the use of the landscape by wildlife. This is important because the use of riparian zones by wildlife could be influenced by livestock.
A second type of behavioral interaction between livestock and elk that could influence the degree of impacts on riparian zones by elk are social interactions. Several studies have found that elk avoid livestock and human activities. Lyon and Ward (1982) noted that elk will avoid sheep herds, especially if a herder is present. Stevens (1966) also noted the avoidance of sheep by elk. A study by Knowles and Campbell (1982) found that elk avoid pastures being grazed by large concentrations of cattle. Even after cattle were removed the elk avoided the heavily grazed pastures.
In the Pole Mountain area, Wyoming, Ward (1973) and Ward et al. (1973) found that elk and cattle appeared to be compatible when forage was adequate. Elk were observed grazing in close proximity to cattle and using the same salt licks. Most other studies show that elk are repelled by cattle.
The outcome of studies on the behavioral relationships between elk and livestock have varied (Lyon 1985). In a review of literature from the Missouri River breaks areas of Montana, Eng and Mackie (1982) concluded that evidence for livestock influence of wildlife behavior was inconclusive.
Assessing livestock influences on the use of riparian zones by elk is difficult and studies addressing this issue have not found. Social interactions coupled with stocking levels and habitat or forage availability must all be considered when trying to determine effects of livestock on use of riparian zones by large wild ungulates.
Mule deer
Mule deer are found throughout Wyoming in grasslands, shrublands, riparian zones, and desert (Hoover and Wills 1984, Clark and Stromberg 1987). They are not considered highly gregarious or solitary. Mule deer typically occur individually or in small groups, although habitat limitations may force large numbers of onto winter feeding grounds. Like elk, mule deer are migratory in the winter and spring.
Mule deer are intermediated feeders, consuming browse, grasses, and forbs (Hoover and Wills 1984). Because mule deer inhabit many different habitat types, the importance of forage classes, by season, has been found to vary from location to location (Hansen and Reid 1975, Knowles 1975, Hansen et al. 1977, Miller 1982,). In southern Colorado, Hansen and Reid (1975) found that mule deer diets consisted mostly of browse in the summer and early winter. Forbs were consumed in small amounts in spring and summer only.
Mule deer use a variety of riparian habitats in Wyoming (Gerhart and Olsen 1982). Collins and Urness (1983) reported tame mule deer prefer wet meadows for forage. Skovlin (1984) stated that mule deer are dependent on riparian areas for forage and water. Mackie (1970) found that water did not seem to be significant in determining mule deer distribution in the Missouri River Breaks, Montana.
Mackie (1970) found that 50% of the mule deer observed were on slopes between 11 - 45 ° . They made greater use of gentle slopes during the winter and spring, while in summer they used steeper timbered sites. Komberec (1976) found that mule deer used slopes of > 10 ° in winter and spring.
As with elk, very limited information is available on the impacts of mule deer on riparian zones and water quality. In a study of aspen (Populus tremuloides) along Pacific Creek, Wyoming, Weinstein (1979) found that aspen were damaged by ungulate browsing and regeneration was being hindered. Elk were identified as the most abundant browser, but mule deer and moose also used the area.
Interspecific competition between mule deer and livestock may influence the degree of impacts that mule deer have on riparian zones. Mule deer diets overlap very little with either cattle or sheep (MacCracken and Hansen 1981). At Douglas Mountain, Colorado, Hansen et al. (1977) found that cattle dietary overlap with mule deer was very low (4%). Hubbard and Hansen (1976) noted a dietary overlap of < 11% in the Piceance Basin, Colorado.
Besides the use of different forage, mule deer and livestock also differ spatially. McLean and Williams (1982) stated that mule deer preferred the steeper terrain than cattle. Allen (1968) stated that competition with mule deer would be insignificant because mule deer use uplands while cattle prefer bottomlands. Berg and Hudson (1982) reported similar results.
Mule deer appear to be repulsed by the presence of cattle and prefer to forage in areas not grazed by cattle (Austin et al. 1983, Austin and Urness 1986). McIntosh and Kraussman (1982) reported that mule deer observations decreased when cattle were introduced. Dusek (1975) noted the avoidance of cattle by mule deer in areas of duel usage. Cattle may limit deer usage of an area by removing needed cover (Crouch 1982, Bowyer and Bleich 1984).
White-tailed deer
White-tailed deer also occur throughout Wyoming. They use most habitat types except dry lowlands and dense coniferous forests (Clark and Stromberg 1987). White-tail deer prefer deciduous riparian habitat with dense cover (Gerhart and Olsen 1982). Because of their affinity for riparian habitats, the possibility that they could cause impacts to the riparian area and water quality exists.
White-tail deer are primarily browsers, but they also consume forbs and some grasses (Hoover and Wills 1984). In the Missouri River breaks area, Montana, Allen (1968) found that browse formed 45, 81, 65, and 43% of their diet in summer, fall, winter, and spring, respectively. The remaining portion of the diet was primarily forbs, with grasses forming a minor percentage. Allen (1968) found that dietary overlap of white-tail deer and cattle was high, particularly in the winter. Because both animals have a strong affinity for bottomlands the possibility for competition for habit is high.
Behaviorally, white-tail deer avoid cattle. In an study of white-tail deer and cattle, deer avoided encounters with cattle at a watering facility (Prasad and Guthery 1986). Deer may avoid riparian areas where cattle have reduced the amount of cover for deer, by trampling and breaking of vegetation (Loft et al. 1987).
Although white-tailed deer use riparian habitat to obtain forage and cover, no literature concerning their impact on riparian zones or water quality was found. They are not gregarious, thus large numbers do not congregate in a riparian area.
Pronghorn
Pronghorn are found throughout Wyoming, preferring high plains and arid shrub grassland (Clark and Stromberg 1987). They are not associated with riparian areas, preferring open sagebrush and grasslands (Gerhart and Olsen 1982).
Browse is the major component in pronghorn diets, with forbs having secondary importance (Bayless 1969, O'Gara and Greer 1970, Clark and Stromberg 1987). In the Red Desert, Wyoming, Severson and May (1967) found that pronghorn diets consisted mainly of big sagebrush (Artemisia tridentata) and_douglas rabbitbrush (Chrysothamnum viscidiflorus var. pumilis). Olsen and Hansen (1977) reported that pronghorn diets consisted of 95 sagebrush in winter and 77% in the spring in the Red Desert.
The degree of forage overlap between livestock and pronghorns varies depending on the geographic region (Severson and May 1967). The possibility of competition for forage is greatest with sheep (Olsen and Hansen 1977, Schwartz and Ellis 1981, McNay and O'Gara 1982). Clary and Holmgren (1982) and Clary and Beale (1983) reported pronghorns avoiding areas grazed by sheep in western Utah. Low levels of dietary overlap were recorded between cattle and pronghorn (8% in winter and 25 in spring) by McInnis and Vavra (1987) in southeastern Oregon.
Although it has been shown that proximity to water is a critical need for pronghorns (Sundstrom 1968), literature concerning impacts to riparian zones or water quality was not found.
Moose
In Wyoming, moose are found in spruce-fir, willow, and riparian communities (Gerhart and Olsen 1982, Clark and Stromberg 1987). They require access to water and are primarily browsers (Clark and Stromberg 1987) with aquatic and phreatophytic plants forming most of the diet (Hoover and Wills 1984). In southwest Montana, Dorn (1970) reported that moose occupied the willow communities in wet lowland areas along streams 84% of the time in summer and 93% in winter. Diet was almost entirely browse in both seasons. Literature concerning impacts to riparian areas or water quality by moose was not found. Weinstein (1979) mentioned that moose were browsing in habitats where aspens were being damaged. The damage was attributed to elk because elk were the only species numerous enough to cause impacts. Although moose use the riparian zones a majority of the time, there solitary nature may prevent damage to the riparian zone.
Big Horn Sheep
Big horn sheep inhabit mountainous regions of Wyoming. They forage on grasses, forbs, and browse (Clark and Stromberg 1987). Because they occupy rugged terrain, they are not considered to be associated with riparian zones (Gerhart and Olsen 1982). Literature on impacts to water quality or riparian zones as caused by big horns was not found.
Bison
Bison are of very minor concern to the issue of riparian impacts as they only occur in the national parks in northwestern Wyoming and on a few private ranches. Historical accounts of bison impacts to the riparian zones have been recorded (Skinner 1986), but these occurred when bison numbers were in the millions.
Conclusion
Overgrazing of riparian areas by wildlife may occur, but this situation is likely only if the wildlife do not have adequate upland forage or numbers are very high (Claire and Storh 1977). In both instances, improper land management may be the issue, not the behavior of the wildlife.
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