Riparian ecosystems occupy the transition between upland and water ecosystems and include floodplains, stream banks, lake shores, and wetlands. They are some of the most productive resources found on public or private lands. They comprise less than 2 percent of the western landscape, yet are prized by communities for their recreational, fish and wildlife, water supply, cultural, and historic values, and for their economic values, which stem from use in livestock production and forest management (Cooperative Riparian Restoration Montana 2006).
Riparian/wetland sites in the Planning Area are described as lentic or lotic. Lentic refers to standing water such as in lakes, springs, and bogs. Lotic refers to flowing water such as rivers and streams.
Documented riparian/wetland areas in the Planning Area range from cottonwood galleries along major rivers, to wet meadows and seeps and narrow ribbons of willow/water birch, sedge, rush, and/or grass that run along small streams. Some of the surface water features that support riparian/wetland areas can be dry for long periods and experience wide variations in the frequency and magnitude of flood events. Native cottonwood galleries along riparian corridors provide habitat for neotropical migratory birds and owls and for white-tailed and mule deer. Many terrestrial wildlife species use more than one riparian habitat type, although some use only one or two.
Riparian/wetland areas in the Planning Area perform important ecological processes and functions such as water, energy, and nutrient cycling. Healthy riparian/wetland areas support stable banks and shorelines; floodplain maintenance; clean and stable water supplies; aquifer recharge; flood-energy dissipation and moderation; fish and wildlife habitat; livestock and wildlife forage; opportunities for recreation; carbon sequestration; and scenic values.
Riparian/wetland communities in the Planning Area include forest-dominated riparian areas, shrub-dominated riparian areas, and graminoid/forb-dominated wetlands, as described below.
Forest-dominated riparian areas are dominated by tree species. In the Planning Area, these are usually cottonwood species, but also can be aspen, boxelder, a variety of conifer species, and Russian olive (an introduced nonnative species considered to be a noxious weed). Trees must occupy more than 25 percent of the vegetative cover within a riparian zone to be classified as forest-dominated riparian. Diagnostic plant species include eastern cottonwood, narrowleaf cottonwood, quaking aspen, boxelder, and conifer species.
These riparian areas are characterized by areas where shrubs comprise more than 25 percent of the vegetative cover and where trees occupy less than 25 percent of the total vegetative cover. Shrubs often include willow species, sagebrush species, and greasewood. Other shrubs, including hawthorn, wild plum, birch, alder, shrubby cinquefoil, and Tamarisk (an introduced nonnative species considered to be a noxious weed) might also be present. Alpine riparian zones are generally dominated by willows or other shrubs.
These areas are characterized by grasses or forbs; trees or shrubs cannot occupy more than 25 percent of the total vegetative cover. This wetland type includes communities such as wet and moist meadow grasslands, marsh and swamp wetlands, cattail, bulrush- and sedge-dominated wetlands, and inland saltgrass/alkali sacaton-dominated wetlands, including both low- and high-salinity wetlands. Low-salinity wetlands are characterized by cattails, Baltic rush, sedges and rushes, and prairie cordgrass. High-salinity wetlands are characterized by alkali sacaton, alkali cordgrass, saltgrass, sea blight, and riparian wheatgrass.
Riparian/wetland areas in the Planning Area are inventoried to estimate their functional status using PFC assessment methodologies developed by the BLM, USFS, NRCS, and others (BLM 1998b; BLM 1999). These methodologies employ an interdisciplinary team that inspects and analyzes the attributes and processes associated with a riparian/wetland area’s hydrology, vegetation, and soils to estimate its relative health. In the Planning Area, inventoried riparian/wetland areas include approximately 1,617 acres of lentic and 1,205 miles of lotic riparian/wetlands (BLM 2009m). Table 3-23 provides the results of the riparian/wetland PFC inventories for the Planning Area.
Table 3.23. Wetland Inventory Data
| Functional Status | Wetlands (lentic features)(acres) | Riparian (lotic features)(miles) |
|---|---|---|
| Proper Functioning Condition | 136 | 417 |
| Functioning‐at‐Risk Upward Trend | 155 | 225 |
| Functioning‐at‐Risk Downward Trend | 355 | 213 |
| Functioning‐at‐Risk No apparent Trend | 963 | 182 |
| Non‐Functioning | 8 | 99 |
| Unknown | 0 | 69 |
| Total | 1,617 | 1,205 |
| Sources: USFWS 2008; BLM 2009m | ||
Based on PFC assessments, many riparian/wetland areas in the Planning Area have improved over the last 15 to 20 years in response to implemented changes in grazing and other management actions. During this time, livestock grazing schedules have been modified to reduce or eliminate growing and/or hot-season use and increase dormant and cool-season use and/or rest periods to provide plants with recovery time.
Vegetation in riparian areas is the first of the functional components to respond to changes in management. The establishment of species, such as sedges and rushes that capture sediment and stabilize stream banks, indicates an upward trend in functional status. The physical attributes of the streams (sinuosity and width to depth ratio, erosion and deposition, lateral and vertical stability) respond slower than vegetation, because their development and stability depends on healthy, vigorous riparian/wetland vegetation.
There are a number of indicators used to evaluate the condition of riparian/wetland areas, as described below.
Obligate Plant Species and Facultative Wetland Plant Species – Obligate plant species (plants that occur more than 99 percent of the time in wetlands) and Facultative Wetland plant species (plants that occur 67 to 99 percent of the time in wetlands) are used as riparian indicator plants. Some of the more common indicator plants in the Planning Area include, but are not limited to, Baltic rush, Nebraska sedge, tri-square bulrush, willows, cottonwood, cattails, spikerush, and alkali bulrush.
Proper Functioning Condition – PFC is a riparian health assessment and communication tool that focuses on the attributes and processes associated with a riparian/wetland area’s hydrology, vegetation, and soils instead of its values or uses. Indicators considered when assessing the functional state of lotic riparian/wetland areas include:
Hydrologic Indicators.
Floodplain above bankfull is inundated in “relatively frequent” events.
Where beaver dams are present, they are active and stable.
Sinuosity, width/depth ratio, and gradient are in balance with the landscape setting (landform, geology, and bioclimate region).
Riparian/wetland area is widening or has achieved potential extent.
Upland watershed is not contributing to riparian/wetland degradation.
Vegetation Indicators.
There is diverse age-class distribution of riparian/wetland vegetation (recruitment for maintenance/recovery).
There is a diverse composition of riparian/wetland vegetation (for maintenance/recovery).
Plant species present indicate maintenance of riparian/wetland soil moisture characteristics.
Stream bank vegetation is comprised of plants or plant communities with root masses capable of withstanding high streamflow events.
Riparian/wetland plants exhibit high vigor.
Adequate riparian/wetland vegetation is present to protect banks and dissipate energy during high flows.
Plant communities are an adequate source of coarse and/or large woody material (for maintenance/recovery).
Erosion/Deposition (Soil) Indicators.
Floodplain and channel characteristics (rocks, overflow channels, coarse and/or large woody material) are adequate to dissipate energy.
Point bars are revegetating with riparian/wetland vegetation.
Lateral stream movement is associated with natural sinuosity.
The system is vertically stable.
The stream is in balance, with the water and sediment being supplied by the watershed (no excessive erosion or deposition).
Indicators considered when assessing lentic riparian/wetland areas are similar to those used for flowing riparian/wetland areas, but they have been modified to address wave, wind, and/or overland flow energies instead of the high water flow energies experienced by flowing water systems.
Invasive Species – Invasive plant species displace native riparian/wetland plant species and can disrupt or degrade riparian/wetland areas to the point that they no longer function properly or provide habitat for riparian-dependent native flora and fauna. In the Planning Area, riparian invasive species include nonnative bromes, Russian olive, Tamarisk, and Russian knapweed.
Although 2009 was an above-average precipitation year, precipitation has been below normal in 6 of the 9 years since 2000. Small streams and portions of larger streams have experienced minimal or no flows. The reduced amount of available water has resulted in lower flows in unregulated streams, and lower outflows from reservoirs in and around the Bighorn Basin. Reduced amounts of water due to drought have had an adverse impact on riparian/wetland habitat improvement. In general, the most common adverse impacts include a slowing in the rate of improvement in those areas where appropriate management has been implemented and an increase in the rate of decline where appropriate management has not yet been implemented. This has had a greater impact on fisheries than on riparian conditions. Thus, riparian conditions continue to improve while some fisheries appear to be declining (BLM 2009b).
Sixty-seven of the 252 livestock grazing allotments that have been evaluated for conformance with the Wyoming Standards for Healthy Rangelands failed riparian/wetland area standard #2 (Appendix N). Standard #2 states that “riparian and wetland vegetation has structural, age and species diversity characteristic of the stage of channel succession and is resilient and capable of recovering from natural and human disturbance in order to provide forage and cover, capture sediment, dissipate energy, and provide for groundwater recharge.” Allotments can fail standard #2 for many reasons. If failure to meet the standard is attributable to existing livestock grazing management or utilization level, then the BLM must make management changes to correct the issue. If failure to meet the standard is attributable to other factors (e.g., encroaching juniper, recent wildfire, discontinued historic grazing patterns, or the presence of noxious weeds), then the BLM is not required to make changes to livestock grazing.
Proactive management practices such as prescribed fire, brush mowing/beating, successful reclamation of surface disturbance, applying BMPs and standard surface-disturbing guidelines, travel management, and implementing riparian/wetland compatible livestock grazing management can have a beneficial influence on associated riparian/wetland areas and their watersheds.