This riparian system is a seasonally flooded shrubland found at montane to subalpine elevations of the Rocky Mountains. Shrubs dominate this system, with total shrub cover ranging from 20 to 100 percent. It occurs as linear bands of shrub vegetation lining streambanks and alluvial terraces in narrow to wide, low-gradient valley bottoms and floodplains with sinuous stream channels. Flooding creates and destroys sites for the establishment of vegetation through the transport and accumulation of coarse sediment (Melanson and Butler, 1991). Sediment accumlating in these systems can form gravel bars at or near the surface of the river, creating bands of mixed vegetation that occupy different stages of succession (Melanson and Butler, 1991). Ground water seepage from snowmelt may create shallow water tables or seeps that vegetation depends on for a portion of the growing season. This system often occurs as a mosaic of multiple communities that are shrub and herb dominated. The structure of vegetative communities in these systems can vary depending on latitude, elevation and climate. In Montana, these systems are dominated by willows, including Drummond’s willow (Salix drummondiana), Bebb’s willow (Salix bebbiana), planeleaf willow (Salix planifolia ssp. planifolia), undergreen willow (Salix commutata), Idaho willow (Salix wolfii), booth willow (Salix boothi) and Geyer’s willow (Salix geyeriana). Typical herbaceous vegetation found in the understory includes beaked sedge (Carex utriculata), bluejoint reedgrass (Calamagrostis canadensis), and northern reedgrass (Calamagrostis stricta). Generally, the upland vegetation surrounding these riparian systems are conifer dominated forests. Shrubland riparian systems are important for bank stabilization, organic inputs to the adjacent stream, shade cover and wildlife habitat values.
This riparian system is a seasonally flooded shrubland found at montane to subalpine elevations of the Rocky Mountains. In Montana, this system typically occurs at elevations between 1,750 and 2,693 meters (5,740-8,830 feet). This system consists of narrow bands of shrub vegetation lining streambanks and alluvial terraces in narrow to wide, low-gradient valley bottoms and floodplains with sinuous stream channels. This system is also typical around seeps, fens, and isolated springs on hillslopes away from valley bottoms. Sediment that accumulates in these systems may create gravel bars at or near the surface of the river where colonizing vegetation creates bands of mixed vegetation that occupy different stages of succession (Melanson and Butler, 1991). Ground water seepage from snowmelt may create shallow water tables or seeps that vegetation depends on for a portion of the growing season.
Plant community composition and structure can vary depending on latitude, elevation and climate. For example, in southwest Montana Drummond’s willow occupies higher elevations while Geyer’s willow and booth willow are found at more intermediate elevations. In the northwest region of Montana, Geyer’s and booth willow are barely present and Drummond’s willow dominates most riparian areas (Hansen et al, 1995). Bebb’s willow, planeleaf willow, undergreen willow and Idaho willow are frequent associates. Barclay’s willow (Salix barclayi), shortfruit willow (Salix brachycarpa) and grayleaf willow (Salix glauca) become common at higher subalpine elevations. Sageleaf willow (Salix candida) is indicative of fens and occurs in association with other willow species to form the shrub-dominated carr layers within riparian areas feeding into or out of fens. Redoiser dogwood (Cornus sericea), shrubby cinquefoil (Dasiphora fruticosa), alder (Alnus spp.), currant (Ribes spp.) and Rocky Mountain maple (Acer glabrum) are common associates. Water birch (Betula occidentalis) or bog birch (Betula nana, glandulosa) may also be present.
Dominant graminoid vegetation in the herbaceous stratum of these shrubland riparian systems includes bluejoint reedgrass, northern reedgrass and Northwest Territory sedge. Common forbs include dwarf fireweed (Chamerion latifolium), field mint (Mentha arvensis), glaucous willowherb (Epilobium glaberrimum), western mountain aster (Symphyotrichum spathulatum), and tiny trumpets (Collomia linearis). Sharptooth angelica (Angelica arguta), starry solomon’s seal (Maianthemum stellatum), sweet-cicely (Osmorhiza species), common cow parsnip (Heracleum maximum), clasp-leaf twisted stalk (Streptopus amplexifolius) and green false hellebore (Veratrum viride) are frequent at higher elevations. Within rich fen-carr shrublands, graminoid and forb species diversity is typically higher than other sites supporting these riparian shrublands.
Flooding in these systems influences vegetative communities by transporting sediments and creating establishment sites for colonization. Many plants in these high-energy systems that experience large disturbances from floods have acquired adaptive traits. Some have flexible, resilient stems and specialized cells to hold oxygen so that they can survive large flood events. These species also have reproductive adaptations such as water-dispersed seeds and are able to sprout quickly from flood damaged stumps. Ground water seepage from snowmelt may create shallow water tables or seeps that vegetation depends on for a portion of the growing season. Sites that are over-browsed will become dominated by Bebb willow, a shrub that is more resilient to heavy grazing. In sites where there is prolonged disturbance, willow coverage will decrease, resulting in a more open canopy. Herbaceous vegetation will transition to a grass-dominated system including fowl bluegrass (Poa palustris), Kentucky bluegrass (Poa pratensis) and field horsetail (Equisetum arvense) (Hansen et al, 1995).
Stochastic flood events and variable fluvial conditions are crucial to the development of establishment sites for riparian plants, and act as a primary control on plant succession. Steep gradients and high-energy flows controlled by precipitation cause flooding events that transport coarse sediments. Scouring out and accumulation of sediments constantly creates and destroys sites for the establishment of vegetation (Melanson and Butler, 1991). Accumulating sediments often create gravel bars at or near the surface of the water where colonizing vegetation creates bands of mixed vegetation occupying different stages of succession (Melanson and Butler, 1991). Ground water seepage from snowmelt may create shallow water tables or seeps that vegetation depends on for a portion of the growing season when stream flow is low.
Grazing along narrow low order streams results in increased erosion and channel downcutting (Mitsch and Gosellink, 2000). Sites that are over-browsed will become dominated by Bebb's willow, a shrub that is more resilient to heavy grazing. In sites where there is prolonged disturbance, willow coverage will decrease, and herbaceous vegetation will transition to a grass dominated system including fowl bluegrass, Kentucky bluegrass and field horsetail. In addition, fire suppression, timber harvest and reduced flood frequency can affect the succession of riparian communities.
Restoration strategies will vary based on the degree and type of disturbance event. Restoration efforts must first concentrate on restoring the stream's hydrology, so the floods can re-occur. In-stream habitat enhancement (e.g., additions of logs or boulders) should be employed after restoring natural processes or where short-term improvements in habitat are needed (e.g, for species in recovery).
Removing grazing from this ecological system will allow the system to recover if hydric soils have not been lost due to extensive soil compaction, pugging, or down cutting of stream channels, and if there are existing populations of herbaceous native species (Carex, Juncus, and native grasses) that possess rhizomatous root systems capable of re-colonizing bare soils. However, rhizomatous, highly adaptable exotic grasses such as Kentucky bluegrass, common timothy and smooth brome, and pasture forbs such as clovers (Trifolium species) and common dandelion (Taraxacum officinale) will persist on the site and may compete with existing populations of native graminiods and forbs. In these cases, land managers must decide if the exotic density is sufficiently small that an adequate stand of native graminoids and forbs can become established on the site if reseeding efforts are used. In all cases, grazing by cattle and wildlife should be excluded for several years to allow adequate re-growth and recovery of existing shrubs and the herbaceous understory.
Because all major shrub species within this riparian system are capable of re-sprouting and typically possess extensive, spreading root systems, modified land management practices in areas of low to moderate impact can minimize additional restoration needs. Vigor, health and degree of vegetative regeneration of existing shrubs must be evaluated to determine if these components of the community are capable of recovery in an acceptable time frame. Intensive revegetation efforts should be limited to sites where a catastrophic wildfire or prolonged heavy grazing has destroyed existing shrubs and the seed bank.
Ellis, Janet H., and Jim Richards. 2003. A planning guide for protecting Montana's wetlands and riparian areas. Bozeman, MT: Montana Watercourse.
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