Montane Swale Drummond’s willow (Salix drummondii)-alderleaf buckthorn (Rhamnus alnifolia)

Description

Montane swale sites are dominated by the tall statured shrub Drummond’s willow (Salix drummondiana). Drummond’s willow is a deciduous shrub generally between 2-4 m or 6.5 and 13 feet tall (Hitchcock, 1964). Other willows, particularly Booth’s willow (Salix boothii) and Bebb’s willow (Salix bebbiana) other shrub species including twinberry honeysuckle (Lonicera involucrata), alderleaf buckthorn (Rhamnus alnifolia), prickly currant (Ribes lacustre) and common snowberry (Symphoricarpos albus) can be present at the site. Though infrequent, other shrubs may represent a high cover percent including rose species, redosier dogwood (Cornus sericea ssp. sericea), Sitka alder (Alnus viridis ssp. sinuata), russet buffaloberry (Shepherdia canadensis) and American red raspberry (Rubus idaeus). On hummocks within the understory of the willow dominated swale, moss species dominate along with obligate wetland species purple marshlocks (Comarum palustre), bog laurel (Kalmia polifolia) and dwarf red blackberry (Rubus pubescens). The understory is generally dominated by the grasses, bluejoint (Calamagrostis canadensis), mountain brome (Bromus marginatus) and rough bentgrass (Agrostis scabra), with a variety of sedge species including smallwing sedge (Carex microptera) and golden sedge (Carex aurea). A variety of forbs are present including fireweed (Chamerion angustifolium), field horsetail (Equisetum arvense), fragrant bedstraw (Galium triflorum), common cowparsnip (Heracleum maximum), feathery false lily of the valley (Maianthemum racemosum), wild mint (Mentha arvensis), western sweetroot (Osmorhiza occidentalis), alpine leafybract aster (Symphyotrichum foliaceum), western meadow-rue (Thalictrum occidentale), stinging nettle (Urtica dioica) and American vetch (Vicia americana).

When this ecological site is found near the vicinity of a beaver dam, then the water table will be higher, ponding will last for a longer duration and the understory will be dominated by the sedges Northwest Territory sedge (Carex utriculata) and or shortstalk sedge (Carex podocarpa). Beaver damming, within the areas that do have some water flow in channels, can lead to changes in plant species composition by flooding one area and concomitantly drying another. These are viewed as naturally functioning disturbances that would lead to ponding and inundation of an area and therefore drying of another area. Presence of beaver damming would potentially lead to a mosaic effect on the plant communities potentially as opposed to the typical willow swale vegetation within a larger landscape of conifer dominated environment.

Drummond’s willow is a prolific seed producer and colonizes recently scoured alluvial surfaces (Haeussler, 1986). Over time, fine particulate matter and litter collect beneath willows eventually raising the water table above the annual flood stage and grasses develop in the understory. This ecological site is maintained by occasional flooding and or frequent ponding of the site. If water table balance changes significantly, then species changes can occur to transition the community phase from the reference phase of this ecological site. If flooding, ponding or water table increase then sedge species may increase and outcompete grasses, forbs and willows. If flooding, ponding or water table decrease then upland plant species including shrubs, grasses and conifers will invade, establish and increase in numbers. Beavers are important to the health of wetlands by creating dams and ponds which aid in controlling channel down-cutting, streambank erosion, and downstream movement of sediment. Dams raise the water table and trap sediments creating a broad wetland environment.
In a study of willow establishment within Rocky Mountain N.P., Cooper (2006) found that landform and effective flood regime determined establishment patterns and that climate change could affect this process. Specifically, willows established on point bar landforms that were formed from meandering streams and had moderate to high flood flows (2-5-year return interval flow) and had continuous establishment at intermediate elevations above channel. Abandoned beaver ponds created when beaver ponds drained, needed infrequent large flood event (>5-year return interval flow) and had periodic establishment prior to dam breach and brief episodes of widespread establishment following abandonment. The establishment was at high elevations relative to the active channel. Abandoned channels, created by channel avulsion, were associated with moderate to high effective flood flows (2-5-year return interval flow) and willow establishment was continuous over limited period of time (as oxbow fills). The establishment was at low to moderate elevations relative to active channel.
While fire is relatively infrequent in the moist habitats that this ecological site is found within, it can occur during dry conditions. Generally, these swales are so saturated that fires will move around these low lying areas and stay within the conifer community. Low or mixed severity fires only account for 32% of the fires and have a mean interval of 750 years in the Northwest (USDA, USFS, Fire Effects Information System, Fire Regimes). High severity fires that occur during severe drought years, account for 68% of the fires occurring and have a mean interval of 350 years (USDA, USFS, Fire Effects Information System, Fire Regimes). So, fires are rare within this site, but would serve to limit conifer encroachment. Drummond’s willow vigorously resprouts following fire, therefore prescribed fire is an effective method of rejuvenating decadent stands (Boggs, 1990). Drummond’s willow will sprout from root crown following top kill by fire. Quick, hot fires increase sprouting response of willows. The wind dispersed seed is an important colonizer of burned areas. Therefore, Drummond’s willow is a “survivor” species and an off-site colonizer species in response to fire.
Overgrazing by wildlife or livestock can reduce vigor of this ecological site and result in willows of uneven stem age distribution, highlining, clubbing or dead clumps. The understory structure would also change with overgrazing. There would be a reduction in bluejoint and tufted hairgrass (Deschampsia cespitosa) and an increase in stinging nettles and field horsetail.
This ecological site is important to wildlife. Moose consume large amounts of Drummond’s willow in the winter (Chadde, 1988). Elk and white-tailed deer have light use of willow. Drummond’s willow is palatable to livestock and big game, even though its protein value is poor and energy value is fair. Plants can recover well after overgrazing, if grazing and browsing are excluded for a period of time (Chadde, 1988). Drummond’s willow creates thickets from 8 to twelve feet high and provide cover for songbirds.

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Description

This state has sustained prolonged and/or intensive overgrazing by livestock and/or overbrowsing by wildlife particularly moose and elk. Ungulate grazing would be considered within the range of normal functioning disturbances (Community Phase 1.3) that may change some species composition but is considered capable of returning to the reference phase, if it were light grazing, seasonal or rotational, did not lead to extensive trailing, wallowing or cut banking of flow through channels within the swale or drainageway. Ungulate hoof action can break up the soil, which can lead to unvegetated microsites conducive to weed species establishment (if seed propagules are present); in addition, pugging and hummocking can create some surface flow patterns which may accelerate water loss from the swale. Urine and feces can change nutrient concentration as well. If the ungulate use is low, then it is viewed as normally functioning. The saturated soils likely are susceptible to trampling and compaction though high water tables throughout the growing season tend to limit access by livestock and thereby reduce impacts. If the ungulate use is high, concentrated or during sensitive periods of plant growth, the impact can be severe and cause a state change by affecting soil compaction, water loss through trailing, pugging, hummocking changing surface flow patterns, severe changes in nutrient concentration through very high levels of urine and feces as well. These disturbances also could be exacerbated by drought or other disturbances higher upslope in the watershed that affect surface sheet flow. A state change has occurred when montane weed species dominate the vegetation community with a concomitant reduction in the reference community species of Drummond’s willow, Sitka willow, Booth’s willow, prickly current, Sitka alder, and bluejoint.

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