Ecological dynamics

Ecological Dynamics of the Site
This ecological site is primarily in swales or drainageways on glacial moraines or glacial valley floors, but can also occur in sloughs in floodplains. These shrubby swales are within the lower subalpine lifezone which includes the subalpine fir (Abies lasiocarpa)-Engelmann spruce (Picea engelmannii) ecological zone and within these cool habitats are not restricted to streamsides but also occupy moist, well-aerated soils of meadows, broad valley bottoms, side slope seeps and stream and pond margins (Boggs, 1990).


STATE 1.0
These shrubby swales are within the subalpine fir (Abies lasiocarpa)-Engelmann spruce (Picea engelmannii) ecological zone and within these cool habitats are not restricted to streamsides but also occupy moist, well-aerated soils of meadows, broad valley bottoms, side slope seeps and stream and pond margins (Boggs, 1990). Shrubby swale sites are dominated by the tall statured shrub Drummond’s willow (Salix drummondiana). Drummond’s willow is a deciduous shrub generally between 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).

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 effect 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. 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.

COMMUNITY PHASE 1.1:
Drummond’s willow (Salix drummondii)-Alderleaf buckthorn (Rhamnus alnifolia)/bluejoint (Calamagrostis canadensis)/field horsetail (Equisetum arvense).

Summarization of canopy cover of species present at community phase 1.1 of this ecological site, including constancy and average canopy cover value, 8 sites (includes 4 NPS original site data and 4 NRCS revisits and 4 NRCS only sites). Species with high constancy occur often, those with low constancy are rare. The average canopy cover is the average of the values for which it occurred. Therefore, species that are rare (only occurred once) show the canopy cover value for the one time it was found. Minimum and maximum canopy cover show the range of cover that the species was found. Drummond’s willow is the indicator species with very high frequency and canopy cover. Other frequently occurring species include common snowberry, alderleaf buckthorn, field horsetail, and bluejoint.

Summarization of total annual production by species in pounds per acre for the reference community (1.1) of this ecological site, 8 sites. Drummond’s willow dominates this ecological site in average annual production with secondary species including stinging nettles and bluejoint. At one site only, Northwest Territory sedge dominated the understory.

TOTAL ANNUAL PRODUCTION 1925#/acre-(4367#/acre was a particularly lush site of Salix drummondiana overstory with Carex utriculata understory)

Community Pathways

1.1a- Fire disturbance leading top-kill and then resprouting of shrub species and bluejoint; establishment of post-fire colonizers (fireweed). Low severity, fast moving fire which does not severely affect shrub and grasses growing points allows these shrubs and bluejoint grass to resprout. The bare mineral soil is also capable of sustaining colonizing herbaceous species that are wind driven onto the site.

1.2a-Time without disturbance transitioning shrub resprouts to mature shrubs; diversification of understory species. The post-fire disturbance vegetation community of resident shrub species and bluejoint grass continue to grow to maturing and herbaceous colonizing species such as fireweed gradually reduce their understory dominance as other forb and grass species are introduced or longer duration growing forbs reestablish.

1.1b-Overgrazing and/or overbrowsing of plants reducing vigor and change shrub structure leading to a reduction in vigor and changing species composition away from (reduction) of palatable species such as bluejoint to less palatable species such as stinging nettles and field horsetail.

1.3a-Rest from grazing and/or browsing which allows the species composition and vigor to return to the reference community by allowing the recovery of bluejoint and shrub species.

T1A Overgrazing and overbrowsing; change in hydrology leading to drier site conditions; introduction, establishment and dominance of weeds.


STATE 2
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.