Ecological dynamics

Overview
These wetland communities occur in peatlands dominated by all wetland obligate species meaning that they almost always occur (estimated probability greater than 99 percent) under natural conditions in wetlands. These occur on depressions within meadows in valley or glacial basins near sloping uplands or ground moraines. They are typically surrounded by forested areas. These areas have been kept free of upland shrub and conifer species establishment through saturated soils that are generally intolerable to shrub species and conifers of the surrounding areas. Soils are saturated from ground water discharge, sheet flow and periodic ponding. The melt out of snow in spring produces ponding of cold water that, with cold soil temperatures lowers the decomposition rate of plant material leading to accumulation of peat (organic material mantle). Typically, the native plant species within the reference phase are all obligate wetland carex species that have high foliar cover, and are very productive. In other areas with slightly less saturated soils, carr type (shrubby) fens occur which are dominated by wetland affiliated shrubs Betula nana and or Salix drummondiana with an understory of carex and juncus species. This ecological site spans the ranges of types (rich to intermediate to poor types) of basin fens which are based on proportion of sphagnum to brown moss cover, productivity and species of vascular plants and acidity of the water and soil. The foliar canopy cover is high, and the community is very productive in the rich type and is dominated by brown mosses and is more likely basic. The poor type is less productive, with lower foliar cover and is dominated by sphagnum mosses and is more likely acidic. Intermediate type fens span between these two opposite types. Fens described in this ecological site are intermediate to rich types of the plate basin fen.

Disturbance Dynamics
Dynamics within State 1:
Disturbance dynamics within the natural functioning state include: fire, beaver dams, low precipitation or snowpack years and ungulate grazing. These disturbances are viewed as potentially changing the plant population composition to a minor extent from one phase to another within State 1 but with the ability to return to any phases with time after disturbance. These disturbances affect hydrology which is critically important to this site. Moderate disturbance will increase baltic rush (Juncus balticus) and associated forbs (Hansen, 1992), while severe disturbance may lower the water table and cause the site to be dominated by species such as Kentucky bluegrass (Poa pratensis), fowl bluegrass (Poa palustris), common silverweed (Potentilla anserina) or redtop (Agrostis stolonifera) (Hansen, 1992). Moderately disturbed sites will improve rapidly with protection due to the rhizomatous nature of many sedge species that occupy this site. This site is flooded long enough to provide nesting habitat for waterfowl but has limited use by songbirds and small mammals because of the lack of diversity and flooded soils. It is an important habitat for raptors, deer, and elk. Beaver dams assist in controlling the downcutting of channels, bank erosion, and the movement of sediment downstream (Gordon and others 1992). When beaver construct a dam, they raise the water table in the area, which provides water for hydrophytic plants. The beaver dam also slows down the water in the channel, which allows suspended sediment to be deposited behind the dam. The combination of sediment deposition and plant reproduction raises the channel bed (Hansen, 1992).
Fire can occur, though rarely and only in dry years within fens. These fires would eliminate conifer and shrub encroachment on the site and maintain the reference phase community dominated by sedges. Typically, fires would only top burn the current year’s growth of the sedges. Carex lasciocarpa and Carex utriculata are resistant to damage by fire through their extensive root system and resprouting capabilities, except where hot fires penetrate the peat soil. As well, Carex utriculata can be in the soil seed bank up to 18 inches deep, so it may establish from on-site seed after fire. Fire in fens is highly dependent upon the surrounding vegetation type carrying the fire to these saturated sites. Within the Seely-Swan Ranger District of the Flathead National Forest, the subalpine fir/queencup beadlily ecological site typically surrounds these fens, which has low occurrence but high severity fire regime and has a fire free interval of approximately 130 years. Generally, these fens 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 percent 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 percent 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 and shrub encroachment. If a severe fire would occur within a fen and destroy the rhizomes of the sedges, then a threshold would be crossed, and major species composition could occur. Fire in surrounding forested communities could also impact the hydrology of the fen and cause increased runoff, and potentially groundwater flow, by decreasing live trees upslope and potentially change the species composition of the fen (Steve Shelly, personal communication, 2015). As well, extensive epidemics of forest disease or pests that lead to large scale death of trees could attain the same result. Two sites were on the boundary of major fires on the west side of the continental divide (Robert fire in 2003 burned 54,191 acres and the Moose fire in 2001 burned 66,688 acres). However, the sites did not have evidence of burning.
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 leading to potentially shrub invasion and if long enough, conifer invasion to a small scale. Presence of beaver damming would potentially lead to a mosaic effect on the plant communities potentially as opposed to the typical saturated fen with sedge vegetation within a larger landscape of conifer dominated environment or a less saturated carr type of fen with Betula nana or Salix species.
Low precipitation or drought years that impact precipitation and snow melt could potentially cause change in plant species composition by allowing shrubs in invade the site. Less precipitation and snow melt would decrease current year growth of the dominant sedge species at the reference phase, and allow drier site shrubs to potentially invade, but would not cause a state change since a resumption of normal precipitation would generally lead to resumed saturated conditions that preclude shrub encroachment. A severe drought that would adversely affect the sedge community and allow the establishment of dry site species would have crossed a threshold and cause a state change.
Ungulate grazing would be considered within the range of normal functioning disturbances that may change some species composition within State 1 if it were light grazing, seasonal or rotational, did not lead to extensive trailing, wallowing or cut banking of flow through channels. Ungulate hoof action can break up the rhizomatous sod, which can lead to unvegetated microsites conducive to shrub encroachment; in addition, pugging and hummocking can create some surface flow patterns which may accelerate water loss from the peatland. Urine and feces can change nutrient concentration as well. If the ungulate use is low, then it is viewed as normally functioning. Carex utriculata is considered moderately tolerant of grazing, though it may be replaced by other species when heavily grazed over extended periods. 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 groundwater discharge and surface sheet flow.
Large scale timber harvesting upslope or higher in the adjacent watershed to the fen can cause a state change to occur. If there were a large, extensive clear-cut that caused abrupt changes in the hydrology upslope of the fen and affect groundwater or surface flows these would cross a threshold and cause either a state change to dry site species, or an increase in run-in to the peatland since the removal of trees reduces the water uptake. In addition, loss of shading by adjacent conifers may likely be beneficial to the peatlands as most of the species are shade-intolerant. Very small scale timber harvesting or that was not clear-cut prescription, would not cause a threshold to be crossed and a state change to occur. This dry site species community could be more at risk to weed species invasion including timothy (Phleum pratense), Canada thistle (Cirsium arvense) or reed canarygrass (Phalaris arundinacea). Overstocked surrounding forests can potentially alter the water balance of fens by taking up more water in the trees than a non-overstocked forest.
Road building upslope or higher in the watershed from a fen could cause a threshold to be crossed and a state change to occur if it impacted surface flow to a degree that most of the upslope water is diverted away from the lower fen. Less groundwater or surface flow would cause drying of the site leading to dry site species invading and possibly weedy species as well. Water well establishment in the vicinity or upslope of the fen could cause less groundwater available to maintain saturated soils for the site and could cause a threshold to be crossed and a state change to dry site species to occur. As well, any ditching or draining of fen would cause a threshold to be crossed in the normal functioning hydrology of the fen and a state change to dry site species would occur. This site would be more vulnerable to weedy species invasion. Peat mining could also cause a threshold to be crossed if it greatly impacted the hydrology or was extensive enough that the sedges were unable to recolonize the impacted areas. Point source pollution that degraded the plant community functioning, vigor or changed the hydrology or nutrient concentration significantly could cause a threshold to be crossed and a state change to occur.

Dynamics that cause a State change:
Three major disturbances that can occur in this ecological site that could cross a threshold triggering a state change would include a significantly altered hydrologic regime and invasion by reed canary grass. If the hydrologic regime has been severely altered and causes a significant reduction in water flow into a fen, then a state change can occur causing dry site or upland species to invade and succeed in the fen. Once this threshold has been crossed significant human input is required to revert the site to its natural hydrologic regime and native vegetation. Dry site or upland species are not dependent on a hydrologic regime and would outcompete the native wetland obligate sedge species. Once upland species have outcompeted and dominated the vegetative community, associated upland weed species can also thrive given adequate propagules.
A weed species of critical importance to this ecological site is the escaped cultivar of reed canary grass. This cultivar is exceeding competitive against the native community with the addition of nutrients from agricultural run-off. Therefore, a review of scientific literature on reed canary grass and other upland weed species follows.
A fen can be converted to a plowed field of either pasture or cropland grass species after the fen has had its hydrologic regime severely altered through ditching and or draining.

Effects of land management practices on ecological dynamics and invasive species invasion theory
Invasion of weedy species into native vegetation communities requires an understanding of the processes and mechanisms by which an invasion occurs. Resistance and resilience of the native community are essential elements in predicting the success of the invasion. There are two counter point theories on invasive species. The driver theory considers the invasive species to be driving species decline while the passenger model sees the invading species as filling in empty niches left by habitat alteration (Didham, 2005). The passenger model suggests that disturbance is the cause and if stopped, invasion can be reversed. Potential mechanisms of invasion include theories such as novel weapons, enemy release, competitive superiority, and manipulation of environment. Novel weapons include biological weapons or associations with micro-organisms that allow the invader species to either access new resources or steal them from indigenous plants (Tannas, 2011). Specifically, arbuscular mycorrhizal fungi may provide a substantial competitive advantage to spotted knapweed by carbon parasitism (Carey, 2004). In these cases, the invader uses these weapons to drive the invasion process. Enemy release describes the concept that once invader species are released from their native predator species or chemical warfare within their original community, they are more aggressive in their new community (Blumenthal 2006, Callaway and Aschelhoug 2000). The invader species may have characteristics that allow it to be more competitive than resident plant species such as grazing resistance, adaption to a harsh environment or another competitive ability (Tannas, 2011). Invading species can manipulate the environment to their advantage through resource competition. Mechanisms include modifying light interception, water uptake efficiency or change in soil water holding capacity, nutrient uptake and cycling (D’Antonio and Vitousek, 1992). The final outcome of invasion is establishment of the invading species which occurs as either dominance, coexistence, or exclusion from the indigenous plant community (Seabloom, 2003). D’Antonio and Vitousek (1992) stated grass invasions are particularly important because they are actively moved by humans and exotic grasses compete effectively with native species in many ecosystems. In addition, dominant grasses may change nutrient cycling, modify regional microclimates and alter fire dynamics.
Wetland Designations
Weedy species can be divided into categories based on affinity to wetlands through the Wetland Indicator Status by the 1988 US Fish and Wildlife Service’s national list of plant species that occur in wetlands.
Species categorized as obligate (OBL) are hydrophytes that almost always occur in wetlands. The sedges within the reference community of this ecological site are within this designation.
Species categorized as facultative wetland (FACW) are hydrophytes that usually occur in wetlands, but may occur in non-wetlands. Reed canarygrass is in this designation and may occur in this ecological site.
Species categorized as facultative (FAC) are hydrophytes that occur in wetlands and non-wetlands. Weedy species found in this ecological site that are FAC include: quackgrass, redtop, timothy, creeping meadow foxtail, Kentucky bluegrass and Canada thistle. Canada thistle is on the Montana state noxious weeds list.
Species categorized as facultative upland (FACU) are non-hydryophytes that usually occur in non-wetlands, but may occur in wetlands. Weedy species found in this ecological site that are FACU include: orchardgrass and dandelion.
Weed species designated facultative wetland:
The following weedy cultivar species is found within State 1 in lower amounts and as a dominant species in State 3.
Wetlands have a higher percentage of weed invasions compared to other vegetation communities. As a whole, wetlands serve as sinks for nutrients, water and sediments (Zedler, 2004). These abiotic attributes as well as changes from disturbance that affect hydrology, vegetation canopy gaps, soil structure exacerbate invasions, particularly of aggressive, weedy invaders that form monospecific stands. A particularly aggressive wetland invasive plant is Phalaris arundinacea (Phalaris). Phalaris is native to North America and can grow in a non-invasive way. Numerous introductions of the European population of Phalaris has potentially caused these two to hybridize and become invasive (Lavergne and Molofsky, 2004). The invasive form is likely an admixture of these populations. Phalaris is a C3 type, cool season, 1 to 2 meter tall, long-lived perennial that produces dense crowns and a prominent network of rhizomes (Hitchcock, 1950; Lavergne and Molofsky, 2007). Phalaris can establish early and quickly in wetlands due to its early season growth, clonal growth form, morphological plasticity, high architectural plasticity, ability to quickly assimilate nutrients and increase aboveground growth substantially, adapt to various flooding regimes and even drought (Gebauer et al 2015; Lavergne and Molofsky, 2004; Herr-Turoff and Zeller, 2007; Green and Galatowitsch, 2001; Kercher and Zedler, 2004). Phalaris can establish through its substantially numerous outcrossed seeds, in a yearly seed crop. It can also reproduce vegetatively by propagation of vigorous rhizomes and tillers. It can establish in the early growing season and thereby attaining larger size and height in comparison to other plant species and be able to outcompete for light, thereby shading competitors (Herr-Turoff, 2007). This is also enhanced by its rapid stem elongation. Kercher (2007) concluded that Phalaris invasion can be summarized as a three step process. Initially, resident native species decrease with prolonged flooding and sediment additions. These factors along with increased nutrients, accelerated Phalaris aboveground growth and led to a monospecific stand. Finally, native species further declined with an increase in Phalaris. Disturbances exacerbate this process. Resident native plant communities in areas with minimal disturbance can remain dense and vigorous. Therefore, when anthropogenic disturbances coincide with an increase in gross supply of resources, the more tolerant and fast growing and morphologically plastic plants like Phalaris can invade rapidly. Once established, Phalaris can grow as a sward in lower water conditions (intermittent and early season flooding), or as a tussock in higher water conditions (constant flooding) (Herr-Turoff, 2007). Early season flooding increased the lateral spread of individual shoots of Phalaris causing a sward. In the tussock growth form, Phalaris tolerated longer durations of flooding and more than doubled its aboveground biomass. Phalaris has the highest level of root airspace when compared with numerous other wetland plant species (Kercher and Zedler, 2004). Thereby, it can tolerate numerous flooding regimes. It can change the ratio of shoot to root growth, depending on environmental conditions. In high nutrient conditions, Phalaris is able to absorb and use nutrients quickly to accelerate shoot versus root growth. The greater plasticity in root / shoot allocation with changes in nitrate-Nitrogen additions and proportional allocation to root biomass that was greater than the native community are factors that account for the dominance of Phalaris (Green 2001). It can also increase tiller length and angle of branching to daughter tillers (Martina, 2013). Phalaris produced significantly more tillers that were more widely dispersed in saturated conditions. Increased soil nitrogen did not affect the spatial pattern of tillers, but did affect biomass production, shoot to root ratio and the biomass per tiller. This allows it to spread quickly throughout an area. Phalaris also has a plastic response to carbon gain to nitrogen supply (Holaday 2015). When nitrogen is high, Phalaris strongly increases CO2 assimilation, photosynthetic nitrogen use efficiency and respiration. When it is deprived of nitrogen, Phalaris has a decrease in leaf nitrogen but not vacuolar membrane nitrate (while both decreased for native species). Phalaris doubled CO2 assimilation in 12 days after being supplied nitrogen after being deprived. This plasticity was not absorbed to this degree in other wetland native plants. Therefore, Phalaris can quickly respond to changes in carbon and nitrogen. Additions of nutrients into natural wetlands can be a problem in urban and agricultural areas. Phalaris produces a dense, high carbon to nitrogen litter layer that impedes the germination and growth of competitor plant species (Molofsky et al 2014). Along streams, Phalaris can increase sediment deposition and reduce water circulation through dense stands that grow into the stream channel (Werner and Zedler, 2002). Phalaris can also tolerate drought conditions. In dry soil, it has significantly higher growth and fecundity versus in saturated soil conditions.
Numerous control strategies have been developed for Phalaris. The successful strategies include adapting restoration to a landscape scale size and using physical and chemical control coupled with hydrological management and subsequent restoration on native community structure and composition (Lavergne and Molofsky, 2007).

Weed species categorized as facultative species:
The following weed species can occur in the natural hydrologically intact State 1 community of wetland obligate sedge community or in the severely altered hydrology community in State 2. These weeds are able to thrive in both wetland and non-wetland environments.
Quackgrass (Elymus repens) is an undesirable weed species. It is a cool season, exotic, perennial, rhizomatous graminoid. It propagates mainly by rhizomes, but also from seed. It is adapted to certain seasonal fires because of its rhizomes. It is best eradicated by a combination of mowing, burning and chemical applications.
Redtop (Agrostis gigantea) and creeping bentgrass (Agrostis stolonifera) are both invasive weedy species. They often hybridize and therefore are treated the same here. It is native to Europe and was introduced as a pasture grass. It is perennial, rhizomatous, coo season, sod forming grass with either erect or decumbent stems. It regenerates vegetatively and by seed and spreads rapidly with strong rhizomes. It tolerates some flooding but is not tolerant of drought. It is fairly resilient to fire because of its rhizomes and buried seed. Fire does top kill redtop.
Timothy (Phleum pratense) is an introduced (from Eurasia), cool season, perennial bunchgrass that grows to 20 to 40 inches tall. It can grow on a variety of habitats but is best suited to well drained moist clay or loam soils. It was cultivated for hay and pasture use. It is palatable and nutritious forage for cattle and big game. It is generally short-lived (4 to 5 years) but can live up to 6 to 7 years. It has a moderately shallow and fibrous root system which can extend to 48 inches into the ground. Timothy is non-rhizomatous and forms vesicular-arbuscular endomycorrhizal associations. It reproduces mainly from seed and vegetatively by tillering. It is a prolific seed producer. Timothy and Kentucky bluegrass are of great concern since they establish quickly, spread vigorously and usually escape early detection. Control should include elimination and simultaneous introduction of desirable competitor native species. Timothy is well adapted to fire since fire stimulates production of reproductive tillers. Although it can be harmed if burned when actively growing in the spring and summer. It is fairly tolerant to fire when dormant.
The weedy species creeping meadow foxtail, Alopecurus arundinacea has numerous cultivars. The cultivar “Garrison” was released by the NRCS in 1964. It is from Eurasia and is an aggressive invader of wetland areas. It came to NA from settlers from eastern Germany and western Russia. It is a perennial grass, 3 to 6 feet tall, fairly vigorous rhizome, with a very large root system. It can grow 4 feet of crown diameter growth per year. Therefore, it is grazing tolerant. As well it is tolerant of a wide range of pHs and high levels of nitrogen and moderate salt levels, very flood tolerant and fairly drought tolerant. It is adapted to cold temperatures and is extremely winter hardy. It has early spring growth and grows quickly and can outcompete native vegetation. It proliferates by wind and water born seed. It can grow in many soil types even sand, clay, peat, and muck.
Kentucky bluegrass (Poa pratensis) is an introduced, perennial, and short to medium tall, cool-season, sod forming grass. It is shallow rooted and is intolerant to drought. It is found in moist sites in areas with cool and humid climates or riparian areas. Kentucky bluegrass is a vigorous herbaceous competitor with rhizome expansion, abundant seed, good seedling recruitment and quick establishment on disturbed sites. It is well adapted to meadows which have seasonally high water tables and mid-summer drought. It is naturalized and can dominate meadows, particularly ones that were once dominated by tufted hairgrass (Deschampsia ceaspitosa) and sedges. It is highly palatable to cattle. The rhizomes of Kentucky bluegrass help it survive quick moving fires, though postfire vigor and density are greatly affected. The most damaging fires occur in late spring after Kentucky bluegrass has been growing at least a month. Cool fires conducted when plants are dormant have little effect.
Canada thistle (Cirsium arvense) is a perennial, introduced (from SE Europe) forb with creeping horizontal lateral roots with dense clonal growth and a dioecious habit. Canada thistle has deep and wide spreading root system with a slender taproot and far-creeping lateral roots. It reproduces sexually by seed (this is the long distance dispersal strategy) and vegetatively by creeping roots (local spread strategy). It is adapted to survive fire on site with its root system and colonize recently burned sites with bare soil by seed. It has invaded nearly every type of upland herbaceous vegetation community, particularly prairie and riparian areas. Montana State listed Noxious Weeds List.
Weed species designated facultative upland species:
This weed species is found primarily in upland environments found in State 2.
Orchardgrass (Dactylis glomerata) is an undesirable weed species. It was introduced to eastern US from Europe in 1760. It is a cool season, perennial bunchgrass, which is nonrhizomatous but does produce a dense sod of medium sized roots. It reproduces largely by seed and tiller formation. It is reported to increase or remain stable after fire. It does not withstand continuous heavy forage use by cattle.