Loamy Overflow

Description

This State represents what is believed to exist prior to European settlement. The Reference State may exist but is unlikely to function within the natural rage of variability due to the spread of Kentucky bluegrass and smooth brome onto this site. In the Reference State, this site is dominated by warm-and cool- season grasses, and various shrub and tree species that are scattered across the site. Grazing or the lack of grazing, flooding or lack of flooding, fire, excessive haying, and invasion of non-native cool-season grasses are the major drivers of this State. Flooding and no fire on this site can cause a transition to a Woody Overstory State (4.0).

Submodel

Description

This State has a significant amount of Kentucky bluegrass or smooth brome in the plant community but they have not become the dominate species. In this State, Kentucky bluegrass makes up less than 30 percent of the plant community composition (by weight). This State is at risk of transitioning to a bluegrass dominated Invaded State (3.0).

Submodel

Description

This state is the result of invasion and dominance of introduced species. This state is characterized by the dominance of Kentucky bluegrass and smooth brome, and an increasing thatch layer that effectively blocks introduction of other plants into the system. Plant litter accumulation tends to favor the more shade tolerant, introduced grass species. The nutrient cycle is also impaired, and the result is typically a higher level of nitrogen which also favors the introduced species. Increasing plant litter decreases the amount of sunlight reaching plant crowns thereby shifting competitive advantage to shade tolerant, introduced grass species. Studies indicate that soil biological activity is altered, and this shift apparently exploits the soil microclimate and encourages growth of the introduced grass species. Once the threshold is crossed, a change in grazing management alone cannot cause a reduction in the invasive grass dominance. Preliminary studies would tend to indicate this threshold may exist when Kentucky bluegrass exceeds 30 percent of the plant community and native grasses represent less than 40 percent of the plant community composition. Plant communities dominated by Kentucky bluegrass have significantly less cover and diversity of native grasses and forb species (Toledo, D. et al., 2014).

Submodel

Description

This State is the result of the establishment of a tree overstory and shrub mid-story canopy. This State is more common on the lower reaches of the site. The dynamics of this State are largely due to flooding and successional changes, starting with cottonwood and shrub establishment, and eventually the development of a green ash and boxelder plant community. The successional process can restart following another flooding event. Water control structures which limit flooding, livestock grazing, heavy wildlife browse, fire, and the introduction of non-native, cool-season grasses can alter the dynamics of this site resulting in old remnant stands of trees with little, if any regeneration.

Down cutting of the drainageway or stream channel will eventually leave the overflow site on a higher and drier landscape position. In this case the site will be described as the Loamy Terrace Ecological Site (R060AY022SD).

Submodel

Description

This State developed as a result of the invasion of Russian olive and/or saltcedar in combination with continuous season-long grazing, or continuous seasonal grazing, or fire. With time, the cottonwood, boxelder and ash trees that survive become mature, and little or no regeneration occurs. This is due mainly to grazing of seedlings and saplings. Wildlife browse can also contribute to the loss of native tree and shrub regeneration. Grazing that limits regeneration also results in a reduction of the desirable native herbaceous species, often resulting in a dominance of species such as bluegrass and/or smooth brome, and forbs such as western ragweed, Canada thistle, burdock, and hound’s tongue.

Submodel