Limy Subirrigated

Description

The Limy Subirrigated site typically occurs along the edges of drainageways or closed depressions. Soils are somewhat poorly drained which have a water table within 2 to 5 feet of the soil surface that persists longer than the wettest part of the growing season typically until the month of August. Soils will effervesce with hydrochloric acid at or near the surface. The central concept soil series is Davison, but other series are included. This state represents the natural range of variability that dominates the dynamics of this ES. This state is typically dominated by warm-season grasses, with lesser amounts of cool-season grasses. Before European settlement, the primary disturbance mechanisms for this site in the reference condition included periodic fire, grazing by large herding ungulates, and fluctuations in the water table and ponding frequency and duration. Frequent surface fires (3 to 5 years) and grazing coupled with weather events dictated the dynamics that occurred within the natural range of variability. Mid- and tall stature grass species could have declined with a corresponding increase in short stature warm-season grasses and cool-season grass-like species occurring. Presently, the primary disturbance is from a lack of fire, concentrated livestock grazing, and weather fluctuations. Species that are desirable for livestock and wildlife can decline and a corresponding increase in less desirable species will occur. Today, a similar state, the Native/Invaded State (State 2) can be found on areas that are properly managed with grazing or prescribed burning and sometimes on areas receiving occasional short periods of rest. These sites are differentiated by the presence of exotic species such as Kentucky bluegrass and smooth bromegrass. On most Limy Subirrigated ESs within the MLRA, these species have invaded and are now present. It is likely that attaining the reference state as described here (without the presence of exotic herbaceous species) is not possible.

Submodel

Description

This state is very similar to the Reference State and represents the more common range of variability that exists with higher levels of grazing management but in the absence of periodic fire due to fire suppression. This state is dominated by warm-season grasses, but invasive cool-season sodgrasses are now present in all community phases of the state. Taller warm-season species can decline and a corresponding increase in short statured grass will occur. It can be found on areas that are properly managed with grazing and prescribed burning, and sometimes on areas receiving occasional short periods of rest.

Submodel

Description

This state is a result of encroachment mainly by invasive introduced cool-season grasses such as Kentucky bluegrass. Kentucky bluegrass has a high tolerance for calcium carbonates and a fast vegetative response to disturbance. 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. The ecological processes are not functioning, especially the biotic processes and the hydrologic functions. The introduced cool-season grasses cause reduced infiltration and increased runoff. 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. The opportunity for high intensity spring burns is severely reduced by early greenup and increased moisture and humidity at the soil surface, and grazing pressure cannot cause a reduction in sodgrass dominance. Production is limited to the sod forming species. Infiltration continues to decrease and runoff increases and energy capture into the system is restricted to early season low producing species. Nutrient cycling is limited by root depth of the dominant species.

Submodel

Description

This state is characterized by the production of annual crops using a variety of tillage and cropping systems along with management practices. Cropping on this site is enabled during years with drier than normal precipitation or with artificial drainage (surface or subsurface).

Submodel