Deep Loess Exposed Backslope Savanna

Description

The reference plant community is categorized as an oak savanna, defined by a continuous ground layer of grasses and forbs, a ten to 30 percent canopy of oaks, and a sparse layer of shrubs (Asbjornsen et al. 2005; Nelson 2010; NatureServe 2015). The two community phases within the reference state are dependent on a fire frequency of every one to ten years (LANDFIRE 2009). Shorter fire intervals maintain dominance by grasses, while less frequent intervals allow woody vegetation to increase their importance in the community. Grazing and drought disturbances have less impact in the reference phases, but do contribute to overall species composition, diversity, cover, and productivity.

Submodel

Description

Long-term fire suppression can transition the reference savanna community into a fire-suppressed closed-canopy state. As the natural fire regime is removed from the landscape, encroachment by shade-tolerant species ensues as the overstory canopy becomes denser (Asbjornsen et al 2005). Succession to this state can occur in as little as 25 years from the last fire (LANDFIRE 2009).

Submodel

Description

The cool-season pasture state occurs when the reference state has been anthropogenically-altered for livestock production. Fire suppression, seeding of non-native cool-season grasses, removal of woody vegetation, and grazing by domesticated livestock transition and maintain this simplified grassland state (Rosburg 1994). Early settlers seeded such non-native cool-season species as smooth brome (Bromus inermis Leyss.) and Kentucky bluegrass in order to help extend the grazing season (Smith 1998). Scattered bur oaks may have escaped harvest by settlers and could be present. Over time, as lands were continually grazed by large herds of cattle, the non-native species were able to spread and expand across the prairie habitat, reducing the native species diversity.

Submodel

Description

Savanna reconstruction has become an important tool for repairing natural ecological functioning and providing habitat protection for numerous grassland-dependent species. The historic plant community of the tallgrass oak savanna was extremely diverse and complex, and habitat replication is not considered to be possible once the native vegetation has been altered by post-European settlement land uses. Therefore ecological restoration should aim to aid the recovery of degraded, damaged, or destroyed ecosystems. A successful restoration will have the ability to structurally and functionally sustain itself, demonstrate resilience to the natural ranges of stress and disturbance, and create and maintain positive biotic and abiotic interactions (SER 2002). The reconstructed savanna state is the result of a long-term commitment involving a multi-step, adaptive management process. Bur oak plantings or selective tree thinning of non-oak species will be required in order to reproduce the overstory canopy (Asbjornsen et al. 2005). Diverse, species-rich seed mixes may be important to utilize as they allow the site to undergo successional stages that exhibit changing composition and dominance over time (Smith et al. 2010). On-going management via prescribed fire and/or light grazing will help the site progress from an early successional community dominated by annuals and some weeds to a later seral stage composed of native perennial grasses, forbs, shrubs, and eventually mature bur oaks. Establishing a prescribed fire regime that mimics natural disturbance patterns can increase native species cover and diversity while reducing cover of non-native forbs and grasses. Light grazing alone can help promote species richness, while grazing accompanied with fire can control the encroachment of undesirable woody vegetation (Brudvig et al. 2007).

Submodel