Natural communities are assemblages of interacting plants, animals, and other organisms that occur repeatedly across the landscape under similar environmental conditions and are structured by natural processes rather than modern, anthropogenic disturbances; thus, they provide the kinds of high-quality habitat types that our priority bird species evolved with. The Central Hardwoods Joint Venture takes a “natural communities” approach to terrestrial conservation planning, focusing on the following general community types:1. Prairie/Grasslands: dominated by perennial grasses and forbs with scattered shrubs and very few trees (less than 10%); they typically occurred on flat to gently rolling topography where they graded into savanna and woodlands if the terrain became more dissected; most have been converted to agriculture.
2. Prairie/Savanna (Barrens): large expanses of prairie-like grasslands interspersed with isolated patches of fire-tolerant trees and shrubs, and sometimes shallow wetlands; occurred primarily in certain landscapes within the Interior Low Plateaus portion of the Central Hardwoods Bird Conservation Region.
3. Glades/Savanna/Woodland Complexes: open, rocky, barren areas with shallow soils that support unique communities of drought-adapted forbs, warm-season grasses and a specialized fauna; are most often located on western or southern exposures or on the high summits of ridges, knobs, domes or escarpments where soils are thin and moisture conditions favor drought-tolerant species, but also can occur in low basins where certain edaphic conditions foster their development.
4. Open Oak Woodlands: scattered trees form a canopy of 20-50%, with an open understory and rich herbaceous ground cover; typically occur on high flats, ridges and slopes with thin soils and exposure to sun and wind.
5. Closed Oak Woodlands: trees form a canopy of 50-80%, with an open understory and rich herbaceous ground cover; typically occur lower on slopes than open woodlands where more moisture can accumulate.
6. Pine-Bluestem Open Woodlands: shortleaf pine with an open understory of warm season grasses and forbs are prominent on dissected plains in portions of Missouri and Arkansas, with a canopy cover of 30-60%.
7. Pine-Oak Closed Woodlands: typically occurs on mid-to-low, gentle-to-moderately steep, north- and east-facing slopes and/or on low-to-mid south and mid-north slopes where the fire frequency was less than that in pine-bluestem systems. If slopes are very steep, pine is less typical or drops out. The percentage of pine to oak can range from 80/20 to 30/70 depending on fire behavior.
8. Forests: dominated by trees forming a closed canopy and interspersed with multi-layered shade-tolerant subcanopy trees, shrubs, vines, ferns and herbs; occur in lower landscape positions of deeply dissected terrain, floodplains and swamps.
With the exception of mesic forests, all are fire-maintained, although even mesic sites were exposed to large-scale fires that periodically occurred after long droughts.