Fuels Management in the Subtropical Mountains Division

The heterogeneity of the forests west of the Mississippi River in the Southern United States is strongly influenced by physiography and topography. The west Gulf Coastal Plain of southern Arkansas, northwestern Louisiana, and eastern Texas features highly productive pine-dominated forests (Pinus spp.) on gentle terrain that are interspersed by major and minor alluvial bottomland hardwood forests. The Ozark Mountains are an uplifted eroded dolomitic plateau in northern Arkansas, eastern Oklahoma, and southern Missouri; they feature primarily oak-hickory (Quercus spp.–Carya spp.) forests with a minor and varying pine component that was far more widely distributed 150 years ago than it is today. Both of these areas support forests similar in species composition and fire dependency as types farther to the east. Between these two areas lie the Ouachita Mountains of western Arkansas and eastern Oklahoma, among the most ecologically unique ecoregions of the South. Three elements contribute to that uniqueness. First, the general orientation of Ouachita ridges runs from east to west, perpendicular to most other mountains and hills in the continental United States. This points to the second unique element; forest types are closely associated with aspect, with xerophytic pine-dominated forests on the south-facing slopes, and mesophytic oak-dominated forests on the north-facing slopes. The third element is unusually important—the dominance of shortleaf pine (Pinus echinata) in the Ouachitas. East of the 100th meridian, shortleaf is the most widely distributed of the southern pines (Guldin 2007), and is generally found in mixture with other pines or in pure stands of limited extent. But in the Ouachitas, shortleaf reaches its ecological maximum, where it is the only naturally occurring pine and the dominant tree species in many stands. As a result of this unusual ecological association among tree species, forest types, and physiographic conditions, the area has a separate classification as the Ouachita Mountains Mixed Forest–Meadow Province within the Subtropical Division (Division 230). It is somewhat warmer, less wintry, and wetter than the Ozark Broadleaf Forest of the Hot Continental Division (Division 220) to the north. However, it is more prominently mountainous than the Southeastern Mixed Forest Province to the south or the Mississippi Alluvial Bottomland Forests to the east, both of which also lie within the Subtropical Division. And, it is more densely forested than the Prairie Parkland Province that lies to the west—although prairie elements do exist in the Ouachita forests. Finally,