Arkansas is often called “The Natural State” for its varied terrain, but it lies overwhelmingly within a single, expansive biome: the Temperate Deciduous Forest. This biome is characterized by a specific climate, distinct vegetation, and specialized animal life that have all adapted to those conditions. The physical landscape of Arkansas, however, is so diverse that this broad biome is expressed through several unique regional ecosystems.
Arkansas’s Primary Biome: Temperate Deciduous Forest
The overarching biome of Arkansas is defined by the presence of four distinct seasons, which include a long, warm growing season and a period of winter dormancy. Annual precipitation is abundant, typically falling between 30 and 60 inches across the state, and is distributed relatively evenly throughout the year. This consistent moisture supports a rich forest canopy primarily composed of broadleaf, or deciduous, trees.
The forest is dominated by species of oak (Quercus spp.) and hickory (Carya spp.), which are the characteristic trees of the eastern United States’ temperate forests. These species have adapted to the cold season by shedding their leaves each autumn, a process that conserves water when the ground is frozen. The decomposing leaf litter from these trees contributes to the development of the rich, fertile soil layers found across much of the state. This general forest type covers the majority of Arkansas, but its expression changes dramatically depending on the local topography and soil conditions.
The Ozark and Ouachita Highlands Ecosystems
The northwestern and central-western parts of the state are dominated by the uplifted and heavily eroded ancient mountain ranges of the Ozark and Ouachita Highlands. These regions modify the general deciduous forest biome with rocky, thin soils and significant changes in elevation. The Ozarks, which are technically a dissected plateau, feature karst topography with limestone and dolomite bedrock, leading to numerous springs, caves, and sinkholes.
The Ouachita Mountains, in contrast, are characterized by folded ridges of sandstone and shale that run in an unusual east-west direction. Forests in the highlands are often a mixture of hardwoods like white oak and hickory, interspersed with conifers, most notably the drought-tolerant shortleaf pine (Pinus echinata), which thrives on drier, south-facing slopes. Unique habitats such as rocky glades and fast-flowing, spring-fed streams also occur here, supporting endemic species like the Ozark hellbender, a large aquatic salamander adapted to the clear, cool waters.
The Delta and Gulf Coastal Plain Ecosystems
Moving away from the mountainous regions, the ecosystems transition to the low-lying, flat terrain of the east and south. The Mississippi Alluvial Plain, commonly known as the Arkansas Delta, is defined by the massive influence of the Mississippi River and its tributaries. This area consists of deep, fertile alluvial soils deposited by millennia of river flooding, creating a landscape of swamps, bayous, and oxbow lakes.
The dominant vegetation here is the bottomland hardwood forest, which includes species that can tolerate prolonged periods of standing water, such as water tupelo, bald cypress, and overcup oak. To the south, the Gulf Coastal Plain is characterized by rolling, sandy hills formed from ancient marine sediments left behind by a receding ocean. While less fertile than the Delta, these areas historically supported extensive loblolly and shortleaf pine forests, as well as the unique Blackland Prairies.
Climate, Water, and Geological Influences
Arkansas’s diverse ecosystems are rooted in its humid subtropical climate and geology. The state’s position in the interior South places it in a zone where warm, moist air masses from the Gulf of Mexico provide abundant precipitation. This high annual rainfall is the primary reason the state is overwhelmingly forested.
The underlying geology shapes the regional ecosystems. The ancient, uplifted, and heavily folded rocks of the Ozark and Ouachita mountains in the northwest create steep terrain and rocky soils that limit the retention of water and nutrients. Conversely, the flat geological history of the Delta and Coastal Plain, with their layers of rich alluvial silt and marine sand, allows for the formation of deep, productive soils ideal for wetlands and bottomland forests.