Pre-Columbian savannas of North America

Fire regimes of United States plants. Savannas have regimes of a few years: blue, pink, and light green areas.

Pre-Columbian savannas once existed across North America. These were created and maintained in a fire ecology by Native Americans until the 16th century death of most Native people. Surviving natives continued using fire to clear savanna until European colonists began colonizing the eastern seaboard two hundred years later. Many colonists continued the practice of burning to clear underbrush, reinforced by their similar experience in Europe, but some land reverted to forest.

Postglacial events

During the Last Glacial Maximum about 18,000 years ago, the influence of Arctic air masses and boreal vegetation extended to about 33° N. latitude, the approximate latitude of Birmingham and Atlanta. Southeastern forests of the glacial period were dominated by various spruce species and jack pine; fir was abundant in some locations. With the exception of the absence of certain prairie elements, the understories of these forests were generally typical of modern spruce-fir forests within and near Canada. Humans spread across the continent as five thousand years passed following the retreat of the glaciers, while deciduous forests expanded northward. In the east, pockets of boreal elements remained only at high elevations in the Appalachian Mountains and in a few other refuges.

Warming and drying during the Holocene climatic optimum began about 9,000 years ago and affected the vegetation of the southeast. Extensive expansions of prairies and savannas occurred throughout the southeast, and xeric oak and oak-hickory forest types proliferated. Cooler-climate species migrated northward and upward in elevation. This retreat caused a proportional increase in pine-dominated forests in the Appalachians. The grasslands and savannas of the time expanded and were also linked to the great interior plains grasslands to the west of the region. As a result, elements of the prairie flora became established throughout the region, first by simple migration, but then also by invading disjunct openings (including glades and barrens) that were forming in the canopy of more mesic forests.

At about 4,000 years BP, the Archaic Indian cultures began practicing agriculture. Technology had advanced to the point that pottery was becoming common, and the small-scale felling of trees became feasible. Concurrently, the Archaic Indians began using fire in a widespread manner. Intentional burning of vegetation was taken up to mimic the effects of natural fires that tended to clear forest understories, thereby making travel easier and facilitating the growth of herbs and berry-producing plants that were important for both food and medicines. The result in many regions was "the conversion of forest to grassland, savanna, scrub, open woodland, and forest with grassy openings". After the death of 90% of the native population around 500 years ago, grasslands, savanna, and woodlands succeeded to closed forest.

File:Grand Bay NOAA Nerr0754.jpg

Maritime slash pine savanna

For reasons that are unclear, approximately 500 years ago, aboriginal populations declined significantly throughout Eastern North America and more broadly throughout the Americas. ... Thus, by the time the first European observers were reporting the nature of the vegetation of the region, it is likely to have changed significantly since the regional peak of Indian influence. A myth has developed that prior to European culture the New World was a pristine wilderness. In fact, the vegetation conditions that the European settlers observed were changing rapidly because of aboriginal depopulation. As a result, canopy closure and forest tree density were increasing throughout the region.

Historic or remaining savanna areas

Savanna surrounded much of the continent's central tallgrass prairie and shortgrass prairie. Fire also swept the Rocky Mountains aspen as frequently as every ten years, creating large areas of parkland. In the far southwest was California oak woodland and Ponderosa Pine savanna, while further north was the Oregon White Oak savanna. The Central Hardwood Region covers a wide belt from northern Minnesota and Wisconsin, down through Iowa, Illinois, northern and central Missouri, eastern Kansas, and central Oklahoma to north-central Texas, with isolated pockets further east around the Great Lakes. The Eastern savannas of the United States extended further east to the Atlantic seaboard.

In the southeast, longleaf pine dominated the savanna and open-floored forests which once covered 92,000,000 acres (370,000 km²) from Virginia to Texas. These covered 36% of the region's land and 52% of the upland areas. Of this, less than 1% of the unaltered forest still stands.

In the Eastern Deciduous Forest, frequent fires kept open Kentucky bluegrass areas which supported herds of bison. A substantial portion of this forest was extensively burned by agricultural Native Americans. Annual burning created many large oaks and white pines with little understory.

The Southeastern Pine Region, from Texas to Virginia, is characterized by longleaf, slash, loblolly, shortleaf, and sand pines. Lightning and humans burned the understory of longleaf pine every 1 to 15 years from Archaic periods until widespread fire suppression practices were adopted in the 1930s. Burning to manage wildlife habitat did continue and was a common practice by 1950. Longleaf pine dominated the coastal plains until the early 1900s, where loblolly and slash pines now dominate.

At low altitudes in the Rocky Mountain region, large areas of Ponderosa pine and Douglas fir had an open park-like structure until the 1900s. In California's Sierra Nevada area, frequent fires kept clear the understory of stands of both Ponderosa pines and giant Sequoia.

Destruction of the savannas

Industrialized sawmills in the early 20th Century cleared many tall savanna old-growth trees, while fire suppression methods adopted in the 1930s and 1940s stopped much of the regular burning which the savanna required. By the latter half of the 20th Century many researchers had rediscovered both the prehistoric use of fire and methods to practice burning, but by then almost all prairie and savanna lands had been converted to agriculture or succeeded to full-canopy forest. Modern conservation of savanna includes controlled burning, and at present about 6,000,000 acres (24,000 km²) a year are burned.

See also

Oak savanna with Buttercups in Sam's Valley, Oregon.

• Eastern savannas of the United States - Savanna in southeastern regions.
• Oak savanna - Savanna in west coast, western, and central regions.
• Native American use of fire - Other native uses of fire.
• Terra preta - Use of burning in South America agricultural use rather than grassland.