Natural History: Cast-Iron Forest - Cross Timbers, Texas

Remnants of a dense oak forest survive in Texas, Oklahoma, and Kansas.

Most people heading for Lake Mineral Wells State Park, thirty miles west of Dallas/Fort Worth, Texas, are drawn by the prospect of boating, swimming, or rock climbing. Ask one of them what "Cross Timbers" means and you're likely to get a blank stare. But a century ago, almost everyone in the area would have used that term to describe the kind of scrubby oak forest found on the east side of Lake Mineral Wells. A forested archipelago awash in a sea of prairie, the area known as the Cross Timbers once ranged from north-central Texas well into Oklahoma and as far north as southeastern Kansas. Dominated by post oak and blackjack oak, the forests followed the lay of the land, doing best in sandy soil and in the rugged sandstone uplands. Prairie grasses, on the other hand, flourished in soils derived from limestone.

The earliest historical references to the Cross Timbers come from eighteenth-century Spanish explorers, who called it the monte grande (great forest), a designation they based on Indian names for the conspicuous landmark. The English term "Cross Timbers" (occasionally" Cross Timber") was in use by the 1820s, but its origin is uncertain. Some people say it arose because the forests crossed the great rivers of the region--the Brazos, Red, Washita, Canadian, and Arkansas. Others believe the reason was that the settlers had to cross through the timbered lands on their way west. Then again, post oaks are also known as cross oaks, so the name may simply derive from one of the region's principal trees.

Early observers, such as naturalist Thomas Nuttall (1786-1859), noted the connection between the forest's vegetation and its geology. Climate, too, has been an important influence. The Cross Timbers straddle an intermediate zone between the humid eastern part of the continent and the semiarid lands to the west, forming an outpost of eastern moist forest within the western prairies.

About 11,000 years ago, near the end of the Ice Age, the wetter, cooler climate here supported a forest comprising mainly spruce and other conifers. As the area dried out, the forest composition changed, and fires--which suppress woody vegetation--fostered the spread of grassland. Fires do occur naturally, but the people who began to occupy the area as the climate became warmer and drier may also have played a role: hunters may have deliberately set fires to drive their prey and for other purposes, such as to encourage the growth of vegetation attractive to game.

The Cross Timbers occupied about 30,000 square miles when farmers and ranchers began to arrive in the early nineteenth century. While some of their activities, notably fire prevention and cattle grazing, promoted the growth of trees, the farming of cotton and other crops tended to work against preservation of the forests. Nonetheless, substantial portions of the Cross Timbers were left alone: as the settlers soon realized, the prairie lands were much better suited for cultivation. In addition, the post oaks and blackjack oaks made poor structural lumber--in part because they grew neither tall nor straight. As a result, they were spared the wholesale cutting that removed much of the hardwood forest in the East.

Perhaps as much as 15 percent of the original Cross Timbers survives, mostly as haphazard patches of woodlots and scrub forest scattered amid the pastures, fields, and small communities. Nearly all of it is in private hands, but the forests can still be enjoyed in a number of public places, including the 3,000-acre Lake Mineral Wells State Park, whose lake was created during the 1930s through dam construction. Here the forest occupies a ridge east of the lake--a rugged, marginal location that was never heavily used. Some of this park's venerable post oaks may be more than 250 years old (although usually less than thirty feet tall and not more than two feet in diameter). Another good site to visit is Keystone State Park, which encompasses Keystone Lake near Tulsa, Oklahoma.

Back in 1831, while traveling through what is now Oklahoma, statesman-writer Washington Irving encountered the Cross Timbers. So tough was the going that he described the vegetation as "forests of cast iron." Yet today large portions of the Cross Timbers have almost vanished, not only from the land but from public consciousness. Historians and ecologists, however, have begun to urge preservation of its remnants, which provide habitat for animals, protect the soil from erosion, replenish the underlying aquifer, and also contribute to our understanding of humankind's complex relationship to nature. As private landowners come to realize that their patches of scrubby-looking forest represent a cultural heritage and a natural resource, they too may join the cause.

For visitor information, contact: Lake Mineral Wells State Park 100 Park Road 71 Mineral Wells, Texas 76067 (940) 328-1171

www.tpwd.state.tx.us/park/lakemine/ lakemine.htm

HABITATS

Cross Timbers forest is dominated by post oak (Quercus stellata) and blackjack oak (Q. marilandica), but other trees abound, including live oak, black hickory, cedar elm, hackberry, and eastern red cedar. Along with sassafras and other bushes, the understory is often thick with vines and brambles, including catbrier, Virginia creeper, poison ivy, and raccoon grape.

Prairie openings contain an array of grasses, including big bluestem, Indian grass, side-oats grama, buffalo grass, and silver bluestem.

Forest edge habitat, especially on drier sites, often features yucca and numerous kinds of prickly pear cacti. Mesquite, though native to the area, has become more common in the last century, in part as a result of grazing.

Streamside vegetation is found along watercourses that have not been inundated owing to dam construction. The willows, white oaks, cottonwoods, and pecans that grow here are normally much taller than the oaks of the Cross Timbers forest.

Richard V. Francaviglia is a professor of history at the University of Texas at Arlington, where he also directs the Center for Greater Southwestern Studies and the History of Cartography. His latest book is The Cast Iron Forest: A Natural and Cultural History of the North American Cross Timbers (University of Texas Press, 2000).