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Forests on the Fringe

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Published on: Oct. 2, 2001

Throughout its history, Missouri has been known as a border state. It is a place where north meets south, and east meets west. It is also where the forests of each of these regions come together.

Missouri lies at the western fringe of the central hardwoods, a transition zone between forest and tallgrass prairie. This makes for a diverse and complex landscape. Trees typical of Ozark and Appalachian forests grow in north Missouri woodlots, while islands of tallgrass prairie are found deep in the Ozark hills.

Stretching from the Appalachian Mountains to the Great Plains, the central hardwood forest blankets the nation's mid-section. It is one of the largest forested areas in the country, and it contains a great diversity of plants and animals. This diversity includes more than 70 hardwood trees, several conifers and many shrubs and plants. The great richness of plants and animals is the result of the wide diversity of soils, geology, geography and climate in the region.

Other boundaries also put Missouri's forests on the fringe. Glaciers advanced about as far south as the Missouri River during the last ice age. They scoured north Missouri flat and left behind a thick layer of glacial till. Plants retreated ahead of the glacier to sanctuaries in the Ozarks, where some remain even today. In the southeast corner of the state, the Ozarks drop abruptly into the Bootheel and the lush, alluvial land of the Mississippi River. With different geographic and climatic regions pushing against it, Missouri serves as a haven for a variety of plants and animals from all sides.

If you were to drive from the northwest corner to the southeast corner of the state, you would get a sense of the richness of our forests and the variety of life they support.

Geologically speaking, North Missouri was covered by glaciers in recent times. About 500,000 years ago, the Kansan glaciers retreated, leaving a layer of soil and rock several hundred feet deep. In presettlement times, we think the region's vegetation consisted of upland and bottomland prairies with relatively large tracts of forest in the river bottoms and steep side slopes. This vegetative pattern still holds true today, except much of the prairie and bottomland forest is now agricultural land.

Bur oak is more prevalent in northwest Missouri than white oak, but white oak is more common over the rest of the state. Bur oak's thicker bark makes it more resistant to the prairie fires that helped shape this region's landscape. Although eastern redcedar is found here, it is not as invasive in old fields and abused woodlots as honey locust, elm and Osage-orange.

Those who look for the blooming of flowering dogwood as the harbinger of spring will be disappointed. It doesn't grow in northwest Missouri. Neither does sassafras. Taking their place in the forest understory are pawpaw and eastern hophornbeam, also called ironwood. In some places they can grow so thick they shade out oak and hickory seedlings.

A few tree species are unique to north Missouri. Quaking aspen, northern pin oak, rock elm and bigtooth aspen can all be found here, but are more common in forests farther to the north. Perhaps after the glaciers retreated, these species found some Missouri sites to their liking, or they may be slowly migrating back north.

Heading southeast from the glaciated plains, the next natural feature a traveler would encounter is what is commonly called the river hills. The River Hills are the bluffs and steep hills along the Missouri and Mississippi rivers. An unusual characteristic of the River Hills is the loess soils. These windblown soils formed after the last ice age and have the remarkable ability to erode into nearly vertical slopes. Loess hills are best developed along the Missouri River from the Iowa line to Kansas City, but loess soils are found along most of the length of the Missouri and Mississippi.

These soils are rich, but because they're too steep to be farmed, they grow a wide variety of trees. Many species of oaks and hickories are found here, as well as ash, sugar maple, walnut, cherry and elm. This variety of trees, along with the beauty of the river bluffs, makes the river hills a favorite place to view fall color.

After crossing the Missouri River, you are in the Ozarks. This region makes up about half the state and is roughly bounded by a line from St. Louis to Boonville to Springfield and Joplin. It is the most complex region of the state, geologically, topographically and botanically. Ancient volcanoes, caves, springs, sinkholes, steep hills and swift rivers all contribute to this complexity.

Oaks and hickories are abundant here. Missouri is home to 21 different species of oak and eight species of hickory, nearly all of which are native to the Ozarks. White, black and northern red oak, as well as shagbark and mockernut hickory, are common on better soils. Post and blackjack oak, and black and pignut hickory, are found on dry sites. Several southern oaks are at the northern extent of their range in the Ozarks. Southern red oak, swamp chestnut oak, water oak, Nuttall oak and willow oak are more common in the forests of the southern United States.

Shortleaf pine, Missouri's only native pine, grows in the Ozarks. It once dominated much more of the Ozark landscape than it does today. The appeal of quick profits from milling the big pines attracted eastern lumbermen to the Ozarks in the late 19th century. The pine was cut for building material and the oak for railroad ties. By the 1920s, most of the Ozarks had been cut over. Past land practices of livestock grazing and wildfires prevented shortleaf pine from regenerating, and oak took its place. Today we know that certain sites where oak is found today should be returned to pine to improve the health of the forest.

Missouri probably has more glades than any other state, and most of these glades are found in the Ozarks. Glade comes from the Old English "glad," meaning a shining place, which a glade may seem to someone after a long hike in the woods. Glades are areas of thin soil and exposed bedrock. They are usually found on steep south- and west-facing slopes. The plants growing on glades must endure environmental extremes, from heat and frost heaving to drought and soil saturation.

The plant community found on glades is similar to that of prairies. Stunted trees of winged elm, redcedar, post oak, blackjack oak and sumac may be found on the edges of glades. Glade openings grow or shrink depending on precipitation cycles. During a wet cycle, openings shrink as trees invade. During droughts, glades get larger as trees unable to survive on the drier soil die.

The Ozarks are home to dogwood, blackgum, serviceberry, walnut, white ash, sassafras, scarlet oak, mulberry and sugar and red maple-just to name a few. These are familiar trees, but the Ozarks also contain some unusual trees that are more common in other states.

In southwest Missouri, several tree species reach into the state from Texas and Oklahoma. Smoketree, Ashe juniper, fringe tree and yellowwood are found only in the White River drainage. Western soapberry and Ozark chinkapin are native only to the southwest corner of the state. Osage-orange, now found in nearly every part of the state, is thought to be originally from Texas and Oklahoma. It was brought to Missouri by American Indians for use in bow making. In southeast Missouri, Ozark witchhazel is known only from the St. Francois Mountain region.

Not long after dropping off the Ozark Plateau in southeast Missouri, you will cross a low ridge. After driving through the steep hills of the Ozarks, it is hardly cause to slow down. However, Crowley's Ridge is a unique land feature in the Bootheel, a remnant from the time when the Mississippi River followed a different channel. Evidence indicates that the Mississippi River flowed on the west side of Crowley's Ridge until recently in geologic terms, when the channel of the river changed to its present course on the east side of the ridge.

The vegetation supports this theory. Some of the species found on Crowley's Ridge and the rim of the Ozark Plateau are at the western limit of their range. Trees that seem more at home in the southern Appalachians are found here, including tulip-poplar, sweetgum, American holly, American beech and cucumbertree.

East of Crowley's Ridge are Missouri's southeast lowlands and the head of the Mississippi Embayment. This is the warmest and wettest part of the state. The flat, alluvial plain was formed by the river. Most of the region was originally forested with a dense growth of deciduous trees, many of which are typical of the Gulf Coastal Plain. The trees were cleared and the swamps drained to make the Bootheel one of the state's richest agricultural areas. A glimpse of the original Bootheel landscape can still be seen at Allred Lake Natural Area, Mingo National Wildlife Refuge, Big Oak Tree State Park and Donaldson Point Conservation Area.

Many of the trees that grow here, such as cottonwood, sycamore, willow, green ash, silver maple, hackberry, box-elder and elm, are the same species found in bottomland forests throughout the state. However, some trees found in the Bootheel are found nowhere else in Missouri.

Small differences in elevation determine which trees grow where. Completely different species will grow on "ridges" that are only one or two feet higher than the surrounding land. In the permanently wet swamps, the dominant trees and shrubs are baldcypress, water tupelo, water locust, swamp cottonwood, buttonbush and corkwood. The low flats next to backwater sloughs support water hickory, pumpkin ash, Nuttall oak and overcup oak. On higher ground where soil drainage is better, sweetgum, swamp chestnut oak, willow oak and cherrybark oak are found. Swamps are complex places with a great variety of plants, each finding its own niche in the ecosystem.

Across Missouri, you'll find many interesting niches harboring a diversity of tree and plant life. Missouri allows you to enjoy forests from other parts of the country without leaving the borders of the state.

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