OUTDOOR CORNER: THE MIGHTY OAK IS ABUNDANT IN MISSOURI

The forests of Missouri are dominated by oaks and nearly everyone in the state lives beside or within walking distance of one. Of those oaks found north of the Mexican border, 21 species or nearly half are native to Missouri.

Collectively, Missouri's oaks that grow above the flood plains, wetlands and river margins make up the oak-hickory forest type. Oaks are the most abundant species in these upland forest, but hickories are a consistent component. Often grouped as one, Missouri has five true and three pecan hickories.

As the glaciers retreated from Missouri, spruce-fir forests were replaced by oaks, hickories and other species. The pollens from these species appeared around 10,000 years ago in core samples taken in Ozark bogs. Today, the oak-hickory forest occupies over 75 percent of Missouri's 14 million acres of tree-covered lands.

This large association stretches westward from Jefferson County into the central section of the state and southward into the Ozarks. Fingers of oak-hickory forest extend into Missouri's prairie region and follow the limestone bluffs that border streams flowing to the Missouri and Mississippi rivers. Upland oak-hickory forest are absent from the Bootheel region and poorly represented in northwestern Missouri and along the Kansas border.

This association of oaks and hickories is characteristic and most widespread within the Ozarks' limestone/dolomite uplands. There, closed canopy forests of white and black oaks with pignut, bitternut and mockernut hickories grow 60 to 90 feet in height and shade-tolerant flowering dogwood, redbud, hophornbeams form the understories.

On gentler slopes with deep well-drained soils and on Missouri's glaciated lands, northern red oaks, shagbark hickories and sugar maples join the white oaks. Along lower slopes and in coves, oaks can exceed 90 feet in height and herbaceous ground cover becomes abundant. These choice environments invite competition and sugar maple, white ash, basswood and black cherry challenge the sun-loving oaks for growing space.

Oak-hickory forest growing on the thin ridgetop soils and rocky side slopes and in southern Missouri form canopies 20 to 60 feet in height. On several sites where forest development is restricted, only blackjack and post oaks prevail. Where moisture is more available, black hickory joins black, white and scarlet oaks in this open upland forest. Scattered shrubs along with dogwood, blackgum and sassafras represent the understory of these dry, cherty forests with their soils full of rocky fragments.

Soils, geology and weather elements control the character, composition and growth in Missouri's 10.3 million acres of oak-hickory forest. These factors influence the ability of species and individual trees to cope with normal environmental stresses and attacks by insects and disease organisms.

The forests of Missouri were markedly changed by European settlement that began in the early 1800's. By the 1920's most of the forested lands had been cut over and subjected to repeated burning and unregulated grazing by free-roaming livestock. Less than one half of the state's original forestland remains. Only 7,900 acres, now in tracts of a few hundred acres or less in protected public ownerships, are still considered to have old growth characteristics.

Most of the larger trees today in the oak-hickory forests are between the ages of 70 to 90 years. Their year of origin can often be dated to a period when forest fire control began, fencing laws were enacted and agricultural uses of the lands started to decline.

As oaks and hickories are prolific "sprouters", dominant individuals in these forests are often growing from older root systems. Droughts, windstorms and lightning are some of the natural causes of change in the oak-hickory forest. Severe droughts during the mid 1950's and early 1980's led to the decline and death of scarlet and black oaks over extensive areas of the Ozarks. Periodically, high winds and tornadoes cut swathes through these forests and cause structural damage to individual trees.

Following these events are the two-lined chestnut borer and fungus causing shoestring root rot, agents that attack and kill stressed trees. These native insects and disease-causing organisms are part of nature's recycling process, thinning our weakened individuals and initiating the cycle of decomposition. Oak wilt, a fungal disease, is spread locally through root grafts and kills clumps of trees, mostly those belonging to the black oak group.

In addition to organisms and events that cause death, there are hundreds of insects and disease-causing organisms that annually attack trees. Spring cankerworms (inchworms) feed on oak and hickory leaves early in the year and variable oakleaf caterpillars and redhumped oakworms can usually withstand a defoliation, such damage when coupled with drought can cause extensive tree mortality.

People have always had a place within the oak-hickory forests. Around the great oaks where firewood and acorns were once gathered, treaties signed, camps made and villages formed, large cities have taken root. We are attracted to these upland forests with their well-drained soils and sturdy trees.

Fire, a natural factor in these forests, can be damaging when improperly used by man. A light burn when trees are dormant can improve the seedbed for oaks and hickories and reduce competition from other plants. Fires when trees are actively growing can be very damaging, even resulting in their death. Many older trees in these oak-hickory forests carry large "fire scars" as a result of wildfire. Unhealed basal-wounds reduce the structural strength of trees and provide entrances for wood-rotting fungi.

Similarly, lawn mowers, weed chips and automobiles can severely damage the trunks of trees and affect their long term health. The root system of trees in these urban forests are vulnerable to damage by construction. Trees lose their anchorage and ability to support a healthy crown of limbs and leaves as roots are cut or the soils around them are compacted by streets, home construction, sidewalks and the constant pressure of human foot travel.

People create challenging environments for the trees of the oak-hickory forest. Changes in air and water quality and drainage are reflected in the appearance and health of foliage and small limbs. Their vulnerability to the damaging elements of weather, insects and disease-causing organisms is increased as they become isolated individuals in yards or along city streets.

In rural settings domestic livestock selectively feed on understory plants. The crowns of trees grow shorter as cattle seeking shade compact the soil causing a reduction in the oxygen needed by tree roots.

The greatest potential threat to the oak-hickory forests come from a non-native, the Gypsy Moth. Brought into this country to establish a silk industry, it escaped in 1896 and has established populations in 14 eastern states including Michigan. It has few known natural enemies to check its population and artificial control is difficult. Although it feeds on the leaves of a variety of hardwoods and conifers, it prefers those of oaks. There are no established populations in Missouri, but by the year 2020, there likely will be and the result may be major tree losses.

Joe Garvey is a district forester for the Missouri Department of Conservation. Some information was provided by Jaw Law, a retired forester fo the U.S. Forest Service.