Fire and Storm

Fires may seriously wound tree bases in upland hardwood stands, weakening and killing them. However, it has been shown in the uplands of Virginia and the Carolinas that repeated fires favor oaks over other species. The relationship may occur in other broadleaf forests with a significant oak component. The condition of the forest also often relates directly to its fire history.11 Repeated burning sometimes encourages replacement of woody plants with an abundance of legumes, nutritious food for quail and deer.

Ice storms glaze over the foliage and branches of upland hardwoods, especially in stands above 3000-feet elevation in the Southern Appalachian Mountains. Along with glaze, late freezes damage trees. With abnormal cold and sudden drops in temperature in spring, buds and new foliage quickly freeze and die. Loss of leaf buds prevents regrowth of leaves that year. Freeze damage usually occurs in valleys and hollows, probably because buds and leaves in these ordinarily warmer sites

Figure 4.9 Heavily overcut second-growth mountain mixed-hardwood stand. Wildfires and light prescribed fires reduce sprout growth, allowing the more vigorous stems eventually to reach maturity. (Georgia Forestry Commission photo)

expand earlier in the spring than do buds and leaves on trees higher up the slopes. In the coves, wind may be insufficient to move cold air out of the hollows and over the mountains.

Disease-causing Agents

A disease called nectria canker, caused by Nectria cinnabarina, attacks most severely in forests of soft maple, black birch, and weed cherry species at high elevations. High-value trees, possibly because of their vigor, fortunately are often spared.

Dutch elm disease, introduced from abroad, spares no elms. The causal fungus, Ceratostomella ulmi, carried on the bodies of European elm bark beetles, entered North America simultaneously with the beetle. Otherwise, the disease would not have attained its foothold. The insect adults carry the sticky spores from egg galleries under the bark of diseased trees to the crotches of young twigs or leaf axils of nearby healthy stems, there to chew through the bark and introduce the fungus. The elm, America's favorite shade tree, its crown shaped like a huge vase of flower stems, disappeared from town streets and campus lanes as well as from the Southern Appalachian woodlands. The malady's spread seems unimpeded. Phloem necrosis, an infection with similar symptoms to those of Dutch elm disease, also attacks species of the genus Ulmus.12

Oak wilt presents another type of infection. The disease, entering the South from the Lake States, was first detected in the Southern Appalachian Mountains in 1951. Little infection occurs on high-quality soils of alluvial or limestone origin. Fungus mats, root grafts, and bleeding wounds

Figure 4.10 Oak wilt fungus, carried by Chalara quercina, found its way by the 1980s to the Post Oak Belt of Texas. Forest trees as well as landscape stems are killed. (Texas Forest Service photo by R. Billings)

provide entry points for the fungus Ceratocystis fagacearum into trees of the genus Quercus. Ax cuts, insect holes, and branch stubs that hold water serve as favorable environments for the fungus' growth. Sap-feeding beetles also carry the spores from scattered mycelia mats to fresh wounds on healthy trees. Ironically, foresters' increment hammers and borers spread the disease as they sample radial growth patterns. The holes made by the instruments, like any cavity that holds water, become receptacles for the culture medium and innoculum. Dipping increment cores in a fungicide and replacing the cores in the holes from whence they were extracted provides protection. If cores must be retained for study, a cork dipped in a fungicide and inserted into the hole serves similarly.13

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