Environmental Damage

Trees may be damaged by airborne chemicals, machinery, soil-related problems, too much or too little water, and severe weather.

Airborne Chemicals

Airborne pollutants from industry, automobiles, fires, and other chemical sources can harm trees. Symptoms include defoliation; browning or yellowing leaf margins, tips, or tissue between leaf veins; and stunted foliage growth. Herbicides Herbicide damage on black walnut seedlings (Thumbnail) may cause distortion, curling, and browning margins, or leaf drop in deciduous trees and may cause conifer needles to turn yellow or brown, and succulent shoots to curl and deform. If trees survive such damage, their growth may be stunted or their shape deformed. Where air pollution could be a problem, plant resistant species and maintain well-thinned stands. When applying pesticides, follow label directions and standard application guidelines to minimize chemical injuries. Some pesticides may need to be applied by a licensed pesticide applicator. Herbicide damage on oak trees (Thumbnail)While most pesticide damage is caused by herbicides, insecticides and fungicides also can damage trees if the tank mix is too strong. Herbicide drift often originates on neighboring properties, so be sure to let your neighbors know the value you place on your woodland. Ask them to take special care when applying chemicals on their own properties to avoid damaging drift to your property.


Damage from logging equipment is a concern in any stand where some trees will be left after the harvest. Logging Skidder damage on red pine tree (Thumbnail)equipment can knock over small trees, break branches, tear bark, and destroy roots near the surface. Careful and experienced equipment operators can avoid much of this damage. Creating a physical barrier between the trees that will be left to grow and the equipment also helps.

Heavy equipment used in plantations (such as cultivatorsCultivating hybrid popular (Thumbnail), mowers, and pesticide applicators) can sever small trees, break branches, Mechanical damage on hybrid popular (Thumbnail)or tear bark. Reduce damage by planting trees in rows that are 2 to 4 feet wider than the equipment, plant trees in straight rows, and maintain even spacing between rows. Set cultivation equipment to run as shallowly as possible to avoid cutting tree roots. Consider using an herbicide rather than cultivation or mowing equipment.
Figure 7-4. Heavy equipment can easily damage young trees in plantations.


Soil compaction cuts off water and carbon dioxide to tree roots. Compaction slows tree growth and interferes with root suckering in aspen stands that are clearcut. Compaction may be indicated by dying leaves on mature trees and dying branches on younger trees, but most often reduced growth is the only sign of it.

Soil compaction is a problem mainly on wet clay or silt soils. It occurs where heavy equipment has been driven across a site. Old farm fields may have a compacted plow pan a foot or two below the soil surface. Wooded sites may be compacted on the surface. Compacted soil takes decades to loosen up through freezing and thawing cycles. Reduce compaction in the first place by operating heavy equipment only when the soil is dry or frozen. On farm fields with a plow pan, deep chisel the site to break up the compacted layer, then plant trees. Changes in the soil level around a tree also affect its growth and odds of survival. Excavating soil and severing roots may lead to windthrow or root diseases that kill trees. Adding soil decreases air movement to the roots and may kill the tree. Therefore, avoid removing or adding soil near trees.

Mineral deficiency causes a range of symptoms from foliage discoloration to reduced foliage size. A soil analysis will indicate which minerals are deficient. Soil types vary considerably in their natural nutrient content. Always try to match the tree species to sites that meet their nutrient needs. See Chapter 6: Managing Important Forest Types for more information on the soil requirements of various forest types and species. While timber harvesting removes some nutrients from a site, most nutrients are stored in the branches and bark of trees, so leaving those materials on the site after harvest will recycle the nutrients. Nutrients also enter a site from precipitation and air exchange. Lake States woodlands rarely have significant nutrient deficiencies in stands that are managed over normal rotation lengths. Nutrient deficiencies may occur with repeated short rotations, especially when all woody material is removed from the site (called biomass harvesting). Ask your forester about best management practices for biomass harvesting.


Drought damage occurs when water loss through the leaves exceeds water uptake by the roots. It is most common on sandy and gravelly soils, which do not retain much water. It also occurs if the water table drops suddenly and remains low, depriving trees of the moisture they need. Drought symptoms include leaves wilting or turning brown—beginning with tissue between leaf veins, off-color foliage, and a general decline in vigor. Newly planted trees are especially vulnerable to drought because their root systems are not well developed. Crowns of larger, drought-stricken trees usually die from the top down. Insect attacks often are triggered by drought. For example, wood boring insects may invade drought-weakened trees. Trees already stressed by disease or physical damage may die in a drought.

To minimize drought damage, match tree species to the sites where they grow best. Some species are more drought resistant than others, so manage drought-tolerant species on dry sites. Plant new trees in the spring or fall when soil moisture is high. When soil moisture is low, plant seedlings with soil around their roots, such as containerized stock. Do not plant shallow-rooted species in areas of low rainfall or on sandy soils. Thin stands before they become overstocked, but do not thin during a drought.

American elm
Black ash
Eastern cottonwood
Silver maple
Balsam fir
Black spruce
Black walnut
Bur oak
Eastern white pine
Jack pine
Northern white-cedar
Quaking aspen
Shagbark hickory
Swam white oak
Yellow birch
Bigtooth aspen
Bitternut hickory
Northern red oak
Red pine
Sugar maple
White ash
White birch
White oak
White spruce
Figure 7-5. Red oak leaves damaged by
Table 7-1. Flood tolerance during the growing season of seedlings of selected tree species.

Extended flooding can suffocate roots and kill trees. The extent of the damage typically depends on the tree species (Table 7-1), time of year, tree size, and tree vigor. Flooding for short periods in winter or early spring is seldom a serious problem, but flooding during the growing season can kill seedlings in just a few days. Completely submerged seedlings will be killed more quickly than trees with their crowns above water. In flood-prone areas such as river flats, plant only tree species that tolerate flooding.


High temperatures and drying winds cause rapid water loss from tree leaves. Water loss causes leaf margins to turn brown and leaves to fall prematurely. Do not plant susceptible trees (such as sugar maple) in locations that are exposed to strong sunlight or wind.

Early fall frosts or extremely cold weather shortly after leaf fall can injure succulent twigs and buds. Late spring frosts can kill buds that have begun growing. Trees usually survive these frosts, but their growth, stem quality, and vigor can be dramatically reduced. To avoid freeze damage, plant trees from seed sources that originate no more than 200 miles south of the planting site. (Near the northern edge of a tree species’ range, do not plant trees from seed sources more than 50 miles south of the planting site.) If your planting site is in a low-lying, frost-prone area, select a species that breaks bud relatively late in the spring to avoid frost damage. For example, black spruce buds break dormancy about ten days after white spruce.

Winter sunscald occurs in early spring when the sun heats and activates tissue during the day and then freezing temperatures kill the active cells at night. The injury appears as peeling bark over an elongated canker on the south to southwest side of the tree stem. Thin-barked trees such as young maples are most susceptible. The tree rarely is killed, but diameter growth is reduced, decay-causing organisms often enter the tree, and logs become degraded or ruined. In hardwood stands, avoid overthinning or pruning that might expose tree stems to too much direct sun, especially if the trees are growing near the northern limits of their range. Winterburn and winter drying are caused by warm spring winds that dry the foliage while the roots are still frozen in the ground and cannot replace the lost moisture. This damage is common on most conifer species and may be recognized by the reddening and browning of needles in the spring. Trees usually survive this, but massive defoliation may occur on trees located along exposed plantation borders or on trees that grow along highways, where road salt exacerbates the problem.

Strong winds can topple trees or break their branches. To prevent wind damage, leave a dense row of trees with intact lower branches around the perimeter of woodlands. When thinning old, dense tree stands, progress slowly over a period of years to minimize windthrow. Figure 7-6. Strong winds can uproot trees.

Hail can break off buds and branches and shred tree foliage. There is no way to prevent or control this type of damage.

Lightning can split trees, cause spiral cracks in their trunks, shatter limbs, and start fires. Trees with crowns high above the general canopy level are most subject to lightning strikes. There is no control for lightning other than to remove high-risk trees before damage occurs. Once a conifer is struck by lightning, remove it quickly before bark beetles attack it and build up a population that can spread to other trees.

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