Environmental And Human Hazards

This is an excerpt from the Book called “The Homeowner’s Complete Tree & Shrub Handbook “ by Penelope O’sullivan. Continue reading to learn more about Environmental And Human Hazards, thanks to the author.

You can’t control weather, but you may be able to manage other environmental risks to the trees and shrubs on your property. Construction damage is the biggest and perhaps most destructive trauma trees can endure. Soil compaction on residential lots, trenching in root zones, grade changes, and bad pruning are some of the ways that people harm their trees. Ozone pollution, energy-sapping suckers or root shoots, and chemical damage from maintaining a perfect lawn may all contribute to the deterioration of your trees. The good news is that you can preserve trees from most human damage and find trees that remain vigorous and beautiful in stressful environments. In this section, you’ll read about challenges faced by trees and learn how to keep them safe from harm.

Death By Digger

Although the homeowners clearly wanted the birches in their front yard, aback-hoe crushing the root zones and excavating root-filled soil doomed the trees to an early end. To prevent such tree damage, erect fences around pleasing trees before construction begins, giving them as much room as possible. At a minimum, the productive barrier for a tree with a 6-inch caliper should be at least 6 feet away from the trunk on each side, and no one should walk on or throw trash into the fenced space.

Construction Damage

Building a house may be thrilling for you but traumatic for your trees. Construction equipment rolls over root zones, squeezing air from the soil and slowing water drainage. Rainfall on the bare soil increases compaction, as do the human footfalls across the root zone. Because compacted soil is denser than well-aerated soil, it’s harder for roots to penetrate. Root growth and spread is hindered, making it harder for trees and shrubs to absorb water and nutrients. Drought stunts trees growing in compacted soils, while flooding lessens the amount of air that gets to their roots. Disturbed, compacted, urban and suburban soils may lack mycorrhizae and essential elements, making it hard for trees to establish. In neighborhoods with underground utilities, laying electrical cable from the electrical box to the house often cuts through the precious top foot of soil where most tree roots lie, wrecking the network of roots the trench encounters. There also may be trenches for gas, telephone, sewer, water, and cable television. Remember, even if a trench seems far from the tree, the root zone may be double or triple the diameter of the crown.

New construction may necessitate grade changes to improve drainage on the property. Roots that were formerly in the top few inches of soil may be buried alive under loads of sand and topsoil to ultimately suffocate and die. To preserve existing trees, avoid raising or lowering the soil level under the canopy of the tree.

Building a tree well is one way to maintain air circulation and drainage in the root zone. Tree wells are walled shafts to the original soil grade in landscapes where soil levels have been artificially increased. Digging old-fashioned tree wells dug near a trunk doesn’t work. Dr. Edward Gilman, a professor and tree specialist at the University of Florida, notes that if you’re trying to save a tree with a tree well, you must build it beyond the tree’s dripline, then grade the soil outside the well to keep runoff from flowing into the well. There’s no guarantee that the tree will survive construction, but you improve its chances by leaving undisturbed the trunk and as wide an area as possible around it.

Another common practice that actually harms, rather than helps, is removing part of a tree’s canopy to balance roots killed during construction. The fact is that to survive root disturbance, trees need their leaves to provide nutrients. Removing part of the crown reduces the number of leaves that are processing nutrients. If some limbs ultimately die from root damage, you can ask your arborist to remove them.

Chemical Damage

Trees and shrubs can also sustain damage from herbicides formulated to destroy unwanted plants or stop their growth. Even those herbicides considered safe around people and pets may not be safe your trees. My husband and I learned that lesson the hard way. On a muggy Delaware day with hardly any wind, Bob sprayed herbicide on some persistent weeds near a weeping Japanese maple. A breeze moved the air while he was spraying. We didn’t realize that any herbicide had migrated to the tree until we noticed the decline and death of a small branch near the area where he had been.

Out Of Harm’s Way

Heavy construction equipment isn’t the only thing that can damage a tree trunk. Dinging the trunk with a lawnmower, string trimmer, or any other machine can kill the tree. Even a small bark hit may hurt the part of a tree that carries food and water to and from the leaves and roots and the cell band from which the tree grows. The tree declines, becoming vulnerable to disease-causing organisms. Very young trees with thin bark are particularly at risk from these injuries.

The best way to protect your trees from mechanical harm is to mulch the area beneath them with wood chips, bark nuggets, or shredded bark. A 2 – to 3-inch layer is plenty. Keep the mulch away from the trunk flare. You’ll save mowing time and won’t have to buy new trees.

At Risk From Within

Many tree cultivars have been grafted onto a sturdy rootstock to enhance their growth and vigor. It’s important to remove suckers from these plants. Suckers are the shoots that grow from a tree below the bud union (the swelling where the two plants were joined, usually near the base of the tree). Because of their vigor, suckers can take over a tree or shrub, killing off the less dynamic scion (grafted plant). A pink rosebush can become a red rosebush after the rootstock takes over. Similarly, twisty Harry Lauder’s walking stick (Corylus avellana “Contorta”), can turn into its straight-stemmed species rootstock, C. avellana, if you don’t remove the suckers before they have a chance to grow.

Ozone Pollution

City life has its benefits, but one of its draw-backs is air pollution. You don’t have to live in a city, however, to experience the effects of pollution. Winds, air currents, and moving vehicles carry pollutants across the country and up and down the coasts. Different kinds of trees and shrubs, like individual people, have different tolerances to pollution exposure. Some gets sick fast, while others go on and on, showing few signs of stress. In the landscape, it pays to plant pollution-tolerant plant material if you live in a polluted place or downwind of a polluted environment.

The most prevalent air pollutant hurting trees is ozone. Not all ozone is bad for trees. Beneficial ozone from the earth’s upper atmosphere protects earth from ultraviolet light. But the harmful and excessive ozone in the lower atmosphere comes from everyday things that people do. We drive cars and keep our houses warm in winter, cold in summer. We use more and more energy and demand the manufacture of more sand more goods. Car engines and power plants are among the biggest offenders when it comes to this pollution. Burning coal and gasoline results in the release of gases that combine with oxygen to make ozone. The most harmful ozone develops on warm sunny days, especially in early evening or late afternoon.

Ozone enters a tree through little openings in the leaves. Its presence in leaves reduces the amount of food the tree can make through photosynthesis. Ozone damage can kill or weaken a tree. It becomes vulnerable to pests and debilitating conditions such as stunted development, early leaf loss, and whitening or yellowing of foliage. Leaves can burn at the edges and you may see spotting on the leaf surface. The lists on the following page can help you choose trees to plant if air pollution is a problem where you live.

Pollution-Tolerant Landscape Trees And Shrubs

Hedge maple Acer campestre

European hornbeam Carpinus betulus

Hackberry Celtis occidentalis

White fringe tree Chionanthus virginicus

Hawthorn Crataegus species

Ginkgo Ginkgo biloba

Thornless honey locust Gleditsia triacanthos f.inermis

Longstalk holly Ilex pedunculosa

Golden raintree Koelreuteria paniculata

Crape myrtle Lagerstroemia indica

Magnolia Magnolia species

‘Donald Wyman’ crabapple Malus ‘Donald Wyman’

Amur corktree Phellodendron amurense

White spruce Picea glauca

Japanese black pine Pinus thunbergii

Yoshino flowering cherry Prunus x yedoensis

Douglas fir Pseudotsuga menzisii

English oak Quercus robur

Red oak Quercus rubra

Sumac Rhus species

Chinese scholar tree Sophora japonica

Arborvitae Thuja species

Little-leaf linden Tilia cordata

Landscape Trees Intolerant To Air Pollution

Sugar maple Acer saccharum

Red maple Acer rubrum

Serviceberry Amelanchier species

Catalpa catalpa species

Larch Larix species

Black tupelo Nyssa sylvatica

White pine Pinus strobes

Lombardy poplar Populus nigra ‘ Italica’

Quaking aspen Populus tremuloides

Flowering plum prunus cerasifera

Willow Salix species

American elm Ulmus Americana

When Storms Come Your Way

When a weather disaster occurs, landscape trees can’t evacuate. Rooted to the spot, they rely instead on certain inborn characteristics to survive. If weather-related damage to your trees creates hazardous conditions for you, your pets, or your neighbors, call an arborist immediately. An arborist may be able to save your tree and, will remove it safely from your property.

Snow and ice look magical on trees but they can destroy them. The weight of snow can crush evergreens, breaking them apart. It can weigh down deciduous tree limbs until they also break. Sometimes it weighs so heavily on a treetop that it lifts the root mass right out of the soil. Ice-coated trunks and branches bend low and sometimes snap. When a coastal ice storm hit Maine and New Hampshire one year, every young paper birch along I-95 bowed to the ground. Some broke apart, but many still survive, stooped testaments to the storm. You can help avoid permanent damage by gently brushing snow off branches you can reach. An arborist may need to stake or cable trees vulnerable to folding under the weight of ice. Whether cabled or not, let the ice melt naturally. Prune any damage so the tree will not create a hazard. Well-pruned trees and shrubs stand up better to snow and ice than trees with weak branch crotches or more than one leader (main stem). Typing up boxwood or erect evergreens like red cedar and arborvitae may help prevent injury. Crisscross the entire crown with nylon cord or fishing line, removing it promptly in spring. Protect smaller shrubs with a teepee made from two leaning boards or pieces of plywood.

Wind

Healthy trunks and branches bend to some extent with the wind. The branches most susceptible to breaking are heavy ones that join with the trunk at an acute angle. Choosing healthy, well-formed trees can prevent this damage. If it’s too late for that, you can have an arborist help you shape they tree for added strength. Wind protection is particularly important for evergreens, which keep losing water through their leaves during the winter. Making sure these trees and shrubs are well watered before the ground freezes helps prevent the foliage from turning brown. Although you should cut back the volume of water you give your trees in early fall so they can harden off for winter, keep watering them until the ground freezes.

You can also avoid damage to evergreens through proper planting. Never plant evergreens susceptible to wind damage, like arborvitae and yew, on the south or southwest sides of your house. In most of the United States and southern Canada, the westerlies or prevailing winds move from the west or southwest toward the east or northeast. Local geography, including large bodies of water and tall buildings, may affect wind speed and direction in a particular place. West-to-east airflow snakes in ridges or crests and troughs or depressions going north and south. Winds on the west side of a ridge are from the south-west (warm) and those on the east side travel from the northwest (cold). If you must, build a two-or three-sided wind fence out of stakes and burlap to block the prevailing winter wind and the southern and the southwestern exposure of the evergreens.

Lightning

If a lightning strike hits a tree on your property, you may not see the injuries, but they can range from burnt roots to systematic damage inside the tree. External damage takes many forms. Long strips of bark many hang loosely from the tree, a branch may explode, or pests may overwhelm the injured tree, which dies. Popular landscape trees like pine, oak, and maple are among the more susceptible trees to lightning damage. Although you can’t prevent a calamity, you can plant trees less vulnerable to strikes such as birch and beech. If lightning strikes a tree without doing too much damage, you can help it bounce back by first cutting off hanging bark, the fertilizing the plant, keeping its root zone mulched, and watering it during dry spells.

Flood

Unless you plant trees and shrubs that tolerate wet feet for long periods of time, flooding can have disastrous effects on your landscape. Flooding may wear away topsoil or dump slit and debris over the root zones of your trees, either of which harms them. Flooded soil deprives tree roots of the oxygen they need for nourishment. Most tree roots are in the top foot of soil because that’s where most of the oxygen is, and tree roots breathe like we do. When water fills the air pockets in the soil, it leaves no room for oxygen. Wert roots are susceptible to rot. As they give out, leaves sag, yellow, and even drop; and limbs die back. Before pruning branches, wait a year and see if limbs show signs of recovery. Fertilizer or a mycorrhizal product applied to the root zone may help restore the plant’s vigor. If areas of your land flood regularly, you may be able to improve the drainage in those spots by incorporating compost or other organic material into the soil. You can also consult a landscape contractor or architect about installing a drainage system of connecting pipes to carry off excess water to a pond or drainage culvert.

Drought

A lack of water in the soil affects trees and shrubs by decreasing their vigor and even killing them. Drought destroys feeder roots and root hairs, which provide the avenue for most water absorption. Because these are mostly in the top foot of soil, they are quickly affected by moisture loss. The tree suffers stress, and leaves may wilt, scorch, or drop. Spider mites, leaf-eating insects, or wood borers are active in hot dry weather and invade the drought-stressed tree.

If you live in an area known for dry soils and you lack access to irrigation water, plant only drought-tolerant species such as haw-thorn, green ash, Kentucky coffeetree, juniper, American plum, and limber and mugo pines. If you live where drought is infrequent, keep trees and shrubs well watered during dry spells and remember that it’s better to water deeply and less frequently instead of briefly watering the soil surface every few days. During a drought, water newly planted trees weekly, evergreens and transplants up to five years old every two weeks, and established shrubs every four to six weeks. To water a tree deeply, set up a trickling hose around the drip line (below the crown’s outer edge) and leave it in place for 30 minutes. Move the hose one-third the way around the tree and water again for the same amount of time. Repeat one more time. If the tree is very big, you’ll need to move the hose to more spots around the drip line. Recently transplanted material needs special care and plenty of water to help it become established. Newly planted balled-and-bur-lapped trees and shrubs are particularly vulnerable to damage, since many of their feeder roots were cut in the harvesting process.

Sunscald

In winter, the sun is lower in the sky and warms the south and southwest sides of tree trunks, killing the inner bark on the south or southwest side of young deciduous tree trunks, especially thin-barked species such as maple, ash, honey locust, linden, and willow. Sunscald is particularly likely when winter days are warm and sunny and nights are below freezing. The hot sunlight activates dormant cells, which freezing nighttime temperatures destroy. Trees are less affected in places where cloudy skies and consistently cold temperatures are the norm and when planted on the east and north sides of buildings. Sunscald happens frequently in parts of the Southwest. In New England, you may see these conditions during the typical January thaw, when temperatures warm up and skies are sunny. Using commercial tree wrap to prevent sunscald on a newly planted tree is usually not necessary and can hurt the trunk, especially when wrapped too tightly. When making a decision to wrap or not, consider the kind of tree you’re planting., its location on your property, and whether you’ve seen sunscald on other young trees in the same area. If you decide to wrap, keep the material on a newly planted tree from November to March and then remove it promptly.

Leaf Scorch

When you notice that the edges of leaves turn yellow and then brown, you may be observing leaf scorch. It usually occurs as a result of dry soils, dry winds, and hot weather. Leaf scorch reduces the vigor of woody ornamentals and can lead to pest and disease problems. Similarly, woes that weaken a tree can lead to leaf scorch. Ash, oak, linden, and maple are among the trees that develop leaf scorch. To help prevent leaf scorch during hot dry periods, water trees deeply and mulch them to conserve moisture.

Conifers, like pine and spruce, and broad-leaf evergreens, like Andromeda, mountain laurel, and rhododendron, are susceptible to leaf scorch in both summer and winter. Conifers and broad-leaf evergreens are particularly vulnerable on sunny or windy winter days, when the damage is known as winter burn. To prevent winter burn, keep these plants well watered throughout the growing season and water them deeply if there is a dry spell in late fall. Be aware of what you plant in the path of prevailing winter winds. You can make a wooden structure to protect evergreens or rap them with burlap. Spraying broad-leaf evergreens with an antidessicant is another possibility for late fall and midwinter. You may have to tolerate occasional winter burn on your evergreens if you don’t have time for these precautions.