Archive #28 from Online Seminars for Municipal Arborists (on-line-seminars.com) September/October 2009
ISA will accept test scores for articles in this Archive. 

List of articles
The Value of Trees
Custom Soils
Tree of the Seminar
Contract vs. In-house Staff
Emerald Ash Borer Update
Watering Established Trees
Soil Compaction
Dealing with Soil Compaction
Research Briefs
Root Forms

The Value of Trees
By Robin Morgan

People give trees many different values. Here are some of the subjective reasons to appreciate trees. The monetary value of trees has received a considerable amount of research so this subject follows in the next Seminar.

Psychological and Aesthetic Values
Although difficult to gauge, uplifted spirits is one of the most important benefit of trees. Other emotion-based commodities, such as flowers, perfume, property views, prestige automobiles, and entertainment, are readily assigned monetary values. Measuring the benefits of trees is more difficult but researchers are currently working to tie monetary values to the emotional values of trees.

Data on the connection between vegetation and human health are beginning to accumulate. For example, surgery patients who could see a grove of deciduous trees recuperated faster and required less pain-killing medicine than matched patients who viewed only brick walls. Prisoners with cells overlooking green landscapes used prison health facilities significantly less than prisoners whose cells provided views of other prison facilities. Children who play around trees every day are less likely to vandalize than those who seldom see trees. The enjoyment people associate with trees may be subconsciously related to the substantial health benefits that trees provide.

Social Values
In one California city, a neighborhood tree planting program generated community identity, cooperation, and benefits similar to those reported for urban gardening. After coming together to plant trees, the residents continued working together with "paint-up-fix-up parties", neighborhood protective societies, and community gardens.

Historic Values
Trees provide important symbolic links with the past. If a living tree is associated with important events, the tree takes on historical values unrelated to aesthetics or usefulness. A tree would also be valuable if planted by some important figure in history. Aside from specific events, old trees may be regarded as important simply because they have lived through eras with which we have few other connections.

As for emotional and aesthetic values, historic values of trees depend primarily on community attitudes. If historic trees are threatened by changes, such as new buildings and street widening, the issue will usually be settled by public pressure, not by market forces.

Environmental Values
People value both the aesthetic and physical quality of our environment. Trees contribute to this quality by modifying local climates, reducing noise and air pollution, and by protecting soil and water.

Climate Control
Climate control is one important service that trees provide naturally in the landscape, but the urban landscape is far from natural. Streets, parking lots and buildings have changed the climate of urban areas by absorbing solar radiation. Water that once percolated into the soil and later evapotranspired from soil and plants now drains away or dries on the hard surfaces.

These changes have increased the temperatures of cities. Compared to the surrounding rural areas, the urban "heat islands" are 5° - 9° F (3° - 5° C) warmer. Trees help moderate the "heat island" effect. On hot days, trees pump hundreds of gallons of water through their foliage. This water evaporates, keeping the tree and its immediate surroundings cool.

While groves of trees reduce local air temperatures, individual trees increase human comfort primarily by controlling solar radiation, not air temperature. Trees and other vegetation shield people from direct sunlight. Trees also shade soil, pavement, buildings, and other surfaces that would absorb solar energy and then radiate that heat back to the surroundings. Without the protection of trees, city dwellers are literally surrounded by radiant heat.

At night, radiation moves heat in the opposite direction: from the relatively warm earth to the relatively cool sky. Again, tree cover steps in by blocking radiant heat loss from homes and people. Icy mornings provide evidence of this process when lawns white with frost often have green circles under the trees.

Indoor air temperatures are also affected by trees growing around buildings. During hot weather, trees reduce cooling costs by buffering high air temperatures and blocking unwanted solar energy. But during winter months, solar gain is desirable, because it cuts heating costs. To get the best balance, plant deciduous trees that have thin, open branches on the south and west sides of buildings to allow winter sun penetrate into the building. In addition, the schedule of leaf growth and leaf drop should coincide with the need for heating and cooling. Few, if any, species will meet these requirements perfectly, but it's wise to select species that give the best possible match.

Air Pollution Control
Air pollution control is another way that trees improve the urban environment. But reductions in air pollution are modest, and air pollution poses some risk to the trees themselves.

Trees are fairly effective at removing both solid and gaseous particulates from the air. In one study, stands of trees reduced particulates by 9% to 13%, and the amount of dust reaching the ground was 27% to 42% less under a stand of trees than in an open area. Among gaseous pollutants, ozone, chlorine, fluorine, sulfur dioxide and PAN (peroxyacetylnitrate, a photochemical component of smog) are all absorbed by trees. In most cases, these gases also damage the trees. Unfortunately, trees remove little, if any, carbon monoxide which amounts to roughly one-half the total weight of air pollutants in the U.S.

Increasingly, carbon dioxide is being recognized as a "greenhouse gas" pollutant with potentially devastating consequences, such as global warming, dramatic changes in rainfall patterns, and the resulting rise of sea levels that threaten flooding in coastal cities. Since photosynthesis in green plants consumes carbon dioxide, plants could help to counteract the increase of this gas in the atmosphere. Planting urban trees could reduce heating and cooling demands enough to significantly cut fossil fuel consumption. Urban trees could be about 10 times more effective than forest trees for lowering carbon dioxide in cities.

Noise Pollution Control
Noise pollution from highways and other sources can be reduced with trees. Used alone, trees must be planted in belts 35 to 100 feet wide to create significant reductions. However, earth berms can cut traffic noise by up to half if they are tall enough to hide the source of noise and are planted with trees, shrubs, and grasses. Where this kind of adjustment to the topography is not possible, a row of trees and a solid wall reaching up to the base of the crowns will provide a similar reduction.

Soil and Water Quality Improvement
Soil and water quality are protected by trees. In urban settings, large areas are covered by buildings, pavement, and other impervious surfaces. Instead of percolating into the soil, rainwater and snow melt are concentrated and accelerated, increasing soil erosion and silt accumulation in streams. Trees and other vegetation protect the soil from erosion. Along watercourses, roots and fallen leaves help hold the soil together and shield it against the cutting forces of surface water. Vegetation also absorbs some of the force of failing rain, so soil particles are not dislodged. The leaf litter that accumulates under trees creates an environment for earthworms and other organisms that help maintain soil porosity.

Source
Morgan, Robin, “The Value of Trees”, World Forestry Center in Portland, Oregon

To earn ISA-CEU’s for this article, click on TEST for Certified Arborist, Utility Specialist, Tree Worker Specialist, Municipal Specialist, Aerial Lift Specialist, or BCMA management credits. The ISA will award you with 0.5 CEU's when you score 80% or better on the test. Be sure to add your ISA cert. no. after your name when you sign in.

CaUFC credits for this article will be awarded upon request. After taking the test above, please contact us at: test@on-line-seminars.com, say “Send ___ test score to CaUFC” and we will send your score to them as well as the ISA.


Custom Soils Lock CO2 Away
Edited by Len Phillips

Could part of the answer to saving the earth from global warming lie in the soil beneath our feet? Using calcium-rich soil in landscaping and agriculture, thousands of tons of carbon dioxide (CO₂) could be fixed in the ground each year, compensating for a significant fraction of annual greenhouse gas emission. This approach can be put into practice quickly and with limited investment. A research team from Newcastle University in the U.K. says custom soils can remove carbon from the atmosphere permanently and cost-effectively. However, they claim this has never been attempted anywhere in the world.

Exploiting a Natural Cycle
The concept underlying this initiative exploits the fact that plants, crops, and trees naturally absorb atmospheric CO₂ during photosynthesis and then pump surplus carbon through their roots into the earth around them. In most soils, much of this carbon escapes back to the atmosphere or enters groundwater.

But in soils containing calcium-bearing silicates (natural or man-made), the research team believes the carbon that oozes out of a plant’s roots may react with the calcium to form the harmless mineral calcium carbonate. The carbon then stays securely locked in the calcium carbonate, which simply remains in the soil, close to the plant’s roots, in the form of a coating on pebbles or grains.

The scientists are investigating whether this process already occurs in some locations, as it may encourage the growing of more plants, crops, etc. in places where calcium-rich soils already exist. It would also open up the prospect that certain soils can be modified with added calcium silicates, or by growing specific plants to optimize the carbon-capture process. Such soils could play a valuable role in carbon abatement all over the globe.

Making Custom Soils
The research team will:

1. try to detect calcium carbonate in natural soils that have developed on top of calcium-rich rocks or have been exposed to concrete dust which contains man-made calcium silicates.

2. study artificial soils made from a mixture of compost and calcium-rich rock.

3. grow plants in custom-made soils containing a high level of calcium silicates and monitor the accumulation of calcium carbonate there.

The multi-disciplinary research team, including civil engineers, geologists, biologists and soil scientists, is led by David Manning, Professor of Soil Science at Newcastle University.

Scientists have known about the possibility of using soil as a carbon ‘sink’ for some time. But no one has tried to design soils expressly for the purpose of removing and permanently locking up carbon. Once the feasibility of this method of carbon sequestration is confirmed, a computer model will be developed that predicts how much calcium carbonate will form in specific types of soil and how quickly it can be developed. This information will help develop soils with optimum qualities from a carbon abatement perspective. A key benefit is that combating climate change in this way promises to be cheap compared with other processes.

Potential Applications
This concept could allow incorporation of calcium-rich, carbon-locking soils in land restoration, land remediation and other development projects. Growing bio-energy crops on these soils could be another attractive option. The process might be able to contribute significantly to carbon reduction targets in the future. Potentially there could be applications in 2-3 years, including a number of ‘quick wins’ in the land restoration sector.”

Organic Alternative
An alternative report from the Rodale Institute's long-term studies comparing organic and conventional farming methods indicated that organic practices are very effective at removing CO₂ from the atmosphere and fixing it as beneficial organic matter in the soil. The organic approach does not rely on high-tech solutions. It harnesses the same symbiotic relationships among beneficial soil organisms that have maintained the productivity of soil for millions of years.

As we all know, plants remove CO₂ from the air and convert it to organic material using photosynthesis. The oxygen in the CO₂ molecule is released back to the air and the carbon becomes part of the plant tissue. The carbon is later released when the plants die and are decomposed by soil microorganisms. Carbon is also stored in the soil through the activities of soil organisms. These microorganisms produce humus, a rich, dark colored soil component and glomalin, an organic glue. Both products are loaded with carbon captured by mycorrhizal fungi. Glomalin acts to bind organic matter to mineral particles in the soil as tiny clumps which improve soil structure and the carbon is deposited on the surface of these particles. This process locks carbon in the soil.

Researchers have discovered that the higher the atmospheric CO₂ level, the more glomalin that is produced by mycorrhizal fungi. The more glomalin in the soil, the more carbon is added to the soils and the richer the soil becomes with biological activity.

Fertilizer
Much of today's agriculture, turf care, and landscape management practices reduce mycorrhizal activity in soil. Chemicals, cultivation, excavation, compaction, erosion, and other artificial soil impacts can all have adverse affects on carbon levels. Chemical fertilizers not only require large amounts of energy to make the product, they are essentially salts that can dehydrate beneficial soil microorganisms.

On the other hand, the use of organic fertilizers, biological inoculants, compost, and mulch store significant amounts of carbon. At the same time, the use of these products is more ecologically sound, more efficient, more productive, and healthier for the soil and plant. Carbon enriched soil absorbs and retains more water, while mulch prevents evaporation and erosion.

Carbon Sinks
Trees have woody stems and roots that are excellent long-term storage sites for carbon. The simple act of mulching around a tree can provide many benefits including adding significant amounts of carbon to the soil. As the mulch breaks down, it contributes nutrients such as carbon for the tree, thereby reducing the need for chemical fertilizers. The soil carbon is also locked in to add to the carbon sink.

If landscape management professionals and arborists, all decided to adopt organic methods, we could leave our planet healthy for generations to come.

Sources

• Amaranthus, Mike and Larry Simpson, “Soil Live & Carbon”, Tree Care Industry, August 2009

• Newcastle University (U.K.), Engineering and Physical Sciences Research Council, February 2009

• “Specially-designed soils may help combat climate change”, Science Centric, April 2008

To earn ISA-CEU’s for this article, click on TEST  for Certified Arborist, Utility Specialist, Tree Worker Specialist, Municipal Specialist, Aerial Lift Specialist, or BCMA science credits. The ISA will award you with 0.5 CEU's when you score 80% or better on the test. Be sure to add your ISA cert. no. after your name when you sign in.

CaUFC credits for this article will be awarded upon request. After taking the test above, please contact us at: test@on-line-seminars.com , say “Send ___ test score to CaUFC” and we will send your score to them as well as the ISA.


Tree of the Seminar
Edited by Len Phillips

Royal Raindrops Crabapple is ideal for urban sites. It has good disease resistance and excellent year-round color. This information has been gathered from personal observations of the Editor, living in New England, Zone 5, and information provided by J. Frank Schmidt & Son.

Trade Name: Royal Raindrops® Crabapple
Botanical Name: Malus 'JFS-KW5'
Plant Patent: #14375
Parentage: Seedling selected by Keith Warren at J. Frank Schmidt & Son Nursery
Family: Rosaceae
Year of Introduction: 2004
Height: 20'
Spread: 15'
Form: Upright spreading shape
Bloom Period: Early spring
Flower: Magenta to pink blooms
Fruit: Tiny, ¼” diameter, persistent, sparkling red, prized by wildlife, add winter interest
Spring Foliage: Leaves emerge glossy deep purple
Summer Foliage: Deep purple cutleaf foliage
Autumn Foliage: Fall color is bronze, orange-red, and purple
Winter Color: Persistent red fruit
Bark: Dark brown to gray, flaky with age
Hardiness Zone: 4 – 9
Growth Rate: Fast, quickly gains caliper while developing a sturdy, well-tapered trunk
Site Requirements: Tolerates urban conditions, prefers moist soils, any pH, very heat and drought tolerant
Pest Resistance: Resistant to the four major diseases
Storm Resistance: Excellent due to strong upright branches, strong wind tolerance
Salt Resistance: Good
Planting: Easily transplanted, fibrous root system, spring only
Pruning: Prune in late summer, if needed
Propagating: Rooted cuttings, budding, or grafts
Design Uses: Fine texture, good for homes, streets, parks, and commercial landscapes. Deep roots will not cause sidewalks to buckle.
Companions: Looks good with evergreen ground covers
Other Comments: Refined, uniquely shaped leaves, flowers, fruits, and fall color give year-round appeal
Available from: Most large nurseries
Website: Royal Raindrops

To earn ISA-CEU’s for this article, click on TEST  for Certified Arborist, Utility Specialist, Tree Worker Specialist, Municipal Specialist, Aerial Lift Specialist, or BCMA science credits. The ISA will award you with 0.5 CEU's when you score 80% or better on the test. Be sure to add your ISA cert. no. after your name when you sign in.

CaUFC credits for this article will be awarded upon request. After taking the test above, please contact us at: test@on-line-seminars.com, say “Send ___ test score to CaUFC” and we will send your score to them as well as the ISA.


Contract vs. In-House Staff
Edited by Len Phillips

Is it less expensive to use a contractor, paid by the job, plus profit, or have in-house forestry staff, paid year round, plus benefits? This question is often asked by city forestry managers as they search for ways to provide the required municipal services for less cost.

Pros and Cons
Forestry services can be accomplished by using contractors, in-house staff, or a combination of both. Typical contracted services include tree planting, tree growing, pruning, removals, stump grinding, wood disposal, and electric line trimming. Consultants can also provide services such as inventories, master plans, write and oversee contracts, and prepare all types of documents and regulations.

Contracted services have the following advantages:

Emerald Ash Borer Update
Edited by Len Phillips

The Emerald Ash Borer (EAB) (Agrilus planipenni), is an invasive insect pest introduced from Asia that attacks ash trees. The EAB is primarily a temperate/cold-temperate species and is native to China, Japan, Korea, Taiwan, and the Russian Far East, where it is an insignificant pest of ash trees. Discarded solid wood packing material from Asian cargo ships or airplanes is suggested as a possible source of the North American infestation.

This insect pest, an exotic species previously unknown in North America, has been attacking ash trees in southeast Michigan for several years. Experts feel that it may have been in North America since the 1990s based on the age of trees affected and when tree dieback was first observed.

EAB, originally found in Detroit, Michigan and Ontario, Canada in 2002, has now killed over 40 million ash trees in Michigan, Illinois, Indiana, Maryland, Missouri, New York, Ohio, Ontario, Pennsylvania, Quebec, Virginia, West Virginia, and Wisconsin.

EAB has caused regulatory agencies to enforce quarantines in these states and impose fines to prevent potentially infested trees, logs, and firewood from being moved out of areas where EAB occurs. The cost of dealing with the pest, to municipalities, property owners, nursery operators, and forest products industries, is in the tens of millions of dollars.

This non-native pest poses an enormous threat to our urban and rural forests. The EAB is so aggressive that ash trees may die within two or three years after they become infested with the beetle. If it is not contained and eradicated, the impact of Emerald Ash Borer beetle attacks on ash trees in North America will be similar to the devastation from Chestnut Blight and Dutch Elm Disease that destroyed woodlands and urban forests in the 20th century.

Ash Trees
Ash trees are important ecologically and economically in the forests of the northeastern United States and eastern Canada. They were sought out for urban tree planting because they are not defoliated by the gypsy moth and because they transplant easily, among other reasons.

EAB attacks only ash trees (Fraxinus sp.), but all 16 native ash species are probably susceptible to EAB attack. EAB is a secondary pest and prefers to attack trees stressed by environmental conditions. However, the insect will also attack healthy trees once the sickly trees have died. In the lower peninsula of Michigan and in northwest Ohio, trees in the landscape, in nurseries, and in wooded areas have been detected with infestations. Usually the infestation goes undetected until the upper third of the tree has died back, followed by death.

The Beetles
EAB beetles have dark metallic green wing covers and coppery red or purple abdomens. They are 3/8 to 5/8 inches (1-1.5 cm) in length and 1/16-inch (0.2 cm) wide. Males are smaller than females and have fine hairs on the ventral side of the thorax. The adult beetles begin emerging in late May with peak emergence in late June to early August. The beetle appears to have a one-year life cycle.

Mating occurs during the first 7 to 10 or more days after emergence, with females mating multiple times. Each female lays an average of 77 eggs in bark crevices from after mating through August and September. Larvae hatch in 7 to 9 days. The larvae enter the tree and feed in the vascular cambium on the nutrient rich conductive tissues. The creamy white larvae live under the bark and tunnel in the cambial layer. As they feed on the inner bark they disrupt the tree's ability to transport water and nutrients and this causes stress and eventual death of the tree. Larvae feed aggressively until cooler fall temperatures arrive and then they overwinter within the tree. Woodpeckers like to eat the EAB larvae; so heavy woodpecker damage on ash trees may be an early sign of infestation.

Pupation occurs in late April to June. The pupal chamber is constructed by tunneling into the sapwood at a shallow angle. Newly formed adults remain in their pupal chambers for 8 to 15 days, and make a D-shaped hole approximately 1/8 inch wide when they bore through the bark to the outside. Adults nibble on ash foliage but cause little damage.

The EAB is a good flier and adults can fly at least ½ mile (2000 m) from the tree where they emerge. Most likely, local spread occurs by movement of infested material and adult flight, while long distance spread occurs only due to movement of infested material or other human activities. Many infestations have been started when infested ash trees, logs. or firewood was moved into uninfested areas.

Control
A concerted effort to stop the EAB has been launched by state and federal officials. This consists of research at local universities to develop an understanding of the EAB’s life cycle; finding ways to detect new infestations; control of the adults and larvae; and containment of the infestations. Containment efforts consist of treating all host trees within a half-mile radius of an infested tree and conducting visual surveys to limit the area of infestation. Insecticides have not been effective in totally eradicating EAB infestations.

Treatment options can be any of the following:

• In situations where the EAB population is very low or as a preventative measure, a soil-applied systemic insecticide (imidacloprid) is applied as a drench or by soil injections, mixed with water and applied directly on the soil within 6” – 18” (15 – 45cm) of the trunk. This allows the insecticide to be taken up by the roots and translocated throughout the tree. This is done between mid-April and mid-May.

• Trunk applied insecticides (imidacloprid or emamectin benzoate) can be injected directly into the trunk. These products are injected just after the leaves have opened from mid-May to mid-June. A single treatment of emamectin benzoate provides excellent control for two years and may even last for three years.

• Trunk sprays of insecticides (imidacloprid or dinotefuran) cover the lower six feet (2 meters) of the ash trunk with a low pressure spray that penetrates the bark and moves systemically though the tree. The addition of a surfactant to the insecticide has had only mixed results.

• Protective cover sprays of the entire tree are designed to kill newly hatched EAB larvae before they enter the tree and adults before they lay their eggs. These sprays should be applied around the time that black locust bloom and again, four weeks later. The sprays include the following:

• The best Onyx treatments reduced the density of new galleries by 71 – 74%. Onyx treatments did not yield a higher level of control in the second year.\
  BotaniGard reduced the density of new galleries by 53%.

• Tempo (cyfluthrin), Sevin SL (carbaryl), and Orthene (acephate) have been more effective than other treatments, especially when applied in mid-May and again in early July. Tempo is more effective sprayed over the entire tree than just the trunk.

 

Success with insecticides is not guaranteed; in some studies the treatments were effective, but in other trials the same treatments failed. In some studies EAB infestations continued to increase despite ongoing treatments. Current research suggests that the best control can be achieved when insecticide treatments are started in the early stages of infestation or just before the trees are infested.

Quarantine
Quarantines prohibit the movement of ash wood to areas outside of the specified quarantined counties. At this time treatment options for ash logs and lumber include fumigation or kiln drying only. Additional treatments may be permitted once there is evidence of their effectiveness.

APHIS
The Animal and Plant Health Inspection Service (APHIS) and the US Forest Service (USFS) notified their cooperators in northern states to be on the lookout for EAB and to pay close attention to forest health monitoring sites showing signs of ash decline. In addition, APHIS has asked city foresters and arborists nationwide to examine their ash trees for signs of the beetle, especially in areas suffering severe ash decline. They need to act quickly and would like to get your observations ASAP. If you see evidence of this pest, report your findings to the appropriate plant health official in your State. A listing can be found at: http://www.aphis.usda.gov/npb/npbmemb.asp

Despite quarantine and insecticide efforts, there seems to be no stopping this pest. The economic costs of ash mortality in urban and forested areas, restrictions on shipments of nursery stock, logs and firewood are already in the tens of millions of dollars. Potential costs of EAB are estimated to be in the hundreds of billions if this pest continues its spread across the U.S. The ecological consequences of EAB are not yet well known, but the beetle is likely to have a major impact on our urban and natural forests.

More information about the beetle and the outbreak can be found at:
http://www.treeresearch.org 

Sources

• Personal conversations with Paul Dykema, Forestry Manager, Lansing Parks and Recreation

• Personal conversations with the staff at Arborjet, Inc.

• Phillips, Leonard, “Emerald Ash Borer”, City Trees, The Journal of The Society of Municipal Arborists, Vol. 38, Number 5, September/October 2002

• Williamson, R. Chris, and Fredric Miller, “Emerald Ash Borer”, Tree Care Industry, June, 2009.

• USDA Forest Service, state agricultural departments, and universities collaboration website: http://www.emeraldashborer.info/index.cfm, 2009

LATE BREAKING NEWS
Kentucky and Minnesota have just reported outbreaks in these states.

Not all is doom and gloom. One of the U.S. Forest Service research stations has found EAB predators that, in the lab, do a good job of controlling this pest. The researchers have petitioned APHIS for permission to do field tests.

To earn ISA-CEU’s for this article, click on TEST  for Certified Arborist, Utility Specialist, Tree Worker Specialist, Municipal Specialist, Aerial Lift Specialist, or BCMA science credits. The ISA will award you with 0.5 CEU's when you score 80% or better on the test. Be sure to add your ISA cert. no. after your name when you sign in.

CaUFC credits for this article will be awarded upon request. After taking the test above, please contact us at: test@on-line-seminars.com, say “Send ___ test score to CaUFC” and we will send your score to them as well as the ISA.


Watering Established Trees
Edited by Len Phillips

Water plays many key roles in the lives of trees. The amount of water a soil can hold is called field capacity. A tree's roots take in water, at and below field capacity. When water is reduced below field capacity, it is available to the tree until it reaches the permanent wilting point. When water is in short supply, landscape plants cannot function normally and will eventually die if the deficit is not corrected.

Watering Established Trees
Normally, a tree's roots are between 8 – 18 inches (20 – 45 cm) under the surface and they spread out to a radius that exceeds the height of the tree. In situations where grass is growing under a tree's branches, the grass will out-compete the tree's roots for moisture, oxygen, and other nutrients. Therefore, trees should have their own irrigation system that will provide water at a slower rate over a longer time period to moisten the soil deep beneath the grass roots. Sprinkler heads should have low volume nozzles. Soaker hoses and drip irrigation are other options. When irrigating trees, enough water should be applied to penetrate at least 12 inches (30 cm) deep. Because soil soaker hoses tend to soak in less deeply, they may need to be left running overnight to adequately water a large tree. Sprinklers are the best because the spray will wash dirt and pollutants off the leaves, increase the humidity, and lower the temperature. The water will readily soak into mulch and the system can be easily checked for maintenance.

On the other hand, when the irrigation system is set for watering grass only, the tree roots will eventually grow into the upper 6 inches of soil, seeking moisture, and they will out-compete the grass roots. Then the grass will suffer and eventually die.

For the most part, trees can only take up water from soil in proximity to the roots. Established trees are in contact with greater volumes of soil due to wide-spreading root systems and are more capable of obtaining water. Trees that have had their root systems severed to facilitate transplanting or construction have fewer roots and a smaller soil volume in contact with roots.

Mulch reduces the amount of evaporation from the soil and thus is very useful in keeping the soil moist. Mulch also keeps soil temperature cooler and reduces the number of weeds competing for soil moisture. In a good year, with regular and adequate rainfall coupled with a layer of mulch over the tree’s root system, irrigation should never be necessary.

Soil texture, structure, and percolation also influence the amount of water available to a tree. Trees growing on sandy soils will probably need irrigation more frequently, especially for larger trees in sunny, windy, and hot climates. Conversely, trees planted in clayey soils that do not percolate adequately require less irrigation. In fact, frequent irrigation may do harm by displacing essential soil oxygen. Examine the soil moisture 4-8 inches (10-20 cm) deep to determine the need for water. If the soil feels dry or just slightly damp, watering is needed.

Large trees lose lots of water daily. For an example, a 90-foot (28 m) oak with an equal spread may lose 90 gallons (340 l) of water and a quarter inch of soil moisture when the temperature is 90° F (32° C), daily. Watering should occur when less than an inch of rain has fallen in a two-week period and temperatures have passed 85° F (30° C). While the soil surface is drying out, deep moisture concentrations are attracting roots. Additionally, root growth increases at lower soil levels since soil temperatures are cooler twelve or more inches deep. The end result is less root death due to temperature extremes.

Trees need water in order to manufacture food. Water dissolves fertilizer salts that can then be absorbed by the roots. Water is a key part of the system that transports nutrients and hormones throughout the tree and a part of biochemical reactions within the tree. Water also acts as a coolant by evaporation through the leaves, keeping the tree from overheating on summer days.

Symptoms of water stress include wilting and loss of leaves. Branches may bend, also.

Most of the tree roots that absorb water, called feeder roots, are within the top fifteen inches of soil. These roots are generally congregated at the outer branches of the plant. Mature trees may have feeder roots extending fifty feet past the drip line. Few water absorbing roots are under the plant’s canopy or near the trunk. Feeder roots are not large. Most are finer than a strand of hair. They are easily severed when digging or can dry out during droughts. On the other hand, they are easily replaced.

Recycled Water
Recycled water from sewage treatment plants is often of poorer quality than potable water and is therefore unsuitable for use in landscapes. Recycled water often contains high levels of salts and nutrient ions that are detrimental to tree growth. The use of recycled water should only be considered if the plants will tolerate salt, boron, and other chemicals found in this water. The use of this water also requires a long-term effort to monitor plant health and soil chemical changes. Good drainage is also especially critical for plant survival.

Wetting Agents
Water molecules are strongly attracted to one another and this attraction often results in the water clumping together in the soil’s pore space rather than spreading evenly throughout the soil. The problem is especially pronounced at boundaries between soils of different textures, as between the root ball and backfill or between the topsoil and layers of subsoil. Water does not move readily through these boundaries from one soil into another.

Wetting agents are materials that make the water molecules less attractive to each other so these molecules move more quickly through the soil pores and more effectively through any boundaries of soil. Soil microbes will also use the wetting agent as an additional food source.

Wetting agents should not be considered a substitute for other soil preparation or maintenance needs. They only make water “wetter”, hence more readily absorbed by the plant's roots. Wetting agents do not change a plant's water needs either. One inch of water per week is required, with or without wetting agents. Management practices such as topdressing, mulch, compaction management, etc. should continue.

Wetting agents must be applied according to the manufacturer's instructions. Using too much can cause harm to the soil and to the plant's root system. Wetting agents are most effective for relieving extremely dry soil. Using these materials for routine watering is a waste of the product. Wetting agents can be purchased from horticulture or arboriculture supply houses.

Frequency of Irrigation
The amount and frequency of irrigation needed depends on several environmental, soil, and plant characteristics. In general:

• Supplemental irrigation is rarely needed during rainy periods.

• The need for irrigation increases with increasing temperature.

• Windy conditions may necessitate more frequent irrigation.

• Poorly drained, clay-type soils require less frequent irrigation than sandy soils.

• Plants with small or poorly developed root systems are particularly sensitive to moisture deficits.

• Newly planted trees and shrubs rely heavily on ample soil moisture in the root area throughout the first growing season.

• Root growth is slowed or will stop completely in soils that are too wet or too dry.

• Until roots begin to grow into the backfill, moisture available to newly planted trees can be depleted very quickly.

 

Too Much Water
Plants may wilt if there is too much water in the soil because the oxygen and gas exchange is blocked. Plants may also wilt because of soil compaction or diseases that affect cell membranes.

Antitranspirants
Antitranspirants (also known as antidesiccants) have been suggested to aid transplant success. Antitranspirants reduce water loss through stomates either by causing stomate closure or by covering stomates with a waxy film that is a barrier to water loss. Although antitranspirants seem reasonable in theory, in practice they may lengthen the establishment period. Closed or blocked stomates may reduce water loss, but they also decrease carbon dioxide entry into leaves, thereby reducing the manufacture of energy compounds from photosynthesis.

Sources

• Appleton, Dr. Bonnie Lee, "Modification of Tree Roots", City Trees, The Journal of The Society of Municipal Arborists Vol. 37, Number 5 September/October 2001

• Barton, Amy J. and Christopher S. Walsh, "Effect Of Transplanting On Water Relations And Canopy Development", Journal of Environmental Horticulture. 2000. 18(4): 202-206

• Clatterbuck, Wayne K., "Post-Planting Tree Care: Fallacies and Recommendations", Agricultural Extension Service, The University of Tennessee, 2008

• Harris, Richard W., “Arboriculture”, Prentice Hall, 1992, p. 174-184, 273-276, 324-327.

• Iles, Jeff, "Tree Planting Basics", http://turfgrass.hort.iastate.edu, 1997

• Kozlowski, T.T., “Soil moisture and absorption of water by tree roots”, Journal of Arboriculture 13(2):39-46.

• Meyer, Kenneth D., "Tree Care Practices" Arbor Age, Vol. 15, No. 8

• Neely, Dan, and Gary Watson, "The Landscape Below Ground II", International Society of Arboriculture, 1998.

• Powell, Charles C. "How to Water Plants", NM/PRO, March 2004.

• Robson, David, "Watering", Horticulture Extension Report, University of Illinois, 2007

• Smith, Karen D et.al, "Influence Of Waterlogging On Trees", Journal of Arboriculture 2 7(2):49 - 56

• Trowbridge, Peter J. and Nina L. Bassuk, "Trees in the Urban Landscape", John Wiley & Sons, Inc. 2004

To earn ISA-CEU’s for this article, click on TEST  for Certified Arborist, Utility Specialist, Tree Worker Specialist, Municipal Specialist, Aerial Lift Specialist, or BCMA practice credits. The ISA will award you with 0.5 CEU's when you score 80% or better on the test. Be sure to add your ISA cert. no. after your name when you sign in.

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Soil Compaction
Edited by Len Phillips

Pore space exists around soil particles, structural units, and the interfaces of infrastructure and soils. Large sized soil pores are usually filled with air and provide good aeration but have poor water holding capacity. Small soil pores are usually filled with water and have large water holding capacity but poor aeration. Soils dominated by small soil pores have more total pore space than soils dominated by large pores. Small or capillary pores are divided between tree-available water-filled pores and tree-unavailable water-filled pores. Tree-unavailable water resides in the smallest soil pores, where the tree cannot exert enough force through transpiration to remove the pore water.

Three attributes of soils:

1. Soil depth – With increasing soil depth there is an increase in carbon dioxide (CO2) concentrations and a decrease in oxygen (O2) concentrations. The balance between these two gases will vary depending on water content and biological activity.

2. Organic matter – Organic matter provides cationic exchange, water holding capacity, essential elements, detritus food, and pore space. Organic matter is deposited on the surface as plant litter and near the soil surface as roots break down. The decomposing materials then move downward through the soil.

3. Developed structure – The basic soil particles (sand, silt, and clay) are held together in clumps or structural units. Between structural aggregates are soil pore spaces filled with air or water.

Compaction
Compaction is a soil condition that makes it impossible for trees to grow. Compaction prevents roots from penetrating the soil and causes systemic damage and decline of a tree. An ideal soil has 50% pore space, divided among air-filled and water-filled pores. In addition, 45% of an ideal soil is composed of mineral materials and 5% of organic material. This ideal does not exist in a compacted state. The volume of soil space penetrated by tree roots is directly related to tree health. In heavily compacted sites, roots cannot grow normally and instead will be concentrated around the edges of the compacted soil and infrastructures and will fill any moist air space.

Compaction creates many negative impacts:

• the volume of ecologically active space is decreased,

• root space is decreased and made more shallow,

• the soil web is disrupted and modified,

• the diversity of living things declines,

• beneficial microorganism associations are eliminated, harmful pests become more numerous, and roots are unable to defend themselves,

• tree roots become more prone to damage and attack at a time when sensor, defense, growth regulation, and carbon allocation processes are functioning at reduced levels.

Components of Compaction
The components of soil compaction do not necessarily occur in order, or on any given soil.

• Compression is most prevalent in wet soils. Compression occurs when large air-filled pore spaces are crushed, leading to more small water-filled pores.

• Compaction occurs from the movement of sand, silt, and clay particles, destruction of aggregates, and collapse of aeration pores.

• Consolidation is deformation of the soil, destroying any pore space and structure as water is squeezed from the soil matrix. This process leads to increased internal bonding and the elimination of pore space.

The following components represent the extent and depth of a damaged top surface layer. They can generate soil conditions difficult for tree health.

• Crusting is the packing of fine particles and organic matter on the soil surface, preventing water and oxygen infiltration. The primary cause of crusting is the impact of raindrops or sprinkler water.
  
• Puddling and rutting produces a dense crust on the soil surface caused by pressure from foot and vehicle traffic. In saturated soils, there is no place for non-compressible water to go under a surface load except to the side, squashing soil structure and eliminating pores.
  

Measuring Compaction
The primary soil factors critical to tree growth are oxygen availability, gas exchange with the atmosphere, and soil strength values. The most commonly used measure for soil compaction is bulk density.

Bulk density is the weight of the soil per unit volume (usually in g/cc). As bulk density increases, total pore space declines and aeration pore space is destroyed. Bulk density, as a measure of soil compaction, rapidly increases with the first few impacts on the soil surface and then levels-off. In other words, it is not years of traffic but the first 4 trips that cause the majority of compaction damage to a soil.

Biological Disruptions
Compaction disrupts the respiration process that powers every function of a tree. As a result, growth regulators are destroyed prematurely or allowed to build up, causing changes in tissue reactions. Highly modified growth regulation patterns will change carbon allocation, food production, storage, use, and transport processes. The presence of toxic materials can be highly disruptive to soil health. As oxygen concentrations decline, greater quantities of reduced compounds are generated by the tree roots and associated soil organisms. These reduced compounds can build up in compacted soils, damaging organisms and moving the soil toward anaerobic conditions. In normal soils, these materials, if produced at all, are quickly oxidized and removed.

Structural Disruptions
The structure of the tree can be directly and indirectly impacted by compacted soils. Root decline and death can lead to catastrophic structural failures. Top and root dieback as well as branch drop can also occur. Reduced rooting volume mechanically destabilizes the whole tree.

Sources:

• Coder, Kim D. "Compaction Tolerant Trees", City Trees, Vol. 38, Number 2, March/April 2002

• Coder, Kim D. "Soil Compaction Impacts on Tree Roots", City Trees, Vol. 38, Number 4, July/August 2002

• Coder, Kim D. "Tree Root Growth Requirements", City Trees, Vol. 38, Number 2, March/April 2002

• Gilman, Edward F., "Planting Trees in Landscapes", Environmental Horticulture Department, IFAS, University of Florida, 2008

• "Guide to Arbor Care", Plant Health Care, Inc. 2008.

• Neely, Dan, and Gary Watson, "The Landscape Below Ground II", International Society of Arboriculture, 1998.

• Rivenshield, Angie, "Soil Amendments to Reduce Compaction", Graduate Thesis, Cornell University

• Trowbridge, Peter J. and Nina L. Bassuk, "Trees in the Urban Landscape", John Wiley & Sons, Inc. 2004

To earn ISA-CEU’s for this article, click on TEST  for Certified Arborist, Utility Specialist, Tree Worker Specialist, Municipal Specialist, Aerial Lift Specialist, or BCMA science credits. The ISA will award you with 0.5 CEU's when you score 80% or better on the test. Be sure to add your ISA cert. no. after your name when you sign in.

CaUFC credits for this article will be awarded upon request. After taking the test above, please contact us at: test@on-line-seminars.com, say “Send ___ test score to CaUFC” and we will send your score to them as well as the ISA.


Dealing with Soil Compaction
Edited by Len Phillips

Compaction is a soil condition that makes it impossible for trees to grow. Correcting compaction will allow roots to penetrate the soil.

Compaction Effects
Major soil compaction effects on trees are defined below:

1. Reduced Elongation Growth – As compaction increases, roots are physically prevented from elongating into the soil by a lack of oxygen, by decreasing pore size, and by increased soil strength. As roots are put under pressure, elongation slows and stops.

2. Shallow Rooting – As roots survive in a steadily diminishing aerobic layer, and as the anaerobic layer expands toward the surface, the physical space available for living roots declines, which means roots are subject to greater stresses.

3. Constrained Size of Root Systems – Compaction limits the depth and reach of a tree’s root system, leading to greater probability of wind throw and problems near the root collar.

4. Essential Element Collection Problems – With less soil volume, there is less physical space to collect resources.

5. Stunted Tree Form – As resources are limited by soil compaction, trees become stunted. Carbohydrate and protein synthesis rates enter decline cycles interfering with nitrogen and phosphorous uptake. The result is a tree with a limited ability to take advantage of resource availability.

6. Seedling Survival Problems – Variability in compaction levels constrains newly planted tree seeds and young trees. Low bulk density and crusting levels are required for the survival of younger trees than for older, established trees.

7. Root Crushing and Shearing-off – The mechanical forces generated in compacting a soil can crush roots, especially small ones. Larger roots can be damaged. Vehicle rutting can shear off roots as soil is pushed to new locations.

8. Aerobes – Soil compaction reduces aerobes and favors anaerobes or low oxygen requiring organisms, like Pythium and Phytophthora root rots.

In response to increased compaction, roots thicken in diameter. Thicker roots exert more force and penetrate farther into compacted soil areas. As roots thicken, growth slows and more lateral roots are generated. If laterals are small enough to fit into the pore sizes of the compacted soil, lateral growth will continue while the main axis of the root is constrained. If the soil pore sizes are too small for even the lateral roots, root growth will cease.

Renovation of Sites
Restoration of soil to pre-compaction conditions may not be possible. In deciding how to proceed, one should consider the following:

• Soil compaction should be considered permanent. Studies demonstrate that after one-half century, compaction still afflicts soils under natural forest conditions.

• Every urban soil has a compacted layer. Changing management may not change the current compacted zone and could even add another compacted zone.

• Management activities should be directed toward increasing aeration space and reducing soil strength.

• Alleviation of future soil compaction should be part of a soil health plan.

• Seek the assistance of a tree and soil specialist to avoid problems on compacted soils.

Techniques
Some techniques for minimizing the compaction of soils include:

• Restricting site access with fences and fines (for construction code violations).

• Selecting working conditions (dry, dormant season, surface mulch, etc) that minimize compaction.

• Restricting the use of vibrating rollers where possible.

• Trying to soften and distribute compaction forces with temporary heavy mulch and plywood driving pads, and by restricting soil moisture content.

Some techniques for correcting soil compaction include:

• restarting or improving the detritus energy web in the soil, including the addition of organic matter and living organisms.

• changing soil physical properties by increasing aeration pore space.

• vertical mulching. This is a technique that can be used to partially alleviate soil compaction within the critical root zone of trees. Vertical mulching is done using a power auger with a 2-inch (5 cm) diameter drill bit. Starting about 8 feet (2.4m) out from the trunk, drill holes 12 inches (30 cm) deep on an 18-inch (48 cm) grid out to the dripline. Try to avoid damaging any roots. The holes should be back-filled with pea gravel, sand, or a mixture with compost.

• installing drainage systems at the point where compacted soil meets non-compacted soil to drain water from the root zone.

• cutting radial trenches starting several feet from the tree by digging slowly while trying to avoid major root loss. At least 10 feet (3 m) of trench should be dug 12 inches (0.3 m) deep sloping downward to a depth of 24 inches (0.6 m). Be sure there is adequate drainage at the deepest point of the trench. The soil that has been removed can be modified to improve its density before putting it back into the trench, and then the entire site should be watered. Turf should also be removed and replaced with mulch.

• tilling farm soil regularly reduces compaction.

• injecting compressed air or nitrogen in a process known as "fracturing".

• using commercial surfactants to improve water penetration, especially when irrigating or applying fertilizers.

• subsoiling techniques, which are useful in treating large areas of compacted soil.

• to encourage rapid recovery from transplanting in compacted soil, loosen the soil around the planting hole in a 10 to 15 foot (3 – 4 m) width.

• when planting, locate about 25% of the root ball above the surrounding landscape soil by planting on a mound of soil.

Compaction Tolerant Trees
There is a great variability among trees in reaction to soil compaction. Compaction tolerant trees are tolerant of poor drainage. No tree is tolerant of high soil bulk density. A tree's ability to tolerate compacted soil conditions is associated with four mechanisms:

1. reaction to mechanical damage that is effective and fast,

2. continuation of respiration under chronic oxygen shortages,

3. ability to continually adjust absorbing root systems,

4. ability to deal with chemically reduced toxics.

Here are lists of compaction tolerant and intolerant trees. The tolerant trees can also withstand poor drainage.
Tolerant                            Intolerant                                Intermediate
Ash: Black, Green               Aspen: Bigtooth, Quaking          Ash: White
Birch: River                         Basswood                                Butternut
Boxelder                             Beech: Blue                             Dogwood: Red-osier
Catalpa                               Birch: Paper, Yellow                 Elm: American, Slippery
Cottonwood: Eastern           Cherry: Black                            Hackberry
Fir: Balsam,                        Fir: White                                 Hawthorn
Maple: Red, Silver                Ironwood                                  Hickory: Bitternut
Oak: Bi-color                       Juniper                                     Honeylocust
Spruce: Blue, Black, White  Locust: Black                            Kentucky Coffeetree
Tamarack                           Maple: Sugar                             Mountain Ash
Willow: Black                     Oak: Black, Northern Pin, Red     White Oak: Bur
Plum                                  Pine: Jack, Red, Scotch, White  Ohio Buckeye
Serviceberry                        Walnut: Black

Flood tolerant trees
Scientific Name            Common Name
Acer negundo               boxelder
Acer rubrum                 red maple
Acer saccharinum        silver maple
Alnus sp.                     alders
Betula nigra                 river birch
Carya aquatica             water hickory
Carya illinoensis           pecan
Celtis laevigata             sugarberry
Celtis occidentalis        hackberry
Cercis canadensis        redbud
Crataegus sp.               hawthorns
Diospyros virginiana       persimmon
Fraxinus sp.                  ash
Gleditsia triacanthos      honeylocust
Ilex sp.                         holly
Juglans nigra                black walnut
Juniperus virginiana       Eastern redcedar
Liquidambar styraciflua  sweetgum
Magnolia virginiana         sweetbay
Nyssa sp.                      tupelo/black gum
Persea borbonia            redbay
Pinus elliottii                 slash pine
Pinus taeda                  loblolly pine
Platanus sp.                 sycamore/planetree
Populus sp.                  cottonwood/aspen
Quercus bicolor            swamp white oak
Quercus falcata            Southern red oak
Quercus imbricaria       shingle oak
Quercus laurifolia          laurel oak
Quercus lyrata              overcup oak
Quercus macrocarpa     bur oak
Quercus michauxii        swamp chestnut oak
Quercus nigra                water oak
Quercus nuttallii            nuttall oak
Quercus palustris          pin oak
Quercus phellos            willow oak
Quercus rubra               red oak
Quercus shumardii        shumard oak
Robinia pseudoacacia   black locust
Salix sp.                      willows
Taxodium distichum     baldcypress
Ulmus sp.                   elms

Sources:
Coder, Kim D. "Compaction Tolerant Trees", City Trees, Vol. 38, Number 2, March/April 2002
"Guide to Arbor Care", Plant Health Care, Inc. 2008
Rivenshield, Angie, "Soil Amendments to Reduce Compaction". Graduate Thesis, Cornell University
The Care of Trees, "Construction Tree Preservation", http://www.thecareoftrees.com, 2009
Trowbridge, Peter J. and Nina L. Bassuk, "Trees in the Urban Landscape", John Wiley & Sons, Inc. 2004
"Vertical Mulching", Tree Conservation Notes, Athens - Clarke County Community Tree Program, 2009

To earn ISA-CEU’s for this article, click on TEST  for Certified Arborist, Utility Specialist, Tree Worker Specialist, Municipal Specialist, Aerial Lift Specialist, or BCMA practice credits. The ISA will award you with 0.5 CEU's when you score 80% or better on the test. Be sure to add your ISA cert. no. after your name when you sign in.

CaUFC credits for this article will be awarded upon request. After taking the test above, please contact us at: test@on-line-seminars.com, say “Send ___ test score to CaUFC” and we will send your score to them as well as the ISA.


Research Briefs
Edited by Len Phillips

Effect of Compost-amended Backfill on Newly Planted Trees
Francesco Ferrini and Manuela Baietto

We compared the effects of compost-amended backfill and of the size of the exposed surface area on trees planted in high-quality backfill on a paved area and a brownfield site. After 3 years, trees with larger surface area and mulched planting areas had higher leaf gas exchange, leaf chlorophyll, and mineral content than those grown surrounded by pavement.

The effects of the different quantities of compost in the backfill were more difficult to assess. Although these effects may become significant in the long term, it is difficult to prescribe compost addition as a useful technique to improve plant growth and physiology when the native soil has been completely replaced by good topsoil.

Arboriculture & Urban Forestry Volume 33, Number 6 November 2007

Reduced Defoliation by Japanese Beetles on Linden
Steven Frank, Robert Ahern, and Michael J. Raupp

Laboratory feeding trials confirmed that leaves from little-leaf linden treated with imidacloprid were eaten by Japanese beetles far less than those from untreated trees. Field studies revealed that soil applications of imidacloprid significantly reduced the degree of severe defoliation caused by Japanese beetles in the year that the insecticide was applied and also in the next year. These findings indicate that imidacloprid is a useful tool for arborists in reducing defoliation by this pest.

Arboriculture & Urban Forestry Volume 33, Number 6 November 2007

Paclobutrazol-induced Drought Tolerance
Glynn C. Percival and Ali Mohammed Salim AlBalushi

The influence of paclobutrazol (PBZ) applied as a foliar spray and root drench on drought tolerance and recovery from drought was investigated. PBZ treatment induced a suite of physiological adaptations that would allow trees to tolerate drought: increased total leaf content of carotenoids and xanthophylls, chlorophylls, proline, superoxide dismutase, and catalase. In addition, PBZ strengthened leaf membrane integrity and increased leaf photosynthetic efficiency and light-induced CO₂ fixation before and at the cessation of the drought treatment. Irrespective of species, recovery rates of droughted trees treated with PBZ were 20% to 50% higher than non-PBZ-treated trees. In all cases, control trees (non-PBZ-treated) had the least capacity for recovery.

Arboriculture & Urban Forestry Volume 33, Number 6 November 2007

Use of Water for Systemic Insecticide Application
Chelcy R. Ford, James M. Vose, Michael Daley, and Nathan Phillips

The hemlock woolly adelgid (Adelges tsugae) is causing widespread decline and mortality of eastern hemlock throughout most of its native range. Stem injection of insecticide is widely used as a chemical control measure, but the effectiveness of this method depends on the hydraulic characteristics of individual trees. We present data quantifying the distribution of water flux within the stems and the seasonal variability of daily water use. Simple mathematical and graphical models derived from these data can be used to estimate the amount and timing of water use by eastern hemlock based on tree size and climatic conditions. We anticipate that the data and models presented will be useful in improving the effectiveness and efficiency of systemic insecticide applications.

Arboriculture & Urban Forestry Volume 33, Number 6 November 2007

Effects of Soil Decompaction and Amendment on Root Growth
William Hascher and Christina E. Wells

An injection device that uses compressed nitrogen gas to fracture compacted soil and permits the subsequent injection of liquid amendments was used to measure fine root growth and architecture in soil that had received one of four treatments: 1) gas injections only, 2) gas injections followed by liquid amendment, 3) addition of amendment only, and 4) an untreated control. The experiment was conducted on red maples growing on a moderately compacted urban clay soil next to a busy road.

Injection treatments had no effect on any root parameters measured. Application of liquid amendments was associated with small, statistically significant reductions in root diameter, root mass density and root surface area density.

Arboriculture & Urban Forestry Volume 33, Number 6 November 2007

Decay Detection in Red Oak Trees
Xiping Wang and R. Bruce Allison

Arborists are often challenged to identify internal structural defects hidden from view within tree trunks. Two century-old red oak trees were visually inspected and then evaluated using a single-path stress wave timer, an acoustic tomography, and a resistance measuring drill. The trees were subsequently felled, and a disk at each test location was obtained and examined. It was found that the visual inspection and single-path stress wave tests correctly identified a general problem but without specificity; the tomograph accurately revealed the general location and magnitude of the defect within the cross-sections tested but required resistance microdrilling to precisely locate defects and differentiate between decay and crack-induced acoustic shadows. For more information on resistance microdrilling, click here. 

Arboriculture & Urban Forestry Volume 34, Number 1 January 2008

Serviceberry Cultivars as Street Trees
Henry D. Gerhold

Through the Municipal Tree Restoration Program, cooperators planted eight serviceberry (Amelanchier spp.) cultivars for evaluation as street trees, typically comparing two in each community. Standardized measurements in years 1, 2, 3, 6, 9, and 12 revealed differences in trunk diameter, height, crown width, and health of foliage and branches.  

• Among the cultivars that have been tested most extensively, the main difference is that Cumulus® and Robin Hill are much taller in the twelfth year than Tradition® and Autumn Brilliance®.

• ‘Cole’s Select’, ‘Princess Diana’, Reflection™, and Spring Glory® also have been performing well for 6 to 10 years, but they have been tested at just one or two locations.

• Survival, growth, and health have been superior on more spacious sites, but with proper care, serviceberry cultivars can do well along downtown streets. All eight of these cultivars are appropriate for planting under overhead wires.
  

Arboriculture & Urban Forestry Volume 34, Number 2 March 2008

Effects of Pruning on Trunk Movement
Edward F. Gilman, Jason C. Grabosky, Scott Jones, and Chris Harchick

We built a machine with a propeller capable of generating 33.5 m/s (75 mph) winds to determine the influence of pruning and American National Standards Institute A300 pruning type on trunk movement of Quercus virginiana at various wind speeds. Increasing wind speed increased trunk movement, and the magnitude of the increase depended on pruning frequency and type.

Increasing pruning reduced trunk movement and the magnitude of the reduction was greater at higher wind speeds. The predicted trunk movement of thinned trees was statistically greater than movement of structurally pruned, raised, and lion’s tailed trees at wind speeds of 20.1 m/s (45 mph) and was greater than all pruning types at 26.8 m/s (60 mph).

There was no difference in movement among reduced, raised, structurally pruned, and lion’s tailed trees; and there were no statistical differences in trunk movement among pruning types at the lower wind speeds. Thinning the outer edge of the crown was one of the least effective pruning types for reducing trunk movement in wind.

Arboriculture & Urban Forestry Volume 34, Number 1 January 2008

Pruning Affects Tree Movement
Edward F. Gilman, Forrest Masters, and Jason C. Grabosky

The goal of this study was to determine how different pruning techniques affect trunk movement on live oak subjected to hurricane force winds. Tree movement in wind on non-pruned trees was compared with movement on trees with crowns thinned, reduced, or raised. Twenty trees were blown using a wind generator up to 45 m/s (110 mph) maintained for 3 min. Each tree was instrumented with three orientation sensors at set heights along the trunk to measure its deflection. Thinning or reducing crowns significantly reduced upper trunk movement at all wind speeds, whereas raising did not. Lower trunk movement was not affected by pruning type. Foliage and branches toward the top of tree crowns were largely responsible for trunk movement in straight-line wind with those toward the bottom less important. Trees that are reduced or thinned in the manner described could receive less damage in windstorms.

Arboriculture & Urban Forestry Volume 34, Number 1 January 2008

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Root Forms
Edited by Len Phillips

Roots survive and grow where adequate water is available, temperatures are warm, and oxygen is present. Roots are limited by low soil temperatures, low oxygen content, anaerobic conditions, and low water depth. Near the base of a tree, deep-growing roots can be found, and these are oxygenated through fissures and cracks generated as a result of mechanical forces moving the crown and stem under wind sway.

Roots can take several forms:

• The taproot - When a seed germinates, the primary root, or radicle as it is called in the embryo, emerges from the seed coat. The taproot system develops from the primary root. It is comprised of one major root that is thicker at its base (junction with the trunk or stem) and tapers toward the growing tip. Taproot systems are found in many dicots and gymnosperms. Taproots penetrate deep in soil and are often used for food storage. They form small lateral roots and provide excellent anchorage for the plant. Most taproots disappear after the seedling stage. With increasing soil density, downward taproot growth is restricted and lateral root growth increases. One research report has indicated that less than 5% of all trees have a taproot system.

• Fibrous root systems consist of many lateral roots that grow horizontally to stabilize a tree. Many if not all fibrous root systems develop from small adventitious roots that develop from stem tissue soon after germination, particularly in monocots. Fibrous roots are shallow, wide spreading, numerous, and good for soil erosion control because they cling well to soil particles. A research report has indicated that over 80% of all trees in nature and 100% of all nursery grown trees have fibrous root systems.

• A combination of both occurs frequently. Many species grow a taproot as a seedling until a certain distance or obstacle is encountered, and then the root system changes and continues to grow as a fibrous system.

• Sloping Root Systems (also called heart root systems) have roots growing at many different angles from the horizontal to the vertical. Research shows that 15% of all trees have sloping root systems where the roots appear to radiate from a common point at the base of the trunk.

• Aerial Roots are roots that do not grow underground. There are a number of different types of aerial roots.

• Prop roots begin as aerial roots but ultimately enter the ground. They generally arise at stem nodes. Prop roots are found in corn and also in some tree species. They provide additional support for the plant.

• Buttress roots are similar to prop roots, except they originate at the base of the stem, rather than further up the stem. They form impressive structures on some large tropical trees.

• Pneumatophores are upward growing (negatively geotropic) roots found on some plants in swampy areas. They extend above the water line and help the roots absorb oxygen. They are common on mangroves. The “knees” of bald cypress (Taxodium distichum) are similar to pneumatophores.

• Propagation Roots – Many trees produce "suckers" from roots. Suckers are adventitious woody shoots. Aspen groves, in which many trees are formed by root suckers from one parent, can cover large areas. Trees in the rose family (Rosaceae) also produce suckers, as do certain grafted trees.

• Root Nodules – Some legumes and a few other plants produce root nodules which contain bacteria or cyanobacteria that can "fix" nitrogen (convert nitrogen into a form that is useful as a plant nutrient). When the bacteria enter the root, they induce the root to form "tumors" which are the nodules. The bacteria then grow and produce the nitrogen products in the nodules.

Root Systems
There are two basic types of roots, woody and non-woody.

Non-woody roots are found mostly in the upper few inches of soil. These roots have very little lignin in their cell walls, and they live for a short time only, from a few weeks to a year. The primary function of these roots, often called feeder roots, is to absorb water and nutrients. These roots produce certain hormones (gibberellins and cytokinins) in the root meristem that are translocated through the plant to control growth and development.

Non-woody roots, particularly those of deciduous trees, often have root hairs, organs that are extensions of epidermal cells. By increasing root surface area, root hairs increase nutrient and water uptake. Many non-woody roots also possess mycorrhizae, fungi that live on or in the feeder roots. These fungi do not cause any harm to the trees, and for some species it is very beneficial for the roots to have this fungal association. Evergreen trees may not have root hairs but usually possess mycorrhizae.

Woody roots are large lateral roots that form near the base of roots and stem (the root collar). The primary purpose of these roots is support and anchorage for the tree. They also provide water and mineral transport as well as carbohydrate storage. These roots are distinct for each tree species and provide the framework for the tree's root system. The general direction for this framework is radial and horizontal. These roots are located 8 to 12 inches (20-30cm) below the soil surface. Woody roots are perennial and show annual growth rings, which are why many tree roots eventually become exposed or surface roots. Woody roots have lignin along with cellulose and hemicelluloses in their cell walls. They also have an outer bark that contains suberin. Suberin gives bark a corky characteristic and "waterproofs" the tissues.

Striker roots will form in drier soils, at intervals along the framework system some tree species. These roots grow vertically downward until they encounter an obstacle or soil with insufficient oxygen for growth, and they often branch and form a second layer of roots deeper in the soil. These roots function as water and food storage areas for the tree.

Adventitious roots will often form spontaneously at the root collar from large woody roots. Although it is not known exactly what causes their formation, they usually develop as a result of injury or excessive soil and/or mulch against the trunk.

Root Functions
Tree roots and soils are a cooperative venture that generates healthy trees and healthy soils. Understanding how roots grow and utilize the soil is critical to proper tree management.

Sources

• Appleton, Dr. Bonnie Lee, "Modification of Tree Roots", City Trees, The Journal of The Society of Municipal Arborists Vol. 37, Number 5 September/October 2001

• Coder, Dr. Kim D. "Tree Root Growth Requirements", City Trees, The Journal of The Society of Municipal Arborists, Vol. 38, Number 2 March/April 2002

• "Guide to Arbor Care", Plant Health Care, Inc. 2008.

• Harris, Richard W., “Arboriculture”, Prentice Hall, 1992, p. 174-184, 273-276, 324-327.

• Keslick and Son, "Technical Tree Biology Dictionary", Modern Arboriculture Associates, 2008

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