Archive #30

Archive #30 from Online Seminars for Municipal Arborists (on-line-seminars.com) January/February 2010
ISA will accept test scores for articles in this Archive. If you would like the tests for this Seminar, please email lenphillips@yahoo.com for Test #30

List of Articles
Systemic Tree Injections
Principles of Tree Selection
Tree of the Year
Deep Roots
Diseases of Crabapples
Rain Gardens
Super Planting Pits
Root Physiology
Research Briefs
Tree Hormones

Systemic Tree Injections
Edited by Len Phillips

Successful control of tree pests is dependent upon delivering a pesticide to the infested parts of a tree. One way this is accomplished is by systemic placement of pesticides into the sap stream of the tree. The chemicals then flow throughout the tree to provide control of the pests.

Injections made into healthy xylem have been used successfully to treat deficiencies of iron, zinc, and manganese as well as provide fertilizer, fungicide, insecticide, and antibiotics. Response to treatment can be evident in as soon as 3 weeks and repeat treatment may be required only after 3 to 5 years. Systemic chemical treatments may be delivered to the tree in five different ways:

macro-injection system
implant system
micro-injection system
micro-infusion system
soil injection system.

Macro-injection System
The key characteristic of macro-injection is that several gallons of dilute solution of material are injected into the tree. Holes 0.4 inches (1 cm) or greater in diameter are first bored into the tree trunk to the depth of the outer layers of sapwood. Then a series of T-shaped nozzles are connected with tubing to a container of the chemical solution. Macro-injection has been used primarily to treat vascular diseases such as Dutch elm disease, because American elms have the xylem porosity to accept large volumes of liquids via trunk injection. Macro-injection can be applied at either low or high pressure, but only trained professional arborists should use this method. With macro-injection, the large volume of solution, if pressured too high, can separate the bark from the sapwood.

Implant System
The implant technique utilizes a tiny bullet-sized plastic cartridge that contains water-soluble chemicals. The chemicals are absorbed into the sap-stream liquid and are released to the tree crown. Implants are easy to use and eliminate the need to dispose of a chemical container since the implant is left in the tree. Implants require holes up to 0.4 in. (1 cm) in diameter. Conifer resin plugging has not had an adverse effect with implants. Implants have become an increasingly popular clinical alternative to spray applications in the treatment of urban trees.

Micro-injection System
Micro-injection allows the low-volume introduction of systemic chemicals, such as antibiotics, fungicides, insecticides, mineral nutrients, and plant growth regulators directly into a tree without any contact with the environment. The micro-injection system consists of a plastic closed capsule containing water-soluble chemicals and a short plastic feeder tube with a diameter of 1/8" (0.44 cm) or less, inserted into a predrilled hole at the base of the trunk or root flair. Micro-injection capsules are under low pressure when they are placed on the tree. The purpose of this low pressure in the capsule is merely to aid in emptying the capsule reservoir and not to force the systemic chemical into the tree. High-pressure injection can injure tree tissues, especially the bark and cambium. Low pressures sufficient to empty the injection reservoir cause the least impact to the tree. Installing the injector unit requires some knowledge and practice, so only trained and licensed pesticide applicators should install them. Since the micro-injection products are concentrated, improper installation can result in chemical burns.

Micro-injection wounds compartmentalize because the drilled holes fill up with callus tissue and wound wood forms over the injection sites. Tree wounds for systemic treatments should be as small as possible and only in healthy tissue. Research indicates that when treatment sites have been correctly drilled and placed, most trees effectively compartmentalize the injured tissue into narrow columns of discolored wood, with little or no other permanent damage to the tree. Research has also shown no evidence of any harmful organisms entering treatment sites. If the manufacturer's instructions are followed, the injection sites will close in the first growing season. Trees should not be injected in new locations until the old wounds have completely closed.

Micro-Infusion^TM System
Micro-Infusion^TM technology was developed to deliver high volumes of systemic chemicals, such as insecticides, fungicides, and mineral elements to large trees and resinous conifers. There are two key components to the system:

dosage in relation to tree size
high capacity delivery system.

As trees increase in diameter, their canopy volume increases exponentially. For example, if a 10" DBH tree has a 1 time canopy volume, a 20" tree will have 8 times the volume of foliage, a 30" tree, 27 times and so on. Using Micro-Infusion^TM technology, dosages are designed to take into account the dilution that occurs in trees as they increase in size. Research has demonstrated the efficacy of higher dosages in larger trees.

This method of application requires a larger capacity compared to micro-injection capsules. A higher pressure is used to counter resin flow of conifers for the duration of the infusion process and not to force liquids into trees. A branch manifold accommodates multiple lines (4 to 16) each of which terminate at an injection needle. The injection needle pierces a rubber septum in a port fitted into the sapwood to prevent liquid back-flow. Like other trunk injection systems, this method requires drilling into the sapwood, so the trees can transport the systemic chemicals.

Soil Injection System
Systemic chemicals may also be applied by soil injection. However, the soil injectors can damage roots and make injured roots susceptible to invasion by root pathogens. Systemic chemicals injected into the soil may also impact beneficial soil microorganisms. In addition, increasing concerns about groundwater contamination have limited the use of soil injections in many areas.

Pros of Tree Injections:

Systemic treatments in the trunk can provide a quick therapeutic response in healthy trees, hold certain elements in storage for the tree's future use, and are especially useful where conventional treatments are ineffective.
Systemic treatments are useful where environmental concerns dictate that sprays cannot be used.
Except for macro-injections, minute quantities of chemicals are delivered into the target tree without exposing the surrounding environment.
Systemic treatments will not harm the applicator, the environment, wildlife, or beneficial insects (depending on the product).
It is generally less expensive to use systemic treatments than conventional spraying.

With training, systemic tree injections are simple to use. Materials can be delivered into the xylem of trees because the pressure in the xylem is below that of atmospheric pressure. Under these conditions, materials will be drawn up and into the crown due to a negative pressure gradient. If the desired site of action is the upper crown, it is best to inject during the active transpiration period of summer, while moving materials into the roots are best done in the late fall or early spring.

Cons of Tree Injections:

Systemic injections cause wounds to a tree. The wound sites compartmentalize and cease to function.
Damage from these wounds is not visible until the tree has died and is dissected.
Abuses such as slant hole drilling and extended-period injections can cause discoloration and cell degradation.
Each injection creates a wound that can be a potential colonization site for decay fungi.
Some dead xylem forms above and below the wound.

Description of Injection Processes:
Trees with large diameter vessels such as oaks, elm, and ash will usually allow rapid uptake of injected materials, while trees with small diameter vessels such as maples, birch, and beech will have slower uptake and should not be injected until the leaves are fully developed and have begun to transpire. Additional time should be planned for treatment of these trees. Resin flow into injection holes of conifers may interfere with uptake of materials.

Carefully drilling the holes and using very sharp drill bits can minimize resin plugging, provided that each feeder or implant is inserted within seconds after the opening is made. Also be sure to remove all the drill shavings before inserting the feeder tube or implant capsule. Injectors should be placed in bark furrows where bark is thinnest.

Injected fertilizer
According to the researchers who have devised these products, injected fertilizers can be the best way to fertilize a tree because the mineral nutrients bypass the nutrient absorbing process, so the tree will not have to spend energy to get minerals into the transport system. Injected fertilizer also enables the arborist to treat trees where soil applications cannot be delivered.

Treatments for Pest Control
Injections are an effective means to control insect pests. When injected directly into the tree's sap stream, the compounds are toxic only to those insects feeding on the tree. A long-lasting systemic insecticide, such as Imidacloprid, can be used to control insects such as the Asian long-horned beetle.

Some fungicides move into the xylem and are diluted by the fluids of the tree to remain at an effective level throughout the trunk, branches, twigs, and leaves. It has been determined that the concentration of fungicides in the crown builds to an effective level for 30 days.

When several systemic treatment periods may be necessary, create drill holes in patterns that will avoid vertical alignment of future treatment sites. Consider not retreating if previous wounds have not closed after one growing season or if fluxing or cracking occurs at the treatment site. Not all trees can tolerate systemic chemicals or the physical wounding. Do not place treatment sites between root flares where cambial growth is narrow and less conductive. Follow the manufacturer's label recommendations and any supplemental guides that are provided. When possible, keep records and monitor all treated trees. Systemic chemical treatments require the same diagnosis and proper selection of product as when using conventional spray methods.

Sources

Doccola, Joseph J. and Peter M. Wild, "Best Management Practices for Emerald Ash Borer: Use of IMA-jet in the Arborjet Tree I.V. as a Method of Tree Protection", Arborjet, Inc., Woburn, MA, July 2007.
Gillman, Jeff and Carl Rosen, "Tree Fertilization", FO-07410, University of Minnesota, Department of Horticulture, 2000.
Phillips, Leonard, "Systemic Tree Injections", City Trees, May/June, 1991.
Tattar, Terry A. PhD, "Micro-injection of Trees", Landscape Management, July, 2002.
Tattar, Terry A. PhD, "Tree Health Care Using Micro-injection Technology", Shade Tree Laboratory, University of Massachusetts, Amherst, MA.
Tattar, Terry A. PhD, "Use of Micro-injection to Solve Tree Health Problems on Golf Courses", Shade Tree Laboratory, University of Massachusetts, Amherst, MA.

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.

Principles of Tree Selection
By Len Phillips

People who regard the use of trees in the urban environment as an aesthetic nicety do not see the whole picture. Arborists must increasingly enumerate and quantify the many functions that trees play in order to justify the need for continued funding of the green urban environment in times of restricted budgets.

What functions do trees play in the urban environment?

Where summer temperatures are very high, trees provide shade and reduced air temperatures.
Tree planting to reduce wind speeds has long been practiced around the world. Research shows that semi-porous windscreens that may include trees and shrubs can have a profound effect on reducing wind. A barrier or hedgerow of approximately 35% transparent material can create a long calm zone that can improve human comfort levels.
A few trees alone do a poor job of reducing noise. However, dense planting, especially when combined with solid barriers or landforms, can reduce noise significantly.
Trees may play a role in reducing air pollution, both particulate and gaseous pollutants. More research is needed on the effectiveness of certain species in the reduction of air-borne pollutants in our urban areas.
Trees play a crucial role in reducing soil erosion as well as trapping and slowing storm-water runoff.
Trees can significantly reduce our reliance on storm-water abatement systems, improve natural water infiltration, and reduce the velocity of water moving over a landscape.
Urban green spaces provide animal habitat, opportunities for recreation, and are places where most people connect with the natural world.
Tree-lined streets are safer and happier places to have a home.
Cities with well-cared-for parks are always listed as more desirable places to live.
Property values are significantly higher near well-cared-for green spaces, just as they are for properties that are considered well landscaped.
Trees can change the sense of scale to a more human dimension.
Trees may be used to design physical barriers, direct foot traffic, or screen unsightly views.
Notable features and architectural lines can be enhanced with appropriate planting.
Historic neighborhoods often have appropriate landscapes that are intrinsic to the historical experience and sense of place.

What about aesthetic appeal?
An appreciation of the vast aesthetic possibilities that trees offer can be overwhelming; yet, by embracing this diversity of seasonal interest, form, color, and texture we can create wonderfully inventive landscapes. The realization of a design vision for a site and its ultimate success as a landscape requires more than creative elements of space, line, and form. It requires a thorough understanding of how people will use the site and how the site may or may not support the long-term biological needs of trees growing there.

How well is the tree adapted to the site?
All trees have a genetic potential to grow to a certain size and shape at a given rate under optimal conditions, but site conditions rarely enable a tree to grow to its full genetic potential. Knowing the tree's potential and matching its needs to the site's ability to meet those needs is the key to achieving the realization of a design vision. If enough of a tree's needs are met, such as appropriate levels of light, water, nutrients, temperatures, oxygen, and carbon dioxide, we can have confidence that the proposed planting will develop into what was originally envisioned.

With all the potential choices in plant materials, the selection process of tree adaptability to site conditions can seem overwhelming. Moreover, it is important to know under what conditions trees will grow satisfactorily, if not optimally. There are many references that can help arborists learn about appropriate planting conditions.

How do we begin matching the tree to the site?
Space - The first consideration for successful tree growth is how that tree can fit into its envisioned space. Given the vast number of tree choices, coming up with the desired size, growth rate, soil, and form for tree growth on the site requires careful selection.

In the urban environment, clear site lines for visual access can be important for pedestrian and vehicular safety. It is important that a tree be chosen that can be branched up to provide these conditions. Or will the natural form of the tree be so altered to fit into a particular space that its aesthetic appeal is lost?

While space for a tree above ground is important, space for root development is even more important. Trees will only grow if there is sufficient space and good soil for the roots to grow. A tree forced to grow in a small cube of soil in a sidewalk will not thrive and will be much smaller than the same tree growing on a lawn area near the sidewalk.

Hardiness - Tree adaptability to extremes of heat and cold would be the next consideration when choosing trees. Knowing the USDA hardiness zone of your site is essential. It is also important to know about any micro-climatic factors such as re-radiated heat, wind, rain, shadows, and frost pockets. There are often sheltered areas in the urban environment that enable a wider range of trees to be grown than would be possible in surrounding rural areas. This is because of temperature, light, and wind-altering effects of buildings and built surfaces. Raised planters can experience lower soil temperatures than the ground. In addition, references sometimes don't agree on the hardiness parameters of trees, and cultivars may have different hardiness ratings compared to the species. It would be wise to consult several local references and experienced professionals. When there is a discrepancy, choose conservatively.

Sun/Shade - Most trees require full sun (at least 4-6 hours daily) to grow to their envisioned size and form. Occasionally a few smaller trees may tolerate partial shade. This can be a significant issue in many landscapes. When it comes to shrubs or perennials however, there are many more choices for plants that prefer partial sun or moderate shade.

Soil moisture - In the natural environment, trees are often grouped by their ability to tolerate similar soil conditions such as soil moisture. These are important parameters that should be used to choose trees. Some trees have the ability to tolerate a wide range of soil moisture conditions, from flooding on one extreme to drought on the other.

Where soil volumes are limited, it is common for trees to experience alternating periods of too wet and too dry soil conditions. When it rains, water does not drain away and the roots experience oxygen deprivation. When the soil eventually dries out, the roots are in such a small area that there is too little water to support tree growth.

Where soil volumes are large and drainage is good, it is possible to grow a large number of trees including those that cannot adapt to alternating soil-moisture extremes.

Knowing the conditions that determine moisture and oxygen availability in the soil are the keys to good design and successful tree establishment. Soil texture, depth, volume, density, drainage, and the presence of irrigation will determine how water and air are available in the soil.

Soils that are seasonably wet, but otherwise well drained will accommodate a larger number of trees than those that are continually wet during the growing season or those that alternate between very wet and very dry. Sites that are dry most of the growing season will also pose challenges in tree selection. It might be necessary to modify soil conditions to provide a better balance between too wet and too dry conditions in order to grow trees successfully on the site. If the soil cannot be easily modified to overcome extreme moisture conditions, the number of tree choices for the site will be severely limited.

Soil pH - Testing soil pH is a simple, inexpensive technique that provides vital information about nutrient availability. Although most trees grow best at a slightly acid pH, there are many trees that will grow well in soil with a pH as high as 8.2. Fewer trees will grow well in extremely acid soils of pH 3.5 - 4.5, but there are some selections for this range too.

It is important that trees be chosen that will do well in the existing soil pH. It is often very difficult to change soil pH, especially when trying to make a permanent change. It is better to choose trees that tolerate the existing soil pH. Research shows that many trees will have acceptable growth in a wide pH range.

Salts - When developing a planting plan, consider trees that tolerate de-icing salts and seashores. There are places where salts may drift aerially to a site such as along the seashore, highway roadsides during winter in northern climates, or soil related conditions as in arid areas, and salt-water intrusions into soils from seawater. All woody trees will be killed by some level of salts, but some trees are quite salt-tolerant. Most salts are quite water-soluble and will wash through the root zone after a good rain if soils are well drained, but poor soil drainage can exacerbate salt contamination. This benefit of good drainage is clearly illustrated in areas where spring rains wash away the road-salt runoff in northern climates.

What are the management issues associated with the tree?
Beyond environmental factors, there are other management concerns that are important in tree selection, including the trees' susceptibility to pests and pathogens, ability to be transplanted, availability in the trade, maintenance requirements, and other considerations.

Pests and diseases - Susceptibility of trees to insect and disease attack is a significant factor in tree selection. Trees that will not need pesticides to grow well should always be a first choice. Check with local growers to find out about locally troublesome pests for a particular tree. Most trees have some pest problems, so avoid trees that have severe pest problems. There is excellent information available in books, the Internet, and local universities and nurseries about species and cultivars that are resistant to particular pests and diseases. (Be sure to read the article about crabapple diseases later in this Seminar.) Also, by planting in sites well adapted for a particular tree, the species will generally suffer fewer pest problems or will be able to recover from an attack more rapidly.

Woody trees that suffer from a lack of water are more susceptible to potentially damaging boring insects. Many times there may be reasonable substitutions for trees that may be troubled by a certain disease or insect.

Dwindling landscape-maintenance budgets and a growing desire to reduce or eliminate the use of chemicals for disease and insect control are driving the demand for hardy, durable, disease-resistant, sustainable trees that require minimal pruning, irrigation, maintenance, and ongoing care. Also, according to recent nursery reports, the demand for native trees and cultivars of native trees is stronger than ever.

Cost and availability - Many desirable trees are not available in appropriate sizes or are too costly to be specified for a landscape planting. Therefore the specifier should substitute trees that are available to meet close to what is desired. Consideration should be given to costs and availability of bare root versus balled and burlapped trees. Also consider that less expensive smaller trees will recover from transplant shock much faster than a large diameter tree of the same species. For example, a six inch diameter tree may be desired for a particular site, but it will require about 6 years to recover from transplanting. However a two inch diameter tree will recover in a couple of years and will resume normal growth so that in six years it may have surpassed the larger tree in size.

Transplanting - Several trees and shrubs are notably difficult to transplant. There are practices that help insure greater success in transplanting, yet some remain difficult even when appropriate transplanting measures are taken. It would be reasonable not to choose too many of the troublesome trees in any one particular installation.

Timing is always important when transplanting. The designer may want to consider availability of trees and inform the contractor to be sure that species and sizes specified can be located. Alternatively, horticultural brokers may be hired to find trees that otherwise would be difficult to obtain. Having gone through the process of site assessment and making the best selections, it is worth trying to find the best tree before contractor substitutions are accepted.

Maintenance issues - Some trees produce an unacceptable amount of fruit or leaf litter under certain circumstances or require regular pruning for an appropriate appearance. There may be small-fruited or fruitless alternatives that have less of a litter problem. If regular maintenance cannot be provided, shrubs and trees that need less pruning should be selected.

Thorns on trees may be an issue in settings where people are likely to be in direct contact with the trees, such as a playground or a narrow street or alley.

'Weak-wooded' is a term that refers to the propensity of trees to break up or drop limbs in high winds or during snow and ice storms. Often, fast-growing trees are the most frequent offenders. Weak-wooded trees should not be planted in areas with lots of pedestrian traffic or where property may be damaged. Trees that may be perfectly acceptable in a natural area may not be suited to certain urban conditions.

Native vs. non-native trees - The most important factor for the success of a tree in the landscape is its adaptability to the site and not its original geographic origin. Most urban sites have been so greatly altered that their original native soil conditions, prior to centuries of development, are irrelevant for the selection of trees today. If a tree was native to parts of New York City in the 16^th century, it may not be the right tree for a particular site in New York City today. Cultivars of the native tree on the other hand, may be the right tree since they are often developed for their urban tolerance. Invasive trees should be avoided.

Diversity vs. Uniformity - The selection and placement of trees in the urban environment is a complex task requiring the consideration of many factors. Issues such as visual access, spatial constraints, and disease and insect resistance can sometimes conflict with design objectives. Perhaps the most troubling conflict arises between the preference for visual uniformity and the practical need for biological and species diversity. Until recently a typical street tree planting consisted of uniform rows of a single species, generally selected for its attractive appearance and high tolerance to urban stresses. However, as over planting has brought about the decline of a number of favorite species such as the American elm, it is clear that design objectives must be balanced against the benefits of species diversity in street tree plantings.

Sources:

Bassuk, Nina, "Principles of Plant Selection and Some Favorite Trees", Online Seminar Archives #1, 2005.
Buley, Nancy "Tree Selection and Planting", Arbor Age, March/April 2009.
Parts of this were modified from the book 'Trees in the Urban Landscape' by Trowbridge and Bassuk, John Wiley & Sons, 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.

Eastern Redbud has been selected by the Society of Municipal Arborists as the 2010 Urban Tree of the Year. Unfortunately, this is not a good tree for city streets, but it does very well in parks and other public landscapes. Plus, it is beautiful in the spring. This information has been gathered from personal observations of the Editor, living in New England, Zone 5.

Botanical Name: Cercis canadensis
Common Name: Eastern Redbud
Pronunciation: SER-sis kan-a-DEN-sis
Family: Leguminosae
Parentage: native to North America
Height: 15 to 30 feet
Spread: 15 to 25 feet
Form: round, irregular outline
Bloom Period: spring flowering; very showy
Flower: generally magenta-pink, but named cultivars vary from purplish-red to bright pink to white.
Fruit: brown pod, 1 to 3 inches long
Summer Foliage: green
Autumn Foliage: yellow
Winter Color: no special winter interest
Bark: dark gray with orange cracks appearing in older trees, bark is thin and easily damaged from mechanical impact
Habitat: tree grows in part shade/part sun, becomes less shade tolerant with age
Trunk: usually multiple trunks, can be trained to single stem
Hardiness Zone: 4B - 9A
Growth Rate: fast in youth, moderate with age
Pest Problems: borers attack the trunk of older and stressed trees, low disease resistance and short life span
Storm Resistance: susceptible to breakage at the crotch due to poor collar formation or the wood itself
Salt Tolerance: poor
Planting: transplant B & B or container grown
Pruning: prune to develop strong structure, will require pruning for pedestrian clearance beneath the canopy
Propagating: seed or grafting onto seedlings
Design Uses: medium texture; container or above-ground planter; large parking lot islands; if used for a street tree, the tree lawn should be more than 6 feet wide
Other Comments: Eastern Redbud is subject to many liabilities. Its functional life is 10 to 20 years in urban landscapes due to a combination of urban stresses, diseases, and pests. The tree is prone to trunk canker, heartwood rot, verticillium wilt, and scales, any of which can be fatal. It is also prone to storm damage with advanced age due to poor collar formation, leaning, and heartwood rot. However, after a long hard winter, its beauty in spring provides a welcome that warms the heart of people everywhere.
Availability: generally available in most nurseries

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.

When the structural root systems of landscape trees are planted too deep in the ground, reduced vigor, decline, and even death can result. Although deep roots have existed for decades, we have become more aware of them recently. Many arborists think the problem is actually getting worse.

Since 2003, Morton Arboretum has been conducting research into the problems associated with deep roots. This article is a report on the results of this effort, focusing on trees of 2-3 in (5-8 cm) caliper, the most common size of tree planted.

Determining Root Depth
The best way to judge root depth is to find where the roots join the base of the tree. If at least three distinct individual roots are visible at the surface, there no need to do anything more. Typically, on a young tree, the point where the main structural roots become distinct from the basal trunk swelling will be just below the soil surface, and some soil will have to be removed to see the roots.

On field grown trees, the upper surface of the uppermost root should be no more than 2 in (5 cm) deep where it joins the base of the trunk. Surface soil conditions such as cultivation in nursery fields can discourage root growth in the top inch or two. In containers, the uppermost roots should be just under the substrate surface.

When trees are purchased in quantity, it may not be possible to check every tree. Then it is important to have confidence that your grower produces quality trees. Checking for root depth on a few trees of each species is advisable. This can be done in the growing fields or in the root balls.

It may be difficult to excavate enough soil to clearly see individual roots, especially on species with deeply angled roots. After partial excavation, probing the soil with a surveyor's chaining pin or stiff wire to verify locations of roots can make the task easier and faster. When burlap over the root ball cannot be removed to locate the roots before placing the root ball in the planting hole, use the chaining pin to probe through the burlap and estimate root depth. After the tree is in the planting hole, the burlap can be removed and root depth confirmed visually.

Structural Roots
Structural roots are the large woody roots giving characteristic form and shape to the root system. They should originate near the base of the trunk, just below the soil surface. There must be at least 3 roots distributed around the base of the tree to support it. If there are fewer than 3 structural roots, the tree may not meet even the most generous interpretation of the American Standard for Nursery Stock.

The connection of the structural roots to the trunk results in development of a pronounced root flare (trunk flare) as the tree ages. In many species, the structural roots remain within a few inches of the soil surface as they spread out. In some species, they may grow down at a steeper angle.

Trunk Swelling
A swelling at the base of the tree should not always be interpreted as the root flare. It could be something else, such as a swollen graft union or cutback wound. Cultivars and seedlings are cut back in field liner production. Many tree cultivars in the northern half of the US are bud grafted, which also causes swelling. This is less common in the southern half of the US. Evidence of the graft union and cutback wound should be visible above ground at the base of the trunk. The roots will be located below this swelling.

Shallow Roots
The roots must be covered with soil. If the roots are too shallow on a small tree, especially on one with horizontal roots, they may not be covered with enough soil to prevent exposure by erosion or frost heaving. As roots increase in size over time, the amount of soil cover will be reduced.

Deep Roots
Roots can be too deep in the root ball when a tree leaves the nursery. If, for example the root ball has 6 inches (15 cm) of soil over the top of the structural roots and the tree is dug to its conventional depth, then six inches of roots at the bottom of the root ball will be left in the soil at the nursery. This results in a root ball with 25% fewer roots than there should be.

Though the problem of deep roots starts below ground, the effects will eventually be seen above-ground. In extreme cases, crown decline can begin to show within a year after planting. The symptoms can also be more gradual.

Symptoms of Deep Roots
According to recent research, above-ground effects of deep roots are visible only when roots collars are 3 - 6 in. (7.5 - 15 cm) or more deep. Effects also vary by species, soil type, climate, drainage, and aeration. Deep roots are also subjected to greater soil saturation and insufficient oxygen. The symptoms can be similar to drought stress.

Under less severe conditions, growth will be slowed and the tree will be stressed. A tree with deep roots may appear fairly normal until it is compared to a tree with roots at the correct depth. Recent research also shows that in field plantings, deep planted trees can have greater defoliation, chlorosis, and leaf curl.

In containers, trunk caliper and height growth increased more slowly as planting depth increased. Stem caliper increase was significantly lower and resulted in smaller root volume. The effects of deep planting are most pronounced three years after planting, when survival and height growth is reduced.

Site Differences
Deep root problems are magnified on sites with heavy, poorly drained soils. This includes residential, commercial, and park properties. Deep root problems are virtually anywhere the land has been reshaped with heavy equipment. Areas of the country with clay soils will have the most severe problems. Trees on marginal sites may not exhibit obvious symptoms of stress from deep roots until triggered by environmental conditions, such as an excessively wet season.

The Morton studies included one being conducted on heavy clay loam soil that resulted in reduced growth of multiple species when trees were planted a little below grade. Root quality was improved by amending the native heavy clay soil with 30% by volume sand or peat moss.

The root system of a tree planted at the correct depth will have shallow laterals with vertical sinker roots growing as deeply as soil conditions will permit. When the roots are planted too deep and must grow up to the surface, the normal root architecture is altered, and the tree may have fewer deep roots to access soil moisture during dry periods.

Site quality also explains why trees can grow nicely in the nursery with deep roots and ultimately be shipped to landscape sites with roots too deep in the root ball. Nursery sites are chosen because of the high quality soil. Under these conditions, there was no growth reduction of liners planted with the graft union up to six inches below grade. A tree growing vigorously in the nursery with deep roots will usually perform poorly on an urban site if planted at the same depth.

Symptoms Vary Among Species
Tree species vary in tolerance to poor soil conditions. In another Morton study comparing the effects of deep planting on hypoxia-tolerant and intolerant species, deep planting reduced the survival of some trees by about 40% after 3 years and others by over 90% within 2 years. Stem caliper increase was significantly lower in some deep-planted trees. Others had a significantly smaller root volume.

Tree Stability
Deep root systems increase tree failure rates. Thirty-three percent of trees with excess soil over the roots failed, compared to only eight percent of trees without excess soil over the roots. In another recent study, 73% of the trees that suffered total failure had four inches or more of soil over the structural roots. Most of these trees also had girdling roots causing stem compression where the trees broke off.

Deep roots have also been associated with greater winter injury in conifers.

Adventitious Root Development
Some species have the ability to produce adventitious lateral roots above existing lateral roots if planted too deep, but these are the exceptions; most species do not have this ability. Production of shallower adventitious roots could allow a tree to adapt to deep planting.

Source
Morton Arboretum, "Deep Roots of Landscape Trees", Landscape Below Ground III Conference, 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.

Diseases of Crabapples
By John C. Fech

One of the most common ornamental trees in the U.S. is the crabapple. Crabapples can be found in most any urban and residential landscape. However, in some locations they can become infected with foliar and systemic diseases that limit their appeal and function in the landscape.

Foliage diseases
Many foliar diseases plague crabapples. Below are the three most common:

Apple scab
Apple scab is favored by cool, moist spring weather. Under these conditions, fungal spores are blown by the wind and spread to other leaves and other trees. Initial symptoms appear as olive-brown, round spots on lower leaf surfaces. The spots are usually the size of a standard pencil eraser. As the disease progresses, the spots change to dark brown or black. Once several spots develop on leaf surfaces, the leaves begin to fall, causing the tree to become thin in canopy foliage. Severe infections can render a tree 60 to 70% leafless by midsummer.

Control of apple scab begins with the selection of a disease-resistant cultivar. Crabapples should be planted in full sun, and where moderate breezes can help dry the leaves. A consistent fungicide spray program can also be helpful in suppressing the effects of apple scab.

Cedar apple rust
The conditions that lead to the development of cedar apple rust (CAR) are similar to those of apple scab. Initial symptoms of CAR are small, yellow to orange, slightly raised spots on upper leaf surfaces. The number and size of the spots depend on the degree of resistance that the tree possesses.

Control of CAR is similar to that of apple scab. CAR is a two-host disease. After infection on lower leaf surfaces of crabapple leaves, fungal fruiting bodies develop, and during periods of cool wet weather, erupt and spread spores to nearby cedar and juniper trees and shrubs. As a result of this transmission, small, tan to brown corky growths occur on infected trees. Attempts to reduce infection by removing cedars are usually not effective, because the spores can travel up to 5 miles in the wind.

Powdery mildew
Unlike apple scab and CAR, powdery mildew does not require moisture on leaf surfaces to develop. Cool, cloudy days and stagnant air are the key conditions that trigger infection. Powdery mildew creates a whitish cast to tree leaves on both upper and lower leaf surfaces. As symptoms progress, defoliation becomes greater, causing the tree to become weak from malnourishment.

Powdery mildew is best controlled with disease-resistant cultivars, followed by proper siting, and pruning practices that allow adequate air flow through the tree canopy. Fungicide treatments are the least preferred option but can be used if the others are not successful.

Woody Diseases
Several diseases invade the woody tissues of crabapples, as well.

Fire blight
Fire blight produces both leaf and stem tissue symptoms. Once infected, leaves turn a gray to blackish color and turn limp. The disease is spread through spores that are released from stem cankers that are oval, slightly sunken areas that look to be dead.

Controlling fire blight is not easy. The best treatments rely on good cultural practices such as proper tree placement, separation of turf and ornamentals, and avoidance of mechanical damage to the trunk and stems. Once a tree is infected, removing cankers through pruning is recommended to reduce the source of inoculum. The pruning process is best done during the dormant season to reduce the risk of spreading the disease from tree to tree or throughout the same tree. Dip the pruners in a 10% bleach solution to clean the tools after every cut.

Nectria canker
Nectria canker attacks several species including deciduous shade trees such as walnut, honeylocust, maple, and linden, as well as crabapple and pear. The fungus lives between the bark and heartwood, killing the cambium and sapwood. Cankers usually develop between nodes of new lateral stems. They can occur on all sides of the tree, and spread to small and large tissues alike.

Cultural management strategies are most effective for controlling canker diseases. Pruning out cankers can remove the source of canker fungi from the tree, reducing the risk of new infections. Be sure the pruning is done in dry weather and at least 4 inches beyond the canker. Do not apply nitrogen fertilizer to infected trees.

Sunscald
In most cases, sunscald is caused by fluctuations of temperature in winter. Sunscald occurs when warm temperatures are followed by sudden temperature decreases, as with 55° F (30° C) one day and 25° F (12° C) the next. In almost all cases, this occurs on the south and southwest side of the tree, where temperature fluctuation is greatest.

Sunscald is best avoided by selecting trees that are resistant. If thin-barked trees are chosen, place them where they are not exposed to afternoon sun in winter. Wrapping the truck is also a control, but it is very labor intensive year after year.

Resistant cultivars
There is great benefit in selecting crabapple cultivars that are less likely to become infected with various diseases. The chart that is linked HERE highlights disease resistance in currently popular cultivars of crabapples.

Source
Fech, John C., "Diseases of Crabapples", Tree Services, March 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 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.

Rain Gardens
Edited by Len Phillips

A rain garden is a planted depression that allows rainwater runoff from impervious urban areas to be captured, retained, filtered, and returned to the ground. This reduces rain runoff by allowing storm water to soak into the soil as opposed to flowing into storm drains and surface waters. The great thing about rain gardens is they change our perception of landscaping from adornments to necessity, as part of a sustainable landscape environment. Rain gardens reduce the amount of pollution reaching creeks and streams by up to 30%. When compared to a conventional lawn, a rain garden allows about 30% more water to soak into the ground than the lawn allows.

Normally, a rain garden, or a series of rain gardens, will be the endpoint of drainage, but sometimes they can be incorporated into a pass-through system where water will percolate through a series of gravel layers and be captured by a drain under the gravel and carried to a storm water system. Rapid pass-through systems reduce peak discharge and extend hydraulic lag time of the discharge, thus reversing urbanization's major flooding impact. However, rapidly drained systems do not attain the pollution removal rates that more slowly percolating rain gardens will provide. Their root systems enhance infiltration, moisture redistribution, and diverse microbial populations involved in biofiltration. Also, through the process of transpiration, rain garden plants return water vapor into the atmosphere.

Rain gardens work in several ways:

they increase the amount of water that filters into the ground,
they recharge local and regional aquifers,
they help protect communities from flooding and drainage problems,
they help protect streams and lakes from pollutants carried by urban storm water, such as lawn fertilizers and pesticides, oil and other fluids that leak from cars, and numerous harmful substances that wash off roofs and paved areas,
they enhance the beauty of yards and neighborhoods,
they provide valuable habitat for birds, butterflies, and many beneficial insects.

Rain Garden Design
Rain gardens are designed to be about one-third the size of the surface area providing the runoff. To determine the suitability of the soil, dig a hole about 6 inches deep and wide, where the rain garden is to go and fill the hole with water. If the water takes more than 24 hours to soak in, the soil is not suitable for a rain garden.

A typical rain garden ranges from 100 to 300 square feet (20 - 30 sq. meters) in area. Rain gardens can be smaller than 100 square feet, but very small gardens have little plant variety. If a rain garden is larger than 300 square feet it takes a lot more time to maintain. A typical rain garden is between four and eight inches (10 - 20 cm) deep. A rain garden more than eight inches deep might pond water for too long and result in plant death. A rain garden much less than four inches deep will need a much larger surface area to provide enough water storage to accommodate the larger storms.

Plant Choices
Native plants and cultivars of native plants are recommended for rain gardens because they generally do not require fertilizer and are more tolerant of the local climate, soil, and water conditions. The plants can be a selection of wetland edge plants, wildflowers, sedges, rushes, ferns, shrubs, and small trees that will tolerate excess water stored temporarily in the rain garden.

Ferns - Depending on the variety, ferns thrive in conditions ranging from dry, sunny areas to moist, shady areas. They are excellent choices for covering the differing areas within a rain garden.

Perennials - Select multi-branched plants, with lots of fibrous roots, which are well adapted to many soils and are able to withstand extended drought conditions. Select plants that encompass several flower colors and shades. Select plants that range in height from 1½ - 3 feet (0.5 - 1 meter) tall in flower and prefer light shade to full sun. Consideration can also be given to cultivars of plants native to wet prairies, plants with deep, extensive root systems, and plants that have a long season for color. Some excellent examples are:

Care and maintenance
Even if the rain garden soil is good, mix a couple of inches of compost into the top six inches of soil to help the plants become established. Rain garden management requires attention to fertility, soils, weeds, trimming, and cleaning up. Rain gardens can be maintained with little effort after the plants are established. Some weeding and watering will be needed in the first two years and perhaps some thinning in later years as the plants mature.

Hemerocallis are a durable choice for the higher and drier portions of a rain garden. Their roots run deep and are quite extensive, allowing them to endure periods of drought while also providing an avenue for rainwater to filter back into the ground.
No rain garden would be complete without irises. These plants are very adaptable to ever-changing moisture conditions. Certain varieties grow in standing water and perform just as well after the water has receded.
If the garden is designed to be in the shade, hostas are an excellent choice. They prefer lots of moisture and have deep roots that will also tolerate times of drought.
Panicums are another group of plants that extend roots deeply into the ground. They bind the soil and perform well under drought conditions.

On a couple of related topics, vegetated walls and green roots might also be considered to provide water runoff reduction.

Vegetated walls - When retaining walls are required, consider using ornamental cement block landscape retaining walls with planted, soil-filled cavities between the blocks. When these areas are planted they enhance aesthetics, improve air quality, provide insulation, dampen noise, and reduce impervious materials and runoff. They can be planted with groundcovers, perennials, vines, herbs, and even edibles such as strawberries, melons, and squash.

Green roofs - Green roofs are replacing traditional roofing materials with plants. Think of the millions of potential square feet this adds to the area of traditional landscapes. There are many aesthetic, environmental, and financial benefits to increasing green space in this manner. Many people consider green roofs are better looking than roofs made from traditional materials such as asphalt shingles, stone, wood, and rubber products. They help to cool the air while the plants and the soil also act as acoustic insulators to reduce noise. Succulent green-roof plants reduce the risk of fire, and green roofs absorb excess rain and reduce storm water runoff. Extreme drought resistance is one of the most important characteristics when selecting plants for green roofs. Other attributes include disease and insect resistance, low maintenance, roof longevity, and aesthetic appeal.

Sources

Bannerman, Roger and Ellen Considine, “Rain Gardens - A How-To Manual for Homeowners”, University of Wisconsin-Extension, Cooperative Extension Publications, 2003.

Howe, Chris, “Rain Gardens”, Nursery Management & Production, December 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.

Root Physiology
Edited by Len Phillips

Trees have two general systems that grow along an axis, the shoot system (with leaves and stems) above ground, and the root system below ground. Because root systems are unseen, many people don't think about them unless the roots have grown so much that sidewalks get cracked and lifted, or a drainage system needs cleaning because roots have invaded the drain tiles. This article will explain how roots work, so the arborist will have more understanding when called for advice on how to deal with problem roots. Physiology of the shoot system will appear in the next Seminar.

Introduction The roots of trees are required for anchorage, absorption of nutrients and water, and the storage of starch. The development of a root system is dependent upon the tree's genetics, the soil, and the environment. A tree's root system must balance its shoot system, but not by weight or dimensions. The root system must supply the shoot system with sufficient moisture and nutrients, and the shoots must manufacture enough food to support growth of the root system.

Trees require water, oxygen, carbon dioxide, light, nutrients, appropriate temperature, correct pH, physical space for growth processes, and open soil surface area for replenishment of essential resources. Roots utilize space in the soil. The more space that is infiltrated by roots, the more potential resources (water and nutrients) are available, and this is directly related to tree health.

Root Parts
Growth in trees represents an expansion of tissues into new spaces. For roots, the tips elongate and the tissues thicken in diameter. Roots develop internally rather than from buds as occur on stems. To develop in this manner, a root has several parts. They are described as follows, from the youngest part of the root to the oldest part:

Root Cap - This part of the root is at its very tip. The cap protects the tip of the root as it is forced through the soil by the elongating tissue behind it. The root cap cells are coated with mucigel, a slime sheath that helps to lubricate the root as it penetrates through soil. These cells are replaced constantly.

Apical Meristem - This part of the root generates the cells that form the root cap in front and the region of elongation behind this area.

Region of Elongation - Cells in their fixed positions elongate to reach mature dimensions in the region of elongation. The vacuole (a large sac of fluid within a cell) plays a major role in this process, using water pressure to push against the walls to stretch the cellulose fibers as the cells elongate. Virtually all increase in root length occurs in the elongation region. Active cell division region forces the root through the soil against the mass of the tree. During this time of elongation, roots are also sensitive to gravity and respond with gravitropism.
Region of Root Hairs or Differentiation - In this area, root cells develop a more mature form and are differentiated into the epidermis and cortex. Differentiation is when a cell changes its structure, such as when a parenchyma cell becomes enlarged to form a vessel; then it is no longer a parenchyma cell. The cell is said to be differentiated, and the process is the differentiation of cells. The outer layer of cells is the epidermis that contains a single layer of flattened cells with very little cuticle or suberin. Root hairs are found in this region. A root hair is the extension of a single epidermal cell. As the epidermal cells mature, the root hairs atrophy and are replaced by root hairs on newer cells in the early stages of maturation. Root hairs absorb water and elements dissolved in the water. Root hairs are organs that grow within days when water, temperature, and soluble essential elements are at optimum levels. Root hairs die and are shed after a few weeks. As root hairs and mycorrhizae atrophy, they add organic material to the soil. Non-woody roots shed dying and dead root hairs and epidermal cells. Soil microorganisms digest the shed cells and recycle elements essential for life. Root hairs do not become lateral roots. Root hairs and mycorrhizae are alive and well in midwinter in non-frozen soil below frozen soils.

Firs, redwoods, and Scots pine do not have root hairs. Instead, they absorb water and nutrients through the thin-walled epidermis. In contrast, some trees such as the redbud and honeylocust have root hairs that last for several years.

The soil area around the root tip and along the absorbing root-soil interface is called the rhizosphere. It is a zone about one millimeter in width surrounding the living root hairs and their mycorrhizae as well as hyphae growing out from some mycorrhizae. Constantly changing mixes of organisms inhabit the rhizosphere and surrounding soil. Bacteria, soil viruses, actinomycetes, fungi, protozoans, slime molds, algae, nematodes, enchytraeid worms, earthworms, millipedes, centipedes, insects, mites, snails, and small animals compete constantly for water, food, and space.

The root cortex is composed of loosely packed round tissue cells with large diameters. Absorbed water moves readily between cells through the porous cell walls of the cortex parenchyma. Cortex cells typically contain amyloplasts, plastids (storage sacs) filled with starch granules that occur in seeds, roots and stems. The pathway of interconnected cell walls facilitating water movement is generally regarded as the apoplast. An alternative water pathway, which carries water from cell to cell through plasmodesmata passing through the interiors of the cells, is called the symplast.
The inner layer of cortex is the endodermis. As roots mature, the endodermis becomes a barrier to further movement of water and minerals between cells.

Within the cortex are the xylem, phloem, and pericycle.

Xylem - The xylem consists of large diameter vessels. Xylem is not wood; it is one of the transport tissues in vascular plants. It transports free water and substances dissolved in the water from absorbing non-woody roots to the leaves. When xylem is lignified it is then correctly called wood. Lignified means that high amounts of the natural "cement" called lignin is deposited within the cellulose strands in the cell walls. This makes the cell walls very tough. Having tough, lignified cell walls is a unique feature of trees.
Phloem, found in patches between the xylem arms, is comprised of sieve elements and companion cells. Phloem is another transport tissue. It transports energy-containing substances (carbohydrates) made in leaves to the roots and other growing parts of the tree.
The pericycle consists of parenchyma cells just inside of the endodermis, forming the rest of the stele other than the xylem and phloem.
Symplast is the network of highly ordered, connected, and living axial and radial parenchyma cells in sapwood and inner bark. The symplast stores energy reserves. The living protoplasm is contained in thin-walled cells called the parenchyma, which have small cell wall openings that act as tunnels where the protoplasm of one cell connects with the protoplasm of adjoining cells. The symplast stores energy reserves. The apoplast (dead fibers and tissues) stores bound water. As the symplast decreases, so does storage space, and as the storage of energy reserves decreases, so does the defense potential. Pathogens seem to know this very well.
Radial Parenchyma - The symplast is made up of radial and axial parenchyma cells. The radial cells run perpendicular in the trunk. Axial parenchyma cells run parallel to the trunk. The radials form the wood rays and phloem rays. Sapwood has an interconnected network of living axial and radial parenchyma.
Cambium - In older parts of the root, another meristem forms between the xylem and phloem. This cambial zone is sometimes called the vascular cambium. It is rarely made up of a single layer of cells. Mitosis in the cambium produces new secondary xylem to the inside and secondary phloem to the outside. The cambium zone in roots is like an accordion; during the resting period it is closed and during the growing season it is open.

Secondary Root Growth
A cambium cylinder develops from parenchyma cells between xylem and phloem in the primary root stele. Once formed, the cambium produces xylem inward and phloem outward. Additional parenchyma cells form rays. Outer bark or periderm is mostly dead cells lined with a fatty substance called suberin or cork. The phellogen (bark cambium) is the outermost part of the symplast and the end of the phloem rays. The annual growth of "wood" and cork-like bark in secondary roots is very similar to stem secondary growth.

Lateral Roots
In the area behind the region of root hairs, lateral roots are formed by sending out a root cap, apical meristem tissue, etc. into a new area of soil. The ability of primary root tips to enter soil pores, further open soil pores, and elongate through soil pores is dependent upon the force generated by the root and the soil's resistance to penetration. Cell division and subsequent osmotic enlargement of each new cell generate root growth forces. Adequate water is required, as well as oxygen for respiration, because tree roots can consume large amounts of oxygen during elongation.

Root Functions
Woody supportive roots account for a small proportion of the tree's total root length and metabolic carbon demand. The larger woody supportive roots extending from the base of a tree are long-lived (often as old as the tree) and comprise most of the lateral root biomass.

In contrast, fine roots comprise only 5-10% of total root biomass, yet can account for up to 90% of the tree's total root length and metabolic activity. In many forests, the annual carbon cost for fine root system production may represent one of the largest carbon sinks in forested ecosystems.

Sources

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.
Phillips, Leonard, "Root Physiology", City Trees, The Journal of The Society of Municipal Arborists Vol. 35, Number 4, July/August 1999.
Richardson, Rosemary, "Biology 203 Course", Bellevue Community College Science Division, Spring 2009.
Rindels, Sherry, "Tree Root Systems", ISU Extension, Prepared by Department of Horticulture, Iowa State University, Ames, Iowa, April 1, 1992.
Topa, Mary A. PhD, "Root Physiology", The Encyclopedia of Forest Sciences, pp. 1606-1616. 2007

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

Minimum Tree Canopy Standards
Buck Abbey and Robert Reich, Louisiana State University

The urban forest is one of a community's primary sustainable features. Green infrastructure will continue to work for the benefit of society if the community's tree policy recognizes the important contributions of trees. It is important for a community to set tree canopy goals within their codes and regulations.

There are several good examples of cutting edge tree ordinances. One of the ideas contained in many outstanding tree preservation regulations is a minimum tree canopy for every development site. This canopy must be preserved or replanted to eventually grow into the minimum canopy requirement.

American Forests recommends cities have a minimum canopy coverage of:

25 - 40%,
35 - 50% for suburban residential zoning districts,
18 - 25% for urban multifamily residential zoning districts,
9 - 15% for central business zoning districts.

The first number represents values in the arid west and the latter the wetter east. Minimum canopy standards can be set for the city as a whole, by zoned land use district, or by each developed building lot. The minimum canopy standard can be measured in one of four ways:

canopy coverage area,
percentage of site ground space devoted to trees,
numbers of tree per development site,
number of caliper inches per acre.

Having canopy standards as part of the landscape ordinance allows a community to have a quantifiable mitigation program to ensure that when existing trees are removed, they get replanted somewhere in the city. Communities can thus maintain a stable urban forest.

http://www.landscapeonline.com/research/article/11640.

The Relationship between Plants and Soil
Dr. Elaine Ingham

Understanding the relationship between plants and soil is key to designing and creating sustainable, ecological landscapes. The more abundant, diverse forms of life that can be nurtured in the soil, the more fruitful and self-sustaining a landscape will be.

A healthy soil food web helps reduce or eliminate the need for fertilizers, pesticides, and irrigation and healthier plants are much less susceptible to insects and disease. It purifies water as it passes through the soil.
Deeper and more developed root systems of well-nourished plants allow the roots to access moisture deep in the soil, making the plants more resistant to drought.
The organic matter produced by soil organisms helps the soil retain moisture during dry periods.
Some soil organisms produce sticky substances that aid in the formation and stability of soil aggregates, which are essential to good soil structure.
The soil food web contributes to the formation of humus, a complex compound that resists further decomposition and stores carbon in the soil for years. Humus holds water and nutrients in the soil and binds to heavy metals such as mercury and lead, making them less readily absorbed by plants or leached into groundwater.
Soil organisms decompose organic compounds such as manure and pesticides, preventing them from polluting groundwater.
Because soil organisms increase soil aggregation and porosity, they improve rainwater infiltration rates, reducing runoff and erosion.

Tree Care Industry - February 2007.

Impact of Pesticides on Insect Emergence from Logs
Pascal Nzokou, Samuel Tourtellot, and D. Pascal Kamdem

The Emerald Ash Borer (EAB) was discovered on North American soil in the summer of 2002 near Detroit, Michigan and has since spread to six states and provinces. To alleviate the costs of controlling this pest, a method of sanitization is urgently needed. This study evaluated different chemical sanitation methods in laboratory and field conditions. Treatments included:

two borate treatments, spray and dip, with concentrations ranging from 5 to 16.5% boric acid equivalents,
Preventol®, a technical grade imidacloprid treatment with solution concentrations ranging from 0.005 to 0.02% applied as sprays.

When logs were reared indoors subsequent to treatment, the technical grade imidacloprid and the borate dip treatments reduced the infection levels significantly. For the outdoor-reared logs, only the technical grade imidacloprid had a significant effect. All chemical treatments did better under indoor rearing than they did under outdoor rearing. This has heavy implications for the development of a sanitization treatment to be used in actual applications. Observations of EAB adults after emergence indicate that borate treatments may negatively affect EAB adult health and survivability after emergence.

Arboriculture & Urban Forestry, Volume 34, Number 3 May 2008.

Comparison of Methods to Reduce Sidewalk Damage from Tree Roots
E. Thomas Smiley

Tree roots growing under sidewalks are known to crack or lift pavement often creating a tripping hazard for pedestrians. An experiment was conducted to determine the long-term effects of below and alongside pavement treatments on tree root development and sidewalk damage. London plane trees were planted next to sidewalks in 1996. Treatments installed at the time of planting were:

Deep Root Universal Tree Root Barrier (UB18-2),
vertical polyethylene sheet,
gravel,
Foamular^®150 extruded polystyrene,
structural soil.

The sidewalks and soil beneath them were removed in 2006. Minimal sidewalk lifting or cracking was associated with the Deep Root barrier, gravel, and foam treatments. Vertical root barriers and foam resulted in fewer and deeper roots under the pavement. The treatments had no impact on tree diameter growth.

Arboriculture & Urban Forestry, Volume 34, Number 3 May 2008.

Edited by Len Phillips

Tree hormones are chemicals produced by trees that alter growth patterns. They can be found in many cells and tissues, although tree hormones seem to be concentrated in meristems and buds. Hormones inhibit and promote cellular activities by sending chemical signals to cells.

One should not confuse hormones with enzymes. Any chemical reaction that occurs in a cell requires a specific catalyst. Enzymes are the catalysts found in cells.

The hormones identified in trees most often regulate division, elongation, and differentiation of cells. Tree hormones work in very small concentrations, affecting membrane properties, controlling gene expression, and affecting enzyme activity. In most cases, the effect tree hormones have on the tree depends on the location and concentration of the hormone relative to other hormones. Hormones often work in conjunction with each other, have overlapping effects, and work with environmental stimuli. There are several classes of tree hormones, including a number of recently "discovered" ones.

Auxins
The concept of chemical messengers in trees was proposed by Charles Darwin in 1881, after he looked at the phenomenon of phototropism in wheat seedlings. When a seedling is illuminated from the side, the shoot will bend towards the light. Darwin did a number of experiments and determined that a chemical located in the coleoptile traveled to the region of elongation and effected a differential elongation of cells furthest from the light sources. The chemical was subsequently studied and named auxin. Chemically, auxin is indoleacetic acid. A primary site of auxin production is the apical shoot meristem.

The most studied function of auxin is cell elongation. This facilitates wall expansion when cells take in more water. Other functions and properties of auxin include:

stimulating cambium cells to divide and secondary xylem to differentiate.
inhibiting the activation of buds lower on the stems. This is known as apical dominance. Cytokinins counter the apical dominance effect of auxins.
promoting lateral and adventitious root development.
promoting other hormone production.
promoting flower initiation.
initiating leaf abscission after the loss of auxin.
requiring the auxin produced by the developing seed.
moving away from a light source.
affecting mostly dicots but not monocots.
being toxic in large concentrations.

Cytokinins
Cytokinins are one of the molecules in DNA. They are found primarily in root meristems, embryos, and fruits, and migrate from roots to the shoot systems of trees in xylem tissue. Biologists have yet to identify the genes for the cytokinins found in trees. One hypothesis today is that cytokinins are made by symbiotic methyl bacteria that live within tree tissues.

The effects of cytokinins are often studied in tissue culture. Parenchyma cells grown in tissue culture will not divide and differentiate unless cytokinins and auxin are present. Cytokinins can promote auxiliary bud growth by overriding the inhibiting effect of auxin. This is one of the ways in which trees balance root and shoot growth.

Cytokinins also retard leaf death, by stimulating RNA and protein synthesis and delaying degradation of chlorophyll. Galls in trees take advantage of cytokinin function. The bacteria that form these tumors contain genes for the synthesis of cytokinins that promote rapid cell growth.

Gibberellin
Gibberellins are the fungus responsible for abnormal growth. The fungus is Gibberella fujikuroi. Over 100 different gibberellins are known and are produced in roots and younger leaves. Gibberellins work with auxins to promote rapid elongation and division of stem tissue. This is seen in:

a reversal of genetic dwarfism,
the promotion of flowering in biennials during the first growing season, a process called bolting,
the signaling of germination activities,
the stimulation of some fruit enlargement,
countering the effects of herbicides.

PBZ (Paclobutrazol)
PBZ is a gibberelin biosynthesis inhibitor that reduces the growth of many species and is commonly used on trees under utility lines or anywhere else where tree size needs to be controlled. PBZ has also been used to stimulate root regeneration after transplanting. It has been studied for the purpose of stabilizing declining trees that have insufficient fine-root development. Treatment should be part of a complete tree care program including mulching. More about tree growth regulators such as PBZ will be appearing in the next Seminar.

Abscissic Acid
Abscissic acid (ABA) is a hormone that functions by inhibiting growth activities in times of environmental stress rather than by promoting growth. It got its name from the erroneous belief that it promoted the formation of abscission layers in leaves and fruits. It does not do this, although leaf abscission accompanies dormancy in many trees.

ABA promotes seed dormancy activities. ABA levels are high when seeds mature, promoting lowered metabolism and synthesis of proteins needed to withstand the dehydration associated with dormancy. Seeds germinate when ABA is degraded by some environmental incident such as when rain has washed the ABA out of the seed coat. Breaking dormancy is related to the ratio of ABA (which keeps seeds in dormancy) and gibberellins (which promote germination). Low levels of ABA in maturing seeds promote premature germination.

ABA promotes stomata closure during leaf-water deficit conditions. ABA in this case originates in roots and detects low water level in root tissues, then moves upward and activates stomatal closure.

ABA derivatives, called dormins, are used in commercial nurseries to keep materials being shipped in dormant conditions. The dormancy can be reversed with gibberellins.

Ethylene
Ethylene is a gas best known as a fruit ripener. Gardeners in China knew centuries ago that fruits ripened better in rooms with burning incense. Citrus growers used kerosene stoves in the rooms in which they ripened their fruit. Today, grocer warehouses have ethylene rooms for ripening most of their produce. Ethylene affects many aspects of growth and development in tissues throughout the tree, but emphasis is on fruit maturation, leaf abscission, and senescence. A shoot tip that encounters an immovable object will grow around the object by changing its growth direction. This occurs through differential elongation of cell walls as ethylene is synthesized, slowing cell wall expansion.

Brassinolides (Brassinosteroids)
Brassinolides are plant steroids discovered in the pollen of mustard plants and best studied in Arabadopsis, which is a small flowering plant related to cabbage and mustard. Chemically they are very similar to animal steroid hormones. Brassinosteroids signal cell elongation and cell division. Brassinosteroids promote differentiation of xylem tissue and can also retard leaf abscission. Absence of brassinolides results in dwarf plants.

Salicylic Acid
Salicylic acid is known to activate defense mechanisms against pathogen invaders. Salicylic acid, a phenolic extract from willow bark, was long used as an analgesic. It is now prepared commercially and is the active ingredient of aspirin.

Jasmonates
Jasmonates are a group of fatty acid derivatives. They appear to have a role in seed germination, root growth, and the storage of protein in seeds. Synthesis of defense proteins may be triggered by jasmonates.

Systemin
Systemin is a small peptide found in wound tissue. It may stimulate defense activities in other parts of the tree to prevent more wounding.

Oligosaccharins
Oligosaccharins are short-chain sugars in cell walls that may have a role in defense against pathogens. They may also help regulate growth, differentiation, and flower development by activating signal pathways.

Sources

Neely, Dan, and Gary Watson, "The Landscape Below Ground II", International Society of Arboriculture, 1998.
Richardson, Rosemary, Biology 203 Course, Bellevue Community College Science Division, Spring 2009.

Online Seminars for Municipal Arborists

Archive #30

articles

vendors