Archive #50 from Online Seminars for Municipal Arborists – May/June 2013
Sections
Methods for Single Tree Appraisal
By James Komen
Trees have dollar value, and it is useful to be able to find that dollar value for purposes of insurance claims, legal settlements, real estate appraisal, and risk management decisions. In this article, I will discuss an abbreviated version of how to appraise a single tree by the methods described in The Guide for Plant Appraisal as published by The Council of Tree & Landscape Appraisers.
An old adage in appraisal is “Something is worth whatever someone else will pay for it.” The biggest problem in appraising trees is there is no easily accessible market for a selling mature tree; one cannot simply uproot and sell a 150 year-old oak. In finance, the term describing this situation is illiquidity. Liquidity is the ability to readily exchange an asset for cash, and an illiquid asset is not easily sold. Trees cannot be easily sold in an open marketplace, so their appraisal becomes challenging. To solve this, a set of proxy methods has been developed to assign a dollar value to trees.
There are three basic strategies for appraising a single tree:
1. market approach
2. cost to cure
3. trunk area formula
Market Approach
Because of their immobility, trees are lumped into the value of the real estate parcel on which they reside. The theory of the market approach is the value of a tree can be derived by finding the difference between the value of the property with the tree and the value of the property without the tree. An appraiser looks for comparables, which are properties that have similar sizes, locations, number of bedrooms, landscapes, etc. The goal is to find identical properties that only differ by not containing the valuable tree. Then an average value of those comparable properties is calculated and is subtracted from the value of the appraised property. The remaining value is then supposedly the value of the tree.
Though simple to explain, the market approach is difficult to implement because real estate parcels differ so widely and small differences in the house, landscaping, and location can all have a drastic effect on the market price. The best way to implement the market approach would be to do a large-scale regression analysis of all properties in the area. However, this would be extremely resource intensive and expensive to undertake and likely not worth the time of the appraiser or the money of the client. Possible future research in this appraisal method may include building a regression model that incorporates a wide swath of variables such as property location, parcel size, square footage of the house, number of bedrooms, tree canopy cover, and real-time real estate market prices.
Cost to Cure
The cost to cure method is the price to return a tree to parity. Parity is the condition that the tree was in before an injury. Cost to cure is the sum of the expenses of the maintenance and the procedures such as pruning, installing cables, treating pests, etc. The theory is if a given dollar amount is spent, then the tree will return to its original health. Cost to cure is only applicable in cases of damage or loss and is not applicable in cases of appraising trees in full health. Sometimes it is impossible to restore a tree to full health, particularly if there was a lot of physical damage done, or if the tree was removed or killed through vandalism.
Trunk Area Formula
The most commonly used strategy for appraising trees is the trunk area formula. It involves measuring the circumference of the tree, calculating the trunk cross-sectional area, and then multiplying this by the unit price of trunk area on commercially available nursery stock. This base value is then discounted by three factors: species, location, and condition. These five values (the trunk area, the base price of nursery stock, the species rating, the location rating, and the condition rating) are all multiplied together to achieve the final valuation.
The most commonly used strategy for appraising trees is the trunk area formula. It involves measuring the circumference of the tree, calculating the trunk cross-sectional area, and then multiplying this by the unit price of trunk area on commercially available nursery stock. This base value is then discounted by three factors: species, location, and condition. These five values (the trunk area, the base price of nursery stock, the species rating, the location rating, and the condition rating) are all multiplied together to achieve the final valuation.
There is necessarily some subjective nature involved in calculating the value of a tree. The species rating of the tree is a subjective rating, but it is decided upon by a committee of arborists and published by the respective regional chapters of the ISA. Condition and location are the largest subjective components to the tree evaluation because they are assigned by the appraising arborist in the field. There is a greater possibility of error because a difference in value of even 10% between different arborists can result in a difference of thousands of dollars in the final result. The circumference of the tree is objectively measured in the field, and does not have nearly as large of a component of error. The appraising arborist has a responsibility to the client to make his measurements and ratings as accurate and objective as possible.
Trunk Area
Trunk area is calculated in three steps:
1. Measure the circumference of the tree at breast height. (4½' ft above grade)
2. Use the circumference to find the diameter at breast height (DBH): DBH = circumference / ?
3. Use the DBH to find the area: Area = ¼ ? x (DBH)2.
The cross section should be measured perpendicular to the axis of the trunk – which will not necessarily be parallel to the ground in the case of a leaning trunk. In the case of multiple trunks, each trunk’s circumference is measured, and the trunk areas are calculated separately and then added together.
Unit Cost of Stock
The value of local nursery stock is obtained by comparing quotes from different nurseries of the same as a type of tree and the prices they charge per unit square inch of trunk area. These values are commonly published by the respective chapters of the ISA. However, it may benefit the appraising arborist to do his own comparison of these values in order to ensure accuracy. The price of nursery stock may vary based on geographic location, and although the ISA published values are specific to a particular region of the country, more specific localities such as a dense urban area or a distant rural may experience higher or lower costs to obtain nursery stock.
Species Rating
Species rating reflects the appropriateness of the chosen species for its climate zone and its overall species desirability. This includes desirability of features such as flowers, foliage, fruit, roots, and bark. It also includes climate hardiness and resistance to pests and disease, frost, salt, soil pH, and drought. The same species of tree planted into different places may have two different values. For example, a Washingtonia robusta palm is highly rated in Los Angeles, but has a lower value in the high desert. Ideally suited species can earn ratings of 90-100%, while noxious weeds rate between 5 and 15%.
Location Rating
The location rating has two components:
1. The contribution to the landscape. The contributions to the landscape includes elements such as shading a yard, cooling a house, redirecting wind, blocking headlights, and adding aesthetic value. For example, a tree in front of a house will have a higher rating than a tree in the corner of the back yard.
2. The site conditions that detract from the tree’s health. Negative location elements include competition with nearby species, root proximity to sidewalks and streets, overhead power lines that will limit the height of a mature tree, and limited growing space.
A value of 100% is usually reserved for golf courses, arboretums, and historical plantings where the tree’s placement is integral to the value of the landscaping.
Condition Rating
Condition rating of a tree is its overall health and vitality. An appraising arborist will look for features such as cracks, rot and decay, poor structure, and broken limbs. Other elements to look for are root crown health and structure, bark expansion from growth, and foliage color and turgidity. A 100% condition rating indicates a tree is in perfect health and morphological form.
Synthesis
All five of these value and are multiplied together using the formula below:
Value = Trunk Area x Unit Cost of Stock x Species Rating x Location Rating x Condition Rating
There are also other variations on the appraisal method formula that are beyond the scope of this article. These include Adjusted Trunk Area for large trees and adjustments for actual incurred cost of planting for recent trees. Other appraisal methods focus on assigning point values, measuring canopy cover, or calculating the volume of space the tree occupies.
Weaknesses of Appraisal Methods
In 2002 Gary Watson of the Morton Arboretum did a study comparing the effectiveness and accuracy of several appraisal methods. He assigned multiple arborists to appraise the same trees with the same appraisal method. The results found that the arborists’ appraisals differed in value by factors of two to five. This implies that the accuracy of the formula may be flawed if the same tree can be valued as such largely different amounts. But currently the trunk area formula that is the best available tool for appraising trees. Future research in tree appraisals should look for a method of appraising trees that consistently obtains similar values across a wide spectrum of arborists appraising the same tree. Such a method would improve the reliability of tree appraisals, and would improve the credibility of appraising arborists.
James Komen is a Certified Arborist with a background in finance and accounting.
The test that follows contains 10 questions. Before taking the test be sure you have read the article carefully. The passing grade is 80% on the entire test. ISA will award .5 CEUs for a passing grade. SAF members will earn .5 CEUs for every 5 passing test scores. The cost for taking this test is $10. If you purchase an annual subscription for 15 credits, the cost per credit is reduced by 50% (see Annual Subscription link below). We will report all passing test scores to ISA. If you are also a Certified Forester, we will report your passing test scores to SAF for no additional cost. Tests with passing scores may be submitted only once to each organization.
Members of ISA may apply the .5 CEU toward Certified Arborist, Utility Specialist, Municipal Specialist, or BCMA practice credits.
Members of SAF can earn 0.5 hour Cat. 1-CT credits for every five passing test scores. SAF requires five passing test scores before reporting.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA and MTOA members may submit your ISA certification record to these organizations and receive credits one for one.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment securely with your credit card or Pay Pal account. After your payment is submitted, click on ‘Return to gibneyCE.com’. That will take you to the test sign in page followed by the test. Members with certifications from both ISA and SAF, please be sure to add both of your certification numbers. These numbers are important for reporting purposes.
To take the test as an annual subscriber with reduced rates, click on Password and enter your test password which will take you to the test sign in page. If you would like to become a subscriber see our Annual Subscription page for details.
All test scores are sent to gibneyCE.com automatically when you press ‘next’ after taking the test and reviewing your answers. You will see a sending responses message after which you will be returned to our website. It is important to go through this process for your score to be recorded properly. All passing test scores are then sent from gibneyCE.com to your organization(s) at the end of every month and they will appear on your certification record 4 to 6 weeks after that.* ISA maintains a record of earned CEU credits on their website
*SAF requires 5 passing test scores before reporting.
Test re-takes are allowed, however you will have to pay for the retake if you are using the pay per test option. You can spend as much time as you would like to take the test but it is important not to leave the test site until you have answered all the questions and see the sending responses message.
Tree of the Seminar 50
By Len Phillips
The Ivory Silk Tree Lilac is a refined cultivar of the Japanese tree lilac. This tree has a uniform growing habit that is oval, with blue green leaves. This information has been gathered from personal observations of the author, living in Massachusetts, Zone 6, and information provided by J. Frank Schmidt & Son.
Botanical Name: Syringa reticulata ‘Ivory Silk’
Trade Name: ‘Ivory Silk’ Tree Lilac
Parentage: This selection was found by Sheridan Nursery in 1975
Habitat: Species introduced from Japan in 1876
Plant Patent: PP#7205
Height: 20' - 25'
Spread: 15' – 20'
Form: Sturdy, compact, oval growth habit
Bloom Period: Mid June to July bloom,
Flower: Large creamy white clusters 6" - 12" long, begin flowering at an early age, penetrating fragrance like privet, not like common lilac
Fruit: Clusters of capsules turn from green to brown, persistent through winter, capsule is three quarters of an inch long
Summer Foliage: Larger than common lilac, blue green color in summer, 3" - 6" long
Autumn Foliage: Autumn color is sometimes green with reddish band on leaf margin, generally no color, spent flowers are considered unsightly by some
Winter Color: Cherry-like bark plus persistent brown capsules provide winter interest
Bark: Cherry-like, reddish brown that turns heavily lenticelled, gray and scaly with age, glossy, straight trunk
Culture: Full sun is best, flower quantity is greatly diminished in partial shade, pH 6.5 – 8, well drained soil, prefers cool summers
Hardiness Zone: 3 – 8
Growth Rate: Medium, 25' high and 15' wide after 30 years
Pest Problems: Resistant to borer, scale, and mildew, most trouble free lilac
Salt Tolerance: Good tolerance
Planting: Transplants easily by bare root and B&B, well-suited for CU-Structural Soil planting
Pruning: Prune at planting and 3 years later to mature form
Propagation: Not true from seed, must be budded onto Syringa reticulata seedlings or by softwood cuttings
Design Uses: Good street tree for under wires, excellent specimen for residential landscapes as a single tree or in groups
Companions: Use with Phlox subulata ground cover
Other Comments: Medium texture in all seasons, uniform shape, selected by the Society of Municipal Arborists as the 1997 Urban Tree of the Year
Photos and Fact Sheet: J. Frank Schmidt & Son, Co.
The test that follows contains 10 questions. Before taking the test be sure you have read the article carefully. The passing grade is 80% on the entire test. ISA will award .5 CEUs for a passing grade. SAF members will earn .5 CEUs for every 5 passing test scores. The cost for taking this test is $10. If you purchase an annual subscription for 15 credits, the cost per credit is reduced by 50% (see Annual Subscription link below). We will report all passing test scores to ISA. If you are also a Certified Forester, we will report your passing test scores to SAF for no additional cost. Tests with passing scores may be submitted only once to each organization.
Members of ISA may apply the .5 CEU toward Certified Arborist, Tree Worker Specialist, Utility Specialist, Municipal Specialist, Aerial Lift Specialist, or BCMA management credits.
Members of SAF can earn 0.5 hour Cat. 1-CT credits for every five passing test scores. SAF requires five passing test scores before reporting.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA and MTOA members may submit your ISA certification record to these organizations and receive credits one for one.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment securely with your credit card or Pay Pal account. After your payment is submitted, click on ‘Return to gibneyCE.com’. That will take you to the test sign in page followed by the test. Members with certifications from both ISA and SAF, please be sure to add both of your certification numbers. These numbers are important for reporting purposes.
To take the test as an annual subscriber with reduced rates, click on Password and enter your test password which will take you to the test sign in page. If you would like to become a subscriber see our Annual Subscription page for details.
All test scores are sent to gibneyCE.com automatically when you press ‘next’ after taking the test and reviewing your answers. You will see a sending responses message after which you will be returned to our website. It is important to go through this process for your score to be recorded properly. All passing test scores are then sent from gibneyCE.com to your organization(s) at the end of every month and they will appear on your certification record 4 to 6 weeks after that.* ISA maintains a record of earned CEU credits on their website
*SAF requires 5 passing test scores before reporting.
Test re-takes are allowed, however you will have to pay for the retake if you are using the pay per test option. You can spend as much time as you would like to take the test but it is important not to leave the test site until you have answered all the questions and see the sending responses message.
Probiotics
Edited by Len Phillips
Probiotics is a new tool to increase yield, improve quality and reduce the cost to maintain your trees. Probiotics are live beneficial microorganisms that, when applied in the correct numbers, break down higher carbon forms and nutrients into more useable forms that trees and other plants can utilize.
Relationship of Trees and Microorganisms
As you know probiotics such as yogurt provides benefits for human health and digestion. Trees also have a digestive system located throughout the soil. The microbes in the soil are as vital or more so for a tree's nutritional needs as microbes are necessary for human digestion. Probiotics are the yogurt for trees, plants, and turf.
Using Probiotics
In many areas, fertilizers are becoming banned or severely restricted in use. This is because surplus fertilizer, especially phosphorus runoff is causing problems with water quality. Soil microbes help to retain, deliver, and cycle existing nutrients in the soil, thus minimizing or negating the need for fertilizer applications. Beneficial organisms fix nutrients into their cell bodies and produce sticky bio-films. This helps retain vital elements and water in the soil and rhizosphere. Microbes also travel through the xylem and phloem and release nutrients as part of their normal life-cycle.
Beneficial microbes also provide and process nitrogen through nitrogen fixation from the air and by cycling higher ammonium nitrogen into nitrates that are useable by trees and other plants. Microbes are also responsible for solubilizing phosphate in the soil. This effort increases the “P” value in soil that is available for plants and trees.
Microbes produce plant growth hormones. This stimulates better root and top growth, better health, yields, and quality.
Probiotics provide Disease Control
In many areas, pesticide use is being banned on school grounds and other public properties. Once again the use of probiotics can be a tool that also provides disease control. Beneficial microbes produce compounds that can directly kill pathogens so pesticides are not needed. One point to keep in mind with the use of fungicides is that the fungicide will kill all fungi – good as well as bad.
Beneficial microbes will also out-compete pathogens. When two species are competing for the same resources, they will not co-exist if all other ecological factors are constant. One of the two competitors will always overcome the other leading to the extinction of the competitor or the competitor will shift toward a different ecological niche. To illustrate, bacteria and fungi compete for the same resources. Bacteria divide much faster than fungi and will often out-compete them for the limited resources.
Beneficial microbes contain proteins and complex sugars that can not be digested by pests but are very beneficial for creating a healthy plant. Pathogens on the other hand, have evolved by eating dead or weakened plant material with simple amino acids and sugars.
Water Retention
Beneficial microbes help with water retention and drought resistance by producing water as a by-product of their normal cellular metabolism. They also form biofilms that can bind and retain water at the root zone. When they die, their bodies turn into organic material which further helps with water and nutrient retention. By incorporating water as part of their cells and releasing this water to the plants, they provide the plant with water when a drought may be occurring.
Poor Management Practices
The following practices will adversely affect soil microbiology:
- Tilling – destroys the complex organization of the rhizosphere and the top layer of soil.
- Glyphosate – can reduce the beneficial organism populations and cause increases in pathogen growths such as Fusarium.
- Fungicides and antibacterials – will kill fungi and bacterial populations in a non-specific manner.
- Insecticides – can cause secondary effects on beneficial insect populations such as colony collapse disorder. Also extensive use of insecticides often kills the predators of common pests, leading to pest outbreaks.
- Excess fertilization with phosphate – is toxic to beneficial organisms at high concentrations . Excess nutrients will stimulate pathogen growth, and will cause pollution in nearby waterways.
Composts
The use of compost is very effective and is a proven practice for encouraging microbial activity in soil. It is more sustainable than other management methods. The wide array of nutrients and natural fertilizer value will greatly enhance soil biology. Plus it is cheap to produce.
On the other hand, composts will not produce consistent results. They can be difficult and labor intensive to apply. If not properly maintained, backyard compost has the potential to grow pathogens or unwanted organisms and should be checked before use with proper testing.
Probiotics Integration
There are several practices and products that stimulate microbes in soil used for growing trees and should be considered by arborists in their tree management practices.
- Use organic fertilizers such as humates, fish fertilizer, manures, and kelp.
- Use probiotics alone or in combination with biological stimulants. Although manures are excellent fertilizers, the odor should be considered before using it.
- Although molasses and sugars induce the growth of all forms of soil microbes, they do not necessarily encourage the growth of beneficial microbes.
Controlled Biological Inoculants
These products require no preparation, just buy and apply. They are consistent because their sources are known and the microorganisms can be counted and verified. The products are concentrated and are tested for safety and pathogens. The products will be stable for years. However, these products are not as sustainable as compost. Without a microscope test or a known reliable source such as JRM Chemical, the products could be colored water. The diversity of microbes is dependent on the strains used and stabilized. The higher product costs will be offset by the lower labor and application costs.
Measuring Soil Biology
Soil microbiology can be measured visually. The fungal growth is visible on roots as web-like structures. Worms can easily be seen. Trees and plants will visibly increase in growth, health, and quality. Soil microbes can also be measured by extracting the soil liquid and counting them under a microscope. This will not provide information on the diversity of species, but total counts will be possible. Bi-products such as gas and sugars excreted, and enzymes produced can all be measured at soil web labs and DNA labs, but these tests are very expensive and not economically viable for routine tree maintenance.
Source
- Magazzi, Joe, “Probiotics: A New Tool to Increase Yield, Improve Quality, and
Reduce Cost”, lecture at New England Grows, February 7, 2013.
The test that follows contains 10 questions. Before taking the test be sure you have read the article carefully. The passing grade is 80% on the entire test. ISA will award .5 CEUs for a passing grade. SAF members will earn .5 CEUs for every 5 passing test scores. The cost for taking this test is $10. If you purchase an annual subscription for 15 credits, the cost per credit is reduced by 50% (see Annual Subscription link below). We will report all passing test scores to ISA. If you are also a Certified Forester, we will report your passing test scores to SAF for no additional cost. Tests with passing scores may be submitted only once to each organization.
Members of ISA may apply the .5 CEUs toward Certified Arborist, Municipal Specialist, or BCMA science credits.
Members of SAF can earn 0.5 hour Cat. 1-CT credits for every five passing test scores. SAF requires five passing test scores before reporting.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA and MTOA members may submit your ISA certification record to these organizations and receive credits one for one.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment securely with your credit card or Pay Pal account. After your payment is submitted, click on ‘Return to gibneyCE.com’. That will take you to the test sign in page followed by the test. Members with certifications from both ISA and SAF, please be sure to add both of your certification numbers. These numbers are important for reporting purposes.
To take the test as an annual subscriber with reduced rates, click on Password and enter your test password which will take you to the test sign in page. If you would like to become a subscriber see our Annual Subscription page for details.
All test scores are sent to gibneyCE.com automatically when you press ‘next’ after taking the test and reviewing your answers. You will see a sending responses message after which you will be returned to our website. It is important to go through this process for your score to be recorded properly. All passing test scores are then sent from gibneyCE.com to your organization(s) at the end of every month and they will appear on your certification record 4 to 6 weeks after that.* ISA maintains a record of earned CEU credits on their website
*SAF requires 5 passing test scores before reporting.
Test re-takes are allowed, however you will have to pay for the retake if you are using the pay per test option. You can spend as much time as you would like to take the test but it is important not to leave the test site until you have answered all the questions and see the sending responses message.
Cultivars of Swamp White Oak
By Len Phillips
Swamp White Oak, Quercus bicolor is an excellent tree for growing in urban areas. Because of its preference for moist bottomland, where it is subject to floods, drought, and other adverse conditions, it is able to tolerate urban soils. The following is an overview of the species. The cultivars at the bottom of this page share the information provided on this overview.
Botanical Name: Quercus bicolor
Common Name: Swamp White Oak
Bloom Period: early spring
Flower: catkins in clumps, male and female on same branch
Fruit: 1” long acorn, usually in pairs and on stems 1” – 3” long with ? covered by the cap, shiny and brown
Winter Color: unusual bark provides winter interest, interesting silhouette is very striking and coarse textured
Bark: grayish brown, flaky, deep fissures, rugged, and handsome
Habitat: native to the eastern half of the US and Canada
Culture: moist bottomland, well-drained, excellent drought resistance, likes acidic soil
Hardiness Zone: 3 – 8
Growth Rate: moderate after a slow start, 30’ in 30 years
Pest Problems: no serious disease or insect problems, very long-lived tree exceeding 300 years
Storm Resistance: excellent
Salt Resistance: good to excellent
Planting: transplant results are mixed, but easier than white oak; B&B or container in spring only, very suitable for use in CU-Structural Soil planting
Pruning: prune at planting if needed and 3 years later to mature form
Design Uses: excellent specimen, good landscape tree
Companions: use with shrubs such as Taxus, evergreen Euonymus, and perennial Hosta
Other Comments: excellent for wildlife
Awards: 1998 Urban Tree of the Year by the Society of Municipal Arborists
American Dream® Oak, Quercus bicolor ‘JFS-KW12’ P.A.F. – height: 50', spread: 40'. Shape: broadly pyramidal; Foliage: bright green, glossy and turns yellow in fall. Vigorous growing and broadly pyramidal with excellent density, this tree shines with bright foliage. Selected for strong resistance to anthracnose and powdery mildew, the broad, handsome leaves turn yellow and then tawny brown as they hold into early winter. Photo Page
Rosehill® Oak, Quercus bicolor x Q. robur 'Asjes' - Strongly resembles English Oak. It is resistant to leaf ailments such as mildew and features a somewhat fastigiate, upright form with lustrous green foliage. The acorns resemble those of English oak.
Beacon® Oak, Quercus bicolor ‘Bonnie and Mike’ – height: 40', spread: 15'. Shape: narrowly columnar; Foliage: green but turns a nice yellow in autumn. This oak has a tightly columnar shape, is urban adaptable, and was discovered by famed plantsman, Dr. Michael Dirr. The stout upright branching structure and dense green foliage makes this an ideal street tree and provide a strong visual statement. Photo Page
Kindred Spirit® Oak, Quercus robur fastigiata x Quercus bicolor 'Nadler' PP 17604 – height: 30’, spread: 6’. Shape: tightly columnar; Foliage: medium green that turns yellow to yellow-brown in autumn. Among the tightest of columnar trees, its growth habit, mildew and drought resistance, and tolerance of urban soils make this hybrid of English and swamp white oak ideal for narrow city streets. A sister seedling of Regal Prince®, the foliage is less glossy but the form is significantly tighter. Photo Page
Regal Prince® Oak, Quercus robur 'Fastigiata' x bicolor ‘Long’ PP 12673 – height: 45’ – 60', spread: 18’ – 25'. Shape: Columnar to narrow oval; Foliage: glossy and bright green that turns yellow in the fall. Mildew-resistant summer foliage is clean, bright green, and awesome all season with a silvery lower surface. This adaptable hybrid of English and swamp white oak is notable for its excellent columnar form. Due to its parentage, this plant is tolerant of a wide range of conditions, including both wet and dry soil. This tree has a stronger and fuller branching structure than other trees in this category. Regal Prince is resistant to mildew.
Photo Page
The test that follows contains 10 questions. Before taking the test be sure you have read the article carefully. The passing grade is 80% on the entire test. ISA will award .5 CEUs for a passing grade. SAF members will earn .5 CEUs for every 5 passing test scores. The cost for taking this test is $10. If you purchase an annual subscription for 15 credits, the cost per credit is reduced by 50% (see Annual Subscription link below). We will report all passing test scores to ISA. If you are also a Certified Forester, we will report your passing test scores to SAF for no additional cost. Tests with passing scores may be submitted only once to each organization.
Members of ISA may apply the .5 CEUs toward Certified Arborist, Tree Worker Specialist, Municipal Specialist, Aerial Lift Specialist, or BCMA science credits.
Members of SAF can earn 0.5 hour Cat. 1-CT credits for every five passing test scores. SAF requires five passing test scores before reporting.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA and MTOA members may submit your ISA certification record to these organizations and receive credits one for one.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment securely with your credit card or Pay Pal account. After your payment is submitted, click on ‘Return to gibneyCE.com’. That will take you to the test sign in page followed by the test. Members with certifications from both ISA and SAF, please be sure to add both of your certification numbers. These numbers are important for reporting purposes.
To take the test as an annual subscriber with reduced rates, click on Password and enter your test password which will take you to the test sign in page. If you would like to become a subscriber see our Annual Subscription page for details.
All test scores are sent to gibneyCE.com automatically when you press ‘next’ after taking the test and reviewing your answers. You will see a sending responses message after which you will be returned to our website. It is important to go through this process for your score to be recorded properly. All passing test scores are then sent from gibneyCE.com to your organization(s) at the end of every month and they will appear on your certification record 4 to 6 weeks after that.* ISA maintains a record of earned CEU credits on their website
*SAF requires 5 passing test scores before reporting.
Test re-takes are allowed, however you will have to pay for the retake if you are using the pay per test option. You can spend as much time as you would like to take the test but it is important not to leave the test site until you have answered all the questions and see the sending responses message.
Research Briefs 50
Edited by Len Phillips
Trees In the African Desert
Elizabeth Daigneau
Climate change is expected to affect the African nations of Niger and its neighbors in Central Africa worse than any other region or continent, according to the United Nations. The deserts are expanding out of control. Historically, trees were considered property of the state and individual farmers had little incentive to grow or protect them. When food production suffered however, the governments around the desert, began changing their laws to recognize property rights. When farmers owned their trees, they began to see the benefits of growing and preserving them.
For generations the farmers throughout the area had cleared tree saplings as they sprouted in their fields. The trees were a problem because they competed with crops. But as crop yields began to plummet in the 1970's and '80's, more farmers opted to let the trees grow. At the same time, they also implemented smarter farming methods such as fortifying the soil with manure, growing different crops on the same piece of land, and relying on natural predators instead of pesticides to combat pests.
Ultimately, mixing trees and crops worked. As the trees grew, crop yields increased and the desert went from brown to green. The farmers in Niger have grown more than 200 million trees and rehabilitated 12.5 million acres of land. The key here is that farmers didn't plant partially grown saplings, they grew the trees from seed. Planting tree saplings, in general, is less successful than starting from seed in the desert. The trees being grown are native species and they are more resilient than saplings from out of the region.
In the United States, urban tree planting campaigns like Million Trees NYC and others have struggled with high mortality rates due to heavy storms, disease, pollution, road salt, acidic soil, and the rigors of urban life. However, these campaigns should not stop. A commitment to planting new trees is essential for the environmental health of the city and its residents. But the experience from the desert region might be a cause for urban foresters in the US to think about growing more trees from seed.
Governing February 2013
Plant Ecology: Forests on the Brink
Bettina M. J. Engelbrecht
An analysis of the physiological vulnerability shows that a majority of tree species around the world are operating on the brink of collapse. If the predicated pace of climate change continues, many may not be able to adapt and large numbers could die off, succumbing to increases in drought conditions. Drought stress creates trapped gas in the water transport system, which reduces the ability of trees to supply water to leaves for photosynthetic gas exchange and can ultimately result in desiccation and mortality.
This study looked at 226 different trees species from 81 sites around the world. The researchers found that 70% of the trees studied adapt closely to the local environment, absorbing just enough water in order to survive, but leaving them highly vulnerable to minor shifts in rainfall and drought stress and therefore potentially face long-term reductions in productivity and survival if temperature and aridity increase as predicted for many regions across the globe. All forests are equally vulnerable to hydraulic failure regardless of their current rainfall environment. Even trees in wet forests are facing drought risk due to hydraulic failure.
Nature November 29, 2012
Ground-penetrating Radar Locates Tree Roots Under Pavement
Nina Bassuk, Jason Grabosky, Anthony Mucciardi, and Gary Raffel
This study involved locating tree roots with a ground-penetrating radar (GPR) system and then examining the excavated roots to measure the accuracy of the GPR system. In 2003, Acer platanoides ‘Emerald Queen’ Norway maples were planted in trenches containing two compacted soils (native silt loam and CU-Structural Soil). The trenches were paved with 10 cm of concrete. In 2008, a GPR system consisting of a 900 MHz antenna mounted on a root-scanning cart was used to conduct linear scans on top of the concrete. Immediately after scanning, the concrete was removed for selected trees and whole root systems were excavated using an air excavation tool. Regression analysis using mixed effect models showed that the radar reliably predicted root presence in both the native and structural soils. This study showed that GPR data reliably predicted the presence and locations of roots under the concrete pavement in two compacted soils.
Arboriculture & Urban Forestry 37(4): July 2011
Tree Deaths Across the West
Phil van Mantgem
Tree death rates more than doubled during the last few decades in old-growth forests of the western United States. A study by the US Geological Survey points to regional warming as the cause. The tree deaths have increased across a wide variety of forest types, at all elevations, in trees of all sizes, and in pine, firs, hemlocks, and other kinds of trees.
The problem: higher tree death rates ultimately could lead to substantial changes in western forests. These changes could have a negative impact on wildlife. The increasing tree mortality rates mean that western forests could become net sources of carbon dioxide to the atmosphere. Tree mortality has been climbing, while the establishment of replacement trees has not.
The study ruled out sources of the increasing tree deaths, including air pollution, long-term effects of fire suppression, and normal forest dynamics. The lengthening summer drought could be stressing trees, leading to higher death rates. Higher temperatures also might favor insects and diseases.
Nursery Management & Production March 2009
Expected Environmental Benefits When Planting Larger vs Smaller Tree Species
T. Davis Sydnor and Sakthi K. Subburayalu
In 1965 two of the original plantings in Brooklyn, Ohio, U.S. included 17 smaller growing, Lavalle hawthorn (Crataegus × lavallei) and 84 larger growing thornless honeylocusts (Gleditsia triacanthos). One consequence of selecting trees is the differing values of environmental benefits generated by trees of various sizes and survival rates. Values of environmental benefits have not been considered in plant selection but the i-Tree free suite of software now allows this to be calculated.
Algorithms recovered from i-Tree Streets were used to calculate environmental benefits in ten, randomly selected trees in each of the two plantings, and adjusted for survival rates. There was an 89% survival for honeylocusts and 65% for hawthorns. When adjusted for survival, honeylocusts deliver USD $430 per tree in benefits in contrast to the $57 per tree for hawthorn. When viewed on a per surviving tree basis, honeylocusts provide more than 7.5 times the environmental benefits. Regardless of how it is viewed there is a significant reduction in environmental benefits when using smaller statured trees compared with larger trees. Communities should consider this aspect when space for larger trees is available.
Arboriculture & Urban Forestry 37(5): September 2011
Effects of Tree Stabilization Systems on Tree Health
Kendra J. Labrosse, Robert C. Corry, and Youbin Zheng
A tree stabilization system (TSS) is specified to promote stability and maintain tree posture at transplanting. However, staking and guying can compromise tree health. Visual symptoms for tree health were recorded for 488 trees with and without TSSs in Guelph, Ontario, Canada. Results showing symptoms of stunted growth, death, and pest/disease were less on trees observed with TSSs. On the other hand, health was negatively impacted by TSSs by from girdled trunks, swelling, and wilting. Trees planted on public land were found to benefit from being stabilized while trees on private land expressed more negative health effects when observed with trunk support. Implications for urban forest professionals include limiting tree stabilization practice to site conditions where their use is warranted along with timely removal.
Arboriculture & Urban Forestry 37(5): September 2011
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