Archive #55 from Online Seminars for Municipal Arborists – March/April 2014
Sections
The Best Time to Prune Trees
By Steve Gardner
There are lots of factors to consider before pruning. Here are several very common landscape tree species and a general breakdown of when and how to prune them that best suits their needs and avoids pest problems.
Oaks (Quercus)
Pruning young oaks is important in order to start the tree with proper structure and a well balanced shape. As they age, pruning involves removing dead and diseased wood rather than maintaining shape. Because of disease, oak trees have a very specific window of when you should NOT prune them. Oak wilt is caused by a fungus (Ceraticystis fagacearum) that is spread by Nitidulid (sap) beetles. These beetles are most active during the spring months, generally from February through May. By not pruning oak trees during this period, sap from the pruning will not attract the insects and provide an easy access for the fungus to get inside the tree. The best time to prune oaks is November through January when the beetles are least active. If making a pruning cut during sap flow, cover the wound with a sealant like a warm wax or pitch specially made for sealing tree grafts and wounds.
Maples (Acer)
Maples are pretty forgiving and do not necessarily have any special considerations for pruning and trimming. The only exceptions are to avoid pruning maples in the early spring or when they are not healthy.. Maple trees move large amounts of sap in the spring and if a cut is made during this time, the tree will bleed heavily. Later in the spring as the tree is budding and growing new leaves, they will not put as much energy into healing the wound as they put into growing their leaves, which could result in disease problems. This also applies to when maples drop their leaves in the fall. Silver maples (Acer saccharinum) sucker often if the tree is over pruned and those suckers can be trimmed at any time of year.
Willow (Salix)
Willow trees in general are one tree that can be pruned just about any time and anywhere. But like most trees, it’s usually best to prune when the tree is dormant in winter.
Keep in mind when pruning a willow:
Elm (Ulmus)
Elm trees need a lot of special consideration when it comes to pruning them because of Dutch elm disease (DED). The only real good time to avoid the spore causing DED from entering vulnerable wounds is in the very early spring. In fact, lots of cities have laws regarding when elms can be pruned to help contain the disease. Elm trees are pruned very similar to how to other trees are pruned. Remove old, dead wood, crossing and suckering branches, and other unsightly, unbalanced growth. Good pruning at the right time can actually help the elm fight off DED and recover from infections.
Poplar (Populus)
Poplar trees are best pruned when they are entering dormancy in the late summer and autumn. This time is also good because they will not put forth the energy to grow suckers. When pruning poplars, take great care to approach cuts with an “easy-does-it” attitude. Avoid tearing bark. To prune poplar correctly, cut the weight off of the branch gradually before making the final cut. Regular pruning of these fast growing trees will extend their life and create a nice mature specimen.
Palms
Palms are monocots and are different from most trees most notably in their basic structure. To learn more about palm pruning click here.
Conifers
Conifers are generally trees that do not require a lot of pruning or trimming, and do not recover well after pruning. The two main reasons to prune a conifer are for health (removing of old, dead, diseased growth) and for size control (which is avoidable by planting a conifer at a place that is the right size for the mature tree).
When and how a conifer is pruned depends on the species.
Fruit TreesFruit trees depend on proper pruning to keep them productive, healthy, and balanced. For more information about the correct pruning requirements for fruit trees, click here.
Hardwood Trees and Shrubs Without Showy Flowers
Prune these trees in the dormant season to:
Flowering Trees and Shrubs
These should also be pruned during the dormant season for the same reasons stated above. However, to preserve the current year's flower crop, prune according to the following schedule:
"All Things Trees Blog”, American Tree Service Supply, 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 0.5 Cat. 1-CF for every five 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 and/or SAF. If you are a member of ISA and SAF we will report your passing test scores to both for no additional cost. Please be sure to add both of your certification numbers when you sign in. 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 practice credits.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA members may submit your ISA certification record to the ASCA and receive credits one for one.
MTOA members must follow the ISA instructions indicated above.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment online 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.
When you have finished answering all questions you will be prompted to click ‘next’ to send your answers to gibneyCE.com. You can then click ‘next’ to view your test summary. A test review of your answers is available upon request.
All passing test scores are 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 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 your answers' response.
By Steve Gardner
There are lots of factors to consider before pruning. Here are several very common landscape tree species and a general breakdown of when and how to prune them that best suits their needs and avoids pest problems.
Oaks (Quercus)
Pruning young oaks is important in order to start the tree with proper structure and a well balanced shape. As they age, pruning involves removing dead and diseased wood rather than maintaining shape. Because of disease, oak trees have a very specific window of when you should NOT prune them. Oak wilt is caused by a fungus (Ceraticystis fagacearum) that is spread by Nitidulid (sap) beetles. These beetles are most active during the spring months, generally from February through May. By not pruning oak trees during this period, sap from the pruning will not attract the insects and provide an easy access for the fungus to get inside the tree. The best time to prune oaks is November through January when the beetles are least active. If making a pruning cut during sap flow, cover the wound with a sealant like a warm wax or pitch specially made for sealing tree grafts and wounds.
Maples (Acer)
Maples are pretty forgiving and do not necessarily have any special considerations for pruning and trimming. The only exceptions are to avoid pruning maples in the early spring or when they are not healthy.. Maple trees move large amounts of sap in the spring and if a cut is made during this time, the tree will bleed heavily. Later in the spring as the tree is budding and growing new leaves, they will not put as much energy into healing the wound as they put into growing their leaves, which could result in disease problems. This also applies to when maples drop their leaves in the fall. Silver maples (Acer saccharinum) sucker often if the tree is over pruned and those suckers can be trimmed at any time of year.
Willow (Salix)
Willow trees in general are one tree that can be pruned just about any time and anywhere. But like most trees, it’s usually best to prune when the tree is dormant in winter.
Keep in mind when pruning a willow:
- that whatever branch is cut off of a willow, many more will take its place.
- to aim for very basic of results such as balancing the weight of the tree, removing dead or diseased wood, and removing suckers.
- be ready to accept whatever shape the tree takes and give the tree lots of room to grow.
Elm (Ulmus)
Elm trees need a lot of special consideration when it comes to pruning them because of Dutch elm disease (DED). The only real good time to avoid the spore causing DED from entering vulnerable wounds is in the very early spring. In fact, lots of cities have laws regarding when elms can be pruned to help contain the disease. Elm trees are pruned very similar to how to other trees are pruned. Remove old, dead wood, crossing and suckering branches, and other unsightly, unbalanced growth. Good pruning at the right time can actually help the elm fight off DED and recover from infections.
Poplar (Populus)
Poplar trees are best pruned when they are entering dormancy in the late summer and autumn. This time is also good because they will not put forth the energy to grow suckers. When pruning poplars, take great care to approach cuts with an “easy-does-it” attitude. Avoid tearing bark. To prune poplar correctly, cut the weight off of the branch gradually before making the final cut. Regular pruning of these fast growing trees will extend their life and create a nice mature specimen.
Palms
Palms are monocots and are different from most trees most notably in their basic structure. To learn more about palm pruning click here.
Conifers
Conifers are generally trees that do not require a lot of pruning or trimming, and do not recover well after pruning. The two main reasons to prune a conifer are for health (removing of old, dead, diseased growth) and for size control (which is avoidable by planting a conifer at a place that is the right size for the mature tree).
When and how a conifer is pruned depends on the species.
- Arborvitaes (Thuja), Chamaecyparis, and junipers (Juniperus) should be pruned to keep their size only. Best done in late spring and early summer. The old wood underneath green growth will not grow back.
- Pines (Pinus) should be pruned by cutting off the candles in late spring to encourage bud formation for next year’s new growth.
- Hemlocks (Tsuga), yews (Taxus), firs (Abies), and spruces (Picea) should be pruned by trimming from late summer to late winter when the tree is dormant. Prune to control height by trimming the leader about a half inch above a bud on the leader. This will encourage branching while controlling height
Fruit TreesFruit trees depend on proper pruning to keep them productive, healthy, and balanced. For more information about the correct pruning requirements for fruit trees, click here.
Hardwood Trees and Shrubs Without Showy Flowers
Prune these trees in the dormant season to:
- easily visualize the structure of the plant,
- maximize wound closure in the
growing season after pruning, - reduce the chance of transmitting disease,
- discourage excessive sap flow from the pruning wounds.
Flowering Trees and Shrubs
These should also be pruned during the dormant season for the same reasons stated above. However, to preserve the current year's flower crop, prune according to the following schedule:
- Trees and shrubs that flower in spring such as redbud (Cercis) and dogwood (Cornus), etc. should be pruned immediately after flowering.
- Trees and shrubs that flower in the summer or fall should be pruned during the dormant season. Flower buds will form on new twigs during the next growing season.
- Dead branches can be removed any time of the year.
- Many flowering trees are susceptible to fire-blight, a bacterial disease that can be spread by pruning. These trees include many varieties of crab-apple (Malus), hawthorn (Crataegus), pear (Pyrus), mountain ash (Sorbus), flowering quince (Cydonia) and Pyracantha. They should be pruned during the dormant season.
"All Things Trees Blog”, American Tree Service Supply, 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 0.5 Cat. 1-CF for every five 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 and/or SAF. If you are a member of ISA and SAF we will report your passing test scores to both for no additional cost. Please be sure to add both of your certification numbers when you sign in. 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 practice credits.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA members may submit your ISA certification record to the ASCA and receive credits one for one.
MTOA members must follow the ISA instructions indicated above.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment online 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.
When you have finished answering all questions you will be prompted to click ‘next’ to send your answers to gibneyCE.com. You can then click ‘next’ to view your test summary. A test review of your answers is available upon request.
All passing test scores are 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 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 your answers' response.
Understanding Branch Growth
By David Lloyd–Jones & Len Phillips
Understanding how branches grow on the tree will lead to an understanding of how to prune trees in a more naturalistic appearance and which results in a healthy tree. We all know that trees grow in annual increments. Those increments begin at nodes from which a stem will grow and become larger in subsequent seasons. Proper pruning requires trimming at the nodes of branches with the cautions that this article will address.
Co-dominant Stems
The most dangerous kind of tree fork or crotch is the two co-dominant stem arrangement. Because they are co-dominant, they both have their own apical buds, both leaders have the same resources and they both grow at the same rate. Because they set off at the same point in time, neither can outgrow the other and they remain locked in a battle for growth that neither can win. The results of such a co-dominant morphology is inevitably strong competition between the two apically dominant buds, and that means strong growth from a weak fork.
Because the two leaders rise closely to each other, the bark becomes included in the acutely angled fork and prevents the sinews of the two leaders from binding properly with each other. The final problem comes when high winds act on the fork and the leaders move back and forth from each other. This can cause a crack to form at the base of the acute fork. The crack propagates down the branch further weakening the fork and eventually resulting in one or both of the leaders falling.
Other Forks
Slightly wider than the co-dominant stems are acute forks. Acute forks or crotches have been extensively studied and as a result are widely understood to be almost as weak as the co-dominant fork and therefore are likely to be a point at which the branch will again fail in high winds. As a result, acute forks are also considered to be detrimental and undesirable.
Simple pulling tests by researchers suggest that co-dominant stems are the weakest forks a tree can have. An acute fork, which is wider than the co-dominant stems, can fail at up to approximately half of the lateral loading that would be required to make a straight trunk or branch of similar dimensions fail. Narrow forks are stronger than acute forks and co-dominant stems, while wide forks are stronger than narrow forks.
So the degree of relative strength goes up with the relative widening of the angle between the branches, or the "decreasing acuteness" of the fork. Consequently, arborists feel that co-dominant stems as well as acute and narrow angled forks are undesirable.
Benefit to Trees
That defect is extremely widespread across all species and whole families of trees. In fact, most trees carry this feature that we call a defect. Therefore, if most trees have acute forks at the end of millions of years of evolution, how can these weak forks still be considered a defect? Furthermore, if acute forks do not represent a defect to the tree, then they have to be a benefit to the tree. So what benefit can trees expect to get by having narrow or acute forks built into their structures?
Trees are relatively stable structures in a world where climatic fluctuations test them all the time. In response to these fluctuations trees do not grow ever stronger to overcome the structural stresses that they periodically endure. Instead they use the variable strength of the branch forks to facilitate their survival strategy and so during a storm, the tree progressively fails by allowing the weakest forks to break off from the outer edge of the branches, inwards. The tree reduces its wind sail by losing the weakest forks in proportion to the strength of the wind. As they do that, the self-optimized structural elements become slightly over-specified for the job of upholding the remaining canopy and the likelihood of the whole tree failing is reduced. Thus, a tree affected or pruned in this way is less likely to fail dramatically in all but a major wind storm, unless some other degenerative process or extraordinary wind strengths are involved.
In other words, trees reduce structural stress in a controlled way by creating some relatively weak branch unions throughout the canopy of mature trees. Arborists should learn to understand this morphological strategy so that they can mimic that same strategy and simulate wind pruning on their own trees.
Source
Lloyd -Jones, David, “Tree Morphogenesis Book 1 Reduction Via Thinning”, Kindle Edition, 2013.
David Lloyd-Jones is an arborist from Knutsford, Cheshire, UK. You may contact him at this address.
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 0.5 Cat. 1-CF for every five 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 and/or SAF. If you are a member of ISA and SAF we will report your passing test scores to both for no additional cost. Please be sure to add both of your certification numbers when you sign in. 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 practice credits.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA members may submit your ISA certification record to the ASCA and receive credits one for one.
MTOA members must follow the ISA instructions indicated above.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment online 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.
When you have finished answering all questions you will be prompted to click ‘next’ to send your answers to gibneyCE.com. You can then click ‘next’ to view your test summary. A test review of your answers is available upon request.
All passing test scores are 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 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 your answers' response.
2014 Urban Tree of the Year
By Len Phillips
The Society of Municipal Arborists has announced the 2014 Urban Tree of the Year, Persian Parrotia, Parrotia persica. Parrotia is a low-branched small tree with unusual form and texture. It has a fall color display that is usually excellent. The following information has been gathered from personal observations by the author, living in Massachusetts, Zone 6, and information provided by J. Frank Schmidt & Son.
The Society of Municipal Arborists conducts the Urban Tree of the Year competition every year to illustrate the importance of selecting the right tree for the right spot. The intent of this program is not to indicate that this is the perfect tree that can grow anywhere, but is to make arborists aware of this tree and they should use it if they have a site suitable for it. The Urban Tree of the Year also provides extra publicity for excellent trees that need planting more often. Our cities often contain too many of the common maples and ash that are cheap, easy to grow and are short-lived. A quality urban tree is a better investment for the future of the city and the urban forest.
Common Name Persian Parrotia
Botanical Name: Parrotia persica
Family: Hamamelidaceae
Parentage: Introduction 1840
Hardiness Zone: 4 - 8
Height: 20' - 40'
Spread: 15' - 30'
Growth Rate: Medium, grows to full size in 30 years
Form: Usually grows with several trunks so prune to single stem if a standard tree form is desired, tree form is a broad oval in shape
Bloom Period: March & April
Flower: Crimson, small, no petals but bright red stamens
Fruit: One half inch long and wide brown capsule
Spring Color: Reddish purple to medium green in spring
Summer Foliage: Dark green in summer, 3" - 4" long leaves
Autumn Foliage: Yellow, orange, and scarlet in autumn
Winter Interest: Exfoliating bark with brighter patches enhance interest in the form
Bark: Smooth gray trunk exfoliates with age to expose gray, green, white, and brown patches under the gray bark
Habitat: Species introduced from Iran
Culture: Well drained, tolerant of most sites once established, prefer loam, slightly acid soil, pH 6 – 6.5, full sun, will tolerate partial shade
Pest Problems: Excellent resistance except Japanese Beetle in the South
Storm Resistance: Excellent
Salt Tolerance: Excellent
Planting: Transplant B & B in early spring, easy to transplant bare root, suitable for CU-Structural Soil planting
Pruning: Prune at planting and 3 years later to mature form, prune in winter, raise branches to encourage a taller tree if desired
Propagating: Seed or softwood cuttings in summer
Design Uses: Good street tree for under wires, excellent specimen for residential landscapes
Companions: Boltonia, Kalimeris, and Gypsophila all look good with Parrotia
Other Comments: It is difficult to get a single stem tree from nurseries, arching branches often touch the ground and obscure the beautiful trunk, prune lower branches in winter if a taller tree is desired. The cultivar 'Vanessa' is a better choice for smaller landscapes or for use near streets.
Photo and Fact Sheet: J. Frank Schmidt & Son
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 0.5 Cat. 1-CF for every five 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 and/or SAF. If you are a member of ISA and SAF we will report your passing test scores to both for no additional cost. Please be sure to add both of your certification numbers when you sign in. 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.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA members may submit your ISA certification record to the ASCA and receive credits one for one.
MTOA members must follow the ISA instructions indicated above.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment online 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.
When you have finished answering all questions you will be prompted to click ‘next’ to send your answers to gibneyCE.com. You can then click ‘next’ to view your test summary. A test review of your answers is available upon request.
All passing test scores are 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 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 your answers' response.
Ten Good Reasons to Plant Trees
By Fred Conacher
Part of the task of 'selling' the idea of street and urban trees is to inform the public of a tree's benefits. A city is a particularly harsh and busy environment for most tree species so the support of the city's residents is essential for a tree's success. I have been working on this list for most of my career to let people know that trees are more than something pretty to see.
1. Trees are good absorbers of carbon dioxide (a global warming gas) which they take from the atmosphere and turn into wood. Depending on the species, each mature tree can ‘fix’ or lock up 20 tons (17 metric tons) of carbon dioxide in a year. This helps reduce global warming and the resulting extreme weather effects.
2. Trees act as air filters. All of their leaves have a surface area as much as 12 times greater than the ground they overshadow, and this canopy helps to trap dust and carbon as well as absorbing harmful ozone pollutants. In other words, trees help to clean the air we breath and make the air healthier.
3. Trees produce useful wood products such as paper, furniture, garden and landscape wood chips, as well as fencing, fuel, lumber, and house construction timbers. The long-term value of timber products ‘fixes’ carbon dioxide in the form of cellulose thereby reducing the globally harmful air-borne carbon dioxide ‘greenhouse’ gas for as long as the wood remains solid.
4. Green leafy surroundings and large branches arching over the street are very attractive and more interesting to travel through than cities and buildings without trees.
5. Tree filled landscapes can promote feelings of well being and provide a conducive setting for ‘recharging a person's batteries’. Contact with nature also reduces vandalism and crime in treed neighborhoods. A study conducted in Sweden showed that wooded rural scenes were much more effective than treeless urban scenes in sustaining people’s interest and the rural scenes tended to result in a lower level of sadness and fear.
6. Trees and shrubs can be effective in absorbing traffic noise, particularly where foliage and branches extend to the ground, like a hedge.
7. In this increasingly man-made and man-modified world, roadside trees and woodlands can bring the natural environment closer to residents, road users, and pedestrians walking beside the road. This contact with nature is increasingly considered to be important for keeping our urban existence in context and for keeping in touch with the passage of time and seasons.
8. Trees and woodlands provide a home for wildlife such as birds, insects, spiders, and squirrels. Bats will use hedgerow trees to help orientate them to their food hunting grounds. Wildlife can find food and shelter in woodlands. Native tree and shrub species are particularly good at providing insect food and serving as an important link in the natural food chain.
9. Roadside trees can provide shelter from the extremes of frost, wind, rain, and snow on roads, making the road safer to use in bad weather. Sometimes trees can be used as a “snow fence” to prevent snow drifts on the street and sometimes trees can be set back to allow the sun to melt the snow and ice quickly.
10. Roadside tree roots bind the soil together and reduce the effect of surface water runoff from fields and hard impervious surfaces such as roads, buildings, and parking lots. Roots will help hold embankments together adjacent to roads which are particularly vulnerable to land slides or soil erosion in heavy rain conditions.
Fred Conacher is a tree consultant and forester in Angus, Scotland, UK
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 0.5 Cat. 1-CF for every five 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 and/or SAF. If you are a member of ISA and SAF we will report your passing test scores to both for no additional cost. Please be sure to add both of your certification numbers when you sign in. 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.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA members may submit your ISA certification record to the ASCA and receive credits one for one.
MTOA members must follow the ISA instructions indicated above.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment online 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.
When you have finished answering all questions you will be prompted to click ‘next’ to send your answers to gibneyCE.com. You can then click ‘next’ to view your test summary. A test review of your answers is available upon request.
All passing test scores are 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 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 your answers' response.
The State of our Urban Forests
By Rick W. Harper
In many areas of the United States today, citizens enjoy larger, more forest-covered tracts of land than they did 100 years ago! There are a number of significant reasons for this. One important and obvious factor is that we have largely shifted away from what was once a predominantly agrarian/local resource-based economy and we have moved to a more urban – suburban way of life. Many of our goods and services now come from other parts of the country and other parts of the world.
Additionally, during the last century our communities themselves have become more “wooded” or shaded under an urban canopy tree cover from tree planting efforts that took place in the middle of the last century. The city of Oakland CA, for example, only featured a 2% canopy cover in 1850. Today, Oakland and other large cities like New York, enjoy a 20% to 30%+ urban tree canopy cover. It is presently estimated that Massachusetts has an inventory of over 1 million street trees with a relatively large proportion of canopy cover in the three largest cities: Boston with 29% cover, Worcester at 37%, and Springfield with 33%.
In addition to our urban areas being more forested, more people now actually live in urban settings. In 2011 it was determined by the US census that about 80% of the population lives in or immediately around an urban area; a century ago it was less than 5%. As with any situation, there are of course benefits and perils that come with this lifestyle where large numbers of people, along with our cars and buildings are now “living among the trees”.
Forest Decline
It is no understatement to say that trees are indeed presented with very challenging growing conditions in the built environment. A relatively recent US Forest Service study presented the state of our urban forests. In looking at 20 cities across the US, this study found that the urban tree cover since the 1960's, 70's, and 80's is now actually declining at an alarming rate of almost 20,000 acres (7900 ha) per year. On a per-tree basis, that equates to about 4 million trees being lost every 12 months!
Tree cover in 17 of the 20 cities analyzed in the study declined, while 16 cities saw significant increases of impervious cover in the form of paved areas and rooftops. This is rather troublesome since not only will there be increasingly fewer trees left to help intercept and mitigate stormwater runoff, the increase of impervious surfaces will make urban stormwater management even more challenging in the future.
Challenges to Tree Growth
When a tree is established, it is important to remember that even with routine maintenance the journey may not be an easy one. According to recent research, important factors like invasive insects and diseases and competition for useable space, above and below ground, may ultimately dictate the survival rates of our urban trees.
Soil compaction is generally considered to be one of the most important factors limiting a tree’s ability to develop a healthy, well-functioning root system. Since healthy roots are essential to a healthy tree “above-ground”, this is an important challenge. It is also important to note, however, that great strides have been made to increase the amount of useable soil in the built environment through the invention and use of techniques like engineered structural soils and suspended paving systems.
Although the benefits associated with larger trees tend to be greater, they can also present a threat to property and life, especially during a high-wind or storm event. Urban trees may be more prone to losing limbs or complete structural failure as they age. We also know that with every new and exciting tree planting event comes the responsibility to perform follow-up care and assessments or inspections. Trees are like any other investment, they require patience and routine maintenance. Failure to take these important steps early in the life of a newly established urban tree may result in a situation that necessitates a more acute intervention in the future, possibly requiring a substantially larger investment of time and money.
Finally, the study touched on the generally aging state of our urban trees and the role this could be playing in the overall decline of our urban tree populations. It is important to note that diversity, both from an age standpoint and tree species standpoint, is seriously lacking in the composition of many of our urban tree populations. In some of the Northeastern states (NY, CT, MA), maple trees (Acer spp.) constitute between 40%-50% of the urban tree genera, with the major species being Norway maple (Acer platanoides). Not only does this exceed best management practices that tend to recommend establishment of no more than 10% of a species and 20% of a genus in a given urban tree population, the practical matter is that a serious pest-outbreak may not only threaten a few trees, but indeed possibly up to half of our urban trees could be killed.
Forest Benefits
Our understanding relative to the overall benefits of trees has increased significantly in recent years. For example, we now know that urban trees provide a return that is as much as three times greater than the costs associated with establishing and maintaining them. A typical urban tree can provide as much as US$2,500 in environmental benefits including carbon sequestration and reduced heating and cooling costs over its lifespan, and the total value of air pollution removed by urban trees in the US is estimated at $3.8 billion.
Furthermore, we know that citizens feel passionately about the well-being of their urban trees/urban green spaces and that the health of the urban forests can actually be linked to the well-being of the community’s economy and the health of the citizens living there.
Optimistic Future
There are many local plans in the works to halt the urban tree decline and increase tree populations and canopy cover across the nation. With all of this said, probably one of the most important mechanisms we have regarding the care of our urban trees is citizen involvement. Volunteer-based shade tree committees continue to play an ever-increasingly active role in the care of local community trees. Citizens should become educated and get involved. To use the expression from Margaret Mead: "Never doubt that a small group of thoughtful, committed citizens can change the world; indeed, it's the only thing that ever has."
Sources
- Personal communications: Bloniarz, D.V. 2012. Urban Natural Resources Institute, USDA Forest Service, Cowett, F., and N.L Bassuk, 2013. Urban Horticulture Institute at Cornell University. Cornell University Department of Horticulture, Ithaca NY.
- Cumming, A.B., D.B. Twardus, and W.D. Smith. 2006. “Maryland and Massachusetts Street Tree Monitoring Pilot Projects”. Northeastern Area State and Private Forestry. Newtown Square, PA.
NA-FR-01-06 - Donovan, G.H., D. T. Butry, Y.L. Michael, J.P. Prestemon, A.M. Liebhold, D.Gatziolis and M.Y. Mao. 2013. “The relationship between trees and human health: Evidence from the spread of the Emerald Ash Borer”. American Journal of Preventative Medicine 44(2):139-145.
- McPherson, E.G., J.R. Simpson, P.J. Peper, S.L. Gardner, K.E. Vargas, and Q. Xiao. 2007. “Northeast
community tree guide: benefits, costs, and strategic planting”. Gen. Tech. Rep. PSW-GTR-202. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. 106 pp. - Nowak, D.J., D.E. Crane, J.C. Stevens. 2006. “Air pollution removal by urban trees and shrubs in the United States”. Urban Forestry & Urban Greening. 4, 115-123.
- Nowak, D.J. and E.J. Greenfield. 2012. “Tree and impervious cover change in U.S. Cities”. Urban
Forestry & Urban Greening. 11(1):115-123. - Shroeder, H., J. Flannigan, and R. Coles. 2006. “Residents’ attitudes toward street trees in the UK and US communities”. Arboriculture &Urban Forestry. 32(5):236–246.
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 0.5 Cat. 1-CF for every five 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 and/or SAF. If you are a member of ISA and SAF we will report your passing test scores to both for no additional cost. Please be sure to add both of your certification numbers when you sign in. 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.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA members may submit your ISA certification record to the ASCA and receive credits one for one.
MTOA members must follow the ISA instructions indicated above.
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Cultivars of Sweet Gum
By Len Phillips
Sweet Gum, Liquidambar styraciflua, has dark green summer foliage and autumn colors that range from yellow, to orange, to pink, to red, to burgundy, and to purple, depending on the cultivar. The following comments pertain to all of the cultivars mentioned in the lower half of this article.
Common Name: American Sweetgum
Botanical Name: Liquidambar styraciflua
Family: Hamamelidaceae
Parentage: Native to the eastern half of the United States
Year of Introduction: Became cultivated in 1681
Size: Depends on the cultivar, up to 120' high in the wild
Flower: Green to yellow
Fruit: Round brownish balls covered with large thorns
Foliage: See comments on cultivars below
Winter Color: Interest in bark and form
Bark: Covered with characteristic corky projections, thornless
Habitat: All of North America except upper Midwest and Rocky Mountains
Culture: Well drained soil, acidic is best, moderate drought and flood tolerance
Site Requirements: Full sun to part shade
Growth Rate: Fast, 2 to 3 ft. a year
Pest Resistance: Pest free but hosts non-damaging insects
Storm Resistance: Excellent
Salt Resistance: Good
Planting: Transplant B&B, bare root, or container only when tree is young, tolerates CU-Structural Soil planting
Pruning: Prune for clearance and single leader
Propagating: Budding, grafting, softwood cuttings in summer
Design Uses: Useful in wide planting areas, parking lots, open spaces, highway medians
Companions: Shallow roots so mulch is best companion
Of the approximately 20 known cultivars, only the following are currently available at selected nurseries.
Emerald Sentinel® Sweetgum Liquidambar styraciflua ‘Clydesform’ PP 10676 – Zone: 5 – 9, Height: 30, Spread: 12', Shape: Narrowly pyramidal to columnar, Foliage: Dark green, Fall Color: Yellow orange to orange. Narrow and compact, with sturdy upright branches, this tree is ideal for busy city streets. Slower growing than most sweetgum, it is valued for not outgrowing its space. Fact Sheet
Gold Dust® Sweetgum Liquidambar styraciflua ‘Goduzam’ – Zone: 5 – 9, Height: 45', Spread: 30', Shape: Broadly pyramidal becoming rounded oval, Foliage: Green with gold specks, Fall Color: Pink, yellow, and burgundy tints mixed. Speckles of yellow appear like gold dust on the sharply pointed, glossy green leaves of this variegated Sweetgum. New growth is splashed with pinkish tones. Fall colors include pink, yellow, and burgundy tints. Fact Sheet
Moraine Sweetgum Liquidambar styraciflua ‘Moraine’ – Zone: 4 – 9, Height: 40’, Spread: 25’, Shape: Pyramidal, Foliage: Dark green, Fall Color: Burgundy-red. This is widely considered the most cold hardy of the sweetgum cultivars, reliably growing further north than other selections. Foliage is darker green, and habit is more compact than others. Fact Sheet
Rotundiloba Sweetgum Liquidambar styraciflua ‘Rotundiloba’ – Zone: 5 – 9, Height: 45', Spread: 25', Shape: Pyramidal, Foliage: Bright green, rounded lobes, Fall Color: Orange to purple, Fruit: Fruitless. This is the only Sweetgum known to be entirely fruitless. The foliage is completely unique among sweetgum cultivars, with smooth, rounded lobes. Fact Sheet
Slender Silhouette Sweetgum Liquidambar styraciflua ‘Slender Silhouette’ – Zone: 5 – 9, Height: 60’, Spread: 8’, Shape: Tightly columnar, Foliage: Dark green, Fall Color: Orange to burgundy. This fastigiate tree grows quickly to form a tall, strikingly narrow column. One of the tightest and narrowest trees available, it is easier to grow than most. Those grown as hedges quickly become an effective visual screen, while single specimens mature to become landscape exclamation points. Fact Sheet
Worplesdon Sweetgum Liquidambar styraciflua ‘Worplesdon' – Zone: 6 – 10, Height: 40’, Spread: 25’, Shape: Broadly pyramidal to oval, Foliage: Green, Fall Color: Orange and purple. Consistently provides good fall color in the Pacific Northwest. Each of the lobes of the leaf is divided into additional lobes, giving the foliage a unique appearance. Fact Sheet
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 0.5 Cat. 1-CF for every five 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 and/or SAF. If you are a member of ISA and SAF we will report your passing test scores to both for no additional cost. Please be sure to add both of your certification numbers when you sign in. Tests with passing scores may be submitted only once to each organization.
*Members of ISA may apply the .5 CEUs toward Certified Arborist, Utility Specialist, Municipal Specialist, Tree Worker Specialist, Aerial Lift Specialist, or BCMA practice credits.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA members may submit your ISA certification record to the ASCA and receive credits one for one.
MTOA members must follow the ISA instructions indicated above.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment online 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.
When you have finished answering all questions you will be prompted to click ‘next’ to send your answers to gibneyCE.com. You can then click ‘next’ to view your test summary. A test review of your answers is available upon request.
All passing test scores are 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 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 your answers' response.
What is Wrong with Urban Soil
By Mike Amaranthus, Ph.D.
Today’s modern urban landscape is a far cry from the native forests that were once spread widely around our globe. Today’s urban landscape faces many threats to the health of trees. These threats include a shortage of organic matter in the soil, compaction, poor soil drainage, disease, erosion, unstable pH, and impermeable crusted soil surface are definitely not the conditions that trees faced in their native forest habitats.
How did trees in the forests attain great ages, heights and diameters, without irrigation, fertilizers, and pesticides? The answer is that soils in undisturbed native forests contain a wide range of beneficial organisms that soils in urban landscapes lack. Probably the most important of these, and the most studied group of beneficial soil organisms are the mycorrhizal fungi. Mycorrhizae, pronounced my-co-RISE-ee which literally meaning - fungus “myco” and root “rhiza”, is a symbiotic (mutually beneficial) relationship between tree roots and certain specialized soil fungi. All known tree species form a mycorrhizal relationship in their native habitats.
For the last 20 years, scientists have been intensely studying these tiny soil organisms that are changing the way arborists think about planting and managing trees.
Ancient Plants
Our landscapes have not always been alive. Back 460 million years ago, there were no plants covering the earth’s land surface. The land was a barren and lifeless surface. Plants only existed in lakes and seas and lacked the elaborate root structure they needed to conquer the harsh conditions on the land.
Then a specialized fungus entered the primitive root of an aquatic plant. The fungal thread secured its energy source from the plant and in return, the fungal filaments explored and mined the harsh earth’s surface. The plant acquired the needed nutrients and water to sustain life from the fungus. The resulting evolutionary leap allowed plants to inhabit the land surface and that has shaped life as we know it today.
The mycorrhizal and plant relationship not only still exists today, but has also become one of the most successful relationships on earth. Today, approximately 90% of the world’s plant species form the mycorrhizal and plant relationship in varied natural habitats everywhere.
Mycorrhizae Function
Mycorrhizal spores (seeds) germinate in response to root activity and penetrate in or around the inside of the root cells. Then they send their filaments (called mycelium) into the surrounding soil, effectively extending the tree’s roots and root absorbing capacity from ten to several thousand times. This is far beyond what the tree can do alone and this improves a tree's establishment and productivity.
Several miles of these ultra-fine filaments can be present in less than a teaspoon of soil. Mycorrhizal fungi supply the water and nutrients needed by the tree for establishment and survival, and in return, receive from the tree roots, sugars and other compounds needed by the fungus. Mycorrhizal filaments are much smaller than roots, so they can easily penetrate into smaller spaces between soil particles.
In the small nooks and crannies of soil, these tiny filaments release powerful enzymes that dissolve tightly bound minerals such as phosphorus, sulfur, iron and all the major and minor nutrients used by trees. The nutrients are organically assimilated by the mycorrhizae and become readily available for use by the trees.
Mycorrhizae provide many other benefits to trees. Tree roots are too thick to access the small pores that retain large amounts of water in the soil. The much thinner mycorrhizal mycelium easily penetrate into smaller spaces between soil particles to take in, store, and provide essential water to the tree during periods of moisture deficit.
The fungal mycelium also bind soil particles into larger aggregates with organic glues such as humic compounds. The resulting soil structure allows air and water movement into the soil, encouraging root growth and distribution.
Need for Mycorrhizae
Natural, undisturbed areas are teeming with a wide variety of mycorrhizal fungi. These areas have reached tremendous productivity and stability without chemical fertilizers, irrigation, and pesticides. Healthy living soils conserve water and nutrients while protecting the trees against stress and environmental extremes.
For a tree to achieve the benefits of the mycorrhizal relationship, they need to be present at the planting site. Most of our man-made environments were built using practices that destroy the soil conditions supportive of beneficial soil organisms. Studies have documented that in highly disturbed environments, trees have not formed mycorrhizal relationships after planting and are subject to greater levels of stress and mortality. Vegetation removal, compaction, erosion, grading, topsoil removal, paving, pollution, over watering, and the use of certain chemicals are just some of the practices that adversely affect mycorrhizal fungi. These conditions are definitely not the conditions that trees faced in their natural forest environments.
Mycorrhizae Application
How do you re-establish mycorrhizal fungi once they have been lost from a site? Recent advancements in our understanding of mycorrhizal fungi and their requirements have led to the production of high-quality, economical mycorrhizal inoculums at affordable prices. Mycorrhizal inoculums are currently available in granular, powder, liquid, and tablet forms.
The most important factor for re-integrating mycorrhizae is to get the mycorrhizal propagules near the root systems of the target trees. Inoculum can be incorporated into the hole at the time of planting, watered into porous soils, mixed into soil mixes, or dipped directly onto the roots of bare root trees using gels. The form and application of the mycorrhizal inoculum depends upon the needs of the applicator. What is clear is that on construction and stressed sites, inoculation is highly effective.
If you are planning to add mycorrhizal fungi back to areas where they have been lost, make sure you use products that have a wide variety of species. Not all mycorrhizal fungi are created equal. They have different capacities and tolerances. For example, some have differing abilities to protect trees from drought. Still others are better at producing enzymes that facilitate mineral uptake such as phosphorous, iron, and other minerals. Some mycorrhizal fungi can access organic forms of nitrogen.
Soil Deserves Respect
Disturbance activities and the widespread use of conventional fertilizers and pesticides have resulted in detrimental effects on our soils and environment. Impacts include high levels of run-off, erosion, compaction, contamination of lakes, streams, and groundwater, salt accumulation, and loss of soil structure.
An attractive tool to diminish the environmental and dollar costs of these activities is to use mycorrhizal fungi as a natural tree growth stimulant. Using mycorrhizal fungi to establish and grow trees is borrowing from nature’s template. Natural, undisturbed areas are teeming with a wide variety of mycorrhizae. Many of these natural forest ecosystems are the most stable and productive on earth, achieving great tree productivity and longevity without irrigation, fertilization, or the use of pesticides.
A healthy, robust, living soil conserves, transforms, and utilizes soil nutrients and water and protects trees from unhealthy soils and environmental extremes. The key for the arborist is to recognize that soil is alive and deserving to be treated like the precious resource it is.
Mike Amaranthus, Ph.D.,is president and chief scientist for Mycorrhizal Applications Inc.
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 0.5 Cat. 1-CF for every five 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 and/or SAF. If you are a member of ISA and SAF we will report your passing test scores to both for no additional cost. Please be sure to add both of your certification numbers when you sign in. Tests with passing scores may be submitted only once to each organization.
*Members of ISA may apply the .5 CEUs toward Certified Arborist, Utility Specialist, Municipal Specialist, Tree Worker Specialist, Aerial Lift Specialist, or BCMA science credits.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA members may submit your ISA certification record to the ASCA and receive credits one for one.
MTOA members must follow the ISA instructions indicated above.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment online 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.
When you have finished answering all questions you will be prompted to click ‘next’ to send your answers to gibneyCE.com. You can then click ‘next’ to view your test summary. A test review of your answers is available upon request.
All passing test scores are 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 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 your answers' response.
Research Briefs #55
Edited by Len Phillips
How Community Group Dynamics Affect Urban Street Tree Growth
Emily Jack-Scott, Max Piana, Blake Troxel, Colleen Murphy-Dunning, and Mark S. Ashton
Over the last two decades, there has been a substantial increase in street tree plantings in major cities across the United States. Many cities have set ambitious planting goals, relying on volunteer community groups to plant the trees. Existing research demonstrates that community stewardship increases the survival of urban street trees. There is a lack of research, however, on how defining characteristics of community groups affect the survival and growth of the trees they plant. This study explores the significance of community group size (# participants), type (apartment, block watch, church, concerned neighbors, park, public housing, school, and social service), planting longevity (# years active), experience level (# trees planted), and neighborhood (geo-political boundaries).
Measured for this study were 1393 trees planted from 1995 to 2007, by 134 groups, through the Urban Resources Initiative’s Community Greenspace program in New Haven, Connecticut, U.S. There was an overall survival rate of 76%. Highest survival and growth was found among trees planted by groups with more planting experience, greater longevity, and more participants. Higher tree survival and growth was observed when trees were planted by groups working in line with their mission (e.g., park groups in working in parks). Lowest survival and growth was found among yard trees planted by public housing groups. Existing canopy cover and neighborhood percent of home ownership had little effect on survival or growth. This research can offer guidance for city managers by suggesting which planting groups require particular or extra assistance in conducting successful, lasting street tree plantings.
Arboriculture & Urban Forestry 2013. 39(4): 189–196
Shading Effectiveness of Street Trees
David Armson, Mohammad Asrafur Rahman, and Anthony Roland Ennos
One major benefit of urban trees is the shade they provide on sunny days. The shade reduces the heat stored in engineered surfaces and lowers the heat load on people, increasing their comfort. This study compared the shading effectiveness of five small street tree species within the urban landscape. The area of shade produced by each tree during early and midsummer was calculated from morphological measurements, such as canopy height, width, and aspect ratio. The effect of tree shade on air, mean radiant, and surface temperatures was also compared and related to the leaf area index (LAI) of the canopy.
It was found that tree shade reduced mean radiant temperatures by an average of 4°C, regardless of tree species and LAI. Tree shade reduced surface temperatures by an average of 12°C, and the tree species and LAI both had significant effects. Tree species with higher LAI, Crataegus laevigata and Pyrus calleryana, provided significantly more cooling than the other species, and surface temperature reduction was positively correlated with LAI. This study has shown that trees are useful in improving both human thermal comfort and reducing surface temperatures in urban areas, and that selection of tree species with high LAI can maximize the benefits they provide.
Arboriculture & Urban Forestry 2013. 39(4): 157–164
Impact of Tree Size and Container Volume at Planting
Edward F. Gilman, Jason Miesbauer, Chris Harchick, and Richard C. Beeson
Some trees uproot in storms apparently due to root deflections that occurred during nursery production. Root deflection in a nursery container may lead to poor anchorage because of insufficient root growth into the landscape soil, and container volume/tree size at planting may also influence root deflection. This study was designed to evaluate establishment, root growth, and anchorage six years after planting Acer rubrum trees of four different sizes from four corresponding container volumes and maintaining them with two irrigation regimes. The impact of mulch on establishment and root growth was also evaluated.
Trees from the largest containers grew slowest in the first three years due primarily to water stress. Trunk tilt during winching tests increased due to greater root deflection, less mass of the root-soil plate, and reduced root growth into the landscape soil with increasing container volume and tree size. In contrast to the poorly anchored larger trees that had most of their large roots retained in the original planted root ball volume, the largest roots on trees from smaller containers grew freely into landscape soil. This resulted in stable trees with many stiff, straight roots pushing down against mineral landscape soil outside the root ball. Trees planted from smaller containers appear to anchor sooner than trees from larger containers and would be more stable in a storm.
Arboriculture & Urban Forestry 2013. 39(4): 173–181
Shoot Growth of Trees From Five Different Production Methods
Anna Levinsson
After transplanting, many trees enter a period of reduced growth that may limit their environmental and aesthetic benefits for several years. A number of nursery production methods have been developed in an attempt to reduce root disturbance, which often causes reduced growth. The main objective of this study was to investigate how five nursery production methods affect root systems and post-transplant shoot growth. Other objectives in the study were of the effect of root structure (i.e., fibrous verses coarse) on trees’ response to different production methods and the effect of the conditions at the transplanting site. Sweet cherry (Prunus avium L.) and red oak (Quercus rubra L.) with a stem circumference of 16–18 cm (6.5 – 7 in) or 6 cm (2 in) in diameter were produced as bare-rooted, balled and burlapped, root-pruned, air-potted, or fabric container grown trees, transplanted at two sites and studied for five seasons.
Visual analysis showed that the production methods had an effect on the root balls at transplanting. However, the differences were not clearly related to shoot growth. All transplanted red oaks, regardless of production method, showed significantly reduced shoot growth compared to pre-transplant growth. Balled and burlapped, root-pruned, and fabric container-grown sweet cherry trees exhibited restored pre-transplant shoot growth three years after transplanting at the more favorable site. The results suggest that the fibrous-rooted sweet cherry was more responsive to production methods designed to reduce transplanting stress than the coarse-rooted red oak, and that site affected the time required for normal shoot growth to be regained. The results do not indicate that different sites require differently produced trees.
Arboriculture & Urban Forestry 2013. 39(5): 201–210
Lawn Gone
Sarah Bergmann
Most parks have plenty of plants that provide pollen for various birds and insects. A study was performed to see if the pollinators would travel from Seattle University campus to a park one mile away along a series of residential gardens planted in the tree lawn or boulevard between the street and sidewalk. The owners of the properties along this corridor of gardens were persuaded to remove their turf and maintain the replacements of pollinator-friendly plants. The gardens were planted by volunteers and homeowners using a plant list supplied by Pollinator Pathway in Seattle. A similar project is being conducted in Portland OR as part of a Portland Urban Meadowscaping Pilot project.
The results have been a two-fold success. First of all, the residents along this corridor are accepting the idea that boulevards do not have to be turfgrass. Second, birds, bees, and butterflies that are all vital to plant reproduction are actually following the linkage.
Landscape Architecture September 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 0.5 Cat. 1-CF for every five 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 and/or SAF. If you are a member of ISA and SAF we will report your passing test scores to both for no additional cost. Please be sure to add both of your certification numbers when you sign in. 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.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA members may submit your ISA certification record to the ASCA and receive credits one for one.
MTOA members must follow the ISA instructions indicated above.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment online 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.
When you have finished answering all questions you will be prompted to click ‘next’ to send your answers to gibneyCE.com. You can then click ‘next’ to view your test summary. A test review of your answers is available upon request.
All passing test scores are 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 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 your answers' response.