LA Course #GCE-1-1904
Note: Click on green text in each section for photos.
A Tree Preservation Case Study
by Richard W. Gibney RLA - ISA
In October 2003, we were called by the landscape architecture firm TPA Design Group to inspect two large Copper Beech trees (Fagus sylvatica ‘Atropunicea’) adjacent to a school that was going to be enlarged in two years. The call was to determine if these trees were worth preserving.
Construction of a new addition to the school was anticipated in 2005. The Copper Beeches were matching 38” (95 cm) caliper trees set symmetrically on either side of a wide concrete entrance walkway that would be converted to an ‘exterior hallway’ connecting the existing structure to the new building, thus forming an “H” shaped complex with the trees in each of the three sided courtyards. Excavations would be necessary on two sides of each tree and well into their root zones. Fortunately, about 70% of the root zones would be left undisturbed. We estimated the age of the trees was more than 60 years old. One of the Beech trees was chlorotic and appeared to be lacking the nutrients that the other was getting. It also had several trunk defects that needed further investigation.
We inspected the trees on site, took soil samples, and sent photographs and bark samples of the trees to Cornell University. Cornell’s plant pathology department confirmed that no dangerous pathogens, especially Phytophthora, were present and that the health and vigor of these trees should help them survive a construction project if properly executed. Soil samples revealed that the available nutrients were low and pH was extremely low (4.8). We recommended nutrient amendments using organic products and the addition of dolomitic limestone as soon as possible. The aim was to get the pH up to 5.3 or higher for optimum nutrient absorption by the trees. Several applications over time would accomplish this. While many tree species are tough enough to survive adjacent construction, Beech trees are especially sensitive to root damage.
In October 2004 we provided complete specifications for the protection of the Beeches that included fencing which limited activity surrounding the trees with a total avoidance of activity in the root zone. We recommended the AirSpade® trenching inside the proposed zone of excavation for the new construction would be done in two phases: 10 feet (3 m) long by 18 inch (0.5 m) deep trenches set 10 feet apart in the fall and trenching of the remaining 10 foot areas in the spring. As trenches were made, roots would be cut cleanly. The trenches would be backfilled with clean compost and irrigated.
The ideal critical root zone (CRZ) for these trees would have been a 76 foot (21 m) diameter circle, however, construction was to take place well within that zone on two sides of each tree. We were able to protect what might be referred to as the interior CRZ which was about half the ideal CRZ. The size and health of these trees made wind failure a consideration but the adjacent building and proposed extension would provide excellent wind protection on three sides of both trees.
The interior CRZ was covered with 0.5 inches (1.27 cm) of compost followed by a 2 inch (5.08 cm) layer of shredded bark mulch. Autumn leaf drop was shredded and added to the compost. Irrigation was specified to be applied as needed to keep the root zone moist before and during construction. One foot around the root flare was left alone to allow for oxygen exchange and so not to encourage epicormic roots or shoots.
Fortunately for the trees, controversy surrounding the project created a one-year construction delay. This allowed the root pruning project to “rest” for a year so that new roots had the opportunity to develop. The construction eventually took place from late 2005 through 2006.
Care was taken to erect a 6 foot high (1.83 m) chain link fence around the CRZ prior to construction and was left in place throughout the construction period. Every worker on the project was informed of the goal to preserve these trees. We specified that all the AirSpade® and remedial work was to be done by an ISA Certified Arborist®. The client complied and hired a leading tree care company that employed arborists with ISA credentials. Strong recommendations were made for aftercare, irrigation and follow-up soil testing for the trees. Again, the client complied.
In addition to the fencing, signs were hung on the fence stating what was taking place and instructing all workers on the site to respect the boundaries set up to protect the trees. They also served to inform the public of our client’s intentions to preserve these valuable local assets. The trees remained protected by fencing throughout the construction project and they were visited and inspected by the arborist on a regular basis to check on irrigation and fence integrity.
The overall cost for the tree preservation project exceeded $15,000 USD and the two priceless trees are thriving as a result. These trees now occupy the two open courtyards within the “H” shaped building where the students can look out the windows to see the magnificence of the Copper Beech.
We have received communications from school personnel and one particular parent of a student thanking us for the efforts and expressing what a great asset these trees are to the school's aesthetics, environmental education programs and the overall well-being of the teachers and students. We received photographs annually.
Steps for the Successful Preservation of Trees During and After Construction
- Plans that are developed for construction around valuable trees should take into consideration the trees’ critical root zones (CRZ) which is a circle around the tree with a radius of 1 foot per inch (30 cm per 2.5 cm) of tree caliper. The more this CRZ is compromised, the lower the chances of tree survival.
- All trees in the vicinity of the construction site should be inspected for health and vitality prior to determining which trees are valuable enough to be properly preserved.
- Trees under 9 inch (24 cm) caliper can often be transplanted using an AirSpade® (or tree spade or hand digging) on or off site as a method of preservation. Trees larger than this would require special equipment, higher cost and longer after care. The costs of transplanting must be weighed against the value of the tree(s) and the developer’s budget.
- When root damage is inevitable, the arborist or LA must consider the possibility of tree failure not only due to root loss but failure caused by wind and lack of soil support. Tree support system(s) and root stabilization might be employed and kept in place temporarily after construction and until it can be determined that the tree is showing healthy new growth. This could be up to three years or more, although root stabilizers can be left in place forever.
- Once tree preservation is determined to be a worthy goal, the root system should be protected from that moment until after construction. If the entire CRZ cannot be protected, it is advisable to root prune the tree at the closest point outside of the proposed excavation and site disturbance (grading, cutting, filling, stockpiling, etc.)
- Erection of a sturdy barrier outside the CRZ and/or outside the root pruning trench prior to any construction activity is essential. Six feet (2 m) high chain link fencing is ideal.
- Soil amendments for proper nutrient balance and optimum pH for the species will promote new, healthy root growth.
- Lightly mulching the CRZ and providing irrigation during dry spells is highly recommended.
- It is vital to inform everyone involved in the construction project to be aware of the tree preservation efforts.
- No activity is to take place inside the CRZ. This includes vehicle activity, parking, cleaning of equipment, supply storage, portable toilets, seating for breaks, etc.
- Fencing can only be removed after the construction and all site activity is completed.
- Tree health should be monitored for several years after construction activity by a qualified arborist. A minimum of two visits annually could determine the onset of any pest or health problems that might be mitigated.
Richard W. Gibney is a NYS Registered Landscape Architect and ISA Certified Arborist for over three decades.
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.
LA CES will award 1.0 PDH (HSW) credit for a passing grade. New Jersey Board of Architects and North Carolina Board of LA will award 1.0 credits for a passing grade.
The cost for taking this test is $20 per credit. If you purchase an annual subscription for 12 credits, the cost per credit is reduced by 50% (see Annual Subscription link below). We will report your passing test score to LA CES. If you are also ISA* certified we will report your passing score to ISA for no additional cost. Please be sure to add your ISA Certification number when you sign in. Tests with passing scores may be submitted only once to each organization.
*ISA has approved this course for .5 CEUs applied towards Certified Arborist, Municipal Specialist, or BCMA management credits.
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 Merchant' / gibneyCE.com. That will take you to the test sign in page followed by the test. If you are an ISA and/or CLARB member, please be sure to include your certification/member number(s) along with your LA license and ASLA numbers.
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. 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.
Test re-takes are allowed, however you will have to pay for the retake if you are using the pay per test option.
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.
LA CES maintains a record of earned PDH credits on their website http://laces.asla.org/
ISA maintains a record of earned CEU credits on their website http://www.isa-arbor.com/
Note: Click on green text in each section for photos.
A Tree Preservation Case Study
by Richard W. Gibney RLA - ISA
In October 2003, we were called by the landscape architecture firm TPA Design Group to inspect two large Copper Beech trees (Fagus sylvatica ‘Atropunicea’) adjacent to a school that was going to be enlarged in two years. The call was to determine if these trees were worth preserving.
Construction of a new addition to the school was anticipated in 2005. The Copper Beeches were matching 38” (95 cm) caliper trees set symmetrically on either side of a wide concrete entrance walkway that would be converted to an ‘exterior hallway’ connecting the existing structure to the new building, thus forming an “H” shaped complex with the trees in each of the three sided courtyards. Excavations would be necessary on two sides of each tree and well into their root zones. Fortunately, about 70% of the root zones would be left undisturbed. We estimated the age of the trees was more than 60 years old. One of the Beech trees was chlorotic and appeared to be lacking the nutrients that the other was getting. It also had several trunk defects that needed further investigation.
We inspected the trees on site, took soil samples, and sent photographs and bark samples of the trees to Cornell University. Cornell’s plant pathology department confirmed that no dangerous pathogens, especially Phytophthora, were present and that the health and vigor of these trees should help them survive a construction project if properly executed. Soil samples revealed that the available nutrients were low and pH was extremely low (4.8). We recommended nutrient amendments using organic products and the addition of dolomitic limestone as soon as possible. The aim was to get the pH up to 5.3 or higher for optimum nutrient absorption by the trees. Several applications over time would accomplish this. While many tree species are tough enough to survive adjacent construction, Beech trees are especially sensitive to root damage.
In October 2004 we provided complete specifications for the protection of the Beeches that included fencing which limited activity surrounding the trees with a total avoidance of activity in the root zone. We recommended the AirSpade® trenching inside the proposed zone of excavation for the new construction would be done in two phases: 10 feet (3 m) long by 18 inch (0.5 m) deep trenches set 10 feet apart in the fall and trenching of the remaining 10 foot areas in the spring. As trenches were made, roots would be cut cleanly. The trenches would be backfilled with clean compost and irrigated.
The ideal critical root zone (CRZ) for these trees would have been a 76 foot (21 m) diameter circle, however, construction was to take place well within that zone on two sides of each tree. We were able to protect what might be referred to as the interior CRZ which was about half the ideal CRZ. The size and health of these trees made wind failure a consideration but the adjacent building and proposed extension would provide excellent wind protection on three sides of both trees.
The interior CRZ was covered with 0.5 inches (1.27 cm) of compost followed by a 2 inch (5.08 cm) layer of shredded bark mulch. Autumn leaf drop was shredded and added to the compost. Irrigation was specified to be applied as needed to keep the root zone moist before and during construction. One foot around the root flare was left alone to allow for oxygen exchange and so not to encourage epicormic roots or shoots.
Fortunately for the trees, controversy surrounding the project created a one-year construction delay. This allowed the root pruning project to “rest” for a year so that new roots had the opportunity to develop. The construction eventually took place from late 2005 through 2006.
Care was taken to erect a 6 foot high (1.83 m) chain link fence around the CRZ prior to construction and was left in place throughout the construction period. Every worker on the project was informed of the goal to preserve these trees. We specified that all the AirSpade® and remedial work was to be done by an ISA Certified Arborist®. The client complied and hired a leading tree care company that employed arborists with ISA credentials. Strong recommendations were made for aftercare, irrigation and follow-up soil testing for the trees. Again, the client complied.
In addition to the fencing, signs were hung on the fence stating what was taking place and instructing all workers on the site to respect the boundaries set up to protect the trees. They also served to inform the public of our client’s intentions to preserve these valuable local assets. The trees remained protected by fencing throughout the construction project and they were visited and inspected by the arborist on a regular basis to check on irrigation and fence integrity.
The overall cost for the tree preservation project exceeded $15,000 USD and the two priceless trees are thriving as a result. These trees now occupy the two open courtyards within the “H” shaped building where the students can look out the windows to see the magnificence of the Copper Beech.
We have received communications from school personnel and one particular parent of a student thanking us for the efforts and expressing what a great asset these trees are to the school's aesthetics, environmental education programs and the overall well-being of the teachers and students. We received photographs annually.
Steps for the Successful Preservation of Trees During and After Construction
- Plans that are developed for construction around valuable trees should take into consideration the trees’ critical root zones (CRZ) which is a circle around the tree with a radius of 1 foot per inch (30 cm per 2.5 cm) of tree caliper. The more this CRZ is compromised, the lower the chances of tree survival.
- All trees in the vicinity of the construction site should be inspected for health and vitality prior to determining which trees are valuable enough to be properly preserved.
- Trees under 9 inch (24 cm) caliper can often be transplanted using an AirSpade® (or tree spade or hand digging) on or off site as a method of preservation. Trees larger than this would require special equipment, higher cost and longer after care. The costs of transplanting must be weighed against the value of the tree(s) and the developer’s budget.
- When root damage is inevitable, the arborist or LA must consider the possibility of tree failure not only due to root loss but failure caused by wind and lack of soil support. Tree support system(s) and root stabilization might be employed and kept in place temporarily after construction and until it can be determined that the tree is showing healthy new growth. This could be up to three years or more, although root stabilizers can be left in place forever.
- Once tree preservation is determined to be a worthy goal, the root system should be protected from that moment until after construction. If the entire CRZ cannot be protected, it is advisable to root prune the tree at the closest point outside of the proposed excavation and site disturbance (grading, cutting, filling, stockpiling, etc.)
- Erection of a sturdy barrier outside the CRZ and/or outside the root pruning trench prior to any construction activity is essential. Six feet (2 m) high chain link fencing is ideal.
- Soil amendments for proper nutrient balance and optimum pH for the species will promote new, healthy root growth.
- Lightly mulching the CRZ and providing irrigation during dry spells is highly recommended.
- It is vital to inform everyone involved in the construction project to be aware of the tree preservation efforts.
- No activity is to take place inside the CRZ. This includes vehicle activity, parking, cleaning of equipment, supply storage, portable toilets, seating for breaks, etc.
- Fencing can only be removed after the construction and all site activity is completed.
- Tree health should be monitored for several years after construction activity by a qualified arborist. A minimum of two visits annually could determine the onset of any pest or health problems that might be mitigated.
Richard W. Gibney is a NYS Registered Landscape Architect and ISA Certified Arborist for over three decades.
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.
LA CES will award 1.0 PDH (HSW) credit for a passing grade. New Jersey Board of Architects and North Carolina Board of LA will award 1.0 credits for a passing grade.
The cost for taking this test is $20 per credit. If you purchase an annual subscription for 12 credits, the cost per credit is reduced by 50% (see Annual Subscription link below). We will report your passing test score to LA CES. If you are also ISA* certified we will report your passing score to ISA for no additional cost. Please be sure to add your ISA Certification number when you sign in. Tests with passing scores may be submitted only once to each organization.
*ISA has approved this course for .5 CEUs applied towards Certified Arborist, Municipal Specialist, or BCMA management credits.
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 Merchant' / gibneyCE.com. That will take you to the test sign in page followed by the test. If you are an ISA and/or CLARB member, please be sure to include your certification/member number(s) along with your LA license and ASLA numbers.
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. 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.
Test re-takes are allowed, however you will have to pay for the retake if you are using the pay per test option.
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.
LA CES maintains a record of earned PDH credits on their website http://laces.asla.org/
ISA maintains a record of earned CEU credits on their website http://www.isa-arbor.com/