Moving Large Trees
By Michael P. Mauer
No other feature in a local environment has the effect on the overall well-being of a community than large trees. Not only do they add aesthetic value, but they tirelessly add to the quality of life, health, and welfare of neighborhoods. Trees in park settings further add to community values and provide places of pleasure, recreation, and celebration. The planting of many smaller trees cannot produce the same environmental and economic impact that a single 24-inch caliper shade tree can provide1.
Why transplant a large tree?
- Site integrity—People become used to large trees and become attached to them.
- Historical significance—According to Morton Arboretum studies, a 24-inch caliper oak tree can easily exceed 100 years in age2.
- Environmental benefits—Large trees provide a cooling effect that reduces energy costs, provide a habitat for wildlife, and mitigate erosion3.
- Property values—Large trees can also have a net positive impact on property values, depending on the land use and surrounding neighborhood character3.
The practice of transplanting large trees is not new. In fact, ancient Egyptians practiced the earliest form of tree transplanting. Pictographs that date back 3,500 to 4,000 years and found in the Temple of Hatsheput, UIr-el-Bahri in Thebes show men transporting large Frankincense trees in containers4. Egyptians figured out early on that the larger the tree to be moved, the larger the root ball needs to be. The Davey Tree Company is generally credited with the advent of modern, commercially moved large trees in 19374. In the 1930s and 1940s, equipment limitations made it difficult to excavate, lift, and transport large trees greater than 12 to 15 inches in caliper, which can weigh upwards of 200,000 pounds. Now there are large tree-moving companies in most regions of the country that also have expanded service areas.
The science of large-tree moving has changed little, but what has changed is the physical ability to move trees with larger root balls. As large tree-moving consultants, Environmental Design & Davey Tree recently moved a 65-inchcaliper oak tree with a root ball of 40 feet in diameter, which weighed 1.3-million pounds5. With proper planning by the design team, including the owner, landscape architect, arborist, maintenance crews, and most importantly the tree-moving company, survivability rates can easily exceed 95 percent.
The cost to transplant trees varies based on the caliper inch of the tree to be moved and where it is to be located. Transplanting trees is commonplace in the landscape industry and refers to any planting of trees, whether from containerized material, balled and burlapped, or machine moved. Transplanted trees from 8 to 10 inches in caliper can be planted with traditional methods by tree spade machines5 and by hand for smaller caliper trees. For larger trees, 10 inches to 24 inches in caliper, unconventional methods are needed. These require multiple steps for digging and preparing the root-ball, lifting, transporting, and installation. Trees over 24 inches are generally referred to as ”mega-tree” moves, and require extraordinary methods, procedures, and equipment. While transplant costs will vary in different parts of the country, a 10- to 24-inch caliper tree will cost +/- $1,200 per caliper inch. Add another 20 to 30 percent if cranes are needed, or if the tree is being moved off-site. Above 24 inches, the costs jump significantly and can easily reach $10,000 per caliper inch, due to the increased tree/soil weight and the equipment necessary to move them5. While transplanting a single 50-inch caliper oak tree at a potential cost of $500,000 is not within the reach of most owners, transplanting trees in the 10- to 24-inch caliper range is cost-effective under certain circumstances, and provides many of the benefits mentioned.
The city of Houston Parks and Recreation Department, along with the OST/Almeda Corridors Redevelopment Authority, committed $450,000 to transplant trees as part of an ambitious renovation of Emancipation Park, of which my firm is a design-team member. Emancipation Park is the state’s oldest public park at 138 years. Located in the city’s historic Third Ward, this 10-acre park was bought by four freed slaves and is one of the homes of the African-American communities’ Juneteenth celebration commemorating the abolition of slavery. The park has faithfully provided a place for recreation and community gathering, but was in need of renovation and expanded facilities. Many of the large oak trees around the site had to be moved in order to maintain the integrity of the site. A total of 33 trees were moved, including six large trees upwards of 24 inches in caliper.
Issues To Consider
Large-tree moves are part science and part art. While much is known about maintaining healthy, vibrant trees, they are ultimately living organisms affected by the environment. There is no substitute for observation and trial and error. Selecting a tree-moving company that has experience and a proven track record is highly recommended. Many factors affect how well a tree will adapt to a new location:
- Is the tree healthy?
- Is it worth moving?
- Will it survive transplanting?
- Is it accessible?
- Is the time of year conducive to moving it?
- Are the soil conditions favorable?6
It is important to understand the type of soil and its characteristics. If a tree is moved from a location with permeable soil to a location where the soil has a heavy clay content, a sub-drainage system is needed to avoid ”drowning” the root ball, which, if not mitigated, could lead to transplant failure.
After resolving all of the pre-planning questions, a detailed implementation plan can then be developed. The most important factor of a successful move is the root ball size. The industry standard root ball for a tree transplant is a 10-1 caliper inch to root ball in feet ratio (e.g., 20-inch caliper tree = 20-foot root ball). However, a preferred ratio is 12-1, but there may be additional costs depending on the method used to transplant5.
Other factors to consider include:
- Will existing utilities be impacted?
- What is existing along the transplant route?
- Are there any other proposed improvements that can be coordinated simultaneously?
- Is there room for the new tree canopy?
- Are there any public-safety issues to consider?
Off-site moves require another level of detail and can add to the total cost of the move. Off-site considerations may require:
- Police escort and traffic control
- Overhead utility coordination
- Site accessibility.
Time To Transplant
Now it is time to prepare the transplant. Root-pruning is important and is needed when roots are dormant, and should happen 6 to 8 weeks prior to transplanting to allow for new root growth5. Encapsulation of the root ball is either done by round ball technique with burlap, or with a square steel or wood box. Proper soil-moisture control is important during this time; too much and the tree will ”drown” but too little and the tree will stress due to root desiccation. Once the roots have had a chance to recover, a shallow entrance ramp is excavated 4 to 5 feet below the finished grade, and metal pipes are driven under the root ball to create a platform for lifting. While there are several ways to lift the root ball, one of the easiest and cost-effective is the use of inflatable air logs. These are less destructive on the site, allow for larger 12-1 root ball sizes, and are very maneuverable. One important planning point often overlooked is the size of the pit that is needed to receive the new tree; it has to be the same size as the original pit, and the same site considerations apply.
For large-tree transplanting, nothing competes with the impact of a large tree. Bigger is always better when done right and with careful planning.
1Diane Cameron and Dolores Milmoe, “Benefits of Preserving and Protecting Large Mature Trees” (Audubon Naturalist Society).
2Morton Arboretum, “Estimated Age of Urban Trees by Species and Diameter (DBH)” Available from http://www.mortonarb.org/learn-experience/educators/arbor-day-classroom.
3U.S. Department of Agriculture, “Trees Pay Us Back” Available from http://www.fs.fed.us/psw/programs/uesd/uep/products/18/808uesd_uep_tpub_Midwest.pdf.
4Richard J. Campana, Arborculture, History and Development in North America (Michigan State University Press, 1999) pp. 2-3, 305.
5Photo and supplemental information courtesy of the Environmental Design/Davey Tree Company, David Marks, November, 2014.
6William A. Rae, “Tree Transplanting” (Journal of Arboriculture, July 1976) p.133.
Michael P. Mauer is a licensed landscape architect and certified arborist with 29 years of experience in park planning and design. He is a senior principal with M2L Associates Incorporated, a Houston, Texas-based landscape architectural, planning, and environmental design company. Reach him at mmauer@M2Lassociates.net.