The original article was written by Michael Ormston-Holloway BSc, MScP, GDHort, MLA, ASLA, CNLA, ISA Certified Arborist of The Planning Partnership (TPP) for Cabbagetown ReLeaf. Michael is a Partner at The Planning Partnership (TPP) and works in both landscape and urban ecology. In addition to his work at TPP, he lectures at the University of Toronto in the Daniel’s Faculty of Architecture, Landscape and Design, the University of Waterloo in the School of Planning division of the Faculty of Environment, the University of Guelph, and OCAD University.
Mature trees provide ecosystem benefits that help reduce pollution, lower energy costs, increase property values and reduce stormwater runoff. Moving large trees can be a good strategy for building momentum around an urban forestry project and for preserving large trees that would otherwise be removed due to development. Unlike mature trees, young specimens take years to reach a size that would provide equivalent ecosystem benefits to those of a large canopy tree.
People have been moving large trees since the 1850s, if not earlier, in fact, there is evidence of the ancient Egyptians transplanting large trees almost 4000 years ago. More likely than not, the Egyptians discovered that to transplant a tree, the size of a tree’s root ball must correspond to the caliper of the tree. Larger trees require a larger root ball in order to transplant. With that said, the physiological changes that affect a tree during transplant are similar regardless of the size or age of the tree.
A tree that has been planted for three or more years has roots that extend well beyond the drip line of the tree. Generally, 60 to 75 percent of an established tree’s root biomass is outside the drip line, meaning that a fully grown tree has roots branching out in diameter equal to two to three times its height.
During transplant, roots are often purposely trimmed back to lateral roots. In response to this pruning, the tree produces more roots and root hairs, increasing the total size of the root ball. Thus, the process of root pruning helps increase the integrity and volume of the root ball, and helps the tree better acclimate to new surroundings, however, root pruning is more widely used on smaller trees. Since roots provide water, minerals and physical support for a tree, problems can arise when the root system of a tree, particularly a large tree, is improperly cut during prior to transplant.
AmericanHort (formerly the American Nursery and Landscape Association) set standards for root ball moving. In general, needled evergreens require a minimum of eight inches of root ball for each inch of trunk caliper and deciduous trees require nine inches of root ball per inch of caliper. After determining the root ball diameter, digging, balling and burlapping by hand help ensure the root ball remains intact.
The Planning Partnership (TPP) is a leading expert in large-tree transplanting methods and has worked with various tree contractors throughout Southern Ontario to move trees 60 ft in height and greater. They worked with the Town of Goderich to redesign and replant their town square park following the F3 (on the Fugita scale) tornado that hit in August, 2011. Goderich, located on the eastern shore of Lake Huron, is home to fewer than 10,000 residents. The 2011 tornado was the strongest tornado Ontario had seen in more than 15 years with wind speeds at 280 kmh (174 mph). While the tornado only lasted 12 seconds, buildings were leveled and trees uprooted or split, leaving the town with $130 million in damages. It’s estimated the town lost more than 90 percent of it’s total tree canopy.
Following the tornado, the town worked with TPP to develop a master plan to combat lost tree canopy on public land. As part of their redesign of the central square, TPP transplanted more than 150 (44 small, 93 medium and 20 large) mature trees from around the region. The transformation of the town center following the tornado included the planting of 60′ tall trees with 30′ canopies. In addition to donations from the community, the trees came with an unusually long warranty, which was critical to the Town’s ability to afford mature trees. The successful transplant of the trees was just the first step to ensuring they thrived in their new home. The Town was committed to helping the trees adapt to the new environment through consistent fertilizing and soil treatment.
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Additional resources on transplanting trees: