How to Preserve Mature Trees During Installs

from The Landscape Contractor magazine JUL.21 DIGITAL EDITION

Shrubs that Dazzle

How to Preserve Mature Spe

By Heather Prince

We have an innate connection

to trees and creating, installing, editing, and maintaining landscapes often involves their keeping and care. Established neighborhoods usually come with a mature tree canopy that not only provides cooling shade, but grounds the homes in the neighborhood and provides unique personality to our built spaces. How do we preserve trees when called in to craft a landscape design? What are some proven techniques to protect treasured trees and keep them healthy? We spoke to Craig Bergmann, RLA, ASLA owner and principal at Craig Bergmann Landscape Design. An award-winning landscape architect, Bergmann and his team work with many properties that feature mature trees on sites with home building projects and landscape renovations.

Why keep mature trees?

“Well, there is nothing that ages a new project better than mature trees,” commented Bergmann. “This said, the shade provided often helps establish new plantings within this shelter and often increases wildlife habitat. It typically is the mature evergreen tree that shelters cardinals and mourning doves that so many of us enjoy in our landscapes. If kept healthy and the landscape is developed with the long-term health in mind of mature trees on new project sites, a symbiotic relationship between old and new plantings can be accomplished.” Large trees also offer a greater amount of ecosystem services including absorbing stormwater, sequestering carbon, cooling the atmosphere and mitigating heat islands, improving air quality, and providing homes for wildlife such as bees, butterflies, and birds.

The ideal situation is for the landscape team to be involved in pre-construction plans from the beginning. This ensures that trees may be protected, buildings could be sited to respond to trees and garden views, and construction scheduling is designed to work for all parties involved. “The major challenge is to educate all members of the construction project team of the program to work on the tree’s behalf and not for just the humans involved,” observed Bergmann. “Mature trees like mature humans resist change, therefore the true landscape professional needs to own the protection of the tree

cimens During Installations

and police the site and program for the tree to even have a chance of survival.”

Phone a friend

Partnering with certified arborists specializing in construction practices can make the project run smoothly and ensure the best results for the trees. The species of tree can also determine protection practices. Oaks and beeches, for example, resent root disturbance to such a degree that they may fail a few years post-construction. Bergmann stressed, “The best partner is time to plan and to pre-project work at the right time of year. Triage work only after the fact seldom results in a living tree after five years.” Construction timing may include working when trees are dormant to minimize stress or soil compaction or pruning trees in the proper season when certain pests and disease are not active. When planning with trees in mind, consulting certified arborists trained in construction mitigation can not only save the trees, but reduce costs of future care. “Plan for construction ahead of time by proper canopy and root reduction if construction impact is imminent. Afterwards, arborists will then enhance future fibrous root growth with root promoters,” recommended Bergmann. Roots are the issue

During construction and landscaping work, Bergmann had a number of tried-and-true practices that have kept mature healthy and vibrant on his projects. “Avoiding the root zone altogether, therefore no change in underplanting, irrigation or construction impact on canopy, trunk or root zone,” can be critical for tree health. “Major protection fencing of the root zone determined by the arborist, not the general contractor,” ensures that proper care is taken for the tree. Soil compaction can be a significant factor in whether a tree makes it through the construction process and remains healthy in the following years. Compaction by heavy machinery, construction material storage, or repeated vehicle traffic presses air and water spaces out of the soil. If you’re working with clay soils, the fine particle size of clay compacts more easily and can create an almost concrete-like post-construction soil where trees will struggle to thrive. If roots are protected, trees can successfully survive and recover from more minor impacts. Sometimes there is no avoiding the need to cut tree roots. “If major tree roots must be cut, then do this work with an arborist not a backhoe,” insisted Bergmann.

Once construction of buildings is complete and it is time to install plant material, how do you plant with mature trees in mind? “Airspading the root zone to expose root structure and then plant only in areas where roots are not damaged through planting of new materials,” Bergmann finds it critical to success. “Replace moved out soil with a light loam for better aeration of soil. Be sure to select and install new plant materials with similar cultural requirements of the mature tree.” Many landscape installations call for irrigation systems for new plantings so they may establish successfully. However, irrigation systems can create more headaches for mature trees. “Do NOT impose automatic irrigation on a mature tree if it was not irrigated before,” emphasized Bergmann. “If not from construction, the next killer of mature trees is imposing excess water from systems not regulated properly for the tree.” Pull the arborist in to consult with your irrigation contractor to determine the appropriate settings for the correct amount of water delivered to the new plantings that will also benefit tree health and recovery. Sometimes, this may involve a diligent hand-watering program with the maintenance crew that will allow for all the plants’ needs and can respond to the increasingly unpredictable weather we experience with climate change. The initial investment in crew time can pay big dividends in keeping trees healthy and saving the hefty expense of removal in following years.

The house is built, the plants are in, what’s next? Ideally, your company has the maintenance contract for the project going forward. Monitoring the trees when you make maintenance visits keeps potential pests and diseases at bay and catches signs of stress. “Seasonal monitoring of health and potential pests and pathogens,” recommended Bergmann means you can potentially nip problems before they become real issues. “Proper available nutrition and water to ensure recovery,” commented Bergmann is also essential as large trees start to regrow cut roots and add new top growth. “A contract with an arborist for mature tree care prior to problems revealing itself,” can make all the difference between the clients enjoying the 80-foot bur oak that creates a dramatic canopy for years to come or starting over after its removal with a three-inch caliper sapling. Having a plan prior to construction, protecting tree roots from compaction and disturbance, underplanting with tree health foremost, and regular follow-up monitoring can ensure the large trees on your clients’ properties are beautiful, highfunctioning specimens for years to come. As landscape contractors, you “are the only tree advocate on the site except for the owner,” Bergmann advocated. “If neither take charge, the trees are what suffer. Being responsible for the environmental and cultural conditions of a site are paramount in long-term landscape health and a great relationship with the client.”