Getting to the root of saving mature trees

With pressure on commercial property owners to "green up" their outdoor landscapes coming from local governments and environmentally conscious tenants, some of them are discovering that saving a distressed mature tree — while not cheap — can be good for both the soul and the bottom line.

While there isn't much argument about their benefits to a commercial property, the trees aren't feeling the love back, arborists and landscape architects say. That's because typical soil conditions around apartment buildings, office campuses and suburban malls are too poor to promote healthy growth, and property owners often seem unwilling to spend upfront to condition their soils properly.

This often results in desperate calls to arborists such as Bartlett Tree Experts to rescue valuable dying trees. To answer the demand, Stamford, Conn.-based Bartlett, which has local offices in Plymouth and West St. Paul, is expanding its services for commercial properties by touting a proprietary "root invigoration" system that uses a supersonic air tool to loosen compacted urban soils around trees.

"After we do a soil analysis, we can use the air tiller to quickly fluff up the soil all the way out to a tree's drip line [the ring on ground level that receives most of the rainwater shed from the tree canopy]," Heaton said. "This allows water and nutrients to reach a tree's feeder roots."

Hoping to get more landscape architects, academic researchers and government forestry officials interested in this so-called Root-Rx process, Bartlett staged a demonstration this week at Como Park Zoo in St. Paul, where zoo officials are hoping to rescue a high-profile bur oak at the entrance of its new, $11 million gorilla forest exhibit.

Arborist Jonathan Heaton and Tom Smiley, a Bartlett arboriculture researcher and adjunct professor at Clemson University, explained to the gathering that workers using a type of "air spade" originally developed to search for land mines can break up compacted soil far more efficiently than previous methods such as drilling holes, all without disturbing a tree's delicate root system.

The next step is to mix in fertilizer, mycorrhizal fungus spores and an organic matter developed by Bartlett known as biochar. This material is derived from biomass such as wood chips, crop residues and manures processed with heat in a low- or no-oxygen environment to produce a carbon-enriched charcoal that promotes microbial activity.

After that's completed, the area around the struggling tree is covered with mulch. The results, Smiley says, are dramatic, with some tree canopies recovering their leaf foliage after just one or two years.

Commercial building owners are noticing and are becoming a bigger segment of the company's clientele, which has historically served residential homeowners.

"Studies have shown that people who live in apartments and office workers appreciate the benefits of tress in the landscape and that it makes a better environment for them," Smiley said.

The work isn't cheap at $750 per tree, but the long-term benefits of saving mature trees are worth it, said landscape architect Peter MacDonagh of Edina-based Kestrel Design Group, whose recent work has included designing green roofs for Target Center and the Minneapolis Central Library.

"I know that this process has worked, we've done it on a number projects over the years," he said. "The key thing to understand is that the value of a bigger tree to a property is not just a little bit more than a smaller one — it's orders of magnitude higher. That's based on U.S. Forest Service calculations of the worth of trees not just for property values, but also for countering air pollution and managing stormwater."

Don Jacobson is a St. Paul-based freelance writer and former editor of the Minnesota Real Estate Journal.