Performing A Tree Species Analysis


Do your clients have too many of too few tree species? Probably. An overabundance of just a handful—such as elm, eucalyptus, Austrian pine, ash, silver maple and linden—is problematic. With species-targeting maladies such as Dutch elm disease and emerald ash borer, over-reliance on a particular tree, tempting as it may be, usually leads to big problems. Any property can be greatly improved with an evaluation aimed towards achieving greater tree diversity.

Have The Conversation

Among the services you provide to clients, is a tree species diversity analysis one of them? Or maybe that’s not the right term. “Right Trees, Right Place” or “Let’s Grow the Good Stuff” might get the point across better to customers. When you’re making the pitch, use terms and concepts they can relate to, such as an HVAC service contract. Create the analogy that periodic landscape assessments are essential to the continued health of the plantings, just as regular heating and cooling system inspections ensure equipment is operating efficiently. When the time is right, a walk and talk with the property owner is a great opportunity to point this out and transform problem plantings into a profit center.

Create A Simple Sketch

No expensive tools are needed for this one—just a sketch pad, or graph paper, and a pencil. Identify each tree and plant grouping and look for ways to introduce a more diverse group of species. A simple tear-off pad with your company logo and contact information on it will help keep the notes you make associated with your business. (Just about any printer can make one up for you in a few days at very low cost.)

When sketching, it’s helpful to designate like-species with similar shapes such as ovals, circles, and other geometric shapes, even if there is only one tree involved. Doing so helps define the space and the plant within it, drawing attention to the current placement in the landscape. After the tree species are identified and marked on the pad, make a couple of quick notes about their obvious condition issues, such as “moderate Diplodia tip blight infection” or “constant Japanese beetle infestation.” These notations will help make the case for removals and replacements as you progress through the process.

Identify Targets

In order to diversify, some ornamentals may need to be removed and replaced. (In fact, “will” is much more likely than “may.”) The most logical approach is to inspect and document the condition of each tree on the property, especially ones close to targets. What are targets? Targets are people and items of value. In the “people” realm, pay close attention to areas where the clients are likely to congregate such as the deck, gazebo, driveway, and porch. How much time do they spend in these locations, aka the “frequency of occupation?” The valuable “items” are generally the obvious ones including the house, and such elements as swing sets and/or fences. However, it’s always helpful to ask the question, “Which areas do you, your family members, and guests tend to hang out?” This question often brings out a response you may not have expected. “Oh, we’re going to install a bocce court over there next week,” or “Herbert sometimes parks his car under that bigleaf maple way over there,” is the sort of information that can affect a landscape plan.

With the targets now in mind, go back to the simple sketch and color the target areas in with a red pencil or similar marker. The key point is to draw associations between problematic trees and property targets. When a client sees them together, s/he is more likely to be convinced to remove and replace less than desirable specimens.

Consider Condition

The next addition is to enhance the initial tree notations with a deeper dive on structural condition defects such as cracks, co-dominant leaders, girdling roots, basal decay, branch/trunk decay, and exposed root damage (See photos for examples). Depending on the age of the tree and the length of time the defects have been in place, it may be feasible to take corrective action, especially if the tree is a valued species. If however, significant trunk decay is present on an overplanted species, then the best move is to mark it for replacement.

In addition to structural condition defects, previous poor arboricultural practices made by inexperienced tree service providers are common in a landscape. Problematic conditions caused by excessive elevation, lion’s tailing, topping (yes, that’s still done today), poor pruning, and lack of proper pest control methods, often leave a tree suffering in a state where it is not likely to return to good health. Make the following four factors known to a client: 1. obvious visual appearance issues; 2. structural condition defects; 3. poor tree care history; and 4. valuable targets within reach. Pointing out these issues can decrease the hesitancy to remove a tree from the landscape.

If yet another convincing influence is needed, inform the client that the standard fall distance associated with any defective species is 1.5 times the tree height, not just the actual height. For clients still clinging to the desire to retain a tree in poor condition, creating a visual helps. Techniques such as asking the client to hold the end of the tape measure while you walk out to the potential fall distance, using bright colored marking paint on the ground, and/or making a dashed line on the simple sketch will provide the necessary visualization.

To add further credence to the tree species analysis, call in a specialist. An International Society of Arboriculture (ISA) Certified Arborist, especially one with the TRAQ (Tree Risk Assessment Qualification) has the training and experience to identify and evaluate the relative risk of each defect found, as well as to point out any additional flaws that were not immediately apparent. ISA Certified Arborists can assist with providing necessary details for the remove/retain proposal.

1/3 Rule, 1/10 Rule

In mowing operations, the 1/3 rule—never taking off more than a third of the leaf blade surface area—is a standard. The 1/10th rule is a good guide for ornamentals. In other words, no more than 10% of any one genus should exist in the landscape. One tenth? Really? Yes, really. Oh, sure you can fudge a little when it comes to diversification within a genus, especially if there are lots of species choices, such as with oak. Shingle oak, red oak, sawtooth oak, bur oak, white oak, English oak, and other oak species can diversify a landscape almost as much as introducing different genera.

The key to following the 1/10th rule is having an “in-hand” list of well adapted, slam-dunk tree species that can work well in various settings. Sometimes called a Plant Palette, it can be created and customized for the local area based on information from nearby arboretums, botanic gardens, university extension staff, and relevant experiences from co-workers, distributors, and veteran nursery vendors. For example, if you’re in the Washington DC area, then Dumbarton Oaks and the National Arboretum are good sources; the Leaning Pine Arboretum and the Santa Barbara Botanic Garden are great resources in the central California area; and the Morton Arboretum and Chicago Botanic Garden provide excellent species information for landscapes in northern Illinois. Just a few I like are the seven sons tree, hackberry, and Kentucky coffeetree (pictured).

The Final Pitch

So what does the final pitch look like? The best pitch has two parts—the current and the proposed. Since greater diversity and improved overall tree health are the goals, drawing in red Xs and adding up the total number of species before and after should be integrated into the tree species analysis. Breaking it down with lists of trees to be removed and replanted, and increased species introduced into the landscape, summarizes the overall plan well for the client. It also helps both client and landscaper start and stay on the same page.

tree species analysis
Kentucky coffeetree is a good example of a tree with attractive fruit, which can be a plus or minus depending on the client.

Cracks are a physical separation of bark, sapwood, and often heartwood. Cracks pose a serious problem to the tree and the landscape.

tree species analysis
Trunk wounds that have failed to close can be problematic long term.

tree species analysis
Co-dominant or tri-dominant leaders usually create included bark and cut off water and nutrient flow.

Girdling roots that wrap around the trunk create a significant structural weakness.

tree species analysis
Noticing previous problems, such as hail damage, might be obvious or may require the assistance of an ISA Certified Arborist.

Included bark causes a constriction of each stem and reduction in nutrient and water flow; structural weakness is also a common outcome.

Hackberry is a sturdy, relatively pest-free species for the overstory.

tree species analysis
Seven sons tree is great for small to medium size spaces and has four-season appeal. (All Photos Credit of John C. Fech, UNL.)

Fech is a horticulturist with the University of Nebraska-Lincoln and certified arborist with the International Society of Arboriculture. The author of two books and over 200 articles, he focuses his time on teaching effective landscape maintenance techniques, water conservation, diagnosing turf and ornamental problems, and encouraging effective bilingual communication in the green industry. He works extensively with the media to extend the message of landscape sustainability, making over 100 television and radio appearances each year.


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