Special guest and consulting arborist Oliver Reichl joined us on Ask A Master Gardener (AAMG) this week to discuss a wide range of your questions about trees!

What is a Consulting Arborist?

While a certified arborist is mostly concerned with the care and maintenance of trees, Oliver’s role as a consulting arborist is relatively new. This work focuses on the assessment of trees in urban contexts, and with tree protection, risk assessment, inventories and reporting. This may include the valuation of a tree, reasons for tree failure, and mitigation strategies for preservation. Consulting arborists provide written documentation for planning purposes and expert witness testimony if needed. Their assignmentments may also include peer report review, maintenance planning, management plans, insect and disease identification and monitoring, structural testing, forensics, and public speaking.

Image credit: UF/IFAS Gardening Solutions – University of Florida

Tree Risk Assessment

All trees may pose a level of risk, potentially causing damage to structures, infrastructure (e.g. hydro lines) or to other trees. In Oliver’s words, the easy and radical solution to a perceived risk is to simply cut down the tree. However, a proper risk assessment will first consider several factors:

  • Is there a target, and if so, is it constant (e.g. a house) or intermittent (e.g. parked cars)
  • Which part of the tree is a concern – all of it, or perhaps just a branch
  • How prone to failure is a particular tree species
  • What kind of failure may occur. An ash tree may break at the base, while a white pine tends to snap off part way up the trunk

Of course, the general age and health of the tree, pests and diseases, and environmental conditions (wind, soil etc) are also evaluated. 

Better arborists obtain a Tree Risk Assessment Qualification (TRAQ), a program design to train those interested in this speciality. 

Many AAMG participants had questions for Oliver, a sample of which are provided below:

Spongy Moth Control

Did you know that the gypsy moth (Lymantria dispar) is now known as the spongy moth?  Three subspecies are recognized: Asian, Japanese, and European/North American. Whatever the name, it is responsible for large-scale defoliation of trees in years when a caterpillar infestation occurs. It occurs in cycles of 7-10 years, each lasting 2-3 years, and most healthy deciduous trees can survive this assault. To help control caterpillar populations in your own backyard, learn to identify the egg masses in early spring, and scrape them off tree trunks (or wherever else you spot them).  Destroy them by immersion in soapy water for several days. For a high value private tree, it may be worthwhile to hire an arborist to remove the egg masses from the crown. Some tree care companies offer this service.

Image credit: Toronto.ca

Some infestations may be targeted with spraying of BTK (Bacillus thuringiensis kurstakion) on foliage, however, it needs to timed carefully as it works when ingested, and the leaf needs to be eaten within a few days of spraying. Spraying is often controversial, but one needs to bear in mind that applications of BTK are about helping to protect high-value trees, not eradicating the moth.

Ginkgo Trees

A participant in AAMG wondered why, after many years of not fruiting, her ginkgo tree recently started producing.  There are both male and female ginkgos and only the female will produce fruit. Like many other species, they will do so on their own schedule, when they are sufficiently mature, and when environmental conditions are right. Be forewarned, the odour is most unpleasant! For this reason, many people choose to plants only male trees.

Roadside Tree Suggestions

Another participant wondered what tree species would do well in a shaded area beside a busy city street, given the high levels of pollution and particularly salt spray in winter. A cluster of eastern white cedars nearby are doing well, which is a unusual in that conifers tend to suffer foliage injury from salt.  Oliver suggests referring to a reliable source online for shade tolerant tree species. Many tree seedlings in the wild, including sugar maples and ironwoods for example, are shaded during their early life by older trees and may do well. 

Of course, other factors – heat, light, moisture and nutrients will affect growth so understanding the site and the tree requirements are important. 

Trees for Wet Places

Now that spring rains are here, wet places in some yards appear and  a question was asked about trees that tolerate flooding. Oliver first recommends avoiding walking or using equipment in the damp area, as it will be prone to soil compaction.  If left undisturbed, the area could support various species, such as tamarack (larch), but again, a reliable source would provide a complete list. Consider native species if planning a new planting! 

Removing Invasive Shrubs

Invasive species are generally defined as organisms that cause economic or ecological harm to an area in which it is not native. The Ontario Invasive Plant Council provides detailed information on species, impacts and management practices. 

Image credit: Ontario Invasive Plant Council

To control these, Oliver explained the mechanism by which these species survive. These perennials use their roots to store energy for subsequent growing seasons. Cutting an invasive shrub will not permanently remove it, as suckers/shoots will spring up, utilizing this reserve energy to re-foliate. However, it cannot do so indefinitely and so continually clipping off new shoots, preventing the shrub from photosynthesizing, will eventually starve the plant.  This requires both patience and diligence as it many take several years of effort.

There is so much more to learn about trees from a qualified arborist – stay tuned for upcoming AAMG sessions!