Pruning & Habitat: Balancing Objectives

Jan-Feb 2013

In forestry as in arboriculture, the main goal of formative (structural) pruning is to develop a stable, natural architecture. Some genera and species develop better with a central leader while others naturally tend to a more open form. (Research by Greg Moore in Melbourne shows that formative pruning is a valuable service that arborists can and should be selling to cities, but that is for another article!) On established trees, the primary goal is conserving that structure while managing growth. When the growth rate of a tree in the plantation forest slows, the tree is “over-mature.” Profit decreases, so the wood is harvested. 

In the urban forest, slower growth is an advantage, a sign that it’s time to preserve structure while managing the tree’s increasing ecology and habitat values. Viewed in “tree time,” maturity is an indefinitely long phase in the tree’s development. Practice points to a variety of ways to manage trees for wildlife, and not just as a feel-good exercise. Providing habitat is a value-added service that many clients will gladly pay for, and have you back regularly to maintain. 

Can Bugs be Our Buddies?
Nora Bryan of Calgary, Alberta, is known as “The Wasp Whisperer.” As she climbs around the crowns, she listens and looks for Vespula sp. wasps that commonly nest in the trees she is paid to prune. Unlike some of her male counterparts who go out of their way to kill the creatures, they don’t bother her much. “I stay still and usually they just calm down and I keep working... slowwwwly!” she explains. “They usually find me before I see them. I have only good words to say about these wasps. Once I backed into a nest at head level. They were on my face and one was even inside my safety glasses. But I only got stung on the arm. They were pretty cool about it. I didn’t bother them any more, and they didn’t bother me. I pruned the rest of the tree, but left that limb alone.”

Nora was following her employer’s policy on protection of native animals and habitat. Adair Tree Care is committed to developing work practices that protect our environment, native wildlife and their habitat. Their policy is to avoid disturbing native wildlife and nesting areas at all times in conducting business. If a native animal is present in or near trees they have been contracted to work on, their policy is to cease work until the nesting period is over and the animal has left. They wisely recommend contacting local authorities if there is any doubt about proper handling of wildlife issues. 

After the client learned why that part of the tree was not pruned, she was delighted with their commitment to “entomo-arboriculture.” She looked forward to their return, when they would check on her new “pets.” The company’s passive conservation of habitat became a value-added service. Like US agribusinesspersons getting paid for fallow fields, they were rewarded – on a smaller scale – but delivering an extra benefit! Active conservation, and even introduction of new habitat, can also be profitable, so let’s look at what’s needed to do the work.

Gear Up! 
Dealing with habitat of all kinds requires some delicate maneuvering. A second rope helps to maintain balance on small wood, and swing more easily in a wide crown. A long lanyard does the same in tight situations. A tool pouch fits on the back of the saddle, so you barely know it’s there. A few light tools can come in handy when managing trees for wildlife:

Camera/Phones. Camera/phones can capture images of bugs, birds and butterflies and send them to supervisors and clients on the ground. I recommend a separate hard case for protection, not only from banging around, but also from bits of dirt that clog lenses and buttons. (Don’t learn these expensive lessons the hard way!) A periodic blowout with compressed air is also a good idea. 

Magnifiers. Using a zoom lens on the camera can be useful, but separate hand lenses are indispensable. No matter how good your vision is, zooming in closer can show you a whole new world. Fungal structures, details of tiny insects and other little objects can have major significance. Some magnifiers come with lights, which can bring out more detail. 

Videos. Videos can bring little bits of tree life vividly to reality for those who can’t see them in person. 90 seconds of video can be sent in a 9-megabyte transmission, small enough for many devices to download. Clients ooh and ahh when they see cute little beasties moving about in their trees.

In Your Toolbelt. A small resin hammer can “tap test” to gauge the location and extent of hollows, and also drive in small, wide-headed nails to support structures like birdhouses and bathouses that bring tree owners no end of enjoyment. Larger metal hammers and nails might also be needed, but consider hand drills and screws, which hold more weight and cause less cracking damage to the tree.

Tying Material. Woven straps like Arbor-Tie can hold branches and structures in place with minimal girdling damage. That or smaller twine can lash trimmings into forks to give raptors and smaller birds a headstart on nest building. Tie loose loops to allow movement, or use cotton or other biodegradable material if future girdling is a concern.

Intentional Wounding: What Would Shigo Do?
Damaging trees for habitat is extremely controversial. Its application in urban areas is limited to places where exposure to people and property, i.e. targets, is low and the value of the specified wildlife is high. In Sweden and England, hardwood branches are sometimes ripped and blasted and sliced and diced with branch ends shaped like little crowns. One justification for this “coronet cutting” was the hypothesis that more exposed cambium would result in more sprouting. Subsequent observations at Burnham Beeches and elsewhere, however, have indicated otherwise. This mutilation might be tolerated due to sentiment in those two countries, where crowned royalty persist in the political environment. 

Another aspect to intentional wounding is the ecological environment created for highly specialized beetles and fungi that rot the wood. It has been hypothesized that these organisms not only coexist with trees, but that their coevolution implies trees’ codependence on the very organisms that decay them! 

This concept may be counterintuitive, or it may be logical, but a review of the literature shows the jury is still out. Likewise, surveys documenting the rarity and value of these organisms aren’t comprehensive or conclusive. Critters are critters, no matter how small, as Dr. Seuss’s Horton the Elephant might say, but accounting for all those beasties must be a daunting task! 

In England, “The Government’s recent proposals to sell the forest estate cast a harsh spotlight on serious protection loopholes,“ reports the Woodland Trust. If trees are managed for fungus and insects, that could bring mycologists, entomologists, ecologists and other natural allies more actively into the battle for tree preservation. It may be a coincidence, but politics has been said to cause strange bedfellows. When tree health and safety are not the primary objectives, arboriculture gives way to vegetation management. Trees are indeed parts of larger ecosystems, but favouring other species over trees seems very different from arboriculture that facilitates the coexistence of trees with people. 

Asian cultures are much older than American and Australian cultures, so it’s natural that older trees and their associates are more highly valued. Their risk tolerance is higher, so they preserve trees and all their associates along with them. When an ancient ginkgo tree in front of the Kanagawa shrine in Japan fell into the busy street, the overriding concern was encouraging the stump to grow sprouts, a form of immortality. Veteran trees are propped in many ingenious ways in China, where the concept of “hazard” prompts creativity, not fear and loathing. 

The International Society of Arboriculture (ISA) demonstrates an increasing appreciation of tree values. In its upcoming guide to Best Management Practices for Tree Risk Assessment, the value of the tree itself is factored along with other property as a potential loss due to tree failure. This is a welcome departure from the old defect-focused “hazard assessment” that cast trees in a negative light, and condemned many before their time. Veteran trees are managed for both structure and habitat in several western countries by a growing number of commercial arborists, and fittingly even by more “conservative” entities.

Hollows: Beings in Nothingness
Tree hollows are used as nesting sites, shelters and safe refuges for over three hundred species of wildlife throughout Australia. The importance of habitat trees as critical parts of active ecosystems has permeated the entire arboricultural industry down under – all the way to line clearance. 

“In southeast Queensland, habitat trees are at a premium.” Matthew Palmer, Vegetation Policy Manager of the utility company Energex, reported at the International Society of Arboriculture conference in Parramatta. “Loss of habitat trees has resulted in the loss of the animals dependent upon them. By working in the risk management zone we are working with habitat trees for the first time. In many places the road reserve is the only place where habitat trees remain, as they have been cleared from freehold land. This is also where our power lines run. In nearly every case, the faulty part of the tree can be removed without removing a hollow.”

“Energex’s practice under VTA (Visual Tree Assessment) is not to remove an active hollow no matter the risk,” Palmer emphasized, bringing to life the company motto, of “positive energy.” The VTA program was based on the work of Claus Mattheck and developed by consulting arborist Cassian Humphreys: “An arborist report assists greatly with communicating with the public. The program is very long term, and requires continual assessment to ensure objectives are met.” Tree preservation, along with reliable electrical service, are objectives that are regularly met, as compromised trees are often scheduled for 10 or 20% reduction and monitored. Tree-centred, proactive VTA contrasts with defect-centred, reactive TRA (Tree Risk Assessment) in the United States. American utility arborists report that, “trees that are at an elevated risk of failure are selectively identified and removed or pruned,” and in that order. What about reliability, the utilities’ bottom line? “Measures from data show that the right areas are being targeted.” Palmer reports.

At Fort Bragg, North Carolina, US Army contractors drill into longleaf pine trees with 5 cm (2”) bits to create nesting hollows for the endangered red-cockaded woodpecker. These birds may be tiny, but their political punch in land-management decisions carries quite a wallop. Creating hollows in urban areas is a different kind of challenge due to safety concerns, so creating and installing artificial hollows is a profitable service for arborists to perform. These provide an opportunity for the public to enjoy native wildlife up close and personal in their backyards, parks or schools. The colour, movement and variety of wildlife bring joy to your clients, and referrals to your business. Artificial hollows and nesting boxes are not a “one and done” job. They need periodic care, which gets you back on the property over time. Predators threaten many hollow-dependent species, so placement and exclusion devices need to be checked.

At last year’s First International Arbor Camp, Philip and Patrick Kenyon gave an excellent demonstration, and offered a list of considerations:

  • Entrance size, for the desired species.
  • Aspect. Openings faced away from worst weather and toward the sun for bats.
  • Temperature. Warm and ventilated, with holes drilled for air movement.
  • Drainage. Waste drains out of nest.
  • Landing platforms, or sticks for birds, are required by some hollow users.
  • Escape ladder for young; smooth walls can turn nest into a tomb!
  • How many habitat sites in each tree, and how close?
  • Discouraging potential predators.
  • Light exclusion for owls and some bats.
  • Complimentary planting to provide food, cover and protection.

A list of references at the end of this article will provide details and more resources to guide the construction and installation of valuable habitat in your clients’ trees.

Deadwooding: Which, Where, Why?
Dead branches are traditionally removed from trees to lessen decay moving into the parent branch or stem, improve air movement, increase stability by lessening load, ease access for climbers and some wildlife, and lessen risk and litter nuisance, among other reasons. Beauty may be in the eye of the beholder, but most clients, as well as most arborists, seem to enjoy the view of the living tree’s architecture more after the dead parts are removed. However, dead branches retain value in the tree, particularly when they provide benefits such as:

Resource Translocation. Some recently dead limbs may still have “juice” stored inside, containing stored resources that are still traveling downward. (These resources are a reason to avoid using the term “deadwood.”) Large branch removal can be done in stages to allow for translocation, which may also result in a protection zone being formed at the final cut.

Support. Dead branches in dense evergreens may be holding up neighbouring branches above. This support can prevent breakage as it increases sunlight to and airflow around living branches.

Habitat. In trees that compartmentalize well and have no major disease concerns, dead branches are retained because some organisms find niches in branches that are not in stems. Or on branches: spider webbing between twigs can catch aphids and other plant pests. Also, dead branches that protrude from the crown provide perches for raptors and other valuable birds.

Damping. Weight in the middle of limbs and trees can absorb load and improve stability.

Final Words...
I hope this view of pruning trees for habitat has been of interest. A kinder, gentler approach to older trees and all their associates great and small can guide them through survival mode, and retain their contributions to your business, your clients and your communities for years to come. 


  • Gibbons, P. & Boak, M., 2000, The Importance of Paddock Trees for Regional Conservation in Agricultural Landscapes, New South Wales National Parks and Wildlife Service.
  • Gibbons, P. & Lindemayer, D., 2002, Tree Hollows and Wildlife Conservation in Australia, CSIRO Publishing, Collingwood.
  • Victorian Tree Industry Organisation (VTIO), 2010, Tree habitat sizes,
  • Grant J., 1997, The Nestbox Book, Gould League Of Victoria Inc.
  • Franks, A. and S. Franks, 2003, Nest Boxes for Wildlife - A Practical Guide, Bloomings Books.
  • Gould Group, 1997. The Nestbox Book, Wilkinson Publishing.
  • Birds Australia:; Info Sheet numbers 9 & 10.
  • fauNature:
  • Backyard Wildlifers:

About the Author
Guy Meilleur is an ISA Board-Certified Master Arborist and a Municipal, Climbing and Utility Specialist. He is a Detective Dendro author (ISA Arborist News) and a former lecturer at NC State University, instructor at Duke University, and staff arborist at the University of North Carolina. Guy’s company, Historic Tree Care, assists arborist associates in the conservation of historic trees by root invigoration, pruning, support and lightning systems, and community education. 

Our mission is to enhance and promote the care and benefit of trees for present and future generations in Ontario through education, research and awareness.