Conservation Arboriculture: It's About to get Weird

Conservation arboriculture sees trees as more than just landscape fixtures, but as whole ecosystems, and argues for the intrinsic value of the macro and microscopic organisms living within mature and veteran trees.   Last week a buddy of mine forwarded me a whitesheet by Neville Fay on retrenchment pruning.  This form of management is a concept practiced in conservation arboriculture.

When trees are damaged in nature it`s usually due to some catastrophic event (i.e. severe wind storm). Branches damaged in this way have wood fibers break and tear, while bark is pulled away from limbs and jagged stubs are left behind. In the aftermath all manner of fungi and arthropods make a home in the tattered remains.  Fungi feed on the newly exposed wood, insects eat the fungi, birds eat the insects, and so on.

In landscapes, trees eventually mature to where their risk of failure reaches a threshold that some mitigating action must take place.  For conservation arborists, this is where retrenchment pruning comes in.  By using coronet cuts to mimic naturally damaged limbs after reduction pruning, conservation arborists invite the natural order of things to take place.  Another technique, natural fracture pruning, is simply tying rope to branches and applying force until the branch breaks. This seems to be most popular in the UK, but I've seen coronet cuts used at The Capilano Suspension Bridge in North Vancouver, British Columbia.

Coronet cut in action. Pic from David Humphries  http://arbtalk.co.uk/forum/climbers-talk/12943-coronet-pruning.html

Final coronet. Pic from David Humphries  http://arbtalk.co.uk/forum/climbers-talk/12943-coronet-pruning.html

Obviously this isn't for everyone, or every tree.  In fact, retrenchment pruning seems to go against all traditional pruning techniques and goals.  This concept isn't meant for the feature tree in the average front yard.  But, this may be appropriate for that mature tree in the wood-line at the back of a property which poses a hazard to the swing set.  This idea may also work for any veteran tree that has fallen into the spiral of decline.  In the Capilano Suspension Bridge example, entrenchment pruning was used on declining trees along forested walkways before they became hazards.

Another thing to keep in mind, retrenchment pruning in its idealistic form can take decades of management.  Vigorous sprout growth can result from damaged limbs, and so with this form of tree management. Talk about commitment from both arborists and tree owners.  The long-term goals of all invested parties need to be discussed before this type of work is performed.

To learn more about entrenchment pruning and conservation arboriculture check out Tree Works Environmental's website: http://www.treeworks.co.uk/press_releases_publications.php

Conservation Arboriculture

Conservation arboriculture is neat.  It seems their are two main ideas behind conservation arboriculture.  The first, trees (especially urban trees) are of themselves complex ecosystems.  There are obvious and not so obvious examples of this.  Obvious examples are the vertebrates (ie. squirrels and birds) that use trees as their home and food source.  Then there are the not so obvious examples, like the invertebrates and fungi species that only a few may appreciate.  The bark alone can be home to arthropods, lichen, and fungi.   Taking an ecosystem view of a tree forces us as arborists to think of tree management differently.  For example, there are dozens of insect and fungi species that rely upon the dead wood in trees for survival, dead wood that an arborist would traditionally recommend for removal.  Conservation arboricultures teaches us their is an intrinsic value to these forms of life living in the tree.

The other idea behind conservation arboriculture, there is intrinsic value to very old trees.  Trees that we consider, due to structure or health issues, candidates for removal.  Some would call these ancient trees, and in places like the United Kingdom there are organizations dedicated to identifying and preserving these trees.  In my opinion the term 'ancient' is relative.  An ancient white oak may be 600 years old, while an ancient aspen may be 70 years old, but to me the idea is the same.  Older trees have a story to tell us, and the older they are, and the more perceived defects they have, the more likely they are to be the home of a variety of life.

As mentioned earlier conservation arboriculture challenges our tree management strategies.  Our first priority is always safety, but our question becomes how can we manage the perceived risk of our ancient urban/suburban trees while maintaining there vitality as a thriving multifaceted ecosystem?  In some cases it may be easy.  Moving a target or erecting a fence to keep people away from the fall zone.  In other cases it may be making the call on questionable reduction cuts, and leaving pieces of dead or dying branches in the tree that would normally be removed.  Would it be crazy to make reduction cuts on an already dead limb to reduce its chance of failure?  And still on our not so ancient trees, maybe we step back and let some deadwood build up or leave some smaller pieces in there.

This approach may not be for everybody, or every tree, but is an important idea to consider as we learn more about the trees we cherish.  Below is a link to an article written by Neville Fay which was run in Arborist News.  It is a real interesting read.
http://www.treeworks.co.uk/downloads/CONSERVATION_ARBORICULTURELearning_Review4-16-06-2011.pdf

The Angel Oak of Charleston, SC