Archive for February, 2010

The Sunken Garden Arbutus Farewell

Wednesday, February 3rd, 2010

James, instructor with NATS and Rupert, head arborist at Butchart Gardens - untying a recently rigged peice that just came down from the tree.

When I answered the phone call from my old friend and colleague Rupert Evans, head arborist for the Butchart Gardens, I thought the call was going to be about planning our next west coast salmon-fishing trip. I was sad to find out that  it was something much more serious and professional in nature.

For those of you who have been to the Butchart Gardens, the tree that I am writing about is very familiar. The Butchart Gardens site is situated on an old limestone cement quarry that went out of production many years ago and the gardens were created by an avid gardener in British Columbia. One portion of the quarry pit not mined stuck out and formed a mound-like island in the middle of the old pit.  Around this island is where the first garden was developed and aptly named, “The Sunken Garden”, like any magnificent garden, this garden needed a centerpiece and soon an idea established in the form of a tree. Not just any tree but an Arbutus tree which was planted on top of the island in the late 1930’s. This arbutus tree, a native west coast species found only in a few regions in the world, with it’s elegant leaves and coppery red bark made it the perfect choice as an accent and center piece for the garden. For seventy years, this beautiful Arbutus has made its home atop the island in the center of the garden and stood over the landscape below as a proud sentinel. This grand tree quickly grew to become the most notable centerpiece and feature of ‘The Sunken Garden’.

Rupert’s call to me was to tell me that this arbutus had finally succumbed to a species-specific fungal attack and the tough decision to remove the centerpiece had been made.  This is where the story begins. Rupert had an idea that together we could turn this sad and negative experience into an educational and positive one. Together we planned to dismantle the tree and use the oppurtunity to raise funds for tree research, and so the idea of a technical rigging clinic was conceived and to donate all proceeds to The Canadian Tree Fund. Through allot of hard work and planning, 20 attendees joined us and the Canadian Tree Fund received a donation last month.

John Ransom, instructor with Arboriculture Canada checks the ropes above him.

The location and venue for this clinic is what made the oppurtunity to learn so unique, challenging and educational. Part of the challenge was the thousands of visitors daily to the gradens; another challenge was the tree’s location in the sunken garden.  This 70-foot tall tree was on top of the small island like mound that extends 50 feet above the sunken garden floor, spectacular.

The work and removal plan had to consider many things, especially from a rigging perspective, because the top of this mound like island is at most fifty foot across at the widest point – making drop zones, crew placement and brush removal a challenge.

 After a thorough assessment of the tree to determine strength and stability, teams of attendees discussed how to get this tree on the ground safely and avoid damage to the thousands of tulip bulbs, rare and valuable dwarf tree species, ornaments, fixtures, and immaculate turf.

Finally, after careful thought and planning it was decided that due to the very limited drop zone and value of all targets below there was only one feasible option for removal – a slide line. This technique is associated with a similar removal technique called speed lining. Tree workers who speed line often make several mistakes; the first is to call it a speed line as this sets a dangerous tone. The next common mistake of speed lining is the line anchored to the top of the tree set to carry tree parts down and away from the drop zone is set with no consideration to bending moment. The final and unfortunately sometimes fatal mistake is that sections of wood dropped intoare the tensioned line causing high shock loads resulting in tree trunk failure.  I want to make it clear that none of this took place during this removal and everything went slow, smooth and safe.

Slide lines, also known as high lines are different in the following ways from speed lines.  When slide lining the line itself is tensioned under control and wood is never dropped into line that is in a pre-tensioned state. Another significant difference when slide lining or high lining is that bending moment is virtually eliminated by guying the tree and slide line anchor point. The guying is done in such way that the angle the high line forms in relation to the trunk is symmetrical to the angle formed by the guy line and the trunk.  This cancels the bending moment and applies the forces exerted by the dismantled parts down the stem on the removal tree.

There was much learning and a lot of fun that took place at this excellent rigging clinic. ‘The Sunken Garden Arbutus’ came to the ground without any collateral damage, using slide line techniques, incorporating balancing, lifting, drifting and transferring systems. There were a plethora of lowering devices, compression tackle, pulleys, rigging blocks, ropes, tools, slings, experience and knowledge. 

The final good news is that the learning and donating can continue as a professional cinematographer filmed the event and a short educational documentary is going to be available soon, with all the profits from the sales of this video going to The Canadian Tree Fund. If you are curious and want to experience and learn more about the rigging tools and techniques used at this great rigging clinic, and if you would like to contribute the tree research in Canada get a copy of the video. Contact The CanadianTree Fund or ArborCanada to find out more about this educational documentary and donation oppurtunity. 
 

A good view of the beginning of the rigging on the Arbutus Tree

James, instructor with North American Training Solutions and Susan, gardener with the Butchart Gardens work in the initial set up of the rigging.

The team works together to set up the first rig.