This was an interesting one…
A couple of weeks back I got a call from an acquaintance I had not heard from in ages because their tree had broken in half during the storm. The pictures she sent looked fairly dramatic, so I went round to have a look at the extent of the damage the following day.
Once on site it became apparent that the tree had sheared in half, leaving one third lying in the acquaintance’s garden, one third in the neighbours garden and one third standing, leaning slightly toward another neighbour’s garden. The tree stood a good thirty meters tall. The day I went there was the Monday after Florim’s accident, so I was hurting pretty badly. I decided there and then that this was decidedly not the right day to attempt to sort this out on – and that apart from that in view of the major mess and the limited access the best bet would be to remove the remaining tree as well as the material on the ground with a crane.
So I fixed up a meeting with the dispatcher of the crane company we work with. This would clearly require some large machinery: the distance from the tree to the road was a good 50 meters. We planned the removal with a Spierings MK110, which can lift 1.7 tonnes at 60 meters! I love these units, as they are super-fast to set up and great to work with… on the down side, it is a pretty sizeable machine, so it required a bit of planning and discussion to identify the correct positioning of the crane. It ended up an snug fit, with centimetres to spare between overhead street lighting cables, street signs, bike stands and garden fences.
I assumed we would be able to remove the tree the end of the following week, but as is often the case with assumptions, this proved to be wrong, due to a misunderstanding it turned out the crane would not be available until the week after. So I phoned the client and explained. She was a bit concerned whether the tree would stand up to another storm. Ach, I said, how high is the likelihood that there will be such a strong storm again in the next couple of days?
Well, upon checking the weather forecast the following Sunday, I found out: very high winds forecast from Tuesday morning onwards until Thursday. The removal was scheduled for the Friday after. Umm…
I felt very uneasy with the prospect of simply leaving the tree, but the window to do something about it was limited to Monday (which needless to day was already booked). So we packed a load of gear and went there to see what could be done. As far as I was concerned there were three options available to us:
- Declare the tree unclimbable and simply accept that there was a risk of further failure, inform the neighbour accordingly and wait to see what would happen. This was not an unreasonable position in view of the fact that at the point of failure 50% of the stem was missing. This leaves you with a residual breaking strength of 25% compared to the original strength.
- Guy the tree. This would have involved placing two low-elongation lines, one facing into the wind, the other 90° to the predicted wind direction. The aim here being to ensure that in case of failure the tree would not be able to fall towards the neighbouring building.
- Climb the tree and reduce it by about 50%, dropping large bits, removing the rest with the crane at the end of the week.
Frankly, I had misgivings with all three options.
Option one is always an option, yet it felt a bit like a last resort.
When guying trees, as in option two, I am always very conscious that the direction you guy in is based upon assumption regarding wind direction, but more importantly you are radically changing the dynamics of the tree, creating new pivot points, which may in turn induce forces leading to unforeseen failure mechanisms.
In the end we decided to get some lines up and work our way through it step by step. After a thorough inspection of the point of failure I felt happy enough to ascent up to into the canopy. There was a bit of rot at the upper part of the tear, but upon probing it it turned out that this did not go very deep before encountering sound wood. Also, the center of gravity of the residual canopy was pretty much above the trunk, so no eccentric loading.
I will admit to some pretty ginger lowering of a couple of side branches. We then pulled off a larger side limb. To do so, I attached a tag line, made a face and back cut, leaving a generous hinge. Before the ground crew pulled it off, however, I got myself out of the tree, because we were not sure how the tree would respond to the backward bending moment caused by the piece breaking off. We did the same thing with the large upright bits, rigging them down with a generous mechanical advantage system… The hinge on the last bit was really wide, it was interesting to see how the back fibres did all the holding, which the fibres in the front part of the hinge were compressed and crushed (see pic above).
All of these shenanigans left us with… mayhem. Still, I was very glad we got the tree down, the winds the following days were indeed very strong.
I thought this was an interesting job: it illustrates how you can work through a tricky situation step by step. At each step I was asking myself the question whether I am letting the circumstances force me to into taking risks which are not reasonable. In view of the fact that the tree posed no immediate danger to anybody in the surroundings, I had no intention of breaking my neck. By being systematic and thorough, with plenty of discussion in the team, in the end we had worked through eventualities and came up with a solution which assessed risks and defined mitigating action which allowed us to perform the work in a safe and professional manner.
What was left to do in the end was the tidy-up, with bits of tree spread over four gardens, so it took a while. Well, half a day… with enough manpower thrown at them, theses things become less of a chore. We left the garden looking halfway decent, the stump ground out.
What do I take away from this?
Trust your gut feeling, do not let yourself be pressured into doing something you feel uncomfortable with, be methodical and diligent in how you perform the work, use all resources available to you in your team – and be prepared for the fact that things may not go exactly as anticipated.