Working on a giant

In dubio pro reo is a Latin phrase which translates as “when in doubt, for the accused”. A defendant may not be convicted by the court when a doubt about his or her guilt exists. This is roughly equivalent to “innocent until proven guilty”.

Yet when it comes to trees it often seems to me that we err heavily on the side of caution, unwilling to take a calculated risk in order to save a tree. Of course, if you remove a tree, it no longer represents a risk – but on the downside you have also put an end to that trees life.

We had an interesting job a couple of weeks back on an impressive Sequoiadendron giganteum here in town. The tree was planted in the 1860s, is therefore one of the earliest specimens in Switzerland and is one of the largest in Basle. A couple of years back it was struggling a bit with a fungus on its needles but has since pulled round well, today it is very vigorous and vital, with new shoots on all branches from the tip to the bottom branches.

In August it was struck by lightning, resulting in a branch being blown out eight meters below the tip (the tree at this point measured about 38 meters). At this point there is an open crack, caused by the lightning, for about four meters, which then continues on down one side almost to the base of the tree.

After an initial assessment by an arborist company who wanted to fell the tree, we were asked for a second opinion. My first reaction when I saw the damage was that it was really serious, and obviously you do consider felling as an option, in view of the fact that the tree is in a densely built up area in a park belonging to a block of flats that is accessible to the public, where safety is a concern. Having said that, it struck me that the damage, whilst superficially substantial was actually fairly localized and there is a large mass of wood that remains sound. We discussed it back and forth, resulting in a proposition to the owners to reduce the leverage on the damaged part of the canopy by removing a good eight meters or so off the top of the tree, shortening the side limbs in the upper part of the canopy, stabilizing the crack by bolting it with threaded bars, and treating the tree for the next five years with compost tee and compost to avoid stress due to loss of leaf mass.

After a number of meetings we got the go-ahead and were able to plan the work and finally got cracking end of February.

First off we strapped up the stem with ratchet straps to stabilize the whole thing, defined the point at which we were going to top the tree down to.

We left about half a meter of intact stem above the last ring of branches, to reduce the risk of the uppermost limbs breaking out. Then we shortened the branches in the upper part of the canopy. The new height of the tree was now 30 meters. The final cut-off point is about three meters above the damaged part and the open crack.

The following morning we started off by preparing all the hardware and hauling it into the tree. The weather was… well, soft. In fact, it was downright miserable, cold and windy. I was glad though, that the rain held off for a good part of the second day, as we had to bring electricity into the tree to power the drills and the angle grinder.

We used 12mm bars with counter-tightened M12 washers on them, sitting on 38x3mm washers. We used a special drill bit to drill through the bark, so that the washers sit flush on the wood. Once installed, the bars were cut to length. In the end, we installed fifteen such bracings.

I had suggested installing lightning protection, in order to avoid further strikes, but the owners did not want this done, which I can also live with, after all, the tree is fair bit shorter that it used to be.

I was really happy with the end result, as I feel we achieved the goals we set out to achieve, namely to make the tree safe whilst respecting its integrity.

Now it remains to be seen how the tree responds to the events of the past few months, but I am confident that in combination with the compost tee treatment, these measures are a viable, sustainable solution to retain this important tree.

What do I take away from this?

Trust trees. They are often so much more robust than we give them credit for. Demanding 100% safety is unreasonable, as I am sure we can agree upon the fact that nothing in life is 100% safe –  so why should we demand that trees be so? It is a question of managing the risk in a responsible fashion, which is not impossible, as I believe this case illustrates. Some trees are worth fighting for, having a cultural, ecological or emotional importance that warrant such efforts. In other cases, it may be more viable to close off an are to let a tree gradually fall to bits. And in other cases again, removing the tree may be the correct response. As professionals, it is important that we question which the right route to follow is and to communicate options, not to automatically choose the easiest one.

Thanks go out to the baumpartner crew for going along with this one and to Vito for the pics.

Oh yes, and don’t forget to enjoy the view while you are up there!