I've been looking through pictures for the website today and came across a number of really interesting projects from the past couple of years, the record of which lies almost solely within my phones photo gallery. In the first of what I plan to be several blog posts I wanted to shine a spotlight on the Three Sisters, located just outside the Woodland Garden on Ardkinglas Estate.
We were contacted for specialist help on two individual trees which presented significant challenges. One of these, the Three Sisters, was a Silver fir (Abies alba) measuring in at over 45m high and with three stems. Each of these stems in themselves were incredibly substantial, and with some degree of decay identified at the main union efforts had to be made to reduce the likelihood of failure.
A Tree survey carried out by Adam Reidi specified heigh reduction pruning, but the real challenge lay in the bracing. There are a number of products widely available for textile bracing in trees. These can be static or dynamic; in the case of static bracing these provide a load support, with very little stretch in the material itself. Dynamic bracing has much more stretch, and rather then cutting out the trees movement it seeks to dampen the natural movements between stems and prevent them reaching a point of failure. Both are extremely effective when implemented, but no off the shelf products exist for trees of this scale.
After some discussion with a bracing manufacturer about the trees morphology and the loads involved, we settled on the installation of a custom triangulated brace lower down. As this was the key area where the support really had to be solid we opted for a 17 tonne Dyneema brace. Dyneema is an incredibly strong synthetic fibre widely used across many industries today. It's stronger than steel and easier to work with, which is quite important when you need to pull it up a tree and then instal it as part of a finely balanced system. Further up we installed an 8 tonne dynamic brace, between the two taller stems to provide dampening of the movement in the tops.
Finally the time came to carry out the installation and pruning, as luck would have it on a very damp and cold January day. Accessing the tops of large trees can be a bit of a fiddle, but we were able to install a 2mm pilot line in the upper canopy which we used to pull up our climbing ropes. First of all we carried out the height reduction pruning, as the removal of this weight could alter the stems positioning relative to each other. Once this was completed we worked our way back down, installing the upper brace, and then the lower one. We used a high mechanical advantage pulley system to ensure the lower brace was under as much load as possible, this also helped to ensure each leg was evenly weight too. You can also see the old chains, estimated to have been installed in the Victorian era to achieve a similar objective. The tree has swallowed these up now and despite their rather robust size they have gradually all broken, the last being during storm Arwen in 2021.
All in all I was extremely pleased with the process and implementation of this project. Having installed hundreds of bracing systems over the years it was nice to deal with something a little outside of the box. We were able to source and instal high quality components within budget within a relatively short space of time. Hopefully this little bit of support will see this iconic tree standing for generations to come.
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