Thinning: the beginning

As you may have gathered from the management plan post, the main initial operation in Comar Wood is thinning of the Sitka spruce. I am pleased to say that this is now underway! Progress has been slower than I’d originally hoped because my time has been a bit limited recently. However, I’ve managed to find spare days now and then to work on the thinning and it is starting to make a difference.

There are two main reasons for doing the thinning. One is to remove smaller and poorer quality trees, allowing the remaining trees to grow larger for timber production. The other is to open up the dense stand, giving more space and light to ground flora and any native trees growing amongst the conifers. The spruce in Comar Wood is 35 years old and has never previously been thinned. This is late to be starting thinning (normally done at around 20 years and then every five or so years). The risk is that the stand may become destabilised and more susceptible to wind-throw because the trees are already quite tall. I am therefore being cautious and starting with a fairly light thinning.

Back in the summer I applied for a thinning licence from Scottish Forestry (formerly known as Forestry Commission Scotland). I had to tell them how many tonnes of standing timber there were and how many tonnes I wanted to take out, so I had done some tree measurements (height and girth) in sample plots to get an estimate of this. The area assigned for thinning this year is the western end of the wood, where the new tracks were built last year. I plan to use this as a trial to refine the felling and extraction methods and to help decide whether it is worth trying to thin other parts of the wood.

Commercial thinnings are typically done by taking out an entire row of trees every few rows (often using a harvesting machine). However, I wanted to be more selective in order to achieve my thinning objectives. Before starting I spent some time making the stand easier to access. Using a chainsaw I brashed the lower branches of trees along alternate rows and felled any very small or dead trees that had no timber value. These were cut up and left to rot down. I then walked up and down my brashed rows marking trees to remove. As I can be quite indecisive, I thought it would be better to mark the trees in advance rather than trying to decide which trees to remove with chainsaw in hand because it probably saves time overall.

My plan for the thinning is to extract the trees to the new tracks using a tractor and winch. We are planning to buy our own rather than paying someone else to come in because it should be more cost effective in the long run, as well as giving greater flexibility. We are yet to purchase the machinery, but this does not stop me from starting the work. I have been concentrating on taking out the smaller trees, of which there are a lot. These are trees that are small enough to be pulled down by hand. Given the density of the stand, almost any tree, when cut, does not fall to the ground but just rests on its neighbours. It must then be pulled down from the base of the stem. I am leaving any larger trees until we have a winch, which can then be used to pull these down.

Once felled, the trees are snedded (all branches cut off) and the stems are marked at three metre intervals. They are left full length to be pulled to the trackside once we have a winch. They can then be cut into logs and stacked ready to be forwarded out on a timber trailer (another item on the shopping list!). Trees felled close to the track are cut to length and stacked. The plan is to keep some of the 3m logs to process into firewood and to sell the remainder, probably to go as biomass for heating.

The thinning is not going to be a great money-making exercise, because felling and extraction of smaller trees takes much longer relative to their timber value than for larger trees. However, the buoyant timber market means that we will get some financial return for our efforts. Once we start extracting we will be able to work out how many tonnes we can get out in a day and therefore how much time it is taking to get this return. Even though our rate of return at this stage will be low, the thinning should increase the growth of the remaining trees so when we come to do further thinnings or small-scale clear-fells these operations will be more profitable.

Aside from the financial aspects, the thinning should benefit the woodland ecosystem. It should encourage a richer mosaic of species to start recolonising the plantation, making it more diverse and bringing the woodland into better shape for the future. There is still a lot of work to do but progress to date has started to give a sense of how things are going to change. Recent weather has been very dull, grey and wet but I’m looking forward to some spring sunshine when I can enjoy the newly opened up stands of spruce and start to see how ground flora species like bluebells, wood anemone and wood sorrel are responding to the increased light levels.