Tree Girdling and Safety

I have been girdling trees in my young woodlands for over 10 years now and have written several blogs on the subject pointing out the benefits to silviculture and wildlife. Above all it is a quick and simple method of thinning trees which will enable any woodland owner to start managing their own woodland without incurring the costs and complications of hiring tree felling contractors. Everyone can see the advantages of thinning by girdling, but the sticking point is always safety. Woodland owners are rightly worried about having dead trees in their woodlands which could fall on members of the public. A typical response is, “it’s not a risk that I am prepared to take”. This blog explains how a girdled tree disintegrates in a safe fashion at minimal risk to people and certainly much safer than felling with a chainsaw.

A selected tree is girdled by cutting through the bark to the wood beneath. A suitable herbicide is applied to the cut which stops the bark reforming. The objective of girdling is to cut through the cambium, the layer of cells that produces new xylem cells on the inside and new phloem cells on the outside of the cambium layer. Once the phloem tissue has been cut none of the carbohydrates and other nutrients produced by photosynthesis in the leaves can travel down to feed the tree roots. Sap can still rise up the trunk from the roots because not all of the xylem cells have been destroyed. The roots will slowly starve and die. When the root dies it is unable to pump sap up to the leaves, and so the tree itself dies.

Some trees, such as maples and birches, may continue to produce leaves for 2 or 3 years after girdling. Others, such as oaks, die in the first year after girdling. Once a standing tree dies it starts to dry out and to rot. Small twigs become brittle and drop off within a year. Larger branches and the trunk are invaded by wood boring insects and fungi. These weaken the tree but, because the tree is still firmly anchored into the ground by its root system, the tree does not topple. Instead, it slowly sheds small and larger branches until only a rotten stump remains. By this time the roots are also rotten, and the tree could be toppled if pushed. Left alone, the rotten stump disintegrates into the ground.

By contrast, most broadleaved trees topple in autumn gales when they are still in full leaf and have a large sail area to catch the wind. An inspection of the roots reveals serious decay that must have been ongoing for many years. It is a surprise that the tree has lasted so long before falling. These are the trees that present a significant safety hazard. Girdled trees in a woodland present minimal safety risks. They are an important wildlife habitat for hole nesting birds (eg willow tit), wood boring insects and many fungi. They slowly sequestrate carbon into the woodland soils and recycle nutrients without any help from man and his machines.