…You may well see thinning operations starting to take place.
Last week our blog looked at some thinning work we had recently done - selectively felling a small number of very large Sitka Spruce near Sawrey that were dangerously close to power lines. As the month moves on, and nesting season ends, more widespread thinning operations start in earnest.
Thinning is a normal part of the forestry cycle and plays a key role in ensuring the remaining trees grow stronger, straighter, yield more and stay healthy. A proportion of the trees in woodland are selected for removal – usually between 15% and 30% depending on the current density and the particular situation of the woodland.
Factors that come into play when thinning include the amount of wind a site is exposed to, as well as soil depth and quality, the current stocking levels and species.
As for the specific trees to be removed, the primary consideration is to leave behind strong, straight trunked, healthy trees that will flourish when they get more space and light. Any diseased or damaged trees can be thinned as well as those that are less vigorous or twisted.
Many people are surprised that decaying deadwood is often left in woodlands to rot away. This may be in the form of fallen trees, stumps or snags (standing dead trees). The reason for this is that deadwood provides a highly valuable habitat in the life stages of many small vertebrates and invertebrates, including cavity nesting birds such as the woodpecker, bats, moths and of course lichens and fungi. Birch, which rots from the inside and forms hollow tubes, is a particularly important source of deadwood as it is short-lived. It is often called “instant deadwood”. Dead birch can often be seen with stunning displays of bracket fungus (Fomes fomentaruis) fruiting bodies on its trunks.
Deadwood plays two further key roles in the woodland ecosystem. Firstly, it produces a slow and steady release of nitrogen into the soil – supporting the growth of other plants and trees. Secondly it acts as a carbon sink – capturing carbon for the medium term as it decays.
Healthy thinnings are a good source of biomass fuel – softwood conifers make good chip and hardwood thinnings are excellent for firewood. Thinnings provide an early income from hardwood planting which normally would take many decades to come to maturity. Thinning usually starts 15 to 30 years after planting and then will be done in 5 – 10 year cycles depending on the species. Growth in the popularity of wood fuel has made thinning economic, with the knock on effect of also creating healthier woodlands with greater biodiversity.
Thinning also creates an opportunity to actively plan the development of woodland. Creating space allows for new planting to occur – species can be introduced which are native to the region or diversity can be improved, thereby increasing resilience to disease, pests and climate change. Thinning also creates the conditions for natural regeneration and for a forestry system known as “continuous cover”. This method of management involves thinning, rather than clear felling, allowing natural seeding from the surrounding trees to create new growth and regeneration. Often natural regeneration is supported by selective underplanting to improve species diversity and place trees in the best positions. Continuous cover has many advantages – it keeps the woodland looking good for visitors and recreational purposes, it avoids erosion and keeps the canopy in place this is important in flood prevention. Perhaps most importantly it creates a stable environment for both flora and fauna.
A felling licence will be needed before most thinning work can be started so make sure to check first before firing up the chainsaw!