Climate change

Woodland Management and Climate Change

One of the main overall objectives of woodland management for the UK government and most countries around the world is to improve habitat for biodiversity, as established at the Rio Convention on Biological Diversity in 1992.  For Essex County Council as well, this is a prime driver for managing woodland.

Unmanaged woodland blocks are typically dark under the canopy, where little in the way of flora, tree or shrub regeneration and understorey can exist.  This environment is not used for nesting by birds, which generally prefer a more shrubby, open habitat with warmth, protection and some light, or by other valued native species.

Creating the right conditions means letting in light by felling trees.  Marking trees for felling is done with a number of objectives in mind.  General aims are to have a healthy, resilient woodland with a diversity of species, ages and heights, with some gaps, potentially for natural regeneration or planting.  Veteran trees are “halo thinned”, to give enough light for their crowns not to be out-competed by surrounding trees.  Some species such as oak are favoured over others for the future structure of the woodland, so these are given space, ie there is a judicious marking of trees around them.  If there is a general uniform matrix as though it is a planted crop, this is thinned not so much to give space to retained trees to grow on to a final harvest, at which point there would be a rather shocking clear fell, but to create and sustain a lighter canopy.

As a procedure, marking is done by focussing on the arrangement and competition of crowns in the high canopy, as well as needs of veterans, woodland health, long term stability and ventilation, species choice, composition, shading of some stems and many other objectives.

Woodland Resilience

The concept of woodland resilience to climate change addresses how a new and extreme climate will affect the various species our woodlands are composed of.  Different tree species will tolerate change in different ways, ranging possibly from benefitting from some changes to dying out.  Episodes of drought, heat stress and continual standing water are likely, as well as increasing carbon dioxide and other nutrients in the atmosphere, which are likely to increase vulnerability to existing or new diseases.  Coppicing or creating regeneration gaps in a thinning provides opportunity for rejuvenation and increasing species diversity within blocks, by enabling natural regeneration and supplementary planting.

This felling produces a lot of timber. 

With a new awareness of climate change, some might think it is better to consider trees as a way of storing carbon, and that felling them will release this carbon into the atmosphere.  However, given the above objectives and benefits to biodiversity, there are also other positive outcomes to consider:

  • A proportion of the timber is used for structural purposes, ie building and joinery. This is often chosen as an alternative to energy intensive and polluting materials such as steel or plastic. 
  • Much of the produce is firewood. Those who have a wood stove are directly supporting this very important woodland work.  And apart from firewood being carbon neutral over the life time of the grown timber,  it also substitutes for the use of fossil fuels for heating homes.  The issue of particulates, ie smoke especially in built up areas is as a result of inefficient stoves and burning of unseasoned wood, which the government has said it wants to control.
  • Brash from the branches and tops of trees left on the woodland floor are a resource for invertebrates and serve as some protection for seedlings, nesting birds and against browse by deer.
  • A fully stocked and full height canopy has reached a plateau as far as carbon absorption is concerned. In the growing cycle, uptake of CO2 is most vigorous in younger trees.
  • Where trees fall over and are not used as firewood or construction, the ultimate fate of the carbon from which they are made goes back into the atmosphere as carbon dioxide through the rotting process.

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