We all know how important light is in order for plants to grow. This is as vital, if not more so, for our maturing and ancient trees. Many prefer to be some distance away from neighbouring trees in order that they have access to the most amount of sunlight possible. The more light they receive, the longer they are likely to grow.

Our ancient trees can grow for over 800 years. During this time, they need to maintain the same amount of light and space around them to reach these impressive ages.

When fast growing trees, including plantation trees (particularly conifers or beech), cast heavy shade over the older, slower growing trees - they prevent the light reaching the trunk and lower limbs of our ancients. This causes the branches to die prematurely and limits the ability of the maturing tree to prepare for old age. This all happens very slowly in Oak Trees in particular, where the tree changes shape from being an upright tall tree to becoming a lower squat shape. As well as having hollow trunks the old trees also have a low centre of gravity, so are more robust to survive high winds and are able to survive branch loss at the top of the tree. As the trees become older they become even more important habitats for wildlife including rare insects, plants and many fungi.

As we have some of the largest number of ancient trees in Europe, we need to ensure they live for as long as possible and that new ancient trees are also growing to replace the ones that eventually die.

It is because of this impact of new growth and over-shadowing on our ancients that you may see trees and lower vegetation being removed from around older and maturing trees in woodlands. This is called halo-thinning or haloing - a woodland operation to retain space and light around our old trees - and is good for the tree and for the wildlife that lives in the many niches that these ancient trees provide.

One of the most important groups of species found on ancient trees are the lichens. These are complex organisms formed by a symbiotic relationship between one, or sometimes two, species of fungus and an alga (again, usually one species, but sometimes two). As they are made up of both a fungus and a plant, they straddle two biological kingdoms. The alga converts the sun's energy into sugars by photosynthesis, providing the fungus with food, and the fungus provides protection to the alga e.g. from UV light and from being eaten by slugs. They form numerous different shapes, sizes and structures ranging from tiny 'pinheads', to porridge-like crusts, to large leafy structures that hang in swathes from the trunk. Lichens have evolved to occupy most, if not all habitats on earth (you'll even find then colonising your car), and our ancient trees are no exception.

Our ancient trees support internationally important populations of many species e.g. the shy Cross-your-heart Lichen Crytolechia carneolutea, the fragrant Jelly-lichen Collema fragrans and the Lemon Tart Lichen Lecanora sublivescens. These lichens are often associated with certain features that are found on the ancient trees e.g. the old bark on well-lit trunks, sap runs and wound-tracks resulting from damage to the tree or rot, and the bark crevices on shaded under-hangs.

Just the right level of sunlight and moisture is critical for many of these species and they are dependent on the sensitive management, including haloing, of our ancient trees and the habitat around them - be it parkland, woodland or pasture - and we also need to ensure ancient trees continue to grow in our landscape by providing the 'ancients of the future'.

Paul Rutter

Project Officer


If you have any questions then please email our Ancients of the Future team.


2 thoughts on “Haloing, lichens and our ancients

  1. Do you know where eI can find courses or talks on Lichens. I’m fascinated by them, but no-one locally seems to specialise in them in Brecon recently, but that is too far for me to get to & fro in a day, I don’t have my own transport.
    Regards, Bob Cotterill

Comments are closed.