Caring for Ancient Trees
Out of sight, it is easy to disregard tree root systems except when they hinder modern machinery. Younger trees are often able to cope with more disturbance. For the few special trees on any farm the following will help them thrive:
Hollowing is a sign of age
The old saying ‘an oak tree grows for 300 years, rests for 300 years and spends 300 years gracefully declining’ describes the three main life-stages of a tree: young, mature and ancient.
As trees age and new annual rings are added, the trunk grows fatter and fatter. For many, at maturity after perhaps 90-100 years, they start to hollow. Hollowing is a characteristic of an old tree. As the tree ages, it recycles the valuable nutrients locked up in its heartwood. Trees can sense these changes and will usually adjust their growth by adding new structural wood to support it where it is most needed. Eventually, just a thin rim of living sapwood is left. Keeping this sapwood healthy and full of moisture is fundamental if a tree is to have a long life. This hollowing provides valuable habitat for rare fungi, insects and nests or roosting places for birds and other mammals such as bats.
Open crowned trees can have 20 times more leaves than trees grown in a more enclosed woodland setting, as they have a bigger crown and access to more light, allowing them to expand outwards and thrive.
They are therefore also very rich in flowers, pollen and seeds – a great benefit for wildlife.
Lower large horizontal limbs provide a unique habitat for some lichens and insects.
Leaf and twig fall adds nutrients to soils and is broken down by microorganisms. These and other nutrients are captured by mycorrhizal fungi which feed them to the tree via the roots in return
for sugars from photosynthesis.
Large pieces of decaying wood are important to replenish scarce minerals in the soil.
Respect the tree’s needs
Despite their long lives, old trees are at risk from modern living. Their roots, which have sustained them all those centuries in one spot, can be easily damaged by deep cultivation, overstocking or man-made fertilisers. This decline leads to dieback in the crown which can cause concerns about premature collapse along roadsides and near people, so the trees are removed to avoid risk.
Compaction can destroy soil structure, driving out oxygen and the area can become waterlogged,
reducing air exchange in the soil further. Fertilisers and animal medicines affect the functioning of mycorrhizal fungi – the trees’ lifeline for nutrients, water and resistance to pathogens.
Trees benefit farming
Trees bring many benefits to farms such as shelter and shade for stock. Trees benefit soils by improving structure and feeding it, which enables it to be more resilient to high rainfall and to droughts.
Hedgerows, commons and wood pastures were once full of pollards which were cut for leaf fodder or for other products, such as wood fuel or timber for building. Each traditionally pollarded tree, some of which also served as boundary markers, is a piece of history and part of the story of rural life.
Trees mean history and beauty
Many old and mature trees that were present 150 years ago have sadly disappeared today. In the mid 1800s, the Ordnance Survey Epoch 1 maps (the most detailed mapping ever undertaken) recorded a host of mature and older trees across the land. Comparing this historic map with modern aerial photos reveals many gaps where trees once stood. Securing the future of the few that remain helps us understand the past, provides habitat for wildlife and adds interest to the landscape. These trees help create beautiful landscapes which add to local people’s quality of life and enhance tourism experiences.
A tree needs its roots
Protecting roots is essential to keep trees healthy. In leaf, trees release gallons of water from their crowns and this has to be replenished from the soil via their roots and functioning sapwood. Living wood that is working properly will rarely decay, this is because most fungi cannot grow in wood that is wet and as a result is low in oxygen and high in carbon dioxide levels.
Roots extend out much further beyond the crown than many people think and their mycorrhizae (fungal partners) extend out even further. They are usually in the top 30cms of soil and can be very vulnerable to damage.