If you go down to the wood today, it may appear that there is not much to see in the depths of winter. A botanist can always find something of interest even in a deciduous wood. Have you noticed how some young trees hang on to their dead leaves past autumn? I particularly notice this characteristic on young Beech trees in my local wood.
This phenomenon is known botanically as marcescence. Marcescent leaves are retained by young trees, while older trees of the same species gradually lose this characteristic. The feature is noticeable in young Beech (Fagus), Hornbeam (Carpinus) and Oak (Quercus). The copper-coloured leaves of young Beech are particularly eye-catching in winter sunshine. Beech is a popular hedging tree and you may also notice its dead copper leaves retained in garden hedges too.
Trees prepare to shed leaves by growing a layer of cells between the leaf stem and the tree branch. This is known as an abscission layer. It stops nutrients and water reaching the leaf. The leaf detachment needs to be efficient, clean and smooth. The tree needs to rapidly protect itself from the potential negative consequences of an open wound. The abscission process is much slower in marcescent trees.
There are multiple theories about why young trees keep their leaves. Marcescent leaves are thought to act as a deterrent to feeding deer. Dry leaves with poor nutrient levels are unpalatable. Browsing crunchy leaves is not a silent process and could possibly draw unwelcome attention to the herbivore in the denuded, winter wood.
Marcescent leaves also offer protection to young tree buds. They may guard against water and temperature stress. There may also be advantages in delaying leaf loss to maximise juvenile growth before winter sets in.
Retention until spring also ensures a slower decomposition of the leaves. Marcescent tree leaves do not generally decompose well. A springtime drop delivers timely organic matter and mulch to the young tree as its growth spurts again. Beech trees are well-known for dominating, shading and crowding out other trees and vegetation. Little sunlight gets through to juvenile trees on the woodland floor once the older, dominant trees close the canopy again. They need every advantage they can get.
Beech trees thus provide botanical interest throughout the seasons. This native tree is particularly noted for its fantastic autumn colours. Look out for its long, slender buds tapering to a point in winter. Hopefully, it will not be too long until we see its beautiful, fresh green leaves in spring again.
References and Further Reading
- Barnet, Tonya (2021): Winter Marcescence: Facts about Marcescent Leaves in Trees. Gardening Know How.
- Geitmann, Anja (2018) Bracing for Abscission. Cell. Volume 173, Issue. 31 May 2018, Pages 1320-1322. Science Direct.
- Milner, Edward (2011): Trees of Britain and Ireland. Natural History Museum. London.
- Price, Dominic & Bersweden, Leif (2013): Winter Trees: A photographic guide to common trees and shrubs. Field Studies Council. FSC Publications. Telford.
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