Nature Notes by Ian Brand
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Since I last penned October’s Nature Notes the view from our study window has changed dramatically. The autumn spectacle of orange, yellow and red colours has now almost finished. The deciduous trees have dropped their leaves. The one exception to the outlook being our Beech hedges, where the desiccated copper foliage will remain until next spring.
I am rather fond of Beech trees. They remind me of my early teenage years, cycling from the busy and overcrowded Thames valley up into the Chiltern hills, clothed with hilltop Beech woods and cottages built of flint – a perfect escape from suburbia. Fast forward fifty years and we now have a garden surrounded by tall Beech hedges, turning from bright lime green in spring, to the dark green of summer, and finally the golden brown of winter.
The retention of deciduous leaves throughout the winter is a phenomenon called marcescence. Commonly encountered in Beech, Oak and Hornbeam, it is primarily found in young saplings, the lower branches of older trees, and hedges. Hedging is a way of keeping a tree in a juvenile state, and thereby also keeping its leaves over winter.
There is a lack of scientific agreement why young trees keep their leaves, but there are some definite evolutionary advantages. These include deterring grazing herbivores, protecting next spring’s leaf buds, and providing the tree with much needed nutrition. The leaves also provide a water-conserving mulch when they eventually fall in spring.
Deer in particular are partial to a tasty mouthful of young twigs and their nutritious buds during winter. Young trees by retaining their dead, dry leaves make them both less palatable and nutritious. They are also noisy to eat and may alert predators to the presence of grazing herbivores.
Leaves that fall in autumn will decompose over winter, with nutrients leaching away before spring growth. By falling in spring, they provide the tree with a fresh supply of nutrients and mulch when it brings most benefit.
The retained leaves are also protecting those sensitive spring buds from the drying desiccating winds and cold temperatures of winter.
Regardless of the reason for marcescence, when growth begins in spring, new leaf buds will expand, push the old leaves off and clothe the branches with those wonderful fresh lime green leaves.
Finally happy winter walking and gardening to you all. Wrap up well and get out and enjoy those crisp sunny mornings.