Of Oak trees and their understorey

A delicate green haze seems to have suddenly appeared over many of our trees and hedgerows since the spring equinox. Another visit to my oak tree today revealed buds which are definitely elongating, though there is no real sign of leaves breaking out; oaks are amongst the last trees to do this.

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Incidentally, I’m now pretty confident my oak is a sessile oak, Quercus petraea, having noticed how different the buds look in both colour and arrangement to those on some nearby English oaks.

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The biggest change is, again, in the plants growing beneath my tree. Now the carpet of bluebell leaves is broken by the odd patch of blue, though most flowers are still in bud. In a week or two the carpet will be azure.

Bluebells 2016

It’s easier to see what else is hiding amongst the bluebell leaves now too – wood anemones (Anemone nemorosa) are amongst my favourites. Under my tree these are still in bud.

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but more open, south-facing slopes are already covered with a carpet of white.

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Like the bluebells, these lovely flowers are taking advantage of the early spring sunshine to grow and reproduce before the tree canopy blocks out their light. They enhance their chances of success by having flowers which track the Sun’s movement during the day like a carefully-angled mirror, focussing maximum solar energy on the developing seeds to allow these to ripen rapidly, despite the weak spring sunshine. The same trick is used by many plants growing high in the Himalayas or in the Arctic, where the growing season is short.

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The flower can change position during the course of the day by virtue of special motor cells at the base of the pedicel or stalk. These pump potassium ions into cells on the shaded side of the stalk, which causes them to take up water and elongate, making the flower turn towards the sun.

Once the seeds have set, the leaves die back and the plants becomes dormant until the following spring, when there is once again enough light and warmth to allow them to thrive.

 

 

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