Winter is Coming – The Trees Prepare

The days are shortening and the temperature is falling. This is a signal to deciduous (broadleaf) trees that it is time to close down for the winter, conserve energy and prevent it from losing precious nutrients.

A tree is sensitive to its surrounding environment and responds to changes by hormones which in autumn switch from growing mode to conserving mode. This retains some of the chemicals that are in the leaves which the tree draws back into the main stem and uses again.

As the green chlorophyll is removed this is when some of many other chemicals in the leaf are revealed and the yellow carotene and red anthocyanins show through, producing a final display of rich colours before they are also absorbed and the leaf  is finally shed, from the base of the leaf stalk call the abscission point.

Many of the fallen leaves rot down, helped by water, micro organisms and worms  that enrich the surrounding the soil which the tree uses again in future years. This illustrates just how efficient a tree is and that it wastes very little over its long life. Losing its leaves also conserves energy and prevents the freezing weather from damaging the tree.

The ancient trees have been going through this process for centuries  despite their ageing frame which actually slowly becomes a valuable place for animals to hibernate. The bark is waterproof and the inside of the tree offers a wide choice of niches for fungi, insects, birds and even mammals to hide away from the cold weather.

High winds are also less likely to blow an old tree over if it has  a broad canopy and low branches which help dampen the impact of high winds.

Autumn is also a time of rest and rejuvenation   so despite the dark months ahead, even in autumn the signs of spring are already being seen on the tree. These are the buds and catkins ready and waiting to burst into life as the spring light begins to return.

Paul Rutter

Ancients of the Future Project Officer for Back from the Brink.