NATURE NOTES - Seeing the wood for the trees

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CAN you believe that autumn is here?

What happened to our ‘summer’ again this year? What is interesting is that there are predictions that this autumn will be a blaze of colour with the trees – mind you we all know what happens to predictions don’t we! Fingers crossed they get it right - there are already some good colours developing on some of the trees up here in Haigh. Let’s hope that the leaves stay on the trees long enough to get some amazing colours.

Trees that drop their leaves each autumn are called ‘deciduous’, from the Latin for ‘to fall’. Deciduous trees lose their leaves every winter, rather than keeping green foliage throughout the year like evergreens do.

Often, the trees provide a radiant show of autumn colour before they lose their leaves, and in some regions such as parts of America and Canada this autumn colour is an attraction that visitors from all over enjoy.

There are a number of reasons for leaf loss, but essentially, trees lose their leaves to conserve energy over the winter and prevent damage to the tree. In the spring, the tree puts out new leaves so that the process can begin anew.

Many deciduous trees are found in regions, which have cold, dark, harsh winters. Trees lose their leaves to protect themselves during the winter months, as the cold dry winds in these regions will readily strip moisture from the trees through the leaves, which have a large surface area. By losing their leaves, trees can conserve their moisture in the trunk and branches, rather than drying out and dying. In addition, the leaf loss puts the tree into a state of dormancy, and greatly reduces the amount of energy that the tree needs to stay alive.

During the spring and summer, leaves photosynthesise the plentiful sunlight that falls on them, producing chlorophyll, which turns the leaves green. The photosynthesis provides energy for the tree, and the tree feeds the leaves with nutrients it takes up from the ground to keep them healthy. The bright yellows, oranges, and reds that make autumn colour so distinctive are actually already there, but the chlorophyll masks them. As the days get shorter, the trees have less sunlight to work with, and the efficiency of the leaves starts to decrease. Trees lose their leaves because they become a draw on the energy of the tree, as the tree would otherwise have to feed the leaves through the winter.

As the nights get longer, trees make preparations to lose their leaves, starting with the secretion of chemicals to cut the leaf off from the rest of the tree. Ultimately, trees lose their leaves once the chemicals they secrete have effectively cut the leaves off from the parent branch. These chemicals, primarily ethylene and abscisic acid, make trees lose their leaves by cutting off the link between the leaf and the tree. The fallen leaves provide a layer of protective mulch to insulate tree roots. So all we need is a few weeks of lovely dry crisp cold weather and we’ll be in for a treat!