It’s just wonderful to see plants and trees starting to emerge from their winter slumber. Watching buds swell and leaves unfurl each year is a truly magical experience. As it’s a process which requires a lot of energy and, at this time of the year, you can almost feel this ‘life force’ surging around you on a woodland walk.
Trees ‘hibernate’ for good reason. It seems a wasteful extravagance to discard hundreds of leaves each autumn which have to be regenerated in spring time. But it seems that it has a purpose in nature.
Conifers have been on this planet for around 170 million years but deciduous trees only started to develop around 100 million years ago. So shedding foliage in wintertime is a step forward in evolutionary terms.
In winter, when the ground is wet, tree roots can find it hard to anchor effectively in the ground. And, to add to their difficulties, this is the time when storms put them under additional pressure. A gale force wind can pummel a mature tree with a force equivalent to a weight of around 220 tons.
A tree without leaves can withstand storms much more effectively. By casting off its leaves, a deciduous tree becomes more aerodynamic. It loses a surface area of over a thousand square yards when its leaves fall to the ground. And the combined wind resistance of the branches and trunk is only about the same as that of a modern car.
Woodland trees also ‘help’ each other in storms. Each tree has its own unique physiology of wood which causes it to react to storms in different ways. The first gust of a storm bends all the trees in a forest the same way but each tree springs back at its own individual pace. This causes tree crowns in dense woodland to collide as they swing back up because each is recovering at a different speed. These interactions slow the trees down and reduce the impact of the wind force overall.
However, ivy-clad deciduous trees can suffer in storms as the evergreen cladding – particularly if it reaches the crown – can considerably increase wind resistance.
Shedding their leaves allows deciduous trees to excrete waste. And hibernation allows the tree to recover its energy for the following year. Like humans, trees suffer from sleep deprivation – deciduous trees grown in containers indoors do not flourish because they are not allowed to ‘rest’ in this way.
Leaves are the tree’s way of producing food which it uses to live and grow. Leaves have a green pigment, called chlorophyll, which absorbs light energy from the sun. This energy is then turned into food by the leaves in a process called photosynthesis. As part of this process, the leaves absorb carbon dioxide and transform it into carbohydrates to feed the tree.
In autumn, deciduous trees start to fill their tissues with food – sugar made with energy from the sun. Unlike animals, trees cannot get fatter as their external woody surface does not expand so there is a point when the tree becomes ‘full’. For some species of cherry, this can happen earlier in the year as they lose their chlorophyll and turn red even though there are lots of energy-producing sunny days ahead. Other tree species go on photosynthesising for as long as possible so they may have larger storage systems.
However, the arrival of cold weather eventually puts a stop to the activity of all deciduous trees as the frosts arrive. Because so much of the trees’ activity involves the movement of water, if a tree freezes while its wood is too wet it would burst like a frozen water pipe.
To avoid this danger, trees start to cut back on activity and water content from late summer onwards.
Now in springtime, the buds are starting to develop. This is a slow process as ‘tree time’ is much different to how we humans understand it. Tree activity is at a much gentler pace. Water and nutrients (tree ‘blood’) flow from the roots to the leaves at a rate of only around a third of an inch per second.
Buds will start to form in response to a combination of factors. Trees don’t green up immediately when there is a spot of good weather in January as flowers do. While they do recognise an increase in temperature – they wait until a certain number of warm days have passed before they decide that spring has arrived. So this must mean that trees have some ability to count!
However, it’s not just temperature that sets the greening process in motion – trees also take into account the amount of daylight. Beeches, for example, don’t start growing until it is light for at least 13 hours a day. So this means that trees must have some way of registering light too.
It seems that the buds may be the ‘eyes’ of a tree. We know this because most tree species have tiny dormant buds nestled in their trunks. When a neighbouring tree dies, these buds register the additional light. This causes them to grow and form branches to close up the gap so that so that the tree can exploit the additional light source.
The tightly clenched buds will slowly unfurl as vivid green young leaves. Chlorophyll has a so-called ‘green gap’. This means that it cannot use this part of the light spectrum to produce energy. If it could, leaves would appear black to us. So the restful colour of green – which has proven to be very good for the human psyche – is actually waste light that the leaves cannot use.
Studies have shown that walking in green spaces is restful and rejuvenating for the human brain. While nature engages our attention, she does so in a gentle way which invokes ‘soft fascination’ giving us a break from mental fatigue.
In an era when our brains are being bombarded by non-stop multimedia technology, it is all the more important to allow ourselves to rest in nature. And spring is full of promise and hope and new growth. Enjoy!