Spring has sprung – learn more how about how trees use hormones to begin to sprout leaves again in warmer months
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In the northern hemisphere, the first signs of spring are upon us. Blooming crocuses out in a park, or the sight of sunnier (and hopefully, bluer) skies, are the promising signs that the last of the winter weather is behind us.
Another sign of spring imminently approaching are those tiny new leaves on the tips of trees. But although these form in March and April, the entire process begins months earlier – even as far back as late summer and early autumn the year prior.
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The growth of new leaves isn’t a random process, but instead a carefully calculated plan by trees. As Learning Assistant at Forestry England’s Westonbirt, the National Arboretum, Ellen Whitby explains: ‘Even in winter, trees are super-smart and sensitive. They’re always paying attention to what’s happening around them, like how long the nights are, how much water they have, and how warm it is.’
So how do they grow?
In autumn, trees will begin to sprout tiny buds on their twigs – formed when they have the energy to grow before days get cooler and shorter. As colder weather hits, buds then lie dormant and wait for spring to arrive. It is within these buds that leaves will eventually form.
Then, as spring approaches, a variety of hormones – including cytokinin and auxin – begin to promote growth and encourage cell division within buds. As such minute changes occur, new spring leaves begin to burst outwards, giving once sparse twigs the full, green and bushy appearance that characterises them.
It is at this point that trees carry out photosynthesis, using their leaves to convert water, sunlight and carbon dioxide into sugars that help to power the plant. They do this using the chlorophyll inside them, a green pigment which absorbs sunlight.
Of course, there are exceptions to the rule: warm winters – which many parts of the world now experience due to climate change – can confuse trees and mean they come out of dormancy before their typical timings. But in general, most trees follow this same pattern year after year, seemingly lying dormant but in fact preparing long before those summer months.
