If you weren’t convinced that autumn is in full swing, one look at the trees this week should have changed your mind! Almost all trees had already transformed from lush greenery to a burst of autumn colours, and now they are shedding those leaves at quite an alarming speed! Leaf clearance has been our single biggest job over the last few weeks, as they come down almost faster than we can clear them! But something one of our clients asked got us thinking – why do the leaves change colour and then drop at the same time every single year? We figured you might enjoy the answer, so today we’re bringing you everything you ever wanted to know about autumn leaves.
What Do Leaves Change Colour?
You might be wondering why trees don’t just skip the colour change stage and drop their leaves straight away. After all, changing the colour must be quite an energy intensive process for the tree. But it’s all part of a vital process that helps them prepare for the harsh winter months and survive to see the next spring. The main reason for the colour change is due to the breakdown of chlorophyll, which is the green pigment in leaves. This chemical isn’t just for show it manages the whole photosynthesis process, helping all plants make energy and grow. As the days get shorter and the temperature drops, chlorophyll production slows down and eventually stops, which allows other pigments within the leaves to show through more strongly. Get ready for some long words, because they include:
Carotenoids: Responsible for the orange and yellow colours in leaves. This chemical is also found in carrots and sweetcorn, and is why they have such bright, distinctive colours!
Anthocyanins: Red, purple and crimson. These colours aren’t in the lead all year round, but are produced in the summer as a response to bright light and excess sugar trapped in the leaves. The pigment acts as a protection against direct sunlight, and can be a deter creatures from eating them.
Tannins: You might have heard of these ones, and you might even drink them every day – it’s what makes tea brown! Tannins is all that’s left behind once the chlorophyll and other pigments have been used, which is why older leaves all tend to be various shades of brown.
So Why Do Trees Lose Their Leaves?
Winter months are difficult for deciduous trees, so to survive they essentially go into a form of hibernation. Freezing weather can make water difficult to absorb, and harsh winds can cause damage to the trees, so a big part of this includes shedding their leaves to converse water and energy.
Energy Conservation: Shorter days and less sunlight means less time to photosynthesise, and so getting rid of the leaves means less energy is needed. Once the tree has lost all of its leaves it will enter a dormant state, and its metabolic rate reduced significantly. In other words – it’s not doing much, so it needs less energy to do it.
Preventing Damage: Leaves are the most delicate part of the tree, and they are vulnerable to damage from ice, frost and wind. Dropping the leaves protects the branches and trunk from harm, and makes them less likely to be blown over in heavy wind.
The Abscission Process: This is the name of the process where trees shed their leaves. It happens when a special layer of cells (known as the abscission layer) form at the base of the leaf, gradually breaking the connection between the leaf and the tree. It’s a highly controlled process that allows the tree to seal itself off and prevent damage.
Remember, evergreen trees don’t drop their leaves in winter, because they have evolved to withstand colder, drier conditions than their deciduous cousins.
But Why In The Autumn?
Now here’s the big question – how do the trees know to drop their leaves in autumn? And how do they manage to do it at the same time? It’s not just blind luck – it’s all to do with the environment. Trees have evolved to take their cues from the weather and their environment, and changing, then dropping their leaves is a response to that. There are three main environmental factors that prompt the big lead drop
Day Length: The days getting shorter is the most reliable signal for trees to start the process of changing colour and shedding leaves. While it’s not an exact science, most trees start to do this once daylight gets below 12 hours a day.
Temperature: Cold temperatures make chlorophyll break down quicker, which speeds up the colour change process. Early frosts can damage the leaves and make them go brown early, but if that doesn’t happen, most deciduous trees will lose their leaves when temperatures are consistently below 7°C.
Moisture: Another big hint for the tree is the reduction in moisture. When soil moisture content drops to around 50% of its capacity it stresses the trees, which can prompt them to start shutting down for the winter. So if we have a particularly wet autumn, you’ll notice trees holding onto their leaves for a lot longer!
At Pod Landscapes leaf clearance is one of our most common jobs at this time of year. Leaves keep us busy all winter round, but the work starts now. Because while the first few trees are just starting to drop their leaves, pretty soon you’ll see flurries of them settling on grass and in your car parks.
So, before that happens, get in touch to book your free, no-obligation consultation and get your leaf clearance plan in place. We can offer a regular leaf clearance service that includes safe and regulated disposal, so you never need to worry about leaves on your property again.
