The cooler misty mornings have arrived and we are transitioning from the vibrant summer greens to the golden orange, yellow, and red autumn hues. After explaining the various shades of summer greens early this year, I thought it would be worth exploring a little more about this colour transition and what else we can expect over the next few months as we head toward winter.
Technically speaking, autumn began in March and will continue until the end of May, but with over 300mm of rain during February (half the average annual rainfall), we were able to enjoy the vibrant summer greens for a little longer this year. The brilliance of the colours that develop each autumn season is directly related to the weather conditions that occur before and during the autumn months. The main influences are temperature and moisture in the soil… and this season will certainly be influenced by the higher moisture levels. These factors along with the longer nights, shorter days, and declining intensity of sunlight initiate a complex biological process that results in a change in the level of pigments in leaves.
Where do the golden hues come from?
There are three main factors contributing to the biological colour transition:
Chlorophyll production decreases:
Chlorophyll is the pigment that gives leaves their green colour and enables plants to photosynthesise. As the days get shorter and cooler, the production of chlorophyll slows down and eventually stops, causing the green colours to fade away.
Carotenoid production increases:
Carotenoids are pigments that exhibit orange and yellow colours in leaves all year round but are usually masked by the abundance of chlorophyll. As chlorophyll production slows down, the carotenoids become more visible, resulting in golden autumn hues.
Anthocyanin production may increase:
Anthocyanins are pigments that are produced in some plants in response to a decrease in temperatures and other environmental stress. This results in the red and purple colours we see in some trees.
Why do some trees lose their leaves?
Trees that lose their leaves, known as deciduous trees, use this adaptation to help them conserve energy and nutrients in colder climates and periods of low rainfall during the autumn and winter months. As the veins that carry fluids into and out of the leaf close off, a layer of cells forms at the base of each leaf. These clogged-up veins trap sugars in the leaf which promote the production of anthocyanin and seal off the connecting tissues, causing the leaves to gradually fall. This process of leaf abscission, the technical term for the dropping of leaves, is initially triggered by the degradation of chlorophyll and reduction in photosynthesis. Once all the leaves are dropped, the trees will be dormant for the winter months.
In contrast, evergreen trees have leaves that are adapted to withstand harsh weather conditions and will typically retain their leaves throughout the year. The needles (coniferous trees) or leaves of evergreen trees have a thick waxy coating and the fluid inside their cells contains substances that resist freezing which helps prevent water loss and damage from extreme temperatures.
What else can we expect during autumn?
The autumn hues are not only noticeable in the change of the leaves but in the bright orange flowering aloes and abundance of sunbirds around the camps. While the migratory birds have left for warmer climates, the sound of rutting impalas takes over, which in turn signals the approach of the wild dog denning season (I’m certainly keeping my fingers crossed here). Sunsets and sunrises have that extended golden glow with the increased dust in the air, and of course, there are long evenings of storytelling around the campfire. To me, these are, in and among many others, just some of the joys that autumn brings.