AT this time of the year the natural environment really “shows its colours” as deciduous trees prepare for the coming colder months by shedding their leaves as they are susceptible to being damaged during the very cold and wet weather of winter.
During the spring and summer months the leaves are critical for the production of the nutrients that are necessary for the tree’s growth and survival. The leaves use a process known as photosynthesis whereby the simple molecules of water and carbon dioxide react to form glucose and oxygen. The water is taken up from the ground by the trees’ roots and the carbon dioxide is absorbed from air via tiny holes in the leaves known as stomata.
Light energy is required to drive this chemical reaction and energy from sunlight is absorbed by the green pigment in the leaf known as chlorophyll. The glucose is then further “biosynthesised” using oxygen in a process known as “respiration” to produce the nutrients that the tree needs to live and grow.
Leaves tend to be predominantly green due to the green chlorophyll, being the dominant leaf pigment, masking other pigments in the leaves which range from yellow to purple. During autumn the changes in daylight length and temperature are detected by the trees and they start to shut down the photosynthesis process in the leaves.
Valuable nutrients in the leaves, which are mainly sugars, are reabsorbed by the tree and stored in the roots for later use. In preparation for leaf shedding the tree eventually cuts off the transport of these sugars back to the tree. The green chlorophyll is one of the first molecules to be broken down with the green colour lessening making the colours of the other pigments more prominent.
Any remaining sugars in the leaf are eventually converted to anthocyanins producing other red, purple and pink pigments. Eventually the leaves fall from the tree and a protective layer of cells grows over the exposed area to prevent damage to the tree.
A balance between weather conditions and the underlying chemical processes in the leaves can have a dramatic impact on the depth and colour range of autumn leaves. On bright sunny days photosynthesis can still occur in the leaves due to remaining chlorophyll which then increases the concentration of sugars within the leaves resulting in more eventual production of the redder anthocyanin based pigments.
Dry weather also increases the sugar concentration within the leaves giving a redder colour. Cold nights can destroy the chlorophyll with the leaves fading to yellow. A combination of cold nights, dry weather and sunny days can result in the greatest colour range and intensity of autumn leaf colours.
As the natural world prepares for winter, autumn is a great time to visit one of the Trust’s reserves. If you visit one of our wooded reserves, such as Bunny Old Wood in Rushcliffe, Dukes Wood Nature Reserve near Eakring and Eaton and Gamston Woods near Retford you may be rewarded with some really spectacular autumn colours.