Autumnwatch # 2: Falling leaves


The Autumn colours are starting to appear, and autumn activities are starting to appear in school. Artwork, songs, poems and the like can all benefit from a little bit of subject knowledge. We’ve mentioned the new curriculum’s focus on plant identification before , and the preponderance of leaves in autumn activities provides a great opportunity for embedding some of this. Sending them on a hunt for colourful leaves, for instance? Well, why not give them a leaf ID sheet to throw in some science to the mix. In our Autumnwatch posts we’ll help you identify some of the most colourful, popular and frequently seen leaves, and provide some info and trivia about them. First of all, though, a bit of background to the science behind Autumn leaves…


Leaf fall, or to use its scientific name, abscission, is a result of several factors. Mainly, this is due to trees cutting their losses as winter approaches; it takes a lot of energy to maintain leaf production, especially in the face of cold weather and long dark nights. There is relatively little time for photosynthesis anyway at this time of year, so basically deciduous trees just give up. (Wind and insect predation are also contributing factors).


Leaves are green because of chlorophyll, the pigment used in photosynthesis. There are also yellow xanthophyll pigments and orange beta-carotene in the leaves, but these are masked by the bright green colour. When photosynthesis stops and leaves die off, there’s no need for the chlorophyll either, and it degrades into colourless chemicals. Now, the yellows and oranges are revealed in all their glory. Red colours are a little different; these are actually synthesised as new pigments once about half the chlorophyll has degraded.

Brown colours are not pigments, but the dead cell walls of the leaves.

The colours vary depending on different trees and their different pigments. More info on the different trees and their leaves as Autumnwatch continues…


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