In the recent edition of the Caley Newsletter, David Knott mentioned that the chance of a spectacular display of autumn colour in our trees and shrubs has increased because of the weather conditions that we have had this year. But have you ever wondered why or how the leaves change colour? Stan da Prato explains all:
Autumn colours are the result of chemical reactions that occur as the leaves of deciduous trees die. In summer, leaves produce food from sunlight through green chlorophyll. As summer ends, the cooler weather and shorter days trigger them to stop producing chlorophyll. Other pigments become prominent. Carotenoid turns the leaf golden and anthocyanin produces red.
Different species vary in the amount of these pigments. Interestingly, British native trees tend to turn gold rather than red. Many of the most colourful autumn leaves are on imported trees such as American and Japanese maples. The colours are not the same each year. Windy weather shortens the show. Settled weather with cool nights prolongs it. A dry summer increases anthocyanin production, leading to better reds and bronzes.