Astronomically autumn starts at the equinox (September 23) but meteorologically it starts September 1st so we are nearly 6 weeks into it. I decided to record the changes in my photos throughout the autumn so I will keep adding to my movie as we move through October and November.
Shorter daylight hours and colder nights are what trigger leaf drop – or senescence – but frost and rain can damage leaves and cause early leaf fall. Plenty of sunshine is needed to encourage concentrations of colour pigments which help to intensify leaf colour. Our cold spring and hot summer will have helped ready the leaves for a beautiful autumn display, but it also hinges on what the weather does now. Today was like summer again blue skies and temperatures in the low 20’s.
Leaf fall or senescence, is an “altruistic death” allowing the degradation and redistribution of nutrients produced during growth back to other parts of the plant. This strategy evolved to maximise the fitness and survival of the plant. Leaf senescence is highly complex, involving multiple genes and numerous biological, chemical and physical processes. At the heart of it all is a pigment called chlorophyll. Chlorophyll is what gives leaves their green colour, absorbing and reflecting different hues from the colour light spectrum, as seen in a rainbow. In leaves it absorbs mainly red and blue light, reflecting green, and it is this reflection that makes leaves appear green to the human eye. In autumn, chlorophyll, mainly in deciduous plants, is slowly broken down and reabsorbed by the plant, diminishing the green colour of the leaves. It is this reabsorption that ensures they spring back to life the following year. As chlorophyll is broken down, pigments called carotenoids and flavonoids are revealed and it is these, again, through the absorption and reflection of different colours from the light spectrum, that are responsible for the yellow and orange hues of leaves. Sugar concentration in the leaves also increases anthocyanin production, which causes some leaves to turn a shade of red.
So that’s the science…I will look forward to the next 4 to 6 weeks… but not the leaf sweeping!!
October 23rd - 2 weeks on and there is a noticeable difference in the woodland skyline. The trunks of the trees and many branches are now clearly visible and there is a constant downward fluttering of leaves. A few trees have completely lost their leaves but most still have plenty of leaves. The weather has mostly been warm, sunny and fairly calm with clear azure blue skies. It has been cold at night but we have yet to experience any frosts. Some cold windy weather is on the way so we might expect some dramatic changes in the next two weeks