Autumn colours and leaf fall

Creative Commons Licence [Some Rights Reserved]   Text © Copyright November 2020, M J Richardson; licensed for re-use under a Creative Commons Licence.
Images also under a similar Creative Commons Licence.

Autumn colours and leaf fall

The leaves of deciduous trees in temperate regions change colour, and eventually drop off each year. We may take this process for granted, but it is far from simple. As day-length in autumn shortens, and temperatures drop, deciduous trees decrease chlorophyll pigment production, and other pigments present in the leaf become apparent. The other pigments include carotenoids, that are yellow, brown and orange, and anthocyanins which produce red and purple colours. Different tree species have different proportions and combinations of these various pigments, hence the wonderful, and changing, colours seen in autumn.
NT1635 : Autumn Sycamore at Dawyck Botanic Garden by M J Richardson
A fine specimen of Acer palmatum contrasting with the evergreens.
by M J Richardson

NT2470 : Five shades of Autumn by M J Richardson
Clockwise, from lower left:- Ivy, Hydrangea petiolaris, Sycamore, Beech and Oak.
by M J Richardson

As the leaf comes to the end of its function any remaining nutrients are withdrawn back to the stem and an ‘abscission’ layer forms at the junction of the petiole [leaf stalk] and stem. This facilitates a clean detachment of the leaf from the twig, especially after a frost, when the water in the abscission layer freezes [and expands] and then thaws, so reducing the ‘grip’ that the twig has on the leaf. The leaf scar that is left is often a characteristic shape – this is especially so in the case of Horse Chestnuts; the ‘nails’ in the ‘horseshoe’ are the scars of the vascular bundle that entered the leaf petiole from the stem – see the arrows in the picture below.

 Leaf scars

There is a large Sycamore [Acer pseudoplatanus] to the SW of my house, with a full rounded crown. I photographed it at intervals from mid-October, when it still appeared in full leaf, until mid-November. Even without a frost, however, the leaves will eventually fall and 2020 was one of those years – by 19 November we still had not had a frost at 115 m a.s.l. in Edinburgh – and the tree was almost bare. I selected six of the pictures taken over a 3-week period to show the progression of leaf fall in autumn 2020.

23 October 2020
NT2470 : Sycamore leaf fall - 2020 - 23 October by M J Richardson
The start of the sequence, with a full canopy of leaves.

25 October 2020
NT2470 : Sycamore leaf fall - 2020 - 25 October by M J Richardson
Two days later; not much change, but catching the morning sun.

28 October 2020
NT2470 : Sycamore leaf fall - 2020 - 28 October by M J Richardson
Another three days and there is a little more light showing through as some leaves have fallen.

5 November 2020
NT2470 : Sycamore leaf fall - 2020 - 5 November by M J Richardson
Two weeks after the first photograph, and a definite thinning can be seen.

12 November 2020
NT2470 : Sycamore leaf fall - 2020 - 12 November by M J Richardson
Many leaves have fallen since the last picture a week before.

16 November 2020.

You are not logged in login | register