Temperatures in the high twenties made today an attractive day to go and enjoy the shade beneath my sycamore tree in its full summer foliage.
Sycamores cast particularly dense shade and the tree’s leaves are mostly darker green now, due to the accumulation of secondary metabolites such as flavones and flavonols which protect the leaf tissue from the effects of excessive UV-B radiation. The tree is still producing some new, young leaves though, to replace older, damaged ones; these do have that lovely fresh ‘spring’ green colour.
The deeper shade means that a very limited number of plants flourish now. The bluebells have set seed and many of the seed pods have now dried out and burst, scattering the tiny, shiny black seeds.
Bluebell seeds heads and seeds
Bluebells also spread by way of bulbs, many of which are visible where they have been uprooted by rabbits or squirrels burrowing in the leaf litter.
Only plants such as Wood sorrel (Oxalis acetosella), adapted to low ambient light levels and able to make use of the briefest sunflecks, thrive in the deep shade.
Wood sorrel leaves
Patches of sunlight filtering through the tree canopy mean that the amount of light available for photosynthesis can increase tenfold in a matter of seconds and the plant’s photosynthetic apparatus and stomata must both be able to respond rapidly to this.
The sycamore ‘helicopters’ I found on the tree in June have all been shed now and I have to scrabble around in the leaf litter to find some. Of course, the most successful ones will have used the wind to carry their seeds away, up to 100 m from the parent tree, so the seeds stand the best possible chance of germinating and growing into new trees.
The fruit splits down the centre of the helicopter to reveal a small seed nestling in silky hair in each half – the tree has gone to a lot of trouble and metabolic expense to improve the life chances of these tiny seeds. It’s obviously a successful strategy as sycamores do only too well at spreading themselves about – particularly when disturbance creates a gap in the tree canopy.
Sycamore dispersal – from helicopter to seed release
Of course, I couldn’t resist a quick look at the plants growing in the sun around Mountjoy pond and the scrubby grassland between work and my tree too…