Misty mornings with a slight chill and the smell of damp in the air – the leaves are turning yellow; but what type of Autumn colour will we have this year?
As the daylight hours are shortening and it’s getting cooler, deciduous trees and shrubs are preparing for winter. From oaks to ash, to blackthorn and horse chestnuts they all have two jobs to complete: spreading their seeds, and absorbing energy from their leaves before they shed them.
Nuts and fruits – the seeds of the next generation
There’s another group of nuts and fruits nestled among the fading leaves ready to be spread by animals, the wind or gravity.
The mighty oak enlists the help of jays and squirrels who gather and prudently store acorns in the ground to eat through the winter. Ash and field maple rely on the wind, and as their seed wings spin, it creates a rotating flight that carries them further away from the parent tree.
The vivid red of rosehip seeds and the blue of blackthorn berries makes sure they stand out against the yellowing leaves for the birds to see. If you can get close enough to a blackthorn, you’ll be able to see a dusty bloom on the sloes, which reflects ultraviolet (UV) light and is a signal to birds that the fruit is ready. Its not just birds who like the sloes, wood mice are also partial to the kernels, and will nibble through the sloe stone to reach it. So, keep your eyes peeled for sloe stones on the ground that have little tooth sized holes in them.
Acorns are ‘planted’ by jays and squirrels Beech seed pods ready to fall to the ground Great tit feeding on rose hips Ripening conker
The horse chestnut and beech let their seeds fall to the ground. Heavy hard-shelled conkers roll away from the parent plant, while beech seed pods split when they hit the ground and the seeds or mast are eaten and spread by badgers, deer, mice, and squirrels, as well as birds.
From green, to yellow, and red
With the next generation taken care of, the tree’s next task is to get ready for winter by reabsorbing the nutrients in its leaves. The process produces an annual tapestry of yellows, oranges, and reds but how vibrant the colours will be depends on the weather!
A layer of cells is already starting to grow at the base of the leaves which reduces and then stops the transfer of sugars to the tree. As the chlorophyll in the leaves starts to break down, the distinctive green fades and the yellow and orange colours of the carotenes pigments start to show. As the sugars become concentrated they start to convert into anthocyanins, which gives the leaves their reddish, purple, and pink colours. Nature’s Calendar* volunteers have already recorded this year’s first tinting sightings on beech, field maple, pedunculate oak and elder. Horse chestnuts often look like they have early autumn tinting because they develop brown and white marks on the leaves in late autumn. In 2002 however, these marks were identified as damage from the horse chestnut leaf-mining moth which uses the leaves as a larval food source.
Autumnal oak leaves Autumnal beech Horse chestnut leaves with autumn tinting and damage form leaf-mining moth larvae
If we have cold frost-free nights, the autumnal colours will become more vivid because it will break down the green chlorophyll and increases the level of red anthocyanins in the leaves. If the days are dry, bright, and sunny the reds will become even more intense, because any remaining chlorophyll will be able to photosynthesise, which will concentrate more sugar and anthocyanins in the leaves.
Winter returners with a taste for berries
Two of our winter birds – the fieldfare and the redwing will start returning this month. Flying in from Scandinavia and Russia, you’ll be able to see fieldfare feeding on hawthorn berries, as well as juniper, yew, and holly. With high levels of vitamins B and C, as well as antioxidants, hawthorn berries are such an important food source for fieldfare, they will defend a bush by chasing other birds away. On Dartmoor a year with hawthorns heavily laden with berries is called a Fieldfare Winter.
The dusty bloom of sloes attracts birds. Fieldfare will defend a berry laden bush Redwing is a winter visitor that could be mistaken for the song thrush
Berry-loving redwings are also returning from Iceland, Scandinavia, and the Faroes. Many blue, and purple-black berries reflect UV light when they are ripe, and studies of redwings feeding on bilberries, shows that older birds select the berries that reflect UV light, which suggests they have learnt that the UV colours develop when the fruit is ripe.
Is there a new bee on the ivy?
Mature ivy flowers are still buzzing with insects and since 2001, they’ve been attracting a new bee. Natures’ Calendar focuses on how climate change is affecting native wildlife, and the arrival of the ivy mining bees in southern Britain shows changes in the UK and European climates. First spotted in Dorset, ivy mining bees are slightly larger than a honeybee and have ginger haired thoraxes and broad orange and yellow stripped abdomens. The males appear in late August, and the females in September and you may be able to see them feeding on mature ivy until November.
By Jane Halliday
*Nature’s Calendar is a citizen science project run by the Woodland Trust and the UK Centre for Ecology & Hydrology to study phenology (the impact of seasonal changes in plants and animals).