Nature's Architectural Branches

Without the leaves on the trees, a different set of views is being revealed across East Dartmoor and our local greenspaces. From smooth barks, to ones covered in lichen; from interlocking dense hedgerows to solitary trees; from picture perfect shapes to the craggy hollows in mature trees, the beautiful architecture of branches is reaching for the sky.

Abundant acorns

If you've watched Autumnwatch, or been monitoring your local oaks, you’ll be aware of the huge number of acorns this year. Acorns are a lifeline for wildlife and an oak can drop several hundred in a square meter. Valued for their high energy, a squirrel can gather and bury 3,000 acorns in a season; while a jay spends up to 10 hours a day caching them and can bury 5,000. While some are forgotten and germinate, oaks ensure their survival by having bumper crops every 5 – 10 years. This ingenious solution known as predator satiation provides more food than wildlife can eat ensuring that sufficient acorns grow into the next generation.

• There was a bumper crop of acorns this year

• Photo: WTML/Pete Holmes

• Photo: WTML/Pete Holmes

Mast comes from the Old English ‘maest’ meaning bumper crop and happens in 37 long-lived species, including oak, beech, as well as some pines and spruces. Incredibly, oak mast years are synchronised not just across Britain, but the whole of northern and western Europe, but what signals are the trees responding to?  Nature’s Calendar* data is being used to explore this and it looks like there are links between spring temperatures, flowering, and acorn numbers. The largest oak mast year in the last 20 years was in 2013, and we’ll have to wait and see how this year measures up. Take a look at a year in the life of an oak tree.

The holly and the ivy – sources of winter food and shelter

Once the flowers have finished, ivy’s small black berries start to ripen; until January, the berries will be an important food source that birds, small mammals, and bats can rely on. Their high fat content makes them popular with blackbirds, thrushes, blackcaps, and wood pigeons, and the RSPB have calculated that the dry pith contains as many calories as a mars bar!

• Ivy berries are an important source of food for blackbirds

• Holly with its characteristic red berries (WTML)

A mature plant also creates dense ground cover, which helps keep the earth warm, reduces the effect of frost and helps small mammals to forage through the leaf litter. So, there’s lots of interest to be had in a mature ivy plant and benefits from leaving a patch in our gardens.

Another valuable food source is the holly, and its vivid red berries are already ripe. Popular with returning fieldfare and redwings, mistle thrushes are so partial to the berries they will vigorously guard them and chase other birds away. It’s not just birds that eat holly berries, dormice and wood mice also take advantage of their high energy, while deer eat the smooth leaves. Living for up to 300 years, the dense prickly leaves and branches of a mature holly provides shelter for birds, while the dry leaf litter that develops underneath them is an ideal hibernation home for hedgehogs. (It's worth noting here that we have carried out some sensitive management of the holly at East Dartmoor to benefit lichens, you can read more in this blog).

Hibernation season

It’s not just trees that respond to the colder weather, wildlife spends the last few weeks of autumn preparing for the winter months. The abundant blackberries and hazelnuts will have been a gift for dormice this year, enabling them to double their weight in two to three weeks before going into hibernation. Coming down from the trees to the ground, where the soil temperature and leaf litter make it warmer, they weave a nest just under the surface, often close to tree stumps or log piles where the stable humidity helps them reduce moisture loss. Tightly curled up to conserve warmth, they will lower their body temperature, and can also reduce their heart and breathing rate by 90% to consume the least amount of energy. Another of our hibernators is the hedgehog. Sadly, in decline, this year’s mild weather has seen many second litters, which are still not up to the full weight they’ll need to safely hibernate through the winter.

Hibernating dormouse; Young hedgehogs need to increase their weight to hibernate (Photo: Jane Halliday)

What else to look out for...

Oaks can retain some of their leaves until the new buds force them loose in Spring

While we were all taught that deciduous trees lose their leaves, some species like beech, and oak can hold on to them until the new buds force them loose in the spring. Known as marcescence, it occurs when the corky or abscission layer that forms between the leaf stem and the tree isn’t fully formed. Dropping leaves helps protect trees in the winter, because the water in them can’t freeze, and the wind can move more easily through the branches, so it’s not really known why these trees retain them, but it appears to be more common on younger or ‘juvenile’ branches. More frequently seen on beech hedges, you may be able to see it in gardens and parks.

Written by Jane Halliday, photos by Paul Moody and Matt Parkins (unless otherwise stated)

*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).

With many of the leaves gone from the trees, winter is a perfect time to look for lichens around the NNR or in your local woods. Click here to download our Lichen Trail route.

References

https://www.rspb.org.uk/birds-and-wildlife/natures-home-magazine/birds-and-wildlife-articles/features/birds-and-berries/

https://ww2.rspb.org.uk/birds-and-wildlife/bird-and-wildlife-guides/ask-an-expert/previous/acorns.aspx

https://www.wildlifeonline.me.uk/questions/answer/

https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/british-trees/a-z-of-british-trees/english-oak/

https://www.woodlandtrust.org.uk/blog/2020/10/what-is-a-mast-year/

https://www.woodlandtrust.org.uk/blog/2020/10/why-autumn-leaves-change-colour/

https://www.woodlandtrust.org.uk/blog/2019/09/are-acorns-edible-and-other-acorn-facts

https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/british-trees/a-z-of-british-trees/holly/

https://www.woodlands.co.uk/blog/woodland-activities/leaves-in-winter-marcescence/

https://www.woodlands.co.uk/blog/flora-and-fauna/mast-years/#