In March 2022 we were treated to a wonderful lecture by local conservationist and wildlife expert John Tyler.
John took us on a journey through 100 million years of the Chilterns’ history, from their formation to future challenges.
The chalk of the Chilterns was formed in shallow tropical seas, where the skeletons of microscopic planktonic creatures fell to the seabed and eventually formed bedrock. Millions of years later the Earth’s plates moved and collided, pushing up many areas to form hills and mountains, including the Alps and the Chiltern Hills. Today, any exposed chalk reveals fossils of fellow inhabitants of these ancient seas. These include tiny Lamp shells, bivalves with a feeding tube, whose form looks similar to Roman oil lamps, as well as the plates and spines of sea urchins.
As dead sea fauna decayed, their skeletons dissolved and the silica later recrystalised to form flint. Small roundish nodules of flint are often found locally, which formed around sea sponges – broken open they may reveal the fossilised sponge in the centre.
Time travelling forward to 50,000 years ago John explored the wildlife of the Ice Ages. The coombes that are so typical of the Chilterns were formed when water couldn’t permeate the frozen chalk, instead running off to carve valleys. With so much water locked up in ice, sea levels were much lower than today and Britain was part of a huge land mass extending across Europe and Asia. Ice Age animals could have vast ranges, including bison and the famous Woolly Mammoth. Mammoths used their curved horns to clear snow to expose sedges on which to graze and their huge, ridged teeth can be found on the Thames side of the Chilterns, washed over millennia into gravel beds.
Still surviving from this era is Juniper. It has associated species including the Juniper Shield Bug which is well camouflaged on its green home. One fungus growing on Juniper has a very specific lifecycle. The crispy dried fruiting bodies become rehydrated into golden coral-like spikes in wet weather. Spores are wind dispersed where they only infect Hawthorn. The fruiting bodies now take on a completely different form, spores being released again from little brown nest-like structures that are dispersed to re-infect Juniper. Despite growing for millennia, Juniper is declining across its range with not enough new plants germinating to replace old and dying plants.
The clay that caps the top of the Chilterns was formed from impurities left behind as the chalk weathered. It has enabled clay lined ponds to form, providing a habitat for many animals from amphibians including frogs, toads and newts to dragon and damselflies. Bluebells also fare better on the more nutrient and moisture retentive clay caps.
Water emerges at the foot of the hills at the spring line, feeding chalk streams. These are very rare worldwide, the majority are located in southern Britain. The filtered spring water is pure and of a stable temperature, providing a particular habitat on which some species depend.
10,000 years ago the last ice sheets retreated and trees returned to the area. They colonised in a particular order – firstly Scots Pine, Birch and Willow which were able to grow quickly on the poor soil and their wind pollinated seeds spread widely. Each tree brought with it its own living community, such as Birch Bracket Fungus. Historically it was useful as an antiseptic, as tinder and as a razor strop. Slower to colonise were oaks, whose acorns are spread by Jays. Each bird is estimated to bury 2000-3000 acorns annually as a store of food. They remember the location of most but those forgotten might germinate.
After a thousand years the woodland had developed into a complete mix of species and become home to the people of the Mesolithic period. They were few and their nomadic, hunter-gatherer lifestyle had little impact on wildlife. But all this changed around 6000 years ago in the Neolithic, when the first framers cleared the forest to settle down and grow their crops. Their clearance did enable a new habitat to flourish, super-diverse chalk grassland. The poor soil limits any one species becoming dominant. Many plants are also found on other chalk areas such the Downs, but the Chiltern Gentian is endemic to this area. Many orchids also thrive on chalk, including the specifically local Military Orchid.
The Chilterns are renowned for their Beech woodlands, but these trees are quite new arrivals, only just making it to the UK across the land bridge before Britain was cut off from Europe by post-glacial rising sea levels. For centuries they were coppiced to provide firewood, creating an open woodland where ground cover plants thrived. However, in the late 18th century these were grubbed up and replaced with closely planted new Beech trees, which grew tall and straight to seek out light. These trees were grown for the famous furniture industry. But the canopy of these new Beech woods can exclude 97% of light to the woodland floor and the leaf litter is slow to decay, enabling few plants to germinate or grow at ground level, even beech saplings. One plant that overcomes this and can grow in the deep shade is parasitic White Helleborine, whose roots are connected the fungi which are connected to beech trees.
Whilst few fungi tolerate the poor conditions of chalk grassland, they do thrive in Beech woodland. False Death Cap is specific to Beech, as is Porcelain Fungus, which only grows on dead Beech wood. The delicate, translucent fruiting bodies often grow up high on trees and and have a slimy coating to protect them from the sun. Diminutive Saffron Drop Bonnet fungus only grows on fallen Beech wood.
In recent centuries introduced species have come to call the Chilterns home, including Grey Squirrels, Muntjac Deer and Edible Dormice. Roman Snails, brought over as a delicacy by the Romans, can be seen early on Spring mornings after rain, embraced in their courtship dance.
As we all know, our world is changing fast and many wild species cannot keep pace with this rapid change. Our special chalk streams often only flow in winter when the water table is high enough but climate change, water abstraction and pollution are upsetting their delicate balance. Beech trees don’t tolerate very dry or very wet conditions and may not cope with the predicted more extreme weather. John concluded that we will need to protect and give a helping hand our local wildlife if it is to survive.
Jackie Hunt, Gardener, Turn End