Snelsmore Common

Snelsmore Common. May – June.

David Beeson

Lowland heaths are not common habitats. Over 80% of the lowland heathland in the UK has disappeared in just 200 years. The New Forest’s 10,000ha is the most extensive area remaining in Europe. Snelsmore Common, near Newbury in the M4 Corridor, is a small patch of heather-dominated environment.

Free-draining, surface gravel or sandy soils allow water to pass through easily, carrying any soluble minerals deep into the soil profile. Sometimes the iron in that water, in anaerobic conditions, forms an impermeable iron-pan (layer) beneath the surface that inhibits water passing deeper and the whole area may become waterlogged, especially in winter when rainfall exceeds evaporation. Hence, the place can be dry in summer and very wet in winter – generating an unusual mix of conditions that few plants can tolerate. This happens at Snelsmore, and the effect is increased by a second impermeable layer of clay beneath the iron-pan.

With any mineral nutrients easily washed out of the gravel-enriched soil, and a wet environment, it is little surprise that the vegetation, and subsequently the animal life, is quite exceptional. This is a place where daisy, dandelion and their friends are unlikely to be seen. Heathlands are environmentally very special places and ones to be treasured.

Heathers, especially ling, dominate heathlands but here we will also see two other types: the locally uncommon, dry heath specialist, bell heather and the wet-loving cross-leaved heath. They are all in full flowers in August and September. Other heath plants, such as the ground hugging bilberry and the prickly gorse, thrive here too.

An all-weather path leads me through a gate that keeps the Dartmoor and New Forest ponies from escaping their designated home. These animals have a good life, being free to wander and graze or browse as their mood takes them. To ensure an even more perfect existence they have supplementary hay in winter. The question is: why are they here at all? They are not natives and Snelsmore is an important wildlife reserve. Even a quick look around will alert everyone to the problem: birch and gorse regeneration. Heaths are not fully natural; they are human-made by hundreds of years of domestic animal grazing. ‘Commons’ were communal lands open for anyone to graze their cattle, pigs or horses, to collect firewood and to harvest heather for thatching. With the demise of commoners, the previously intensively-cropped land changed – it started to go through a succession of plants: heather slowly replaced by young gorse and birches, leading eventually to a closed woodland and the death to the heathers. Woodland can soon develop from heathland and with it the loss of all its unique wildlife. Heathers are plants of open skies. They need full sunlight and shade kills them and all the beetles, bees and other creatures they support with their pollen, nectar and greenery.

The ponies, by their nibbling, help to stop succession. Even so, you’ll see that humans have still be used to help by cutting down young birches by the hundreds. Birch seeds, released in their millions, are very effective in producing more birches.

Beyond the gateway there is a contrast in vegetation: a mixed wooded grove to the left and more-open heathland to the right. The difference in ground flora is clear. Woodland and open heathland are very different in the plants they can support.

Smooth-barked beech, silvery white birches and the grey, crumpled trunked oaks are all to be seen to my left. Sweet chestnuts too, but almost no greenery thrives at ground level.

The nesting box has been protected from greater spotted-woodpeckers with a metal protector. Without that, there is a high chance the nestlings would have been reached by the predator enlarging the entrance hole. Result: baby great tits being fed to young woodpeckers. Of course, many free-nesting birds will lose their young to various meat-eaters, yet these nestlings should be safer.

The ground along the edge of this pathway was saturated in early April, with the water stopped from percolating deep down into the underlying chalk by both the iron-pan and the clay layer. Now, later in the year, those pools have mostly been evaporated away and oxygen can again reach the heather’s (ling) roots.

Poor old ling! At one time it has to survive with no oxygen reaching its roots and surrounded by water, the next month being dried out by a hot sun and desperate for moisture. Such is life on the heath and why these specialist plants are found almost nowhere else.

It’s worth looking closely at all there three heathers. Here you will almost certainly be studying at ling. I’d describe it as a small shrub with miniscule tough leaves (2 or 3 mm long and in pairs). The rolled nature of the leaves reduces water loss. It is a species well adapted to the bone-dry soils of summer. Below ground, the plant’s roots are infected with a fungus (mycorrhiza) that is vital in helping the plant secure minerals and water. The ling receives water and minerals, the fungus is donated sugar from the heather in a mutual exchange.

Ling’s shoots are the food of the grouse (not found here), also both the adult and larva of the heather beetle (Lochmaea suturalis) and of a number of Lepidoptera species feed on the plant, notably the small emperor moth (Saturnia pavonia). The nectar feeds myriads of bees and moths in late summer.

Gorse (Ulex europaeus), sometimes called whin, catches the eye. Its bright yellow flowers and delightful coconut aroma make it a popular plant … so long as one does not pick it. It is armed with leaves modified into vicious spines. All the better to stop both browsing and water loss. It is a shrub that thrives in poor soils where its nitrogen-fixing capacity helps it survive.

Gorse is a valuable plant for wildlife, providing dense thorny cover ideal for protecting bird nests. In Britain it is particularly noted for supporting Dartford warblers (Sylvia undata) and stonechats (Saxicola rubicola); the common name of the whinchat (Saxicola rubetra) attests to its close association with gorse.

While management here, until now, has not used burning, gorse is adapted to withstand fires, having seed pods that are to a large extent opened by fire, thus allowing rapid regeneration after they are consumed. Burnt stumps also readily sprout new growth from the roots.

Soon I spot some climbing honeysuckle (Lonicera periclymenum), also known as woodbine. Another plant with a delightful scent that is designed not to delight our noses but to attract pollen distributing insects. At night the sweet smell of honeysuckle is strongest and attracts pollinating moths, such as the distinctive hummingbird hawk moth. Moths can detect the scent of honeysuckle a quarter of a mile away.

Honeysuckle sports near stalkless, oval leaves and a weak twining stem which is supported instead by its host tree or shrub. It bears clusters of red berries in the autumn that are attractive to birds (including thrushes, warblers and bullfinches), but whose seeds pass through their gut undigested and so are spread widely. (Mammals have teeth that can crush and destroy the seeds. Not so with birds.) I will not be chewing any berries as the seeds are mildly toxic to humans.

The white admiral butterfly is a mainly woodland species that relies specifically on honeysuckle. White admiral caterpillars exclusively feed on honeysuckle.

The scots pine is just one of three types of conifers that grow naturally in the UK. It can live up to 700 years, yet most trees here will not live much beyond 100. It is a flowering plant though you need to peer closely to spot the flowers. Male flowers comprise clusters of pollen-producing, yellow anthers at the base of shoots. Female flowers are small, red-purple and globular and grow at the tips of shoots. Flowering occurs in spring with the female structures taking two or three years to develop mature cones containing the seeds. Once the scales of the mature cone open the seeds are exposed to the air and are distributed.

The scots pine is excellent for wildlife. Lichens and mosses grow around and in the cracks on the trunk. Insects live in the tree’s crevices. Birds such as the siskin, greater spotted-woodpecker and crossbill can feed well around a scots pine. Often pine seeds are cached for later consumption, some being left to germinate if the bird dies or forgets that seed.

Mature birch trees abound along the track. It’s a mistake to see them as single plants. They and other trees are colonies of plants. Mosses coat the trunk to soil junction. Lichens and minute, single-celled algae cling to the bark giving it a green tinge; higher up other flowering plants or ferns may have rooted into the bark or at the junction of trunk and side branches. These colonisers are called epiphytes. Many of the trees have an and orange-red lichen epiphyte – called Xanthoria pariena. (You may see it on your own roof. It is a species that enjoys bird droppings.) Xanthoria produces spores from the darker-orange discs you may notice and, like all lichens, the organism is a mixture of both a fungus and an alga.

Having spotted one lichen, I see them everywhere on the trees lining the all-weather pathway. Most appear blue-grey, some encrust onto the branches and twigs, others appear leafy and those least tolerant to pollution look shrubby. They deserve to be better known as they have their own delicate beauty.

To my left, the heath opens out and I spot a second type of heather. It is growing in soil that remains soggy for much of the year. This location is so damp that the ling is easily out-competed by a species that seems to relish these conditions: Erica tetralix – with, as the name suggests, four grey-green leaves in a cross: the cross-leaved heath. The sticky, adhesive glands on its leaves, sepals and other parts of the plant are toxic, containing tannins and oils that discourage them from being eaten.

To survive in this situation the plant contains air cavities allowing the oxygen from photosynthesis to reach the roots (which, like all roots, need the gas to survive).

I’m always thankful I can recognise this plant because walking where it grows can be hazardous. A boot full of water and mud is seldom appreciated!

As my path turns to the right the extent of birch regeneration, despite the effect of horses and conservation teams, is obvious. Silver birch seedlings are tolerant of a wide range of conditions and their roots contain swellings rich in nitrogen-fixing bacteria. These micro-organisms can convert atmospheric nitrogen into nitrate to enhance plant growth. Birch is, therefore, less reliant on soil minerals than many other species.

The delicate grey birch moth (Aethalura punctulate) has a wingspan of 30-35 mm. It is a small organism with a mottled grey ground colour and three darker transverse lines. The adults fly in May and June, and frequent wooded habitats. Birch (Betula pendula) is the main foodplant of the larval stage, but occasionally the alder tree (Alnus glutinosa) is used. The adult, like virtually all animals of a similar design, feeds on nectar or sugars excreted by aphids. 

The birch mocha (Cyclophora albipunctata) with a smaller wingspan of 20-25 mm also has a larva that feeds on birch leaves. It occurs in woodland areas in much of Britain and flies in May and June, with a second generation in August.

Occasionally I can spot the signs of narrow tunnels winding around within the birch leaves (and more often holly leaves). These are the feeding trails of minute larvae that feed on the internal green cells of the leaf. Insects of this type are called leaf miners. A rare miner attacks Scots Pine cones early in their development – their pin-sized exit holes can sometimes be seen.

A full list of the insects feeding off birches would fill half a page, so the tree is important in the food chain. Management here at Snelsmore aims to keep its population low enough that it does not crowd out every other plant yet providing a habitat for organisms needing it. Extermination is not wanted.

By viewing the dominance of young birch trees growing in some locations it is easy to forget the bigger picture – a mature silver birch is a beautifully elegant tree with a black streaked trunk and dangling branches that float and dance in the wind. It is a stunner!

By using a light trap at night Snelsmore’s researchers have recorded hundreds of different night-flying moths, each with possibly only a single plant type providing food for the larval stage. The greater the diversity of plants the more varied are the moths encountered.

Apart from the imported horses and an occasional roe deer this heathland lacks many larger mammals. The reason becomes clear when the flow of energy through the plants and animals is studied. Of the 50,000 kJ* (about 10,000 Calories) of energy a square metre of heathland absorbed by photosynthesis each year about half is used by the plants to keep them alive. Of the remaining energy, which is passed down the food chain, 99% goes to the small organisms (decomposers) that break down their dead leaves, flowers and the like. Only 1% is passed to animals that directly eat the heather. So, unless an animal eats woodlice and other decomposers there is little food available here. Hence snakes, eating slow worms, lizards or amphibians, will always be rare.

*The valley mires (bogs) here are even less efficient at trapping sunlight. They probably only capture 13,000 kJ. A UK forest will absorb at least twice as much energy as the dry heath heathers at Snelsmore and four times more than the mire vegetation.

Snakes need friends; their numbers are declining rapidly across the UK. I have carried out some basic research into adders on an RSPB reserve. They are timid creatures and maintain their distance from humans, horses and dogs – if allowed. They deserve their place on Earth and only eat a handful of, mostly, reptiles each year. If you spot a black and white male or an olive female enjoy their company and leave them alone. They’ll do the same to you.

Research has been carried out here, at Snelsmore, on their adders. They have been radio-tracked. The results showed that the males travel around much more than the sedentary females. With their sensitive nature it is important to stick to the accepted pathways and to control any dogs that accompany you. Snakes are important components of this area.

Grass snakes, olive-skinned reptiles with normally a yellow neck collar, also occur on the site. They can be larger than the adders.

The trackway takes me back to the car park … but I cannot resist investigating one of the valley mires.

Beneath my feet, near the edge of the mire, the ground feels flexible. By jumping, I can even feel the vibrations on landing. It is as if the very soil beneath my feet is alive. And, I’m not too far from the truth.

With a waterlogged soil any fallen or dead vegetation hardly decays at all. It forms deep black peat. It is this water-filled organic component that can vibrate. But, beware … on a field trip to the New Forest an adult, who had been warned and should have known better, decided to run across an area similar to that before me. It took us nearly twenty minutes to extract him from being waist-deep in the mire.

The way to take a vertical soil sample is to screw an auger down, pull it out and this allows one to view the profile of the site. If this was tried here the auger would go straight down and, if one was careless, it would be lost forever. The ‘soil’ is pure peat and hold no firmness when wet.

The soils on Snelmore are acidic. So acidic that the growth-promoting minerals (nutrients) in the soil have been solubilised and washed out, leaving a poor soil barely capable of encouraging plant growth. Nitrates will be at a low level, so some plants have taken drastic steps to gain some more – they have evolved into carnivorous plants. The round-leaved sundew (Drosera rotundifolia) is a small, red-looking, summer plant found in these peat-rich wet soils of the mire.  By looking closely, I can see that some of their hairy red leaves bear shiny droplets onto which insects stick. Once the prey is secured the leaves curl up and digest their prey with enzymes (similar to the ones our bodies employ on a chunk of steak). The digested insect is absorbed and its chemicals used for the plant’s growth.

There is a range of other native UK plants that also extract nutrients from animal prey – other species of sundews, butterworts and bladderworts.

Mires can grow slowly deeper as their peat develops. They can be up to 9m deep. With the anaerobic, wet and acidic conditions the dead plants (especially the sphagnum mosses) and materials such as pollen, fail to break down fully. That is what we call peat. By taking a vertical core out of the mire and extracting the still recognisable pollen grains, it is possible to chart the changes in plant populations in that area over time. The key being that under the microscope pollen from different species can usually be identified.

Each year, for thousands of years, the pollen produced by the local plants has fallen into the mire and been preserved there. The deeper we sample the older the pollen. Indeed, the age of this pollen can be dated to within 100 years. This depends on the fact that Carbon-14, a radioactive isotope of carbon, was absorbed into its structure and this decays at a known rate. It is possible to estimate when the pollen was deposited in Snelsmore’s mire.

Mires hold an accurate chronicle of the past environment.

Soon after the ice departed from Southern England birch trees arrived. Their pollen can be first dated to around 9000BC. As the tree cover was cleared by humans for agriculture the birch pollen decreased and was replaced by grass pollens. That generally occurs around 1500BC. The date for Snelsmore is much later – indicating that the soils here were known to be poor agricultural land and clearance occurred much more recently.

By looking around where there is a slope from dry heath to mire it is easy to see a change in the plants. Those species adapted to dryer conditions fade out as the dampness increases and wet-loving specialists take over.

Within the mire are pools. These support their own wildlife, including some beautiful dragonflies and developing fly larvae.

It’s all to easy to see the wildlife in a place like Snelsmore. A mature wildlifer will look beyond that and see the inter-relationships. Take one organism away and the rest of the jigsaw will inevitably change.

We must strive to protect not only places but individual species.