Presentation on theme: "Heathlands Peter Shaw USR. UK Heathlands These comprise a distinctive family of ecosystems, some forms having declined alarming in recent years. Lowland."— Presentation transcript:
UK Heathlands These comprise a distinctive family of ecosystems, some forms having declined alarming in recent years. Lowland heaths are especially endangered. The UK and Ireland together contain the majority of the world’s stock of Atlantic heath. “What - a globally important site? That patch of heather next to the hypermarket?” (RSPB magazine, heaths issue c. 1997)
Locally.. We are lucky to have some internationally important lowland heaths within an easy drive of campus. Thursley heath (A3 past Gford) is one of the best outside Dorset. Headley and Chobham heaths are also large and important. The stronghold is still in Dorset/new Forest area. Between Poole and Bournemouth was one huge heath – Bourne heath, written about by Thomas Hardy. Upland heath (>300m elevation), also known as heather moorland, is a far commoner habitat, covering large areas of the Pennines, Wales and Scotland.
Not natural! Despite heaths being an important habitat, they are essentially a man-made artefact. By the end of this lecture I intend that: –1: You can name major heathland species –2: You can describe the features that characterise a heath –3: You understand the origin of heaths –4: You understand their conservation.
The main features: Heaths invariably have infertile acidic soils. The definitive heathland soil profile is known as a podsol (Polish: ashy soil). It is pH<4.5 in surface layer, may be as low as 3.0 deeper. There is little vertical mixing due to lack of earthworms. Surface litter Bleached (ashy) horizon Black layer - iron pan. Parent material - usually sand. c. 30cm
We know that most heaths result from man-made habitat destruction. For once, don’t blame the industrial revolution – this damage was bronze age, caused by forest clearance and land over- exploitation in pre-history. Pollen analysis shows this habitat expanding greatly during the bronze age. The original soil profile can be found preserved under bronze-age burial mounds. Brown forest earth Bronze-age burial mound Heathland + podsol
Not quite all man-made.. If heathland were entirely a recent (7000 years) habitat it would not have many habitat-specific species. In fact there are many such species. Heath communities occur naturally where acid infertile soils remain unwooded – cliff edges, above the tree line etc. What our ancestors did was to create a huge opportunity for heathland species to colonise new habitats. (Quite by accident: heaths only support very low human densities – useless for most agriculture) What modern land management is doing is to remove these historic landscapes.
The main players: Heathland is best defined by its plant community – all species of acid infertile soils. The definitive plant even gave its name to the habitat: Heather, or ling, Calluna vulgaris. This forms dense monocultures, covering the land for miles. It undergoes a cycle of life stages covering about 30 years, ending at a “leggy” degenerate phase which is very prone to invasion by pine or birch.
Building phase Mature phase Degenerate phase Heather dead – ground colonised by other spp. Pioneer phase -young heather -plants appear Succession to woodland Cyclical changes in a heather community. 1 cycle is 30-60 years.
Other plants in the heather family grow on heaths: Bell heathers (Erica spp.) prefer the wetter areas of heaths. Rhododendron ponticum is an alien, but destroys heaths with its dense shade. Bilberry Vaccinium myrtilis makes juicy blue berries, almost certainly supplying food to our ancestors. A few grasses are strongly associated with heaths: “Dflex” = Deschampsia flexuosa, and purple moor grass Molinia caerulea are the commonest. Few legumes tolerate these acid soils, but one genus is strongly associated with heaths: the gorses. Common gorse Ulex europaeus and petty whin Ulex minor – both yellow flowered and prickly.
In the wetter regions we have bog asphodel or bone- breaker, Narthecium ossifragum. Both its names refer to broken bones - oddly violent for a little yellow flower. Cattle grazed in its meadows broke their bones because of calcium deficiency. A heathland bog: Narthecium and cotton grass.
Also in the wet areas is cotton grass – Eriophorum vaginatum. Pretty – but avoid walking where this plant grows. Sundew Drosera spp (D. rotundifolia is commonest) and butterwort Pinguicula vulgaris supplement soil nutrients with animal tissue. These carnivorous plants are confined to the boggy areas of wet heaths. Oblong-leaved sundew Drosera rotundifolia
In fact heaths are rather low in botanical diversity. Their conservation value lies more in their animals. All UK reptiles occupy heaths: 2 are found nowhere else. Adder Grass snake Common lizard Slow worm Sand lizard Smooth snake
There are heath-specific birds. Dartford warbler Sylvia undata – our only warbler always to overwinter. This requires a gorse-heather mosaic, and is a mediterranean species at its northern limits on our southern lowland heaths. After the hard winter of 1962/63 the UK population was 30 pairs.
The nightjar, Caprimulga europaeus, is one of our oddest birds. Seeing it is one of the most memorable natural experiences. It nests on heaths, flying at dusk to sing – an incessant mechanical churring noise. Its flight is buoyant, almost ghostly in the gloom, and the song ventriloqual. Recent radio- telemetry work shows that it does not feed on heaths!! It flies to oak woods, where it hunts flying beetles all night, returning to the heath at dawn.
Then we have the hobby Falco subbuteo – a small falcon which hunts swallows and dragonflies. To see hobbies, visit Thursley common in mid-May. Male hobby
Invertebrates Heaths’ main biodiversity value lies in their invertebrates. Many scarce species such as the silver-studded blue butterfly, or the spider Ereseus niger, are confined to small patches of heath and appear to be very poor colonisers. 3 spp of dragonfly are also heath-specific.
A story of decline: Lowland heath peaked at c. 190,000 ha around the 16 th century, when peasant farmers used the common lands for grazing, firewood and turbiary (right of peat cutting). Between 1800 and 1983 the area declined by 75%. Decline accelerated with modern agriculture: Dorset lost 86% of its heaths between 1945 and 1983. When Tess of the D’Urvervilles was filmed, the heath scenes had to be filmed in Holland as the vast heaths of Hardy’s novel just were not there any more.
The problem is a shortage of peasants… To understand why heaths decline we have to understand the socio-economic system which maintained them. They were used by peasants as part of an infield- outfield farming system. Farmstead Infield – intensively managed Outfield – used for grazing by day, but animals brought in at night. Arrows show nutrient fluxes
Peasants used the heaths in several ways: They cut firewood and removed peat. The peaty soil was either burned or used as animal bedding. Gorse was cut for fodder. Animals grazed by day, were folded at night where they deposited dung. This was returned to the infield area as a fertiliser. The heath was burnt, by accident (they are often very dry) or on purpose to stimulate new tender shoots for grazing All these impoverished and acidified the soil- favouring heather and maintaining the ecosystem. Modern heathland management must aim to continue these management techniques, however drastic they may seem. Otherwise you lose the heath to pine forest.
What’s so bad about pine forests? It’s a question of habitat continuity. Ancient heaths have 7000 years continuous management behind them, but are easily lost. Their species are specialists. The species of pine/birch woodlands in the south are rather generalist, with no great conservation value. (Rather dismissive – common crossbills are colonising pines on East Anglian heaths – but you get the idea). BUT: Truly ancient pine forests, such as those in the Spey valley, have scarce specialist species and need conservation. The important theme here is continuity.
Reasons for heathland decline. Agriculture: True heaths are useless for agriculture, but it is possible to “improve” them by adding clay (“marl”) to the soil. Softwood plantations: pines grow well on these sandy soils, and their shade destroys the habitat. Fire: fires on a vast heath just create a habitat mosaic, but on a small heath, a deep-buring fire can sterilise the whole system. Development: because of infertility, heathland is cheap. This + its sandy nature attract developers and road builders. The one useful thing Chris Patten did as environment minister was to stop a new town planned for Canford heath, Dorset.
Roads: the land is cheap so attracts road development. Mineral extraction: Clay is mined under some of the best Dorset heaths. Pollution: The acidity of ‘acid rain’ is no problem for the plants, but nitrogen pollution allows grass to supplant heather. Many Dutch heaths are being overgrown by Molinia caerulea, due to world- beating levels of ammonia pollution. (Wherever dog walkers use a heath, heather is locally replaced by grass.)
But the biggest problem: Is natural succession. Heaths are a plagio-climax community, which depend on constant disruption. Left untended they colonise with pine and birch, losing specialist species in c. 30 years. Simply protecting a heath is not enough. It will vanish. To maintain a heath needs interventionist management. What it really needs is a force of peasants, heating their hovels with peat and grazing their skinny cattle on the heath. This seems unlikely: peasants can’t afford VCRs, and EU CAP money is dedicated to destroying the environment :-)
How to manage a modern heath: (pretend to be a family of peasants) Killing scrub. Wage incessant war on pine/birch seedlings, by hand (worst), herbicide, or graze with goats / highland cattle. Controlled burning – removes plants and nutrients. Burn with the the wind behind the fire, during the winter. Only burn small patches. Remove all topsoil, leaving acid infertile subsoil. Mow it. Heavy-duty mowers can mow a heath like a lawn. Thursley mow their heath quasi- randomly, giving a mosaic of short and long heather.
Your problems in doing so: Labour – this is heavy boring work. Use volunteers. Public objections: Each time you chop down a tree or mow a bush there will be a letter of protest! The SWT operates a policy of pre-emptive strikes, by running newspaper articles weeks beforehand, explaining about heathland work.
Upland heaths (heather moor) This is (rather arbitrarily) defined as heathland above 300m. It is colder and wetter than lowland heath, and lacks the mediterranean species or reptiles (adder excepted). It is noteworthy for birds – red grouse, predators (hen harrier, short-eared owl, merlin), and nesting waders (dunlin, redshank, golden plover, snipe, greenshank).
Economically this is a problem: There are large areas of heather moor in the UK, but nowhere does the land earn its keep. Grouse shooting can earn £, but bags have been in long- term decline for the last 50 years. Sheep are stocked – but at too high a density, destroying vegetation promoting soil erosion. And they still don’t earn their keep. Plantation forestry is widespread – sitka spruce and lodgepole pine do well, and are touted to high- rate taxpayers. In the UK these plantation forests have minimal biodiversity value.
So we should welcome grouse shooting? We sort of, but there is a catch here too. Keepers don’t like hen harriers (or foxes or buzzards …). There was some RSPB-funded research on hen harriers, which sadly confirmed that they do have a significant impact on grouse populations, and despite birds of prey being protected by law, gamekeepers regularly kill these raptors. An obvious solution would be for someone to pay landowners money to rear hen harriers on their land. I wouldn’t hold your breath waiting for this happen! New Scientist 9/3/1996 p.14 on grouse vs harriers.