Transcript Heathlands - Demon Internet

Heathlands
• Peter Shaw
• USR
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
c. 30cm
Bleached (ashy) horizon
Black layer - iron pan.
Parent material - usually sand.
• 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 overexploitation 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.
Bronze-age
burial mound
Heathland + podsol
Brown forest
earth
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.
Cyclical changes in a heather community.
1 cycle is 30-60 years.
Building phase
Succession to
woodland
Mature phase
Pioneer phase
-young heather
-plants appear
Heather dead – ground
colonised by other spp.
Degenerate
phase
• 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.
A heathland bog: Narthecium
and cotton grass.
• In the wetter regions we
have bog asphodel or bonebreaker, 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.
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 < 10 pairs. There are
now several 1000, limited by
heathland habitat. Thursley
common (A3 beyond
Guildford) has >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 radiotelemetry 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
16th 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 infieldoutfield 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 soilfavouring 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 worldbeating 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 quasirandomly, 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 longterm 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 highrate 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
New Scientist impact on grouse populations, and despite
9/3/1996 p.14
birds of prey being protected by law,
on grouse
gamekeepers regularly kill these raptors.
vs harriers.
• 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!