Clean Air and Climate Change:
London’s Increasing Bryophyte
Biodiversity
Silvia Pressel and Jeffrey G Duckett
Researchers in Biodiversity
Life Sciences
Natural History Museum
Today’s presentation
1. An overview of London’s mosses and
liverworts focussing on London and in
particular the effects of the Clean Air Acts
(1956, 1968).
Acknowledgements. Our thanks to
generations of British bryologists who
collect distribution data.
Hunter Gatherers: Some of the 700
members of the British Bryological
Society
BRYOPHYTES
• Mosses, liverworts and hornworts
• Most primitive of all land plants –present
day bryophytes had ancestors going back to
470-480 MYA when plants first colonized
land.
Some numbers
• Bryophytes are very important components of terrestrial
ecosystems.
• 6% of the world’s carbon is locked up in the bog moss
Sphagnum, living and dead. We destroy this at our peril.
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The World
Mosses 10-12,000 species
Liverworts 4-6,000 leafy, 350 thalloid
Hornworts 200-250
Flowering plants 450,000
Ferns 10,000
Sphagnum-the bog moss
Kenwood Bog
The commonest liverworts in
London
• Marchantia polymorpha
• Lunularia cruciata
In pavement cracks, greenhouse pots
London numbers
Middlesex c 200
Includes canals and rivers, chalk and
heathlands in the north west
Middlesex 34 species (8 liverworts and 26
mosses) have been added since 2000
Hampstead Heath 146 (91 in 1998)
Why are bryophytes so small? 1mm
-1m cf flowering plants 1mm-100m
Why don’t we see tree mosses and
liverworts?
• Need to think about the problems of living on
land.
• Intermittent and uneven water supply
• Alternative strategies to deal with this;
• Homiohydry –maintaining water balance
• Poikilohydry – drying out and rehydrationdesiccation tolerance. The bryophyte and lichen
strategy
Homiohydry permits the growth of
large plants, poikilohydry imposes
severe limits on growth
When the plants are desiccated they are
quiescent –this does however allow them to
grow in some pretty inhospitable places eg
bare rocks and deserts. Within minutes of
rehydration they begin to grow again -1
shower/year . Some are extremely slow
growing <1mm/year and are almost
certainly very very old –probably older than
the oldest trees
Extreme desiccation
Syntrichia desertorum
London
LONDON
• London (Middlesex and North Surrey) is a very urban
environment
• Humans destroyed natural habitats a long time ago
Oliver Rackham –of the 12 earliest known herbarium
plants from Hampstead Heath (16 century), 6 no longer
grow there eg Drosera (sundew) –must have been a
wonderful valley bog full of Sphagnum all destroyed when
the ponds were constructed.
• The only near ‘natural’ vegetation is to be found on parts
of Hampstead Heath (Kenwood is ancient woodland),
Scratchwood, Ruislip Woods, Queen’s Wood.
Sphagnum –on the site of the
ponds
The Industrial Revolution
• Urbanization was only one factor that
destroyed bryophytes with it came air
pollution - soot and sulphur dioxide.
• Why are lichens and bryophytes so sensitive
to air pollution?
• Adapted to absorbing nutrients in very low
levels
• The future NOX?
London’s Woods in 1970
• Ancient Woodland –
Oliver Rackham
• Managed as oak
standards and
hornbeam coppice
• Woodland floor with
indicator species
Oak standards and hornbeam
coppice
Before the Clean Air Acts
• London was a mucky
place
• Sulphur dioxide and
soot in 1970
• Blackspots >200ppm
• London , Birmingham.
The North of England
1970
• Moths on soot-blackened trunks
• Melanism –dark coloured
varieties
• Several moth species >50%
melanic
Peppered moth Biston betularia
var typica and var. carbonaria
Woods in 1970
• Epiphytes Lichens and bryophytes
• Wholesale extinctions since the industrial
revolution – why?
• Depend on rain for nutrients, killed by
flooding with sulphuric acid
• Hampstead Heath only 5 epiphytes cf >25
today
Woods in 1970
• Tree trunks Bare wood often >50%, alga
(Pleurococcus) and one lichen Lecanora
conizaeoides
• Tree bases bryophytes confined to bottom
20cm and only 3 species
Bare bark
Bare bark –one lichen one green
alga
Pleurococcus and Lecanora
Today after the Clean Air Acts of
1956 & 1968
• Epiphyte recolonization to the extend that London’s
woodland trees are not very different from those in the
deepest countryside of S E England
• Much less bare wood
• Very little Pleurococcus
• Lecanora conizaeoides Almost extinct-competition
• Mosses and liverworts all the way up the trunks and onto
the branches - up to 25 species
Epiphytes on oaks. A major
change in the last 20-30 years
• Today mosses
growing up the trunks
• Lecanora
conizaeoides virtually
extinct
Orthotrichum pulchellum, Cryphaea
heteromalla and lichens
Why have London’s bryophytes
increased in number?
Better bryologists?
Clean air - much lower sulphur dioxide and
soot but more oxides of nitrogen
Climate change
Orthotrichum lyellii
Cleaner air Ted Wallace 50 years ago wrote ‘a declining
species in Surrey’
1981
Frullania dilatata
Cleaner air Ruislip Woods 1969
Cryphaea heteromalla
Cleaner air + Climate Change
Ulota phyllantha
Ulota phyllantha Climate change previously western and coastal
Cololejeunea minutissima
Climate change - perhaps the most
dramatic example
The Future
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We have a ‘hit list’ and many of the plants on it will
undoubtedly turn up. But in addition there will be
surprises
Current projects (NHM)
The City
The Highgate Cemeteries
The Thames and other waterways
Hampstead Heath
Conclusions
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London bryophytes are extremely beautiful
There is a lot of bryophyte diversity in London
The flora has changed radically in the last 30 years
The flora is still changing
Bryophytes can give wonderful insights into air
quality and climate change
• ‘If a bryologist is tired of London he/she is tired
of life’
Threats: mainly habitat losses
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Cutting down specific trees
Ash dieback, as this tree supports diverse
epiphytes
• Cleaning of stonework
Leave stonework alone!!
Gymnostomum viridulum
Mediterrannean species
Winchester Cathedral and Highgate Cemetery
Bryophyte Projects
• Recording –requires specialist knowledge
• Reproductive cycles
• Epiphyte distributions- new trees, spread on
existing trees
• Recording pollution
Reproductive cycles
• Easy to record
• All new data
• 4 very common London mosses
Grimmia pulvinata
Bryum capillare
Bryum radiculosum
Tortula muralis
Grimmia pulvinata
Tortula muralis
Jan to July
Bryum capillare Jan to Aug
Bryum capillare 2014-15 very
successful reproduction but----
Roadside trees –major
recolonization since 2000
Tufnell Park
2005 and 2012
Frullania dilatata
Ruislip Woods 1969. Mile End 2008. Tufnell
Park 2014
The British Bryological Society
http://www.britishbryologicalsociety.org.uk/
• Field Guide on line
• Excursions –local and to all parts of the
British Isles
• Free tuition and new discoveries almost
statutory