Bog core analysis, succession and climate
change
Technical & Teaching Notes
Introduction
This activity looks at the change in vegetation in a location in Norfolk between c. 12,000 years
before present and 2,000 years BP.
Students carry out a simulation of a bog core analysis, and use the resulting data to think about
either:
 Climate change (14-16 students)
 Succession and climate change (post-16 students)
Context: bog cores and palynology
When plants die, they normally decay. However, in anaerobic conditions, decay is greatly delayed
and a peat bog may be formed. Within the bog, layers of peat represent different periods of
history: the deeper the peat, the older it is. We can derive a considerable amount of information
about previous climates by taking a core sample from a peat bog, and using palynology (the
study of pollen) to identify which plants were present at certain times in the past.
A core sample may be some 10m deep, representing up to 12000 years of history.
To obtain a bog core sample, an auger is needed, as
shown in the image (left).
One commonly in use is the Livingstone corer. This
consists of a hollow 1m metal tube with a piston inside
it. When a core is to be taken, the corer is placed
vertically over the area to be studied. As the corer is
pushed down, soil is forced into the tube, pushing up
the piston. When it is withdrawn, it is laid horizontally
next to a 1m length of aluminium foil, placed over a
1m piece of guttering.
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Bog core analysis, succession and climate change: p. 1
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It may not be photocopied for any other purpose. Revised 2012.
The piston is then pushed, forcing the cylinder of core sample out onto the foil (shown above).
Once out, the foil is wrapped around the sample to protect it and allow it to be kept whole for
transport back to the laboratory in the guttering.
For the next metre of sample, the method is repeated, except that a further section of 1m tube is
attached to the corer, allowing it to be inserted to a depth of 2m. This is then repeated until
perhaps 10m of depth has been removed, i.e. 10 cylinders of core. In the laboratory, strong
corrosive chemicals (such as hydrofluoric acid) are used to dissolve away all the organic matter
and minerals, except for the pollen.
The outer exine of pollen is composed of sporopollenin. This is thought to be a randomly crosslinked macromolecule, composed of carbon, hydrogen, and oxygen, and including fatty, aromatic
and carboxylic acids. It is resistant to enzymatic and chemical treatments, hence the longevity of
pollen in bog cores.
School laboratories will be unable to do such practical work: even in research laboratories, the
most stringent safety procedures are necessary. Therefore to undertake any form of experimental
work, a simulation is required.
Science & Plants for Schools: www.saps.org.uk
Bog core analysis, succession and climate change: p. 2
This document may be photocopied for educational use in any institution taking part in the SAPS programme.
It may not be photocopied for any other purpose. Revised 2012.
Activity
This resource is based on an original teaching activity created by the University Corporation for
Atmospheric Research at Boulder, Colorado.
The data used here comes from bog core samples taken at Hockham Mere, Norfolk, taken by
researchers at the University of Cambridge.
A simulation of a bog core can be achieved by putting different mixes of peat, soil, sand, gravel
and powdered chalk in a series of layers in a transparent plastic tube. By adding ‘pollen samples’
(represented by e.g. coloured paper shapes), students can carry out a simulated bog core
analysis. The data on plant species over time can then be used as an unusual way of looking at
either succession or climate change.
Preparing the ‘bog core’ - optional
1. Before the lesson, prepare an example of the ‘bog core’ to show to students how the
layers vary. The ‘core’ illustrated here is a Perspex cylinder 50cm x 6cm diameter: it is
sealed at each end with a small square of glass glued to the Perspex. Creating the ‘bog
core’ is not crucial to this practical, but it does help the students to understand the
concepts behind it.
Science & Plants for Schools: www.saps.org.uk
Bog core analysis, succession and climate change: p. 3
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It may not be photocopied for any other purpose. Revised 2012.
2. Sticky labels should be applied to show the age of the various layers.
Preparing the other materials
1. Each group of students will need a ‘bog core sample’ representing a layer of the ‘bog
core’. This is a plastic bag of soil, with small coloured shapes representing the different
tree pollen found at that layer. These are mixed in the correct proportions (see the table
‘Relative frequency of pollen at different time periods’, below). There are 11 different time
periods represented in the table. You may wish to have students working in pairs, and
have more than one ‘bog core samples’ representing a given time period.
Science & Plants for Schools: www.saps.org.uk
Bog core analysis, succession and climate change: p. 4
This document may be photocopied for educational use in any institution taking part in the SAPS programme.
It may not be photocopied for any other purpose. Revised 2012.
2. You will also need to complete the ‘tree identification sheet’ given below to indicate which
of your coloured shapes represents which pollen.
Instructions
1. Give each group of students a ‘bog core sample’ from a different layer.
2. Students sift out the different coloured shapes, recording how many of each type there is.
This should be done in a tray, to prevent mess and to ensure the ‘samples’ can be reused.
3. Students should then match each shape to a particular species, using the key, and
record their results.
4. Students now pool their results as a class, and construct abundance (of each species)
against time (years ago) graphs.
5. At GCSE level, students then use the information given in the tree identification key to
identify the effect of climate change over the time period.
Students should be able to identify the change from a woodland dominated by birch to a
woodland dominated by hazel, oak and alder. They will then be able to link the
temperature preferences of the different trees to the change in climatic conditions, with
birches able to thrive in the cooler conditions of the early period, and familiar English
woodland trees taking over with the rise in temperature.
6. At post-16 level, students use the information given to discuss the varying factors
influencing the change in vegetation, including both the impact of succession and of
climate change. If desired, students can then be given the abstract from the original
journal article from which the data was taken, and compare it with their own conclusions.
Science & Plants for Schools: www.saps.org.uk
Bog core analysis, succession and climate change: p. 5
This document may be photocopied for educational use in any institution taking part in the SAPS programme.
It may not be photocopied for any other purpose. Revised 2012.
Apparatus
For the ‘bog core’ - optional




layers for the ‘bog core’, e.g. mixtures of peat, compost, sand, gravel, powdered chalk
transparent plastic tube (e.g. 50cm x 6cm diameter), sealed at each end, e.g. with a
square of glass glued to each end
sticky labels to indicate levels in the plastic tube
coloured shapes to represent the different pollens (9 different varieties)
For the other materials




soil contents for the ‘sample bags’ representing the 11 different time periods sampled,
e.g. mixtures of peat, compost, sand, gravel, powdered chalk
coloured shapes to represent the different pollens (9 different varieties)
plastic bags (e.g. sandwich bags)
trays for students to sort the contents of their ‘bog core sample’
Background information
Relative frequency of pollen at different time periods
This table shows the number of different types of ‘pollen’ to be placed in each ‘bog core sample’,
based on the relative frequency of pollen found in Hockham Mere at different time periods.
For example, the ‘bog core sample’ representing 2000 B.P. should contain 5 pieces of coloured
paper representing birch pollen, 40 pieces of coloured paper representing hazel pollen, 1 piece of
coloured paper representing elm pollen, etc.
Years
before
present
2000
3000
4000
5000
6000
7000
8000
9000
10,000
11,000
12,000
Birch
(approx
%age)
5
5
7
10
7
12
5
12
45
50
40
Pine
Hazel
Elm
Oak
Lime
Alder
Ash
Willow
0
0
0
0
0
3
10
20
5
3
3
40
65
60
30
50
50
70
60
1
1
1
1
1
2
5
10
10
5
10
0
0
0
15
20
18
25
20
20
10
2
0
0
0
2
5
2
5
3
1
0
0
0
0
0
10
11
12
15
10
2
0
0
0
0
0
3
2
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
10
8
8
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Bog core analysis, succession and climate change: p. 6
This document may be photocopied for educational use in any institution taking part in the SAPS programme.
It may not be photocopied for any other purpose. Revised 2012.
Science & Plants for Schools: www.saps.org.uk
Bog core analysis, succession and climate change: p. 7
This document may be photocopied for educational use in any institution taking part in the SAPS programme.
It may not be photocopied for any other purpose. Revised 2012.
Further reading: journal abstract
The data in this resource is discussed in detail in an article in the New Phytologist journal by Prof
K. D. Bennett. We have included the abstract here, both for your own information and for possible
use with A-level students. Students may, for example, wish to compare Prof Bennett’s findings
with their own, and discuss the differences. They will probably find that, with the limited
information at their disposal, their findings were considerably less detailed but still broadly similar
in outline. They may wish to discuss what extra information Prof Bennett had access to which
allowed him to draw his conclusions.
“The sediment and pollen stratigraphy of a radiocarbon-dated sequence from a lake on the
eastern margin of Breckland is described. The record extends from 12620 to 1620 B.P. From
12620 to 9560 B.P. the vegetation was an open Betula woodland. Movement of sand by wind
was one factor keeping the vegetation open. Between 9560 and 9255 B.P. a denser Betula
woodland developed, to be replaced by a closed woodland dominated by Corylus avellana, with
Pinus sylvestris, Ulmus and Quercus. During this period, Quercus gradually replaced P. sylvestis
on the local sandy soils. Corylus avellana remained the woodland dominant until about 7140 B.P.,
when it was replaced by Tilia cordata. Alnus glutinosa expanded in response to raised water
levels at about 6800 B.P., Fraxinus excelsior became an important component of the local woods,
also replacing C. avellana. The elm decline occurred in two phases, at 6000 and 4500 B.P.
Substantial forest clearance did not begin until about 2500 B.P. The spread of heath vegetation
on the Breckland began at about 2250 B.P.”
From ‘Devensian late-glacial and Flandrian vegetational history at Hockham Mere, Norfolk,
England’, K.D. Bennett, New Phytologist, 95, 457-487 (1983)
Available online at http://www.jstor.org/stable/2434313?seq=1
References and acknowledgements
‘Devensian late-glacial and Flandrian vegetational history at Hockham Mere, Norfolk, England’,
K.D. Bennett, New Phytologist, 95, 457-487 (1983)
Pollen: The Hidden Sexuality of Flowers by Rob Kesseler, Madeline Harley and Alexandra
Papadakis
This resource is based on an original teaching activity created by the University Corporation for
Atmospheric Research at Boulder, Colorado. For full details, see
http://www.ucar.edu/learn/1_2_2_10t.htm
Data from Hockham Mere courtesy of Dr Steve Boreham, Department of Geography, University
of Cambridge
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Bog core analysis, succession and climate change: p. 8
This document may be photocopied for educational use in any institution taking part in the SAPS programme.
It may not be photocopied for any other purpose. Revised 2012.
Tree Identification Sheet – GCSE
A
Fill in
appropriate
coloured
shape here
Birch
(Betula)
B
Pine
(Pinus
sylvestris)
C
Hazel
(Corylus
avellana)
Elm
(Ulmus)
D
E
Oak
(Quercus)
F
Lime (Tilia
cordata)
G
Alder
(Alnus
glutinosa)
H
Ash
(Fraxinus
excelsior)
I
Willow
(Salix)
Birches grow in a wide range of places, both in temperate
regions and the extreme north. Young birch trees struggle to
grow without plenty of light. The oldest birch fossils date from
the Upper Cretaceous period – so dinosaurs might have
wandered among birch forests.
Pine trees are well adapted to poor soils, as their roots
extended by mycorrhizae. The first Europeans to settle on
Cape Cod in America cut down the pine forest, expecting to
find rich soil for wheat fields. Instead, they found only sand
dunes, and nearly starved to death. Pine trees grow well in
cold conditions. Young pine trees struggle to grow without
plenty of light.
Hazel trees are the source of hazelnuts, an excellent source
of vitamins and protein. They grow well in temperate regions,
neither too hot or too cold.
Elm trees used to be common in the UK, but were largely
wiped out in the 1970s by Dutch Elm Disease. Elms are
generally large, fast-growing trees, able to grow in cold
conditions.
There are around 450 species in the oak family, which have
adapted to many different habitats around the world. Oaks
grow mainly in temperate regions, which do not have
extremes of either hot or cold. Young oak trees do not need
much light in order to germinate and begin growing.
Lime trees grow well in England and Wales, but are not
usually able to grow in the cooler conditions of Scotland.
When found in British woods, lime trees often indicate an
ancient woodland – a wood that has existed continuously
since 1600 or before.
Alders are fast growing trees, able to grow up to 30m in a
decade. They do particularly well in water-logged soils, as
their roots contain nitrogen fixing bacteria. Alders are found
both in temperate regions and the extreme north of Europe.
Ash is a deciduous tree with a single trunk growing up to 40
m in height. Ash is common in woods and hedgerows. It
prefers temperate climates, without extremes of hot or cold.
In the UK, ash is often the last tree to open its leaves in
spring, and the first to drop its leaves in autumn.
There are about 400 species of willows, growing in many
different habitats around the world. Although some willows
grow in the tropics, most willows are cold tolerant, and are
even found growing next to glaciers. Most willows like the
wet soil on the edge of rivers and lakes.
Science & Plants for Schools: www.saps.org.uk
Bog core analysis, succession and climate change: p. 9
This document may be photocopied for educational use in any institution taking part in the SAPS programme.
It may not be photocopied for any other purpose. Revised 2012.
Tree Identification Sheet – A-level
A
Fill in
appropriate
coloured
shape here
Birch
(Betula)
B
Pine
(Pinus
sylvestris)
C
Hazel
(Corylus
avellana)
D
Elm
(Ulmus)
E
Oak
(Quercus)
F
Lime (Tilia
cordata)
G
Alder
(Alnus
glutinosa)
H
Ash
(Fraxinus
excelsior)
I
Willow
(Salix)
Birches are a fast-growing family of trees, frequently acting
as pioneer species. Juvenile trees are general intolerant of
low light intensities. Birches are geographically diverse,
found both in temperature regions and the extreme north.
They are frequently found in peat lands, on stream banks
and lake shores and in damp woods. Birches are wind
pollinated.
Pines are well adapted to poor soils, as their roots have a
symbiotic relationship with mycorrhizae. The first Europeans
to settle on Cape Cod in America cut down the pine forest,
expecting to find rich soil for wheat fields. Instead, they found
only sand dunes, and nearly starved to death. Pine species
grow in a remarkable range of climates, from extreme cold to
tropical conditions. Juvenile trees are moderately tolerant of
low light intensities.
The hazel is a small tree or shrub, found in temperate
regions. Able to grow in low light levels, hazels are commonly
found in woodland or hedges. Hazelnuts are valued for their
food value, as they are rich in vitamins and protein.
Elm trees used to be common in the UK, but were largely
wiped out in the 1970s by Dutch Elm Disease. Elms are
generally large, fast-growing trees, tolerant of waterlogged
soils, and able to grow in cold conditions.
There are around 450 species in the oak family, which have
adapted to many different habitats around the world. Oaks
grow mainly in temperate regions, which do not have
extremes of either hot or cold. Juvenile trees are moderately
tolerant of low light intensities. Oaks are a frequent
component of climax communities in the UK.
Lime trees are found across the centre of Europe, reaching
as far up as Durham in the UK. When found in British woods,
lime trees often indicate an ancient woodland – a wood that
has existed continuously since 1600 or before. Juvenile trees
are moderately tolerant of low light intensities, and are able
to grow well in dense woodland.
Alders do particularly well in water-logged soils, because
they contain nitrogen-fixing Frankia bacteria in nodules in
their roots. They are a pioneer species, growing rapidly, up to
30m in a decade. Because they fix nitrogen, they are able to
improve the soil significantly. Alders are geographically
diverse, found both in temperature regions and the extreme
north.
Ash is a deciduous tree with a single trunk up to 40 m in
height. It is found very commonly in woods and hedgerows,
especially on lime-rich and heavy soils. Ash is found in
temperate climates, and in the UK is often the last to open its
leaves in spring, and the first to drop its leaves in autumn.
There are about 400 species of willows, growing in many
different habitats around the world. Although some willows
grow in the tropics, most willows are cold tolerant, and are
even found growing next to glaciers. Most willows are to the
wet soil on the edge of rivers and lakes.
Science & Plants for Schools: www.saps.org.uk
Bog core analysis, succession and climate change: p. 10
This document may be photocopied for educational use in any institution taking part in the SAPS programme.
It may not be photocopied for any other purpose. Revised 2012.
A-level students – Questions and answers
1. In your pair or group, identify key factors that you think may have altered
the population of trees growing in the area.
Students might suggest some of the following: global changes in temperature, a
rise in water levels, increased levels of organic matter in the soil from decay of
plant matter, increased nitrogen levels in the soil from nitrogen fixation by the
alder trees, succession, changes in light levels at ground level caused by the
growth of larger trees and (more recently) forest clearance by people
2. Summarise how the tree population of Hockham Mere has changed over
the period under study. You may want to show this as a table, with
columns for time period, tree population and environmental factors
preferred.
The pollen findings should indicate an original woodland comprised mainly of
birch, with some willow trees. Around 9,000 B.P., there was a sudden spike in
the number of pine trees. At around this point, the birches, pines and willows all
gave way to a woodland comprised largely of hazel. To begin with, this hazel
woodland was intermixed with elms, which gradually gave way to oaks. At
around 7,000 BP both limes and alder trees arrived in the woodland, but although
alders became an important component of the natural environment, the limes
remained relatively few. Ash trees arrived c. 6,000 BP but also remained
relatively few.
3. Using the information on the ‘tree identification sheet’, identify the
environmental factors preferred by trees growing at different time periods.
Add these details to your table.
4. Using what you know about succession, how do you interpret the changes
of species over the years?
5. These pollen samples come from the Holocene period, a period during
which the earth’s climate became warmer and wetter (see details on the
Powerpoint). How does this contribute to your understanding of the
changes of species in Hockham Mere?
6. Are there any features of the data that you cannot explain? Are there any
further investigations that you would carry out?
It is difficult to know exactly why this sudden change from a predominantly birch
forest to a predominantly hazel forest took place. Students may have
suggestions for ways to look at this in more detail, for example by comparing the
data with that from other bog cores, finding out how well different pollen types
survive over very long time periods and researching the tree species in greater
detail.
Science & Plants for Schools: www.saps.org.uk
Bog core analysis, succession and climate change: p. 11
This document may be photocopied for educational use in any institution taking part in the SAPS programme.
It may not be photocopied for any other purpose. Revised 2012.
GCSE students – Questions and answers
1. What trees grew in the forest between 12,000 and 10,000 years BP?
Birches and willows
2. What temperatures do these trees need?
Cool temperatures
3. What trees grew in the forest between 5,000 and 2,000 years BP?
Oaks, hazels, ash and lime trees.
4. What temperatures do these trees need?
Warmer temperatures
5. What trees grew in the forest between 9,000 years and 4,000 years BP?
Pines grew in the forest only during this period. Birches were becoming less
common. Oaks, hazels, ash and lime trees were becoming more common.
6. What do you think happened to the climate between 12,000 and 2,000
years BP?
Between about 11,500 BP and 5,000 BP the climate warmed up, glaciers melted
and sea levels rose. After 5,000 BP, the climate in temperate latitudes cooled
again.
7. What other factors do you think might have influenced the change in tree
species?
Other factors might include levels of rainfall, pests and diseases, introduction of
new species (by humans and animals, or carried on the wind or water), change in
soil nutrient levels, and natural succession.
8. How do you think that birds and animals living in the forest were affected?
Old habitats disappeared, and new habitats replaced them. The types of shelter
and food available for birds, animals and insects all changed.
Science & Plants for Schools: www.saps.org.uk
Bog core analysis, succession and climate change: p. 12
This document may be photocopied for educational use in any institution taking part in the SAPS programme.
It may not be photocopied for any other purpose. Revised 2012.