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THE IMPORTANCE OF SCOTTISH
BLANKET PEAT IN CARBON STORAGE:
Visual comparison of peat stored in blanket
peat and commercial forests.
James Fenton, 2010.
Available as a download from www.james-hc-fenton.eu
[email protected]
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Which stores
more carbon?
Forests?
Peat bogs?
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Peat stores carbon: the peat bog on the left is 2 metres thick
WHICH STORES MORE?
Wood also stores carbon
4
This area of peat stores as much carbon
as all the forests in this picture
5
This landscape of peat stores about 20 times more carbon than the same area of forest
6
Trees planted on peaty soils cause the peat to dry and eventually to disappear
– releasing the carbon originally stored in the peat
COMPARISON OF
VOLUME OF PEAT &
TIMBER IN A GIVEN AREA
Peat can be up to 3
metres thick; this bog
is 2 metres thick
A forest growing on the same area as this
bog would produce only enough logs to
cover half the area to a depth of only 15cm
Any peat more than 7.5cm deep will store
more carbon than the average forest
7
8
A forest might produce a stack of logs like this: a peat bog of the same
area stores the equivalent of 20 such stacks
SUMMARY
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An area of blanket peat stores an order of magnitude more carbon than
the average commercial forestry plantation
For example, an area of peat 1.5 metres (5ft) deep stores 20 times as
much carbon as a conifer plantation (of Yield Class 12, i.e. one that
produces c. 12 cubic metres of wood per hectare a year)
For a faster-growing plantation (Yield Class 16) the bog would only
contain 15 times as much
A very deep bog of depth 3m would store 40 times as much
As a rough guide, peat of a depth of 7.5cm (3 inches) will store as much
carbon as a plantation on the same site
Planting trees on peat, in the long term, causes the peat to disappear
(the peat oxidises as the soil dries)
CONCLUSION
Planting trees on peat of any depth will reduce the amount of carbon stored,
and hence not help reduce global warming
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Pictures 4. & 5.
Dry wt organic matter figures are used below. If organic
matter is 55% carbon, then carbon storage can be
calculated by multiplying dry wt by 0.55
BASIS OF CALCULATIONS
Peat 1m thick covering 1ha = 10,000 cu.m = c.10,000t
(assuming a bulk density of 1 – in fact more than this –
wet peat sinks)
@80% water = 2,000t dry wt
@95% organic matter = 1900t dry matter
Peat 2m thick = 1900x2 = 3,800t
Average depth 1.5m = 2,850t, rounded to 3,000t
However, over 2,000yr the peat could have added
4,000t, assuming the bog has previously accumulated
its 10,000t over 5,000yr (2,000t per 1,000yr)
Timber at yield class 12 = 12 cu.m/ha/yr = c.12t/ha
(assuming a bulk density of 1 – in fact less than this –
wet wood floats)
On 50yr rotation = 50x12, = 600t after 50yr
@60% water = 240t dry wt (data shows 50-80%)
If timber felled and replanted, average standing crop
over 50 yrs = 240t/2 = 120t
Note that branches and leaves excluded,
so rounded up to 150t
Pictures 7. & 8
Assuming a plantation of 2,500 trees/ha
Trees with 30cm basal diameter
Trees 15m high
3,000t = 150 x 20
Hence on-site storage of organic matter is 20 times
more on a peat bog than an average commercial
plantation (assuming 1.5m peat & yield class 12)
Figure will be less for plantations in optimal sites: yield
class 16, using the same calculations, will store c. 200t
(compared with 150t - still a lot less than the peat)
If the peat is 3m deep then this will store c.6000t
Long-term effectiveness of forest for carbon
storage is affected by how the wood is used:
If timber is burnt then all the 240t standing crop is lost
and carbon store from the timber goes back to zero
(average standing crop timber is then 240/2 = 120t)
If timber is used for construction, then 240t is stored
for the life of the construction, and the next rotation will
add to this store. If all the timber is stored, it will take 40
rotations (2,000yr at 50yr rotation) for the forest
to catch up with the peat bog.
If the timber is used for paper, then long-term carbon
store depends on life cycle of the paper
1ha = 100x100m = 50 trees x 50 trees
50 trees @ 30cm diameter, if snedded and laid side by side
will cover 15m of ground
At 15m tall, the felled trees will fit into a square 15x15m
Assuming trees go from 30cm at base evenly to 0cm at tip,
then this 15x15m square will take 50x2 = 100 trees
Hence 100 trees cover 15x15m = 225sq.m
& 2500 trees will cover 5625sq.m = c. 0.5ha
However, trees vary from 30cm to 0cm thick on the ground,
so average thickness of all the logs on the ground
will be 15cm
Hence, the amount of timber stored in all the trunks of a
plantation of 2500 trees, where average basal diameter
= 30cm (approximating to yield class 12) will cover
half the total ground surface to an average depth of 15cm
or the whole ground surface to a thickness of 7.5cm
This makes it possible to visualise the amount of carbon
stored in a forest compared to that stored in an area of peat
covering the same area. This crude calculation shows that
the forest is equivalent to 7.5cm peat: any peat more than
7.5cm deep will store more carbon than an equivalent
plantation
This figure of 7.5cm is corroborated by using
the figures on the far left: if a 1.5m deep
peat bog stores 20 times as much carbon
as an equivalent forest, then the forest is
storing the equivalent of 1.5/20m
= 7.5cm peat
Hence planting trees on any peat more than,
say 10cm, is unlikely to cause an increase in
carbon storage if the planting causes the
peat to oxidise (disappear) in the long-term
Presentation produced by
Dr James Fenton, Wester Lairgs,
Farr, by Inverness, IV2 6XH
[email protected],
www.james-hc-fenton.eu
5 August 2010
James Fenton gained a PhD from
studying growth rates of peat in
Antarctica: an Antarctic peat bog is
shown below for interest. Ruler is
1m long