Forests and forestry can be an
important and attractive part of
Mitigation: Planting more trees
Trees store carbon. One of the practical ways to combat climate change is to lock
up or sequester more carbon from the atmosphere through planting more trees -
as long as the right trees are planted in the right place.
Definition: The term mitigation refers
to activities aimed at reducing
greenhouse gas emissions and/or
removal of carbon dioxide from the
A headline statistic is that the carbon
sequestered (or stored) by half a
hectare of conifer woodland over one
rotation can compensate for the carbon
dioxide emissions associated with car
fuel consumption during one average
However, with 30 million registered
drivers in the UK, three quarters of the
land area of the nation would have to
be covered in forest to make car use
alone carbon-neutral. Therefore
planting more trees is an attractive part
of mitigating climate change, but can
clearly never be the whole solution.
Just how much carbon does one
A recent study carried out at Kielder
Forest has calculated that the Forest’s
150 million trees lock up 82,000 tonnes
of carbon* annually. This means that as
a rough estimate each tree at Kielder is
locking up 0.546 kg of carbon per year
– equivalent to 2 kg of carbon dioxide.
Although this example does answer the
apparently simple question ‘how much
carbon does one tree store,’ in reality
the answer is far from straight forward;
it is dependent on species, growing
conditions and how a tree is managed.
For example, 2500 trees might be
planted per hectare in a commercial
plantation (broadleaf or conifer) but only
50–500 remain when the final crop is
harvested as a result of natural mortality
*One tonne of carbon is equivalent to 3.7 tonnes of
Facts and figures
• UK forests and woodlands contain
around 150 million tonnes of
carbon in the biomass and 640
million tonnes of carbon in the soil.
• UK forests and woodlands are a
carbon sink, as they remove about
10 million tonnes of carbon from
the atmosphere every year.
• Current (2008) UK emissions of
carbon dioxide are about 530
million tonnes per year.
• Other greenhouse gas emissions
equate to an additional 100 million
tonnes of carbon dioxide per year.
In addition, young trees absorb carbon
dioxide quickly while they are growing,
but as a tree ages a steady state is
eventually reached. At this point the
amount of carbon absorbed through
photosynthesis is equal to that lost
through respiration and decay.
It is, therefore, a much simpler concept
to talk about how much carbon an area
of woodland can sequester or store.
In the UK, forest soils contain around
four times as much carbon as the trees.
Maintaining the forest area will help
ensure these stocks of carbon are
protected. Soils can release carbon
dioxide when they become aerated as
a result of disturbance (such as planting
and felling) or drainage. This effect is
most marked in organic or peat soils.
On most soils, long-term carbon gains
through new woodland establishment
will outweigh initial carbon losses due
to soil disturbance. The continual input
of organic materials from leaf litter and
decomposing roots will gradually
increase the soil carbon content.
Over a full rotation, including planting to
felling, a conifer forest can sequester
around 14 tonnes of carbon dioxide per
hectare per year. When UK woodlands
are looked at as a whole, the average is
around 5.4 tonnes of carbon dioxide
per hectare per year (or 1.4 tonnes of
carbon per hectare per year), including
broadleaved and unproductive
woodlands. In terms of total carbon
storage, a commercial conifer
plantation grown over 50 years might
sequester 50–100 tonnes of carbon per
hectare. In contrast, an old growth
forest may store up to 250 tonnes
carbon per hectare but over a much
longer period (300 years or more).
Trees and forests have a clear role to
play in helping to mitigate climate
change, and tree planting projects
have been proposed as valid ways to
help ‘offset’ unavoidable carbon
emissions – carbon offsetting.
However, there has been resistance to
such projects for a number of reasons,
including the following:
• Is the activity ‘additional’ or would
the tree planting have occurred
• Will the woodland be permanent, or
will the carbon be re-emitted in the
• Will the carbon be counted only
once – or by a number of
• Are the emissions reductions real?
The most important point is that
offsetting – whether through tree
planting or not – should not be the first
thought; reducing emissions should
always be the main objective.
Secondly, offsetting requires certainty
in the emissions reductions taking
place. This is a very difficult issue for
tree planting projects, which generally
provide funding for carbon uptake in
However, it is undeniable that planting
new woodlands in appropriate
locations removes carbon dioxide from
the atmosphere, and also provides a
number of other environmental and
social benefits that many other
offsetting options do not provide.
For these reasons the Forestry
Commission has developed a ‘Code of
good practice for forest carbon projects’
which will be published in 2010. This
will provide answers to these
questions and provide a ‘standard’
which tree planting projects can sign
up to and be assessed against.
This is the act of removing (literally
seizing) carbon dioxide from the
atmosphere and storing it in biological
A forest is termed a carbon ‘sink’ if there
is a net transfer of carbon from the
atmosphere to the forest. A forest only
remains a sink while its carbon stock
continues to increase.
Wood products are a store of carbon, as
they themselves do not capture carbon
dioxide from the atmosphere, but keep
it locked up throughout their lifetime.
• As long as the right trees are planted in the right place,
planting more trees can be an attractive way of removing
carbon dioxide from the atmosphere
• However overall, tree planting can only ever play a very
small part in climate change mitigation