Forestry and climate change

Forests and forestry can be an

important and attractive part of

the solution

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

atmosphere.

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

driver's lifetime.

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

tree store?

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

and thinning.

*One tonne of carbon is equivalent to 3.7 tonnes of

carbon dioxide.

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).

Carbon offsetting

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

anyway?

• Will the woodland be permanent, or

will the carbon be re-emitted in the

future?

• Will the carbon be counted only

once – or by a number of

individuals/organisations?

• 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

the future.

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.

Definitions:

Sequestration

This is the act of removing (literally

seizing) carbon dioxide from the

atmosphere and storing it in biological

material.

Sink

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.

Store

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.

Summary

• 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