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Cleaner Air - What can forests do? |
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Written by Brian Tobin and Maarten Nieuwenhuis
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Wednesday, 01 December 2004 |
Small scale tree planting can do tremendous good for the environment
Many people have a natural predilection that forests in general are good for the
environment, being nature’s set of lungs for the planet. They take in quantities
of carbon dioxide from the atmosphere and release precious oxygen in return, and
in the meantime create a store of carbon away from the atmosphere where it could
contribute to global warming.
In Ireland forests are sometimes not seen in such exalted light. Rather more as
a dark blanket of coniferous timber factories blotting the landscape. And the
tree species that rouses such ire with most Irish people is Sitka spruce. Of course
here people are right! Currently the species accounts for about 60% of all national
planting and is the single most important commercially planted species. However,
it should be remembered that 100 years ago from this year (1904), when the state
afforestation program was first begun, Ireland's forest cover was a tiny 1.3%
of the island's surface. It has been on the back of this extremely productive
species that forest cover has now grown to about 10% and has enabled the country
to become self sufficient in our soft-wood timber requirements.
As for environmental concerns, what further good can this tree species do for
us? It was acknowledged in the Final Report of the Review and Appraisal of Ireland's
Forestry Development Strategy, published last September by Peter Bacon and Associates,
that "although the impact of sinks cannot be traded under the EU trading
mechanism, there is a value to be realised in terms of a reduced requirement to
purchase green credits." So in other words, what carbon we fix as a nation
can be written off against what we release, thereby reducing the amount of penalties
to be paid by the state for exceeding greenhouse gas emissions levels.
Recently a study was initiated by a UCD project team to study the carbon storage
potential of a Sitka spruce forest ecosystem. To demonstrate some of the results,
let us imagine a landowner who has planted a hectare of Sitka spruce somewhere
in the midlands. The soils being mineral in nature are productive, and so the
trees are of an average to higher yield class. Planted at normal spacing, there
will be about 2,500 trees per hectare. After 10 years the stand will already be
almost 4 m in height. By this time the total amount of biomass (i.e. the living
tree tissue from which the moisture has been removed) will already be 33 tonnes
per hectare. Of this approximately half is entirely composed of carbon, 16.5 tonnes.
Interestingly, just less than 30% of this figure is hidden below ground in the
trees’ rooting systems. Another interesting fact is that over those first
10 years the amount of carbon fixed from the atmosphere by the tree crop is already
more than 9 family cars emit over the same 10-year period.
If we look at the stand again after another 30 to 35 years, when our landowner
is beginning to think about a final harvest, the number of trees has been reduced
greatly, however, the average size of the trees remaining after thinning has grown
enormously, the weight of a single tree at this stage (as it stands in the ground)
is about 1.5 tonnes and a height of about 30 metres! The dry biomass of the hectare
of trees has increased to 490 tonnes, or 245 tonnes of carbon. So by the end of
the rotation, the hectare of forest has fixed the equivalent amount of carbon
that a double-decker diesel bus emits while in regular every-day use for 2 years!
And before considering harvesting, while looking up among the trees, the forest
owner can marvel that approximately 52,500 litres of water is being held up and
contained by the tree tissues all around and overhead!
The carbon fixed by this hectare of trees into its timber is a secure method of
storing carbon. The resulting timber harvested and sold by the landowner will
have a further life span of possibly 100 years or more depending on the end use
of the timber. Even if the wood was burned immediately for heat or as a fuel for
other energy generation, it could replace the use of fossil fuels and other less
sustainably produced fuels. Thus our family in the midlands has enjoyed the shelter
and amenity of their stand of trees, seen their children grow up playing among
them and seen the localised hydrology of their land maintained and protected.
They have produced and sold a valuable quantity of timber in less than half a
century and enjoyed the personal and social satisfaction of contributing to the
protection of the environment and the fight against excessive global warming!
Of course this is very much a small potted example, but it does serve to illustrate
the tremendous good that even small scale tree planting and forestry are doing
for Ireland and all of us.
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