Carbon & the Natural Heritage: Key Facts
There are two key parts of the Carbon (C) cycle that affect the natural heritage; that which is stored and that which is moving. From the perspective of the natural heritage in Scotland the two main stores are trees and soils, especially peat soils. In the context of climate change and greenhouse gas emissions, it is important to retain as much of these stores as possible. Carbon can of course leave these stores by various means: as trees die and rot, as wood or peat is burnt or as peat is harvested or erodes.
However, the stores can be added to as well, and that is how natural systems can be used to reduce the amount of carbon in the atmosphere. For example, more trees can be grown, and damaged peat land can be restored. Various terms are used to describe this addition to the store; capture, accumulation, sequestration etc, but they all mean that the overall carbon store is being increased, contributing to a reduction in atmospheric carbon and hence ameliorating the impacts of climate change. Storing carbon in peat takes a long time, but depletion can be fast.
Consequently protecting what is already there is the best tactic to maintaining a positive carbon balance in the short term.
Each year, Scotland's forests remove about 10% of Scotland's annual greenhouse gas emissions. The average accumulation over a full commercial forest rotation is around 3 tonnes C per hectare per year. Substituting one tonne of concrete or brick with one tonne of timber in, for example construction, saves around one tonne of CO2.
Organic soils (notably peat) in Scotland contain almost 25 times as much carbon as the rest of all the vegetation in the UK. Scotland's organic soils (notably peat) hold almost a third of the carbon held by all of Europe's forests (3 billion tonnes compared with 9.5 billion tonnes). Newly drained peat land releases 2 - 4 tonnes C per hectare per year for the first 2-4 years after ploughing. Thereafter the trees accumulate carbon. Undisturbed peat lands accumulate about 0.25 tonnes C per hectare per year.
Each year, each household in Scotland releases into the atmosphere approximately 0.5 tonnes of C from electricity consumption alone. There are around 1.8 million hectares of peat land and 2.3 million households. If all of Scotland's peat land's were undamaged they would accumulate the equivalent of almost 40% of all C produced by Scotland's households from electricity use.
Wind farms markedly reduce C emissions from fossil fuels, and if built on peat can spend the first two to five years 'compensating' for the loss of peat. The additional Dissolved Organic Carbon loss (carbon dissolved in water in streams and rivers) related to wind farm construction on peat land is estimated at 5g/m2, which is 20% of the annual Carbon accumulation by the vegetation.
Burning a litre of diesel produces around 2.62kgs of carbon dioxide (CO2). Petrol has a lower carbon content and produces around 2.39kgs of CO2 per litre. Intact bog vegetation accumulates around 920kg of CO2 per hectare per year.
Therefore, one hectare of intact bog accumulates the CO2 output from 384 litres of petrol or 350 litres of diesel every year. The cost of this fuel would be around £420 per year (August 2008 prices). The one-off cost of restoring bog is highly variable, from several hundred pounds per hectare, to as low as £8 per hectare for drain blocking in the Flow Country. Restoring Active Blanket Bog of European Importance in North Scotland.
Trees and peat lands are complementary tools in reducing atmospheric CO2. Safeguarding existing stores and managing habitats to enhance future accumulation will contribute not only to climate change amelioration but to biodiversity objectives and a range of other ecosystem services (flood alleviation, water quality etc).
(Extracts from Paper presented to SNH Board 16th June 2009.)
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