The worlds forests and deforestation

The total area covered by forest is almost one-third of the world's land area, of which 95% is natural forest and 5% planted forest.9 About 47% of forests worldwide are tropical, 9% sub-tropical, 11% temperate and 33% boreal.

At the global level, the net loss in forest area during the 1990s was an estimated 940 000 km2 (2.4% of total forest area). This was the combined effect of a deforestation rate of about 150 000 km2 per year and a rate of forest increase of about 50 000 km2 per year. Deforestation of tropical forests averaged about 1 % per year. The rate of loss since 2000 has slightly slowed but not by enough to reduce concern.

The area under forest plantations grew by an average of about 3000 km2 per year during the 1990s. Half of this increase was the result of afforestation on land previously under non-forest land use, whereas the other half resulted from conversion of natural forest.

In the 1990s, almost 70% of deforested areas changed to agricultural land, predominantly under permanent rather than shifting systems.

because of the contribution that loss makes to carbon emissions and therefore to global warming. There is also the dramatic loss in biodiversity (it is estimated that over half the world's species live in tropical forests) and the potential damage to regional climates (loss of forests can lead to a significant regional reduction in rainfall - see box on page 208).

For every square kilometre of a typical tropical forest there are about 25 000 tonnes of biomass (total living material) above ground, containing about 12 000 tonnes of carbon.6 It is estimated that burning or other destruction from deforestation turns about two-thirds of this carbon into carbon dioxide. Approximately the same amount of carbon is also stored below the surface in the soil. On this basis, from the destruction of about 150 000 km2 per year over the decades of the 1980s and 1990s (see box) about 1.2 Gt of carbon would enter the atmosphere as carbon dioxide. Although there are substantial uncertainties in the numbers, they approximately tally with the IPCC estimate, quoted in Chapter 3 (see Table 3.1), of the carbon as carbon dioxide entering the atmosphere each year from land-use change (mostly deforestation) of 1.6 ± 1.1 Gt per year - a larger fraction of the total anthropogenic emissions of carbon dioxide than results from the whole of the world's transportation sector. If all tropical forest were to be removed by 2100, between 100 and 150 ppm would be added to the CO2 concentration at that date.7

Reducing tropical deforestation can therefore make a large contribution to slowing the increase of greenhouse gases in the atmosphere, as well as the


Landsat images of Bolivia taken in 1984 and 2000 show the dramatic deforestation of the Bolivian rainforest. In 1984 the rainforest had been thinned out in places, and by 2000 the rainforest had receded dramatically.

provision of other vital benefits such as guarding biodiversity, protecting water supplies, avoiding soil degradation and preserving the livelihoods of forest peoples. The Stern Review has estimated the cost of emissions savings from avoided deforestation as less than $US5 per tonne CO2.9

Strong emphasis is being given internationally to reduction of deforestation as an essential contribution to mitigation of climate change. Towards the end of 2007, at the Bali conference of the UN FCCC it was agreed to work towards an agreement on deforestation in developing countries to be included as part of a post-Kyoto international Climate Change agreement.10

In the above discussion of deforestation, I have not mentioned the increasing interest in growing biomass for production of energy either directly or through biofuels. Land that is under forest may increasingly be taken over for such crops. This will be addressed, along with other energy issues, in the next chapter.

What about the possibilities for afforestation. For every square kilometre, a growing forest fixes between about 100 and 600 tonnes of carbon per year for a tropical forest and between about 100 and 250 tonnes for a boreal forest.11 To illustrate the effect of afforestation on atmospheric carbon dioxide, suppose that an area of 100 000 km2, a little more than the area of the island of Ireland, were planted each year for 40 years - starting now. By the year 2050, 4 000 000 km2 would have been planted; that is roughly half the area of Australia. During that 40 years, the forests would continue to grow and uptake carbon for 20 to 50 years or more after planting (the actual period depending on the type of forest and site conditions) - and, assuming a mixture of tropical, temperate and boreal forest, between about 10 and 40 Gt of carbon from the atmosphere would have been sequestered or 4 GtCO2 per year. This accumulation of carbon in the forests is equivalent to between about 5% and 10% of the likely emissions due to fossil fuel burning up to 2050. Add to this the emissions reductions that could arise with a near elimination of tropical deforestation and approximately 20% of

Aforestation in Burkina Faso.

anthropogenic CO 2 emissions over the period to 2050 would be accounted for.

But is such a tree-planting programme feasible and is land on the scale required available? The answer is almost certainly, yes. For instance, China is currently adding forests covering approximately 10 000 km2 per year or one-tenth of the area we have mentioned above.12 Studies have been carried out that have identified land which is not presently being used for croplands or settlements, much of which has supported forests in the past, totalling about the area just quoted.13 Estimates of the cost of afforestation range from $US5 to $US15 per tonne CO2 (the lower values in developing countries) not including the value of assocatiated local benefits (for instance, watershed protection, maintenance of biodiversity, education, tourism and recreation).14 Compare these figures with the estimate given in Chapter 9 of between $US25 and $US50 for the cost per tonne CO2 of the likely damage due to global warming. Such a programme therefore appears potentially attractive for alleviating the rate of change of climate due to increasing greenhouse gases in the relatively short term.

Let me insert here a note of caution. As with many environmental projects the situation, however, may not be as simple as it seems at first. One complicating factor is that introducing forest can change the albedo15 of the Earth's surface. Dark green forests absorb more of the incoming solar radiation than arable cropland or grassland and so tend to warm the surface. This is particularly noticeable in winter months when unforested areas may possess highly reflecting snow cover. Calculations show that, particularly at high latitudes, the warming due to this 'albedo effect' can offset a significant fraction of the cooling that arises from the additional carbon sink provided by the forest.16

A possible afforestation programme has been presented in order to illustrate the potential for carbon sequestration. Once the trees are fully grown, of course, the sequestration ceases. What happens then depends on the use that may be

Aforestation in Burkina Faso.

made of them. They may be 'protection' forests,17 for instance for the control of erosion or for the maintenance of biodiversity; or they may be production forests, used for biofuels or for industrial timber. If they are used as fuel for energy generation (see Chapter 11), they add to the atmospheric carbon dioxide but, unlike fossil fuels, they are a renewable resource. As with the rest of the biosphere where natural recycling takes place on a wide variety of timescales, carbon from wood fuel can be continuously recycled through the biosphere and the atmosphere.

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