Deforestation, Prime “Man Made” Contributor to Global Warming
Deforestation may well be the Key “man-made” contributor to global warming. Cut down trees gradually rot, giving off CO2 (carbon dioxide) the most important of the man- made, heat-trapping ‘Greenhouse gases’. Burn them, they give off CO2 faster.
A possible solution is to manage this deforestation prudently, taking only some of the trees, allowing the forest to regenerate, or planting fast-growing species. The new growth will absorb much of the extra carbon dioxide.
But this too may in fact be adding to the problem of global warming, the research shows, the termite may be to blame.
Termites are social insects.
They are known for building large mounds with ventilation systems, and notorious for eating the wood in houses. In the US they cause more damage to homes than storms and fires combined.
Some termites eat soil, and others eat dead wood in tropical forests, aiding the decomposition process. Some termites give off methane when digesting food, by fermentation in the gut, in a similar way to cattle. Methane is another of the Greenhouse gases.
In Y 1982 3 American scientists published a paper in Science, reporting experiments in which they measured the amount of methane produced by termites in test-tubes, then calculated from this the amount they produced in their natural habitats.
Their estimate was large enough to cause concern.
They concluded that termites could produce as much as 150-M tonnes of methane a year. At the same time the amount of methane in the atmosphere was increasing faster than other Greenhouse gases, by 1% a year since Y 1978.
Although there were clearly other sources of methane, coal-mines and rubbish dumps among them termites are to blame for a part of the increase, with estimates ranging from less than 5% to more than 40% of the total annual global methane production.
Termite numbers were thought to be increasing because the forests are being destroyed and termites thrive in the resulting Savannah areas.
Their paper’s conclusions were based on a laboratory study of just one type of North American termite. No one had made an in-depth field study of what happens to tropical forest, dwelling termites when their habitats are disturbed or destroyed, so an important part of the picture was missing.
In fact, forest termites are more abundant than those in the Savannah.
Since then a group of British scientists is carrying on where the Americans left off. Funded by the Natural Environment Research Council, the Terrestrial Initiative in Global Environmental Research (Tiger) project has been sending scientists from the Natural History Museum, Queen Mary and Westfield College, Imperial College, and the Natural Resources Institute, Chatham, Kent, to Cameroon, which has some of the best ‘primary’ (undisturbed) tropical forest in Africa, and is home to up to 100-M termites per hectare.
The group sampled at 5 forest sites around the logging town of Mbalmayo, in southern Cameroon.
An immediate effect of logging is to destroy termite habitats, but invariably only the largest trees are taken away. The rest are usually left on the ground, where they dry out and decay. Then either a slow regrowth takes place, or new trees are planted. Once there is enough cover to allow shelter from the Sun, the termites return to feed on the plentiful dead wood on the forest floor.
Dr Paul Eggleton, from the Natural History Museum, over the years has been identifying and counting the termites collected in Cameroon.
“We were surprised to find that termite abundance and species richness is highest in 2 ‘secondary’ forest areas, one where the forest was logged manually and left to regenerate and one where it was replanted with fast-growing trees. We were expecting the termites to do best in the primary forest,” he wrote.
If termites are a major source of methane, this could have important implications for global warming.
At least 40% of cleared forest is allowed to regenerate across the whole of Africa, and this figure is likely to increase with more agro-forestry projects. In these regenerating areas there could be more termites producing methane.
The Big Q: Do termites really produce the levels of methane estimated?
The Big A: Measuring methane production is not as straightforward as some scientists believed.
Dr David Bignell from Queen Mary and Westfield College, leader of the Tiger termite team, says: “Termites in the lab react differently to termites in their natural habitats, and the amount of methane escaping from termite nests in the field is much less than might be expected.”
Scientists are divided on why this occurs.
Some believe that termites operate an ‘internal methane cycle’ whereby soil bacteria in and around the mounds oxidizes the methane they produce, rendering it harmless.
Others think that the act of measuring emissions disturbs the termites so that they leave the nests and go into subterranean foraging tunnels. Some termite mounds are built wholly under the ground, making it harder to measure emissions. At any time fewer than 10% of termites in an area will be inside mounds, so the likelihood of accurate overall measurements is small, and questionable.
Termites may also contribute to Greenhouse gases in another way.
Termite mounds appear to contain denitrifying bacteria which release nitrogen from the soil. Small amounts of 2 particularly potent Greenhouse gases, nitric and nitrous oxide, are also emitted. Although this goes on in mounds in undisturbed forest, the bacteria seem to be stimulated when the forest is disturbed, especially when fertilizers are used on cleared land.
It is uncertain exactly how much termites contribute to Greenhouse gases, it is certain that for millions of years termites have existed in tropical forests and have done no harm.
The danger lies in upsetting the natural balance of the forest eco- system. ‘Termites are guardians of the gas exchange between the soil and the atmosphere. Destroy the natural habitat of these guardians, upset the system and the consequences are likely very serious.
For years scientists have been warning that the CO2 added to the atmosphere by increased burning of fuel is likely to alter world climates, like a Greenhouse, by inhibiting the escape of heat into outer space.
But, now researchers report that termites, digesting vegetable matter on a global basis, produce more than 2X as much CO2 as all the world’s smokestacks.
Also, it is estimated that bovine flatulence added 85-M tonnes of methane to the atmosphere each year. The new estimate for termites is 150-M tonnes.
Further, termites destroy billions of dollars of wood in houses annually. There are simple and inexpensive ways to halt this destruction without toxic chemicals and pesticides. It begins with the way in which a home is built at its foundation, and considering the damages these pests do over the life of a house, it is not expensive.
Prior to construction of a new home the buyer can specify that the building be designed so that no wood comes in contact with the soil and ‘flashed’ against invasion by any insects. Start at the beginning, halt the damages before they begin.
Paul Ebeling
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