SCI/TECH: Greenhouse gases threaten tree species in remote parts of the Amazon

Over the past 20 years, the delicate balance of tree species growing in remote regions of the Amazon has been altered significantly. Scientists believe it is a direct result of increases in carbon dioxide emissions caused by humans. The discovery comes from a study of 18 undisturbed plots in the heart of the Brazilian Amazon that researchers have been monitoring since the 1980s.

Reuters

Plants need carbon dioxide in the way that animals need oxygen - but the 30 per cent extra carbon dioxide in the past 200 years has begun to accelerate growth and change the composition of the world's biggest rainforest, says a study published yesterday in the magazine Nature.

"The changes in Amazonian forests really jump out at you," said William Laurance of the Smithsonian Tropical Research Institute in Panama. "It's a little scary to realise seemingly pristine forests can change so quickly and dramatically."

Dr Laurance and his team noticed that the growth of large trees in the Amazonian rainforests have accelerated over the past two decades while the growth of smaller ones has slowed.

The levels of carbon dioxide (CO2) have risen because of emissions from cars and industry and rapid forest burning, particularly in the tropics. Much of the increase in CO2, which plants use from the air for photosynthesis, has occurred since 1960.

The scientists suspect the rising CO2 levels are fertilising the rainforests and increasing competition for light, water and nutrients in the soil. So the big fast-growing trees have an advantage and are outpacing the smaller ones.

The odd change in growth patterns could also be a signal for an overall change in rainforest ecology, scientists say.

Researchers have studied nearly 14,000 trees in the central Amazon, scattered across a 31 square kilometre landscape. During the 20-year study most species began to grow faster. They also died faster, to be replaced more swiftly by new, young trees. But the composition of the forests, too, was beginning to change.

Alexandre Oliveira of the University of Sao Paulo, Brazil, said: "There clearly are winners and losers. In general, large, fast growing trees are winning at the expense of smaller trees that live in the forest understorey."

Small trees are highly specialised, often with valuable biological properties. They can flower and reproduce in deep shade. But in the spurts of growth triggered by rising carbon dioxide levels, the bigger, faster growing species tend to take the lion's share of light, water and soil nutrients.

"Sadly, this could be a signal that the forest's ecology is changing in fundamental ways," Dr Laurance said. "Tropical rainforests are renowned for having lots of highly specialised species. If you change the tree communities then other species - especially the animals that feed on and pollinate the trees - will undoubtedly change as well."

To separate the effects of global warming from other stresses, the researchers based their studies on plots of forest chosen because they had not been logged, burned, used for hunting or damaged by wind storms. The next step is to see whether such changes were mirrored in other tropical forests around the world.

Other sources
- New Scientist
- Sydney Morning Herald
- ABC News

One of the largest debates in climate change circles is based upon the close correlation seen in graphs of temperature and CO2 change with time. The popular consensus is to believe that temperatures increase in response to increasing CO2. I am amazed at how little the opposite is considered by atmospheric scientists: that increased global temperatures cause an increase in atmospheric CO2 gas. The climatic system of the earth is a very complex system we still do not understand.

Most people do not realize that higher temperatures will elevate atmospheric CO2 in two profound ways.

1) Microbes in the soil: "bugs in the dirt", which includes earthworms, bacteria, and fungi decompose organic matter. This will release CO2 into the atmosphere. Believe it or not, this produces more CO2 annually than the entire human population does annually. Metabolic rates are significantly controlled by temperature. Imagine a banana peel left in a Brazilian rain forest and one left at the North Pole. Which will decompose first?

A second significant way in which higher temperatures increase atmospheric CO2 is thru the oceans. The oceans are a considerable carbon sink. Gas is less soluble in warmer water, so an increase in global ocean temperatures will result in a tremendous "burp" of CO2 into the atmosphere.

Another consideration: the human population of the Earth has increased by 4 orders of magnitude in the past 2000 years. It has tripled in the past 200 years. Humans exhale CO2. I wonder if anyone has tried to estimate this contribution in ways other than stating it is negligible? Measure it and show me, then I might believe it!

A final note: water vapor is a more efficient greenhouse gas and is more abundant than CO2. What do you think happens to water vapor concentrations in the atmosphere when temperatures increase? They also increase. Water vapor is a much more important "greenhouse gas" than CO2. There are many complex feedback loops in the climate system we still do not fully understand.

There is no denying that modern civilization is contributing CO2 to the atmosphere, but we do not know what effects this will have and what kind of lag time, if any, there might be. The Earth may be in the process of compensating for the additional CO2, but in some way not yet measurable.

Climate change is natural. 15,000 years ago half of North America was covered with ice sheets more than 1km thick. Neanderthals didn't have cars, so something else caused the Earth to warm, melting all of that ice.

sadness
insanity
everything that is going to happen will happen.
effort is needed in awareness to take action concerning rainforests
unfortunately too few care or have the power to affect change

The forests need help