The Fertile Rainforest Soils in Amazon

Low-level slash-and-burn(刀耕火种) farming doesn’t harm rainforest. On the contrary, it helps farmers and improves forest soils. This is the unorthodox(非正统的) view of a German soil scientist who has shown that burnt clearings in the Amazon, dating back more than 1,000 years, helped create patches of rich, fertile soil that farmers still benefit from today.

Most rainforest soils are thin and poor because they lack minerals and because the heat and heavy rainfall destroy most organic matter in the soils within four years of it reaching the forest floor. It means topsoil contains few of the ingredients needed for long-term successful farming.

But Bruno Glaser, a soil scientist of the University of Bayreuth, has studied unexpected patches of fertile soils in the central Amazon. These soils contain lots of organic matter.

Glaser has shown that most of this fertile organic matter comes from ''black carbon'', the organic particles from camp fires and charred(烧焦的) wood left over from thousands of years of slash-and-burn farming. ''The soils, known as Terra Preta, contained up to 70 times more black carbon than the surrounding soil, '' says Glaser.

Unburnt vegetation rots quickly, but black carbon persists in the soil for many centuries. Radiocarbon dating shows that the charred wood in Terra Preta soils is typically more than 1,000 years old.

''Slash-and-burn farming can be good for soils provided it doesn't completely burn all the vegetation, and leaves behind charred wood, '' says Glaser. ''It can be better than manure(粪肥). Burning the forest just once can leave behind enough black carbon to keep the soil fertile for thousands of years. And rainforests easily regrow after small-scale clearing. Contrary to the conventional view that human activities damage the environment, '' Glaser says: ''Black carbon combined with human waste is responsible for the richness of Terra Preta soils. ''

Terra Preta soils turn up in large patches all over the Amazon, where they are highly prized by farmers. All the patches fall within 500 square kilometers in the central Amazon. Glaser says the widespread presence of pottery confirms the soil’s human origins. The findings add weight to the theory that large areas of the Amazon have recovered so well from past periods of agricultural use that the regrowth has been mistaken by generations of biologists for ''virgin'' forest.

During the past decade, researchers have discovered hundreds of large earth works deep in the jungle. They are up to 20 meters high and cover up to a square kilometer. Glaser claims that these earth works, built between AD 400 and 1400, were at the heart of urban civilizations. Now it seems the richness of the Terra Preta soils may explain how such civilizations managed to feed themselves.

We are interested in the preservation of the biodiversity on Earth. What I’ve been working on is rats. Just looking at rats, you can understand continental drift and climate change. We’ve actually rediscovered rats that were thought to be extinct. Darwin was the last one to document them on the Galapagos Islands. People have gone there for hundreds of years and not seen one. In 1997, I went there with my mentor(导师) and another graduate student. Everyone thought I was crazy, why look for something that doesn’t exist? They wouldn’t even give us permits. Our plan was to stop on a beach for a day and then hike up to the top of an extinct volcano where very few people had been:We were on a picturesque, isolated beach. We set out the traps just to see what we might find. The next morning, I checked my traps! I immediately ran back to my mentor. When he looked in the mental trap—I will never forget his face--- It looked like he’d seen a ghost.

I certainly understand the argument: “ Who cares about an extinct rat?” but you have no idea what role that rat plays in that functioning ecosystem. People can appreciate beauty, so that’s why people love pandas and want to keep them around. You never hear, “What good is panda?” Ecologically, these rats are much more important to their ecosystem than those pandas--- not that I don’t love pandas but we have to look beyond the big and beautiful.

I teach conservation biology and evolution. In both you have to appeal to people asking “ Why is this important to me?” Some scientists refuse to do that. That’s my entire approach. I’ll ask “How many of you had a family member who was in a tornado, hurricane or flood?” .And almost every hand goes up. Climate change is suddenly very personal, and now they want to hear what you are saying. You are not looking for sympathy for the rats but for a greater understanding of the system.

Popping food into the microwave for a couple of minutes may seem harmless, and Europe's stock of these quick-cooking ovens give out as much carbon as nearly 7 million cars, a new study has found, and the problem is growing. With costs falling and kitchen appliances becoming frequently updated, owners are throwing many microwave after an average of eight years. This is pushing sales of new microwaves which are expected to reach 135 million annually in the EU by the end of the decade.

A study by the University of Manchester worked out the emissions of carbon dioxide-the main greenhouse gas responsible for climate change - at every stage of microwaves, from production to waste disposal (处理). “It is electricity consumption by microwaves that has the biggest impact on the environment,” say the authors, who also calculate that the emissions from using 19 microwaves over a year are the same as those from a car. According to the same study, efforts to reduce consumption should focus on improving consumer awareness and behaviour to use appliances more efficiently. For example, electricity consumption by microwaves can be reduced by adjusting the time of cooking to the type of food.”

However,David Reay, professor of carbon management argues that,although microwaves use a great deal of energy, their emissions are minor compared to those from cars. In the UK alone, there are around 30 million cars. These cars emit more than all the emissions from microwaves in the EU. Backing this up, recent data show that passenger cars in the UK emitted 69 million tons of carbon dioxide in 2015. This is 10 times the amount this new microwave oven study estimates for annual emissions for all the microwave ovens in the whole of the EU. Further, the energy used by microwaves is lower than any other form of cooking. Among common kitchen appliances used for cooking, microwaves are the most energy efficient, followed by a stove and finally a standard oven. Thus,rising microwave sales could be seen as a positive thing.