Low-level slash-and-burn farming doesn’t harm rainforest. On the contrary, it helps farmers and improves forest soils. This is the unorthodox 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. This 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 (烧成炭的) wood left over from thousands of years of slash-and-burn farming. ”The soils, known as Terra Preta, contained up to 70times 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 wastes 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 (陶器) 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.          低层次的削减、焚烧农场不会伤害热带雨林。相反地，它帮助了农民且改善了雨林土壤。这是一位德国土壤科学家非传统的观点，他指出在亚马逊焚烧小块空地，可以追溯到1000多年以前，帮助形成了大块的丰富、肥沃的土地，农夫们今天仍然可以从中获益。        大多数的雨林土壤是稀薄、贫瘠的，因为它们缺乏矿物质，也因为这猛烈的降雨在不到四年的时间里破会了大多数土壤中的有机物到达了雨林的尽头。这意味着表层土壤包含着更少的需要成为长期成功农场的配料。        但Bruno Glaster，一位Bayreuth大学的土壤科学家，已经研究出了一个在亚马逊中心地区，未预料到的、大块的肥沃土壤。这土壤包含了大量的有机物。        Glaster已经表明大部分的这些富饶的有机物质来自于“黑碳”--这些有机微粒从上千年以前的削减、焚烧农场遗留下来的篝火和烧成炭的木头。“这些土，以大家所知的Terra Preta，跟周围的土壤相比，包含了多达70倍以上的黑碳”，Glaster如是说。        未燃烧的植物迅速的腐烂，但黑碳仍保留在土壤中好几个世纪。Radiocarbon追溯时间表明，这些烧成炭的木头在Terra Preta土壤中是很典型的1000多年之久。        削减和焚烧农场对土壤来说可以是有益的，它（向土壤）提供了并没有完全焚烧全部的植物，而且留下了烧成炭的木头，Glaster说道。“它会比粪肥更好”，只烧一次雨林可以留下足够的黑碳来维持土壤数千年的肥沃。而且雨林很容易地在小规模的空地被焚烧之后恢复起来。与人们的活动破坏环境的传统观点相反，Glaster说到，“黑碳结合人类的废弃物造就了Terra Preta的肥沃土壤”。        Terra Preta土壤在大块地区出现，遍布亚马逊，在亚马逊农夫们大力赞赏。所有的土地块在亚马逊中心地区降到了不足500平方千米。Glaster说陶器大范围的存在证实了这些土壤的人类来源（这个原因）。        这个发现为亚马逊的大块地区已经覆盖了跟过去一段时期的农业使用（由好几代的生物学家对“处女”地的再生长被误解）一样好的理论增加了重量。        在这过去的二十年中，研究者们已经发现好几百的大量土地在丛林深处发挥作用。它们多达20米高，而且覆盖到了1平方公里。Glaster声称这些土地生效着，在公元400到1400年之间构建起来，在城市文明的中心。现在看起来似乎这些肥沃的Terra Preta土地或许可以解释这些文明是如何成功的为他们自给自足的。

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