建筑木材的安全性英文文献和中文翻译(3)
Sustainable forestry
Second only to the oceans, forests are the biggest carbon sinks on the planet. They store roughly 300 billion tonnes of CO2 . Deforestation continues to be a major source of CO2 emissions, but is largely confined to tropical rainforests. In North America, Europe and China, forests are growing, absorbing CO2 and providing a sustainable low carbon material for buildings and products.Trees sequester CO2 from the atmosphere through photosynthesis.During this process they absorb about a tonne of CO for every cubic metre’s growth and store it in the wood. At the same time, they release around three-quarters of a tonne of oxygen. This carbon absorption is fastest when trees are young and slows down as they mature. Eventually it reverses when they die or burn. If the trees are harvested and used before the carbon cycle reverses, carbon from the atmosphere can be stored in buildings and other wood products for their service life. This carbon storage in wood products can be extended through recycling.At the end of life, energy can be recovered from the wood as a biomass fuel.
How does wood construction using products from sustainable forests help reduce climate change? It encourages replanting and planting of new forests, because sustainable forest management obliges forest owners to replace harvested trees and because there is an economic incentive to do so. It provides the market for mature trees, which enables regeneration of new forests which are more efficient at absorbing carbon dioxide. It enables additional carbon storage in the wood products. It reduces the use of alternative carbon intensive materials.Forests cover about 30 per cent of the Earth’s land surface, a total area of just under 4 billion hectares. Forest cover is distributed unevenly. In 2005, 43 countries had over 50 per cent of their land area under forest cover. Five countries, the Russian Federation, Brazil, Canada, United States of America and China, accounted for more than half of the planet’s total forest area.In Asia and the Pacific region (excluding the Russian Federation), forests and other wooded land together cover about a third of the land area approximately 734 million hectares - accounting for 19 per cent of the global forest area. This region experienced an annual net increase in forest area of about 633,000 hectares between 2000 and 2005, mainly due to new Chinese plantations.Tropical areas mostly produce hardwoods, while areas in the north, such as Europe and Canada produce large quantities of softwoods, which are superior for structural use. Over 11 per cent of the world’s forest area has been designated primarily for conservation of biological persity.
In 2005, China had a total forest area of 197 million hectares, with 58 per cent managed primarily for productive purposes. The forest area has been increasing dramatically since 1980, partly in order to stabilize land,reduce flooding and improve air quality.Between the second and the sixth National Forest Inventory periods (1977-1981 and 1999-2003), the total forest area increased by 60 million hectares. The forest coverage rate has been increasing too. In the early 1950s it was 8.6 per cent. In 2008 it had risen to 18.2 per cent. And the government plans to increase the rate to 26 per cent by 2050, with a target of at least 310 million hectares of forested land.China has many native hardwood and softwood species. Important species for wood products include Korean red pine in the northeast, and China fir and Masson’s pine in the south. Common plantation species,which take 20-25 years to mature, include poplar in the north and China fir and eucalyptus in the south.China’s 53 million hectares account for 40 per cent of the world’s plantations. Over the past ten years, government funding on forestry has increased at faster rates than total expenditures in order to meet the long-term objectives for product and land stabilization. This is a remarkable achievement.Recently, China started its Six Key Forestry Programmes on forest protection and regeneration, wildlife and wetland protection. By 2005,the government had spent US $ 22 billion, approximately US $ 6 billion a year, on afforestation and conservation. This represents a significant commitment to the forests and to the protection of the environment.
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