It has taken millennia for rainforest biodiversity to evolve, and we are only now beginning properly to understand the interconnectedness of many of the species. There are still many forest species that have not yet been identified, let alone studied. So while we can replant, it is unlikely that we will ever be able totally to restore what is lost.

Acid rain results from fossil fuel emissions, particularly nitrogen dioxide and sulphur. When these combine with water vapour, sunlight and oxygen in the atmosphere, they create diluted nitric and sulphuric acid - which are washed out of the atmosphere by rain and snowfall often far from where the pollution originated, and are particularly harmful to forests and lakes. The problem has been greatly reduced in Western Europe - thanks to United Nations action - and North America, but is ongoing in Eastern Europe and the Russian Federation, as well as in China, where a parliamentary report recently concluded that a third of the vast country is affected.

There are no global laws to protect virgin forests from being cut down. However, Forest Principles were negotiated at the 1992 Rio Earth Summit. Today, the United Nations Forum on Forests (UNFF), made up of all member states of the United Nations and its specialized agencies, promotes '…the management, conservation and sustainable development of all types of forests', and is working on turning this into a reality.

Wood and other products, including food, can be produced from sustainably managed forests and plantations, which should reduce pressure on natural, old-growth forests. UNFF strongly promotes sustainable forest management under which all types of forests, including plantations, are managed to meet economic, social and environmental goals.

Wood is used in a huge variety of ways, including as building materials, as fuel, in paper, or as part of brushes and other tools, and its sustainable use benefits local communities and entire industries. So some forests can be harvested to meet human, economic and social needs. The problem is unsustainable cutting or logging, which result in the loss of both species and environmental goods and services such as climate regulation and watershed protection, doing irreparable damage to the health and well-being of people and the planet.

Most experts would recommend extreme caution when introducing non-native species extensively, as they may destroy local ecosystems and cause environmental and economic damage. Invasive alien species are a significant threat, and can harm indigenous species and the local environment.

It is a good idea for young people to plant trees as well as promote the sustainable management of forests. Many organizations promote tree planting using appropriate local, native species. Check with your local community to find out how you can help - or join UNEP's Billion Tree Campaign and make a pledge (www.unep.org/billiontreecampaign).