There have been big promises about tree-planting numbers over the last few years - but is there much point in planting more trees, if we're not looking after the ones we've already got? The Woodland Trust estimates that only 7% of the UK's native woodlands are in good ecological condition - with pests, diseases, climate change and development all threats to tree health. Meanwhile a report from Botanic Gardens Conservation International says that a third of the world's trees are at risk of extinction. In this programme, Peter Gibbs finds out what's ailing our trees, and asks what can be done to nurse them back to health. He talks to scientists, campaigners and the government's Chief Plant Health Officer, and finds out about a project where researchers are on the hunt for trees with natural resistance to ash dieback, which may be able to re-populate the ash woodlands of the future. He also visits a 'research forest' in the Midlands, where scientists are piping extra carbon dioxide at some of their trees, to find out what the impact of rising CO2 levels is likely to be for trees in years to come. Produced by Emma Campbell