Environment minister David Miliband yesterday saw first-hand how climate change is already altering the delicate balance of life in Oxfordshire's woodland.

Mr Miliband braved the wind and rain for a walkabout of Wytham Woods, near Oxford, where he was told the woodland had experienced its fourth ever earliest breeding seasons in the last five years.

During his visit, hosted by Oxford University and the Centre for Ecology & Hydrology, he toured a weather station and inspected bird nesting boxes and met Dr Andy Gosler, who has carried out one of the longest running studies into the British bird population at Wytham.

Dr Gosler said: "Because of climate change, the timing of breeding is now happening three weeks earlier than it was 25 years ago.

"Although this isn't a problem if the breeding season gets steadily earlier, it is a problem when the weather becomes variable, because this stops birds and animals making important predictions.

"The climate controls when oak buds burst, which in turn affects when the caterpillars appear that eat these buds.

"And birds like Great Tits, which rely on the caterpillars for food, produce their clutches of eggs around these caterpillars appearing it's all about timing."

Praising the research being carried out at the "precious resource" at Wytham, Mr Miliband, the Secretary of State for the Environment, Food and Rural Affairs said: "The reality of climate change is with us today.

"Here in Wytham Woods, we are already seeing changes in our long cherished biodiversity. We can only expect much bigger changes to come.

"No part of Britain will be unchanged. It is imperative to act now to reduce our emissions of carbon dioxide and combat the effects of climate change on our natural habitats and the plants and animals that rely upon them."

The minister also watched students from across the UK training for an investigation of tree canopies in Borneo.

Declining an offer to scale a tree, he added: "It's tempting, but I'll leave it to the professionals."