Calke Park once spanned three counties and the baronet of that time had to ride for a day to get from one end to the other. Even today the parkland stretches as far as the eye can see. At its heart are 200 of Europe's most ancient trees, including the Old Man of Calke which is 1,200 years old, and was a sapling when the Vikings invaded our shores. When the National Trust took over Calke they decided to leave much of the park wild. Sanjida O'Connell meets Ted Greene, an expert on ancient trees who points out that old dead wood is packed full of life. Mushrooms decay the wood and a slug eats the mushroom - some slug species can't have sex until they've got trace elements from the fungus. Ted thinks there are less than 100 trees of the age and girth of the Old Man of Calke left on Earth. You often hear about the rainforest disappearing, but trees like this are the equivalent of Europe's rainforest.