It’s February in the Cairngorms and this is the Caledonian Pine forest. There are three dominant species here, the birch, the gnarled and the knotty Scots pine and the rugged shrubby juniper, all of them capable of coping with intense cold. The birch does it by shedding its leaves and shutting down all systems for the winter. And the pine and the juniper by adapting their leaves into these fine needles that lose much less moisture than a big floppy leaf, and their sap contains the plant equivalent of antifreeze so they don’t go rock solid in the winter. This forest is so well adapted to the cold that today most of Britain is just too warm for it. But before the great deciduous wildwood, it was this forest that covered Britain, and trees like this that were growing where your garden is. And that means that Britain must have been much colder than it is today.