The Gulf Stream has had a profound effect on our landscape and we know this from pollen. Different kinds of plants produce their own kinds of pollen but pollen is very tough and can resist decay for thousands of years. This means that plants leave a botanical fingerprint behind them, a way of tracking their history. Pollen grains land on the surface of ponds but eventually they sink to the bottom, providing clues to what plants were around in the past. From this we know that birches and pines started disappearing from Britain about 9,000 years ago. In their wake came wave upon wave of new arrivals. Hazel was one of the first to establish itself. Then came oaks, then elms, limes, ash, holly, hornbeam and beech. These rich forests then became home to new animals that had filtered north from Europe to fill this new forest. With every passing year, the new trees spread further and further afield. Some, like the oak, had their seeds spread by animals.