of memory : the genetic code stored in a creature's DNA serves as a memory of how to make or repair one. Our immune system remembers the many attacks it had to fend off, and how to go about them. The landscapes we see, are but memories of the forces that acted on the land, over eons of time. The shape of a tree memorises its entire lifetime; how it grew and fought the elements, and what lived in competition around it. Seed banks in the soil remember what once grew above, after a drought or forest fire. Flocks of birds have collective memory of when to migrate, where to feed, how to mate and so on, which is retained in the flock although individuals die. Fish schools behave similarly. For a memory to work, it must not only be able to store, but also to retrieve information. Thus the action of an immune system is influenced by what has been experienced before. But the erosive forces memorised by the shape of a coast or a landscape, are not necessarily influenced by that shape (but some do, like dunes and many sea coasts). The most important memory of a terrestrial ecosystem is located in its soil, made over thousands of years, by thousands of species above and below, to arrive at the chemistry and composition it holds today. The memory of an ecosystem is also found in its composition and abundance of species. Should one link fail or die, it