When you look at a group of Aspens they may all be the same tree. It forms new shoots from its roots and these can grow into large apparently separate trees. In fact they are the same plant, only when seed is produced are new plants formed. For this reason it is not possible to measure the age of Aspens, only the age of any particular "tree" attached to the root system. Some clones may be many thousand years old and some local clones spread over many hectares.