When a tree seed germinates it sends out a root into the ground and a shoot into the air. The shoot is not woody at this time and is capable of being eaten by many herbivores. The tree produces many seeds so that some may not be attacked. If the seedling of a woody plant survives, it begins to make wood in both its shoot and root. The stem becomes covered in bark which adds extra protection against both herbivores and the weather. The tree at this stage may only be a few centimetres high and it may take a number of years to reach full size. During its early years the small tree is called a sapling.