When a tree finally succumbs to age or a windstorm and falls to the ground, it begins a new life as a log. The downed log serves as homes for many animals. Many plants will take root and grow on these logs. As the logs rot, they become spongy and are able to store lots of water. Other plants will send out roots to use this resource.
Insects deposit their eggs under the bark and the larvae tunnel their way out after they've hatched.
Because other plants are able to take root on these logs and survive off the stored nutrients, they are called nurse logs.