Seeds are the beginning of trees, just as with other plants. The process of tree growth begins when a seed germinates in soil, under certain conditions. For some trees, like jack pines, this includes fire or extreme heat, while others require submersion in water or a period of cold dormancy.
Once seeds are sprouted, they become seedlings. Depending on the tree's rate of growth, they may remain seedlings as long as five or more years before developing into sturdy young trees. Others grow quickly and become saplings in one or two years. Many seedlings don't make it past this stage, eaten by foraging wildlife or losing the competition for resources to larger trees.
Saplings are the next stage of tree growth, larger than tender seedlings but not as large as mature trees. They may be tall and spindly, reaching a good height but not putting on full-fleshed branches and leaves for a few more years. At this stage, the tree's internal and external structure is still developing, as growth layers form and sap increases, nourishing the growing tree.
Once the tree is a few years old, it will begin to reproduce. This stage depends on what type of tree it is; gymnosperm or angiosperm. A gymnosperm or conifer produces cones as seeds. The spring will see soft green male and female cones that expand and dry through the summer in a self-pollination process. It may take months or even years for the seeds to mature. Angiosperms, or flowering trees, produce flowers which will turn into fruits containing seeds. This is usually a yearly cycle relying on birds, bees and other pollinator creatures.
The mature tree then spreads its own seeds. For conifers, this means dropping the old cones, or sometimes spreading them through birds, winds and weather. Angiosperms use similar methods, either dropping fruit, nuts or seeds in the fall, or relaying on wildlife, winds and water to spread the seeds away from the original tree.