Some hardwoods (such as aspen and black locust) can regenerate from root suckers, usually after the parent tree has been cut down. Root suckers grow from live roots, not from exposed stumps. Trees that grow from root suckers are genetically identical clones of the parent tree. A single parent tree may produce several hundred suckers, creating a dense new stand (Figure 4-2). The number of suckers may be reduced if there is too much shade on the forest floor from residual trees left after a harvest; the parent tree is particularly large, old, or in poor health; or timber harvesting damages the root system by cutting or soil compaction.
Figure 4-2. Stand of aspen suckers.
Oak, basswood, birch, maple, and some other hardwoods sprout from stumps. Like root suckers, stump sprouts are genetically identical to the parent tree. The difference is that stump sprouts grow from exposed stumps, not roots. The most vigorous sprouts arise from relatively young stumps cut close to the ground in late fall or winter when there are food reserves stored in the roots. Stumps often send up numerous sprouts, but these usually thin naturally to two or three main stems. You can speed up this process and encourage the strongest stump sprouts by cutting excess sprouts when the sprouts are five to ten years old (12 to 20 feet tall).
Layering occurs when a buried branch on a living tree takes root and develops into a new tree. The lower limbs of black spruce, balsam fir, and northern white-cedar sometimes touch the ground and become covered with organic matter. Roots develop on those buried branches. Layering is not usually an important reproduction method in forests, but may provide additional northern white-cedar for deer browse.