Trees reproduce naturally from seed, root suckers, stump sprouts, or layering (Figure 4-1).
Figure 4-1. Natural regeneration methods.
All tree species can reproduce from seed, but only a very small percentage of seeds will become established seedlings. Success depends on:
The amount of seed available depends on tree species, age, health, and weather. Tree species with very large seeds (such as oak, walnut, and hickory) produce relatively few seeds, while species with small seeds (such as aspen and cottonwood) produce abundant seed. Very young and very old trees produce few viable seeds. Healthy trees with large crowns produce more seeds than trees that are unhealthy, have small crowns, or are suppressed by taller trees. Seeds from some tree species remain viable for only a few days after dispersal while seeds from other species may survive for several years on the tree or on the forest floor. The frequency of good seed crops depends on the tree species, overall tree health, and weather during pollination and seed growth. If your regeneration strategy relies on tree seeds to regenerate the new stand, time your harvest and regeneration treatments to coincide with a good seed year.
Tree seeds are dispersed in a variety of ways. For example, aspen and cottonwood seeds are covered with cotton-like down and may be carried several miles by wind. Maple and pine seeds have wings allowing them to glide in the wind. Cherry seeds frequently are dispersed by birds that eat the cherries and drop the seeds far from parent trees. Walnuts, acorns, and pinecones are carried away and buried by squirrels. Seeds from willows and other shoreline species may be dispersed by water.
Each tree species requires certain seedbed conditions for seedling survival. For many species seed must be in contact with mineral soil so the seed can absorb enough moisture to germinate and grow. Seeds from other species may germinate on leaf litter, rotten logs, or moss, but if those materials dry out, the seedlings will die.
Soil temperature must be high enough so seeds will germinate, but not so high that the seedlings will be killed. Annual weather conditions and the amount of sunlight versus shade will affect soil temperature. Shade may be produced by living plants or harvest debris.
Competition from other vegetation may greatly affect seedling survival. Trees, shrubs, and herbaceous plants may rob delicate tree seedlings of needed sunlight and moisture.
Insects and animals consume large amounts of tree seeds and may eat most of the supply in poor seed years. Damping-off disease kills emerging seedlings too, but its effect varies greatly among tree species.
When you want to regenerate a stand by natural seeding, you?fll need to know how the species you wish to encourage disperses seed, how far its seed travels, how abundantly it produces seed, and what type of seedbed it needs for germination and seedling survival. This information will affect how you harvest and prepare the site. Chapter 6: Managing Important Forest Types provides basic regeneration information for important tree species.