This system leaves mature trees of desirable species scattered throughout a harvested stand at intervals close enough to furnish seed to the entire cut area (Figure 4-8). Residual stocking (unharvested trees left standing) is not sufficient to protect, modify, or shelter the site in any significant way. Once the new stand is established (typically three to ten years after the initial harvest), seed trees may be harvested or left to grow through the next generation. This system is appropriate only for tree species that produce wind-dispersed seed. To obtain maximum seed production, seed trees must be healthy, large-crowned, and wind-firm. Seed trees usually are left singly, but may be left in small groups for wind protection. The number of seed trees required depends on the species?f ability to produce seed and the distance that seed can be dispersed reliably by wind. In most cases three to ten seed trees per acre are left.
The initial tree harvest should occur after seeds have been dispersed in a year when there is a good seed crop. Site preparation usually is necessary before the harvest to create a receptive seed bed.
Figure 4-8. Seed-tree system.
The seed-tree system has several disadvantages: