Tree Species

- Aspen


- Balsam Fir

Aspen

Regneration

Range of quaking aspenRegeneration from seed is possible, but unreliable. Good seed crops occur every four to five years on 50- to 70-year-old trees. Seeds ripen in May to June and are dispersed long distances by wind and water. They require a water-saturated seedbed for germination. A moist, bare mineral soil is best.

Aspen stands most commonly regenerate from root suckers that grow from lateral roots after a stand has been harvested or killed by fire or wind. Because aspen is very intolerant of shade, optimum root suckering occurs when the stand is completely clearcut. Do not leave more than 20 mature trees an acre after harvesting. If logging does not destroy undesirable trees and shrubs, remove them by felling, girdling, basal spraying, or controlled burning. Root suckering is most prolific when:

  • Clearcutting is done when the soil is relatively dry or frozen to avoid damaging the lateral roots within 4 inches of the soil surface that produce the suckers. This is especially important on clay soils with a high water table.
  • Harvesting occurs during the dormant season when food reserves stored in the roots are at a maximum, especially on fine-textured soils.
  • Soil temperature is 74° F. (High soil temperature inhibits suckering.)
  • Parent trees are healthy and have high carbohydrate reserves. Grazing, repeated cropping, killing of sucker stands, and insect defoliation will lower carbohydrate reserves.
  • There is no excess soil moisture (to impede aeration) or severe drought.

If a stand is harvested during the growing season, root suckers will begin to grow immediately after trees are felled. Do not drive heavy equipment across young sprouts or they will be killed. To protect new sprouts begin logging at the rear of the stand, then progress toward the log landing. Harvest stands for pulpwood at age 45 to 55 and for sawtimber at age 55 to 65. Harvest earlier if more than 30 percent of the trees are diseased (indicated by the presence of fungal conks or bark cankers).

Old, decadent stands with low vigor and stands with fewer than 50 mature aspen trees an acre may be difficult to regenerate. Encourage maximum suckering by harvesting these stands during the dormant season when the ground is frozen or relatively dry. If an old stand does not have a merchantable volume of wood, you may kill the old trees and stimulate suckering by felling the trees, by shearing them with a sharp blade on a bulldozer when the soil is frozen, or by setting a prescribed fire.

Two years after clearcutting there should be at least 5,000 aspen root suckers an acre. Some stands may have up to 30,000 root suckers an acre. The more the better, since aspen stands naturally thin themselves. If root sucker density following the clearcut appears low, ask a forester to judge whether the stand is adequately stocked. If stocking is not adequate, wait at least 10 years, then clearcut the stand again. Following this second clearcut, sucker density should improve to a satisfactory level. Aspen will not compete well with other hardwoods such as maple, basswood, ash, and oak. Over time the aspen will die from disease and be replaced by more shade-tolerant species. Clearcutting a mixed species stand favors aspen regeneration. Removing aspen during thinning will favor other hardwood species.

Where you find mature aspen with an understory of white spruce and balsam fir (two shade-tolerant conifers), clearcutting aspen while damaging the conifers will reproduce mainly aspen. In contrast, carefully harvesting the aspen while leaving the conifers undamaged will enable aspen root suckers to survive in scattered patches. In 40 to 50 years the conifers and aspen will mature. Clearcutting then will regenerate a stand of mainly aspen with a few scattered conifers.