The Aspen-Birch Forest Type of Minnesota

The aspen-birch forest type has several products and uses. For instance, pulpwood is produced by bigtooth aspen and quaking. This pulpwood is used to manufacture products such as particleboard and paper. White birch can also produce paper, along with wood for fuel and dowels, but is not as in demand as aspen. Aspen is especially vital to the development of ruffed grouse, moose, and white-tailed deer.

Growing Conditions

Most often, aspen and birch thrive in pure stands. That said, they have been known to grow together and with other conifer species. Aspen is versatile in that it can grow in many different kinds of soil. It grows best with soil that is rich in lime, however. It grows even better if that soil has a high silt and clay content. Low-moisture soils are not as good for aspens, and without the essential nutrients in moist soil the tree will have health problems. If the soil has too much clay, then there will not be enough soil aeration for the tree to thrive.

Regeneration

The best age to harvest aspen for pulpwood is between 45 and 55 years. If the trees are being grown for sawtimber, then 55 to 65 is more appropriate. However, if more than a third of the tree seems to be affected by disease, then it may be a good idea to harvest earlier and salvage what you can. Root suckers, which are sprouts that grow out of a stump or the roof of a tree, can grow into regenerated aspen stands. Aspens can also regenerate from seed, but it has to be in the best possible soil. Aspen root suckers will grow best when they are in the sunlight. Aspens do not like shade, and neither do their root suckers. It is for this reason that aspen root suckers seem to do best on clear cut stumps, since there are no trees left to project shade.

Root suckers also develop faster in the dormant season. This is because it is during this time that the roots of a tree contain the most nutrients. In the spring and summer, the root system is not as nutrient-rich, and the suckers may suffer if they are harvested then. During the growing season, you may see root suckers growing almost immediately after clear cutting. It is important to be careful with driving heavy equipment around a newly clear cut stand, as you may crush and kill the sprouts.

Regeneration is harder with stands that have few trees. Usually it works best in stands with more than 50 trees per acre. If a stand does not have that density, then you can try to stimulate sucker growth by harvesting while the ground is cold and dry. If the soil is good and you’ve prepared the site properly, within two years of clearcutting you should find 5000 aspen root suckers have taken hold. If your root sucker count seems low, then you may have to wait 10 years before clearcutting again to get the right healthy amount.

Aspen does not do well when mixed with other species, especially hardwood species. Those hardwoods, like oak and ash, can take over and the aspen will be pushed out by species that are more tolerant to shade. A mixed hardwood stand should then be managed for one or the other, but not for both.

Treatments

After regeneration, aspen trees can grow quickly. If a stand is dense, then it will thin itself naturally to a more tolerable level. No thinning is needed for these stands, and it may even be detrimental to the health of the trees. Only try pruning and thinning if the situation does not seem to be correcting itself and there is no sign of disease.

Pests, such as the forest tent caterpillar, can also cause damage to an aspen. Specifically, they can increase defoliation. This won’t usually cause death, but it may if the tree is otherwise stressed. Take care of your aspen the right way to make sure that it is in the best shape possible for harvesting.