Summer 2001 Volume 10, Number 2
Common Myths about Silviculture
by Thom McEvoy
Some of the most common misconceptions about silviculture arise because of our difficulty in planning for events that extend beyond our lifetime. We make decisions about a resource that takes nearly two lifetimes to mature, yet by nature we are impatient. For these reasons and others, myths about silviculture abound. Here are some of the most misleading.
Myth 1: Big trees are more mature than little trees.
Reality: Possibly the most common mistake of people who are new to forestry and logging is thinking that the bigger trees in an even-aged stand are older and more mature than the smaller trees. The fact is that the bigger trees are more vigorous and should be left to grow while nearby smaller trees should either be 1) removed from the stand if they are an early-successional species or a mid-successional species that has been suppressed; or 2) retained only if a) they are late-successional species with excellent form and there is a good chance they will reach the overstory before the end of the rotation; b) they will be carried to maturity if the stand is to be converted to an uneven-aged structure; or c) they contribute to other management goals, such as improving habitat.
Sometimes harvesting is done according to diameter limits: only trees exceeding a certain diameter (d.b.h.) are harvested. If the limit is low, as when all trees 12 inches d.b.h. and larger are harvested, 80% or more of the stand's merchantable volume may end up on the landing. This is an extreme case of "making space for the smaller trees" and is a silvicultural catastrophe. Diameter-limit cutting is not a valid guideline for even-aged stands in the Northeast. It is high-grading masquerading as silviculture.
Myth 2: A valid silvicultural treatment is the selective harvest.
Reality: Somehow the term "selective harvest" has become popular in the region. Used to describe a partial harvest (some-thing less than a clear-cut!), it implies only that someone has selected the trees for harvest. It is often confused with those terms used to describe uneven-aged methods, but "selective harvest" has no silvicultural meaning and should not be confused with group and single-tree selection methods. This is another example of high-grading masquerading as silviculture.
Myth 3: If it looks good when you are through it is good silviculture.
Reality: Good silviculture does not always look good, especially in the first year or so after a treatment. Yet many woodland owners equate a good job with good visual appeal. This is not to say that aesthetics are not important. Nonetheless, a prescription should not be compromised just to make it look good. There are many ways to protect the visual appeal of landscapes during and after harvesting, such as leaving buffer strips near trails and roads.
Myth 4: A marked stand is a silvicultural prescription waiting to happen.
Reality: Anyone with paint can mark trees for harvest. Just because a stand is marked does not mean the person who marked it had a silvicliltural objective in mind. Most of the time it is helpful to ask the forester about the marking guidelines and the prescription. Note that once the stand is marked, paint of a similar color is banned from the site and cause for termination of a logging contract.
Myth 5: Silvicultural treatments make stands more productive.
Reality: The long term effect of repeated timber harvests often is a gradual lowering of timber growth productivity. Heavy equipment operating on some sites at certain times of the year can be devastating. However, the practice of silviculture can lessen the impacts of harvesting on sites, and is usually intended to concentrate wood production on fewer stems. Silviculture can increase the productivity of stands for lumber production, but biomass productivity is usually less as a result of repeated timber harvests.
Myth 6: If a stand is suffering from stress, thin it out.
Reality: We used to think that thinning a stand was a great way to help trees recover from insect and disease outbreaks or other stresses. But harvesting is another stress that, compounded with other stresses, can lead to crown dieback and even mortality. If a stand is under excessive stress, the best thing to do is leave it alone until it shows signs of recovery.
Reprinted with permission from Introduction to Forest Ecology and Silviculture (NRAES- 1261, published by NRAES, the Natural Resource, Agriculture, and Engineering Service, Cooperative Extension, 152 Riley-Robb Hall, Ithaca, New York 14853-5701.Phone: (607) 255-7654; fax: (607) 254-8770; e-mail:NRAES@CORNELL.EDU,- Web Site: WWW.NRAES.ORG