This article is not about data logging, which see.
Logging is the practice of cutting trees down, then cutting out their central boles and possibly branches in order to use the wood directly or to market it as an economic resource. Standing trees viewed as a potential economic resources are termed timber.
Most conventional logging is either for pulpwood production for the manufacture of paper products or for sawlogs for lumber production. A significant amount of logging is also done for firewood production, and, today, a very large and growing amount of logging is being done for chipwood production.
There are several methods of logging. The most common in commercial operations is clearcutting, a practice that removes essentially all the trees. In clearcutting for lumber production, where the logging is done in a mixed-age forest, all the large trees are taken and the saplings and smaller trees may be left for regeneration. In the case of a pure-age stand, such as a tree farm, or in certain mature forests, such as some of the virgin Douglas-fir stands of the West, virtually all trees are cut.
Clearcutting in the case of pulpwood production usually involves cutting away all woody plants. This may be also true in the case of chipwood production. This type of clearcut area takes a longer time to regenerate forest and suffers more erosion than does mixed-stand clearcutting that leaves younger trees intact.
There have long been claims that clearcutting is a healthy forestry practice, mimicking the effects of a forest fire. The facts speak otherwise. Clearcutting is done simply because it is the most economically-efficient and thus profitable way to remove timber.
In the case of a forest fire, many standing snags are left for wildlife, and the organic matter is left on-site as ash to fertilize the soil or as partly-burnt wood that will quickly decay into the soil, and the ground is generally intact, or left unbroken, to quickly regenerate groundcover. In the case of a clearcut, especially for pulpwood or chipwood, all woody matter is removed, depleting the ambient stock of organic matter, and the ground is both severely broken, resulting in serious erosion, or compacted, retarding the recovery of any plant life in those places.
Selective cutting is the practice of only taking certain trees that are deemed the most desirable for harvest, and leaving the rest. This is a practice most often engaged in by woodlot owners who wish to sustain their timber yield. Presumably, only the largest trees are cut, leaving younger trees to continue to grow. However, certain trees are always more desirable for either lumber or firewood production, so there tends to be a bias in the cutting. For instance, trees that were originally open-grown have much lower value for lumber than do forest-grown trees, and strongly cross-grained trees such as elms tend to be avoided for firewood production.
A problem with logging in general is that it tends to harvest the best trees, removing them from the seedstock, producing a de-evolutionary pressure. In the ideal selective cutting, a few of the best trees of each species would always be left as seedstock, and a few of the least desirable trees would be girdled and left for dead as snags for use by wildlife.
Trees should also always be left standing along waterways to protect the banks and water quality.