Confusing term
''Selection cutting'' is often (sometimes deliberately) confused with "selective" cutting, a term synonymous with the practice of highgrading (the removal of the most economically profitable trees in a forest, often with a disregard for the future of the residual stand). Often the latter term is used by foresters or loggers to imply the former (which has a generally positive connotation in forestry circles) and mislead landowners into stripping their woodlot of its most valuable timber. Used correctly, the term 'selection cutting', 'selection system', or 'selection silviculture' implies the implementation of specific silvicultural techniques—usually either 'single tree selection', 'group selection' or a combination of the two—to create an uneven-aged or all-aged condition in a forest stand, one more akin to a late successional or ' climax' condition. Partly as a result of such confusion, the term ''Plenterwald'', which is the German term for selection cutting, is being more commonly used as the standard term in English. Increasingly, especially in Britain, Ireland and elsewhere in Europe, the termSingle-tree selection
The most common type of selection system is single-tree selection, in which scattered individual trees of multiple age classes, whose canopies are not touching, are harvested. This type of selection system generally produces small canopy openings especially conducive to the establishment and growth ofGroup selection
Another variation of selection silviculture is group selection. Under this system, a number of 'groups', or small openings created by the removal of several adjacent trees, are created in complement to the harvest of scattered individual trees. If the groups created are large enough, and if seed-bed conditions are favorable, this can allow species which are intolerant of shade to regenerate. Group selection is designed to mimic larger, multi-tree mortality events, which in some environments may represent natural disturbance regimes. The maximum size of a group (before it becomes a patch, or clearcut) is debatable. Some say it may be up to 2 acres (0.8 hectares) in size, whereas others limit it to a maximum of 0.5 acres (0.1 hectares). In any case Plenterwald can operate in a small areas of 1/3 - 1/2 hectare, whereas other systems need a bigger area. Behind this is the philosophical idea that a stand should be balanced (that is equal amounts of land cover for each age class) in the same way that a forest would be balanced under a clear cut régime (that is stands collectively are balanced on yield flow). The reasoning is based on the Normalwald concept, which is a model of a forest over 100 years that will produce an amount of money that is consistent over time with treatments being consistent over time rather than big expenses or big profits at one time and low expenses and low profits at another. Care need to be taken to avoid epicormic shoots growing on trunks of surrounding trees such that they lead to knotty wood, if timber production is desired. It is also challenging to visualize the groups with cuttings over time.Implementing A Selection System
In North America, trees are selected for harvest in a selection system with reference to the Arbogast Method (named after the method's creator). This is also known as the ''BDq'' method. Under this method, a harvest is specified by defining a residual basal area (''B''), a maximum diameter (''D''), and a q-ratio (''q''). The q-ratio is the ratio of the number of trees in a diameter class to the number of trees in the next larger class. Typically diameter classes are either 4 centimeters or 2 inches. When the Q is plotted on semi-log paper it gives a straight slope for uneven aged stands. However, in reality this slope can be seen to vary from what is called an S-curve in old growth forests to cut off the older trees giving a reverse-J curve in a managed stand. The curve is also an ideal curve and there may be variations to some extent, particularly in earlier number of trees where there are many more seedlings and saplings than the model Q-ratio would suggest. Given the BDq, a curve representing the state of the residual stand is computed. This curve is compared to the inventory data from a stand, specifically the curve of the diameter classes of the trees in the stand against the number of trees in each diameter (age) class. Diameter is used as a surrogate for age and thus called an age class even though strictly it should be a size class. The comparison of these two curves tells the forester how many trees of each age-class should remain in the stand. Surplus trees are marked for harvest. If there are too few trees in a class, the forester will determine if it is necessary to reduce the removal of trees from neighboring classes to maintain an ideal q-ratio. The goal of the use of a BDq curve is to ensure the continued development of trees in each age class, and the continued availability of mature timber to harvest on a relatively short cutting cycle (8–15 years). Longer cutting cycles may be used depending on species mix, silvicultural goals and if the aim is amenity or economic forestry in respect to the land. Following this method with well performed forest inventories should see the right amount of cutting. However, reality has shown about a third of forests are overcut and a third are undercut. It appears that the model also departs from reality in many cases, and so cannot be solely relied on. The judgement of an experienced forester is also needed.Tech study questions whether forestry standards are followed May 30, 2014 Dan Roblee, The Daily Mining GazetteSee also
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