Shelterwood cutting
Shelterwood cutting removes part of the old forest stand to allow for a natural establishment of seedlings under the cover of the remaining trees.[1] Initial cuttings give just enough light to allow for the regeneration of desired species. Subsequent cuttings give the new seedlings more light and fully pass the growing space to the new generation.[2][3] Shelterwood systems have many variations and can be adapted to site conditions and the goals of the landowner.[4] There are concerns associated with this silvicultural system due to windthrow and high costs as well as advantages due to improved aesthetics and cost savings from natural regeneration.[1][3]
Variations[edit]
Group shelterwood[edit]
Group shelterwood organizes cutting into concentric circles originating from the first cuts in the patch in the center of the circle.[3] Eventually these concentric circles meet at which point the entire stand has been cut.[5] Sometimes the first cut will simply release a patch of advanced regeneration that will serve as the center of the circle.[2] Usually a third cut is not implemented in these systems since the trees on the sides of the cuts provide shade and a seed source.[4] This has the advantage of eliminating the need to mark trees for removal as the entire overstory is removed in the second cut.[10] It also eliminates the risk of damage to the regeneration from logging equipment.[11]
Strip shelterwood[edit]
Strip shelterwood systems organize cuts into narrow strips.[3] The main advantage of this variation is that it provides protection from blowdown.[5] Cutting is conducted into the direction of the prevailing winds resulting in mature trees always being protected by younger trees from wind damage. In other situations the cuts are oriented to maximize or minimize exposure to sunlight to promote regeneration of the desired species[3] Similarly to in group shelterwoods, when the strips are narrow enough, a total overstory removal during the second cut will often be conducted eliminating the need for a third cut.[5]
Irregular shelterwood[edit]
Irregular shelterwood systems retain the trees left during the establishment cut for an extended period of time resulting in an uneven-aged stand with trees of multiple ages.[11] It maybe done to get additional growth on the oldest trees to get extra-large diameters for wood.[9] It also enhances the scenery, is important for some organisms, and creates old-growth characteristics.[12][11] The irregular shelterwood system can be further divided into three variants:
Advantages & disadvantages[edit]
Shelterwood cutting is ideal for species that are long-lived, have seedlings that would naturally tend to start under partial shade or full shade,[11] and have seeds that are not easily dispersible.[3][2] It allows for natural regeneration from site-adapted trees that are retained because of their good genetics. Further, it has improved aesthetics compared to clearcutting since tree cover is always present on the site.[3] There are, however, several particular problems associated with shelterwood systems. Since multiple rounds of cutting are required and since care must be taken to avoid damaging trees being retained costs can be higher than in other systems. Another issue is that trees left during the establishment and preparatory cuts become vulnerable to wind damage.[1]