The most common clearcut system variations are:
Strip clearcuts are used to harvest a stand over a period of three to seven years by removing several strips rather than harvesting the entire stand at once. Strip clearcutting was developed to take advantage of natural seeding from the leave-strips. In a pure sense, strip clearcut systems have mostly been used in Canada on afew site types with black spruce in boreal forests. The approach is being tried, along with strip shelterwoods, in boreal mixedwood types in northern Alberta as well.
A major concern associated with strip clearcuts is wind damage because the leave-strips expose much more edge for a short period than does one large clearcut. To avoid excessive windthrow, leave-strips should be at least 40 m wide, open only at one end, and harvested as soon as adjacent cleared strips are regenerated, thus minimizing exposure time. Also, boundaries of strips should be carefully located in healthy stands on deep, well-drained soils. Strip clearcuts can be designed in an alternate or progressive fashion.
Alternate strip clearcut
In alternate strip clearcut systems the cutting unit is cut in two stages. The initial cut produces long narrow clearcuts with leave-strips in between. Often leave-strips are narrower than first-pass strips because the leave-strips are cut once the regeneration is established in first-pass strips. The second-pass cuts will therefore need planting, but this requirement can be minimized.
Strip clearcuts, alternate or otherwise, are best oriented at right angles to prevailing winds. The width of the strips will depend on seedfall distances for the preferred species, wind hazard, and other factors.
Progressive strip clearcut
The progressive strip clearcut system accomplishes the same objectives, in essentially the same manner, as the alternate strip clearcut but in three or more passes rather than in two.
Progressive strip clearcuts have two advantages over alternate strip clearcuts:
In block clearcut systems, natural regeneration from adjacent timber is not necessarily relied upon; instead, other considerations dictate block size and shape. These considerations include non-timber management objectives, forest type boundaries, terrain features, windthrow risk, and the limitations of the harvesting equipment to be used.