While all trees require sunlight, each species exhibits a specific level of shade tolerance. Shade tolerance is the ability of a plant to thrive in the shade of and in competition with other trees. Some species can germinate and grow for many years in low light levels, while other species will not even germinate. There are three levels of shade tolerance; intolerant, mid-tolerant, and tolerant. Each tolerance level corresponds with a specific silviculture system to encourage germination and growth of regeneration. These silvicultural systems are chosen based on species present, the health of the stand, and the desired future forest condition. For instance, if the desired future forest condition requires an increase in a species, the silvicultural system may favour that species.
Selection -> Tolerant
With this system, the harvests basically equate to a continued series of thinning on a 15-25 year cutting cycle. The area always remains forested with mature trees making this a very benign management system for aesthetics and results in relatively minor changes to wildlife habitat. These thinnings leave several small gaps in the canopy into which the remaining trees can expand their crowns and, therefore, growth rates. Seedling and saplings also respond by rapidly increasing height growth to take advantage of these gaps. The system is often referred to as “gap-phase” replacement, similar to nature wherein a single tree dies, or one or two trees blow down with remaining trees responding to these gaps.
Shelterwood -> Mid-tolerant
Uniform shelterwood is essentially a clearcut but undertaken in a number of stages to achieve an even-aged or two-aged forest. White pine is the textbook example of a species that can be managed with uniform shelterwood, although low quality maple dominated stands can also benefit from this system. Stands with mid-tolerant species such as red oak, yellow birch, and black cherry may also be harvested with a shelterwood system.
Preparatory cut: A stand will be thinned when it is 60-80 years old. Small crowns have room to expand and produce more seed. A commercial thinning may also be used to accomplish a similar result.
Seeding Cut: Twenty years later, a seeding cut is carried out to provide the necessary light conditions for natural regeneration in the stand (40-50% shade). Mature trees moderate the temperature and moisture of the site.
Removal Cuts: After another 20 years, a removal cut is carried out to increase light levels and growing space for the established regeneration. Depending on a variety of factors, including species, stocking, method of regeneration and access, one or two removal cuts may be required.
Clear Cut -> Intolerant and Mixedwoods
A clearcut is an often misunderstood. The aesthetic transformation of the site can be abrupt and dramatic, effectively removing most of the standing trees on a site in one stage. However, this is necessary and advantageous for regeneration of shade intolerant species that require near full sunlight to be renewed. Species such as aspen and jack pine are perfect examples of species that will not regenerate without a large disturbance.
Although clearcuts are an even-aged form of management that removes most of the cover in one harvest, several individual and clumps of trees are left in the cut that simulates natural disturbance patterns and provides a source of seed. Clearcutting allows managers to create early successional forest, something that is lacking in this forest.
Although clearcutting only accounts for 9% of the planned harvest area in current Forest Management Plan for the French-Severn forest, it remains an important silvicultural system in specific stands to achieve multiple objectives.
- Forest Management Planning
- Areas of Concern
- Forestry Roads