Silviculture is the art and science of growing forests – from Latin silvi (forest) and culture (growing) and is used to manage forests to maintain and enhance multiple objectives simultaneously e.g. wildlife, timber, water and recreation. This is accomplished through regulating the establishment, growth, health, composition and quality of forests to meet diverse needs and values. Successful silviculture depends on clearly defined management objectives; matching the appropriate management treatments to the biological requirements of individual or groups of trees and integrating concepts of ecosystem response to natural disturbance.
Silviculture in the Great Lakes St. Lawrence is commonly practiced using three different systems: Selection; Shelterwood and Clearcut.
The selection system, also known as single tree selection, is applied to uneven aged forest systems. In the Bancroft Minden forest, the selection system is used to manage tolerant hardwood forests dominated by sugar maples. The term tolerant refers to a tree species’ ability to tolerate shade. In this system, individual trees are chosen for removal based on tree quality, defect, disease, vigour and spacing. Trees are selected for removal when they show signs of decline, disease, defect, or if they are impeding the growth of a more vigorous, healthy tree. Trees that have diseases that can be spread to other trees in the forest are preferentially selected for removal. In this system, approximately one third of trees are harvested and the forest that remains after the harvest is healthier, has more access to light and its ability to grow rapidly has increased.
This system also increases the amount of light that can penetrate to the forest floor, but also retains some shade. This encourages the recruitment of new shade-tolerant seedlings and gives young saplings a chance to grow. The time between harvests in the selection system in approximately 20-30 years.
Selection is Applied Through Tree Marking
Hardwood selection is a complex silviculture system to practice as it is based on regulated harvests with prescribed targets for the number of trees per area (called basal area) that must be assessed using a special tool called a prism. Certified tree markers are contracted by BMFC to assess the health and vigor of each tree prescribed for selection management and determine which ones to remove to meet the basal area targets. Tree marking is the key to successful application of this treatment type.
Uniform Shelterwood System
The shelterwood system is applied to even aged forest systems, when the tree species present are moderately tolerant to shade (mid-tolerant). The forest stand is removed in a series of cuts that allows for the establishment of a new forest under the shelter of the old one. Within the Bancroft Minden forest, the shelterwood system is most often applied to White Pine and Red Oak forests. Traditionally, this renewal system occurs in a series of two cuts, which are described below.
The Uniform Shelterwood System is applied in the following steps:
Regeneration or Seed Cut:
This stage of the shelterwood system is designed to create gaps between residual trees that allow for the establishment of new seedlings. Approximately 50% of trees in the forest are removed. The trees with the largest, fullest crowns are selectively retained and evenly spaced, so their seed can be dispersed into openings, while providing shelter for the mid-tolerant regeneration.
This harvest occurs when the established regeneration is well stocked and has reached a height that enables them to have a very high probability of survival. The remaining canopy trees are harvested and the advanced regeneration that has been growing under shelter is now free to grow.
The clearcut silviculture system is prescribed to even aged, shade intolerant tree species. In the Bancroft Minden forest, this most often applies to poplar, white birch, red maple (intolerant hardwoods) and red pine, white spruce and balsam fir (intolerant conifers), or a mixture of these hardwood or conifer species. These tree species are unable to regenerate under a forested canopy, so most of the overstory trees are removed to allow new seedlings to become established. Clearcuts in the Bancroft Minden forest retain a minimum of 25 stems per hectare with the healthiest stems selected to remain for seed production. These trees do not create enough shade to impede the establishment of new seedlings and they provide seed for a new forest, as well as wildlife habitat.
This silviculture system emulates small scale natural disturbances, such as fire and wind events. Depending on the site conditions and the tree species, these harvest areas can regenerate naturally or artificially, through planting.
A Case for Clearcutting
Clearcutting creates young forest habitat that many species of migratory birds, mammals, reptiles and insects rely on. Having a diversity of forest age classes represented on the landscape is the goal when managing for wildlife, as old is not necessarily good from an animal’s perspective. With human interference and decades of fire suppression, we have seen a severe decline in young forest habitats across the landscape.
Some tree, shrub and plant species rely on fire, or open conditions that would be created by fire, to regenerate. These species would be completely absent from the landscape if we did not mimic the conditions a fire would leave to provide space for their growth and subsequently habitat for the species that rely on them.