Woodlot Harvest

 
 
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  Nine things to consider before woodlot harvest | Harvest methods

Timber harvest planning is more than deciding which trees to cut. Harvest design has to take into account the long-term effect on the environment -- water, fish, wildlife, and soil. Proper timber harvest removes timber efficiently, protects site productivity, encourages regeneration of desirable species and minimizes impact on wildlife, water, and soil.

Nine things to consider before woodlot harvest:

The harvest system you choose should be adapted to the site and be the most cost-effective.
Consider the following when choosing your harvest system.

  1. Goals: Review your woodlot management goals to ensure your harvest method will help achieve those goals.
  2. Ecological Conditions: Some tree species are very adaptable and can grow in a wide range of geographical locations, climate zones and soil types. Other tree species only thrive under very specific conditions. Review the ecological information for your woodlot to understand how the ecological conditions affect the growth of the existing tree species and the species you plan to regenerate.
  3. Stand characteristics: Review the stand characteristics from your woodlot inventory (size of the area, species type, tree density, species composition, age, and understory vegetation) to help you to determine which harvest method will work best.
  4. Species regeneration characteristic: Identify the species you want to regenerate, then choose a harvest system. You will need to know the species regeneration characteristics and abilities. For species like aspen, balsam poplar or jack pine, which are shade-intolerant and need the sunlight for regeneration, clear-cutting works best. To regenerate a mixedwood forest of aspen and white spruce, choose the shelterwood system. To regenerate shade-tolerant species like spruce and fir or create a stand with many different species and different age classes, choose selective harvesting.
  5. Age: Determine if you have an even aged or uneven aged stand.
    Even aged stands. Trees in even aged stands are about the same age (+/- 20 years) and form single canopy layer. Natural disturbances such as fire or storms that kill all older trees at once create even aged stands. Also, even aged stands are created by clear-cutting the trees. Pure aspen and jack pine stands are the best examples of even aged stands.
    Uneven aged stands. In uneven aged stands, trees of various ages and sizes are all growing together. There should be a minimum of three distinct age classes and three distinct height levels. The structure of uneven aged stands consists of three layers of trees -- overstory layer, intermediate story and understory layer. The best example of an uneven aged stand is an aspen or balsam poplar in overstory layer with white spruce forming intermediate and understory layers.
  6. Wildlife: Review the information you have collected on wildlife. Wildlife habitat will be affected after harvesting and it is important to maintain a healthy forest after harvesting. Options for maintaining wildlife habitat include: leaving a number of cavity and snag trees; leaving decaying wood on the ground; protecting riparian zones and wetlands; and keeping understory vegetation where possible.
  7. Economics: Determine what markets are available for your forest products and the projected prices for these products. Decide who will do the harvesting and regeneration and find out how much these operations will cost.
  8. Time (season): Harvesting at the wrong time of the year for the site might create problems such as soil compaction, fire hazards, disturbing wildlife during critical times in their life cycles, and damage to the roads. Winter harvest is best to avoid these hazards.
  9. Roads and skid trails: Most of the time, timber harvest requires building the roads and skid trails. Roads and skid trails might be for temporary or permanent use. Building and maintaining these roads and skid trails in the right place and at the right time is very important for protecting soil, water and wildlife. It also minimizes your investment in harvesting.
Harvest Methods

In Alberta there are three main types of forest harvest methods: clear-cutting with various modifications, shelterwood and selective. Each method has its own advantages and disadvantages. Every woodlot has unique characteristics and you need to plan and decide which method will work best on your woodlot.

Selective method
This method removes individuals or small groups of trees. The selective method is best adapted to uneven aged stands of shade-tolerant species such as spruce or fir, or mixedwood aspen/white spruce stands with a wide range of species and various ages. It can also be used to convert even aged stands to uneven aged stands if the species being managed is capable of regenerating in a partially shaded stand. Individual trees or groups of mature, unhealthy or other selected trees are harvested periodically. Most of the trees are left to naturally regenerate the stand.

Before any selective harvesting is done, a forest inventory has to be completed. The inventory identifies the tree species, sizes of trees, the quality and health of the trees and the availability of habitat in the forest.

The advantage of the selection method is that it is often considered to be less visually offensive than clear-cuts. Therefore, selective harvesting is frequently favored in areas where recreation or scenic values are important. Selective cuts may also be used to harvest timber from sensitive areas such as steep slopes or buffer strips where it is desirable to maintain permanent tree cover.

The disadvantages of the selection harvesting include, risk of blowdown, risk of harvest damage on the remaining vegetation, and higher harvest costs.

Road access and a good skid trail network are necessary for selective harvesting. This might be advantage or disadvantage depending on other uses of the trails.

It is also important to remember that this method is often misunderstood. First, this type of harvesting does not apply in every situation (e.g. even aged aspen and pine stand). Second, many landowners have done selective harvesting by taking best trees in their forest leaving poor shaped and unhealthy trees. This approach leaves the stand in poorer shape resulting in forest degradation over the long term. Proper selective harvesting removes valuable, mature stems along with poorly shaped trees, unhealthy, crooked and leaning trees, and broken or damaged trees. The goal of selective harvesting is to improve the forest not degrade it. It is very important to keep this in mind prior harvesting.

Selective harvesting - 22 KB
Selective harvesting

Shelterwood method
The shelterwood method is a combination of selective, clear-cutting and seed tree methods. This method removes trees in a series of two or more partial cuts (preparatory, seed and removal cuts). The first cut is the preparatory cut which may be similar to thinning. Up to 25 % of trees in the stand are removed. Seed cuts remove most of the trees leaving only best trees as seed sources. Removal cuts are done when the new crop is established. These cuts stimulate the germination and rapid growth of a new forest in the shelter and the shade of mature trees. The mature trees usually provide seed for regenerating the site. Main disadvantage of this method is damage to the young trees during removal old ones.

Unlike the selection method, the shelterwood and seed tree methods will not provide a continuous cover of mature trees. Once young trees are well established on the cutover, the remaining larger trees are removed, leaving only the even-aged regeneration.

Windthrow is a serious concern in shelterwood methods. If residual trees are blows down, uprooted stems can displace significant amounts of soil and can be unsightly. The impact on soils, watersheds and aesthetics may be worse than if the trees had been harvested. As well, salvage harvests usually cost more than clear-cutting.

Planning a shelterwood harvesting to minimize windthrow requires considerable expertise. Cutblocks should be designed to minimize exposure to the prevailing wind. The risk of windthrow is related to soil texture, soil moisture, wind speed and the species, age, rooting habit, size and crown development of the residual trees. In general, selection cutting that removes very little of the mature stand in the initial harvest is the least likely to result in windthrow problems.

Clear-cutting method
Clear-cutting removes all merchantable trees from the specified area at the same time. Various factors influence the size and shape of clear-cuts. Tree species and age are most important. Clear-cutting is appropriate for most species but is especially suited to even aged stands of sun loving (shade intolerant) species such as aspen, balsam poplar and lodgepole pine. The size of clear-cut may also vary according to your needs.

You may do a series of small patch clear-cuts or do all the harvest at once. After clear-cutting, the area may be naturally reseeded from trees in the surrounding forest or artificially by seeding or tree planting. If natural regeneration is not successful, the area should be artificially regenerated.

One common misconception about clear-cutting is that you must remove all the forest at once. Although you harvest all the merchantable trees in a certain area, the size of that area can be large or small depending on your objectives. A series of small clear-cuts, promptly regenerated, can provide periodic, sustainable income while maintaining a healthy forest with diverse age classes. This method is the most economical way to harvest.

Advantages of clear-cutting include: more cost-effective, more accessible and economical for site preparation and tree planting, and easier supervision and planning. Some wildlife species prefer this type of harvesting. Clear-cutting is most suited to regenerating aspen, balsam poplar and pine.

Disadvantages of clear-cutting include: increased possibility for erosion and rapid runoff; no timber products for long time after clear-cutting; loss of habitat for some wildlife species; unattractive visual effect; and greater possibility of unwanted shrub and grasses becoming established.

Clear cutting - 17 KB
Clear cutting
Source by: Ducks Unlimited Canada

Sanitation cutting
This type of harvesting is used to rid the stand of trees that was killed or infected by diseases or insects. The goal of this type of harvesting is to prevent the spread of the diseases to nearby healthy forest. Jack pine stands that are infected by dwarf mistletoe are usually recommended for sanitation harvesting. Trees from sanitation harvesting are often only used for firewood.

No Harvest

You may decide not to harvest if the benefits of the forest are worth more to you than the cash value of the timber. However, not harvesting can have long-term impacts. When the forest is overmature or if it consists of an even-aged stand with just one or two tree species, it may be more susceptible to damage from insects, disease or fire. Management activities, including timber harvesting, are desirable to maintain a healthy, diverse forest.

 
 
 
 
For more information about the content of this document, contact Toso Bozic.
This document is maintained by Brenda McLellan.
This information published to the web on February 26, 2002.
Last Reviewed/Revised on October 28, 2014.