Module 3: Thinning for Value

Lesson Four - Other Types of Thinning and Considerations

Semi-commercial thinning is a combination of a PCT and a CT. Much of the wood will remain on site to complement the organic layer as in a PCT, but some will be removed as salable product like a CT.

This type of thinning can produce specialty hardwood pole products, fence posts, rails, and small amounts of pulpwood or fuel. It is not formally conducted in Nova Scotia, but many woodlot owners take a few sticks of product when conducting PCTs. This meets the definition of a semi-commercial thinning.

A treatment similar to commercial thinning is a shelter wood. However, the goal of a shelter wood is to encourage natural regeneration. The best trees are left to produce seed and give shelter to regeneration. Shelter wood harvesting is a single or series of cuts designed to encourage the establishment or development of natural regeneration. This system has been used for more than 500 years in Europe and has been successfully conducted in Canada, including Nova Scotia.

Like a CT, shelter wood is restricted to the most wind firm species and sites. It involves significant removal of upper crown classes, leaving the stand very susceptible to wind damage. Openings in the canopy are necessary to allow sunlight to penetrate to the forest floor. There, seedlings are encouraged to develop. Once the number of seedlings and their height are appropriate, the remaining trees are harvested.

A shelter wood is considered a harvest treatment; more information can be obtained in Module 2.

Selection harvesting involves the removal of a small number of merchantable stems per hectare on a continuous basis. This is the harvesting method of choice for all-aged stands. All-aged stands have healthy crop trees in all age classes. Most people think that this harvesting method most closely mimics tolerant old growth stands of the Acadian Forest.

Stands suitable for this harvest method must be wind firm, have at least three age classes present, and have a high proportion of long-lived shade tolerant species such as hemlock. Because the forest canopy usually remains in tact, many people prefer the look of it.

This is also considered a harvest system and is covered in Module 2.

The meaning of wildlife has changed. The historical meaning brought to mind mammals, birds, fish, amphibians and reptiles. Soil and aquatic invertebrates, plants, algae, lichens, bacteria and fungi were not considered a part of this wildlife group. The new definition includes all non-domesticated species of living organisms. No matter how big or how small, it is a wildlife species.

Even slight changes that we see in the forest will have an effect on some organisms. When one organism is altered, others are affected. For the red squirrel, there will be less food and therefore fewer squirrels if its habitat is thinned. The same thing will affect many ground insect and soil micro-organism populations, but it will be much less obvious to us.

Recognize that changes to less obvious wildlife species will occur.

Always consider wildlife habitat and species diversity when planning a thinning operation. Wildlife Habitat and Watercourses Protection Regulations were proclaimed law in Nova Scotia in 2002. These regulations are the minimum habitat requirements to be met during harvest. Get the brochure listed on page 40 or check for more information.

Wildlife such as deer continue to use a stand after it is thinned because it oftens offers food closer to the ground.

There are other things to consider as well. Uncommon tree and shrub species should be left where possible, unless they are not native to your area. Valuable browse or food species might be selected to encourage wildlife population levels. In addition to stand level consideration for wildlife, you should also consider woodlot and forest level decisions.

The pileated woodpecker requires a large cavity tree in which to nest and care for its young. In addition to a good nesting cavity, it needs a lot of food when rearing its young. When planning to thin a stand near a cavity tree, try to avoid felling the tree unless it is unsafe to leave it. You also should leave a healthy dominant tree nearby to afford it some protection from the wind.

After thinning, conditions will benefit soil organisms that break down organic matter into nutrients. They are at a low population level in a thick, dense forest. Lack of soil warmth due to the shaded understory conditions keep levels naturally low. After the canopy is partially removed, activity in the organic layer will increase. Conditions are now more favourable for wildlife species found in soil, while they are less favourable for canopy feeders like squirrels.

Most of the living organisms found in our forest are well adapted to natural changes in their habitat. The natural process of thinning will benefit some wildlife species, but be detrimental to others.

Try to keep brush off wildlife trails. A thinning will be enough change for wildlife that inhabits your woodlot. They will adapt quickly, but will appreciate trails being left open.

Many songbirds nest in thickets of both hardwood and softwood. If you can avoid doing your PCT until after nesting season, injury to the fledglings will be minimized. Try to avoid the months of May and June.

Leave any residual snag or cavity trees from your earlier harvest. Many standing dead or dying trees will likely remain that way for many more years. These trees generally do not rob nutrients from younger crop trees. Eventually they will contribute their branches and stems to the organic layer, which will quickly recycle it into your crop trees. In the meantime they are a valuable attraction to the wildlife on your site and add structural diversity.

Keep variety in each stand. Conifer stands should have some component of hardwood and vice versa. This is usually not a problem as holes are quite often filled by alternate crop species. Variation should also be encouraged with other plant species. Shrubs and herbs provide food for many wildlife species. Non-commercial tree species can also be valuable for certain wildlife species.

Ensuring that obvious needs of wildlife on your woodlot are met is essential. In addition, you must understand some less obvious needs. Any changes you make will affect some wildlife species that inhabit other parts of your woodlot and even other parts of the forest. The treatments may affect wildlife on your neighbours woodlot and vice versa.

Make sure buffers are maintained along watercourses. These riparian zones are sensitive and support an increased amount of wildlife.

Remember, plants, lichens, fungi, reptiles, amphibians and invertebrates require the same considerations as a hawk.

For more information on improving or maintaining wildlife habitat, see Modules 4 and Module 7.

As already discussed, thinning affects the properties of wood that will be harvested later. Increased growth rates will produce larger, more uniform stems. Thinning leaves behind trees with fewer and more stable knots; larger sapwood area; lower resin content; longer fibres and dimensional stability. This results in superior products.

If you want quality log products, log species should be favoured. It's important to consider what local buyers require. In many cases, your harvest will be many years away and buyers can provide valuable insight. Quality white pine lumber may be in demand 30 years from now while white spruce dimension lumber may not.

Good quality trees left after thinning can be harvested for high value products later.

Most harvests produce multiple products, sometimes as many as six different products from a single site. Harvesting efficiency can be increased when fewer products are generated. Start with as much information about the future product demands as you can and then select your primary species to favour.

Reducing the number of trees with stem or bole defects will improve the stand quality the most. Whatever end product you may be growing, clear stems will be preferable. Increased growth rates will produce larger boles, which will be much faster and easier to harvest. Larger boles are also suitable for a wider range of products.

However, thinning may have some negative impacts. The branch pruning properties of a thicket are very good. The absence of sunlight when the canopy is fully closed will cause lower branches to die and fall more quickly. This produces a stem with fewer knots, which is preferred for lumber. This is especially important for high value hardwood species. You may want to delay your thinning to take advantage of this self-pruning process, but you will lose growth.

Fast growth isn't always desirable. Much of the wood used for musical instruments comes from slow growing trees. The density of the fibres and the appearance of the narrow growth rings are sought after by instrument makers. Clear stems, free from defects are still essential, but opening the canopy too much when growing this product would be detrimental.

Substantial increases in diameter growth may have negative effects on the finished product quality. PCTs can cause an increase in the production of juvenile wood, which has a lower specific gravity. High specific gravities are desired in both finished hardwood and pulp. Keeping spacing to less than 8 X 8 feet slows diameter growth, producing higher gravity wood. This is at the expense of overall or gross volume.

There are trade offs, but wider spacing up to 8 feet (2.4 m) is most common for typical pulp and log species.

For more information on adding value to your wood products, see Module 8, Wood Utilization and Technology.

If you are not planning to do the work yourself, you should be comfortable with the person or crew you hire. If you're uncomfortable with saws or don't have the experience, it's a good idea to get some help.

There are many good contractors. For more information see Module 2.