Shelterwood cutting is a multiple-entry method of timber harvesting focused on establishing regeneration. A shelterwood cut only partially harvests the canopy of a forest, allowing enough light to the forest floor to allow regeneration to grow. Typically, A shelterwood harvest will have two entries into a stand. The first entry is the establishment cut, which removes a portion of the canopy. This is what most people refer to as the shelterwood harvest itself. The second entry, known as a shelterwood removal, occurs only after regeneration has become well established. The duration between these two entries varies depending on whether it is a softwood or hardwood stand as well as the geographic region (unsurprisingly, forests grow faster in warmer climates), but it is only rarely greater than fifteen years. While the shelterwood process is generally two entries, a stand eligible for a shelterwood harvest may have been thinned multiple times prior to the shelterwood harvest.
What Is the Advantage of Shelterwood Cutting?
The advantages of a shelterwood harvest are many and varied:
Because the harvest relies on natural regeneration, it is economical compared to more expensive and intensive regeneration methods like planting. Planting often requires some sort of site preparation, the cost of buying seedlings and the labor to put them in the ground, and often one or more follow-up treatments with herbicide to ensure seedlings are not out-competed by undesirable vegetation. Shelterwood cutting depends on residual trees to disperse seeds (for free!), and the shade from the canopy helps prevent an overgrowth of regeneration that thrives in full sunlight, such as raspberries.
Control of Regeneration
It also gives the landowner and forester more control over regeneration compared to an unmanaged forest or a clearcut left to naturally regrow.
Because trees are removed in stages, it assures that a piece of land is never left bare, which is pleasing to landowners with aesthetics in mind. Instead of having to wait for a clearcut to regenerate (which can take decades, in some cases), a landowner who harvests with a shelterwood cut can retain much of the stand and wait until regeneration is firmly established to remove the overstory.
The multiple entries of a shelterwood harvest also allow for multiple opportunities for cashflow from a piece of land, which can be an important management objective for certain landowners. In the end, the total return should be about the same (unless we factor in net present value, perhaps), but if there is a mortgage on the property or the landowner depends on cashflow from the land, staggering harvest income may be desirable.
Are There Any Disadvantages of Shelterwood Cutting?
The disadvantages of using a shelterwood harvest system primarily relate to the disadvantages of multiple harvests.
Logistics and Economics
Logistically and economically, it can be a challenge to organize multiple harvests. For example, a harvest will typically have certain fixed costs, such as the costs of opening and repairing a road and the costs of moving equipment to an area (lowbed trailers aren’t cheap). It is less efficient to incur these costs for two (or more) separate harvests than to go in and harvest the entire stand in one entry.
Damage to Regeneration
Entering the stand twice can also be damaging to the quality of the residual stand. While modern logging equipment is uniquely adept at protecting the residual stand, driving over roots and thrashing regeneration will take its toll. As a forester, some of the highest quality stands of wood I ever visited regenerated as a clearcut for the simple reason that the regeneration was spared from the trauma of repeated entries.
Potential Loss of Residual Wood
Leaving mature wood in a harvest carries a significant risk of mortality and blowdown. As logging equipment drives over and severs roots, branches are broken, and gaps in the canopy are formed, the ingredients for disease, rot, defect, and even blowdown are formed. While the risks vary greatly depending on species and site and stem quality, it is a consideration. Luckily, an experienced forester will be able to recognize the potential for residual loss simply by walking through a property.
What Types of Stands Are Suitable for Shelterwood Cutting?
Shelterwood cutting is an incredibly versatile system suitable for a wide variety of species and climates. While it is difficult to cover all the management nuances of every species, let’s look at the broad differences between shelterwood cuts in softwood and hardwood stands.
Shelterwood cuts are valuable for regenerating all sorts of spruces, firs, pines, and hemlocks, particularly when the species germinates better in cooler soil temperatures, such as red spruce, or can be damaged or quickly dry out by growing in full sunlight. Because softwood management is often (although not always!) geared toward the production of large volumes of timber over high quality timber, the overstory of a softwood shelterwood is often held for a shorter duration, sometimes as little as two years after establishment. The goal is to provide just enough time for seeds to germinate and to get established, but not so much time that the shade of the overstory slows the growth of the understory. Left unchecked, advanced crown recession can severely hamper growth for years after release. Removing the overstory as quickly as possible can also limit damage to the regeneration. Small, springy seedlings are harder to damage then taller and more brittle saplings.
Just as with softwood, shelterwood cutting is perfect for stands of some types of hardwood, such as maples, oaks, and yellow birch. however, shelterwoods in hardwood stands are arguably more complicated for a variety of reasons.
Hardwoods are generally bunched into two categories: tolerant hardwoods and intolerant hardwoods. The idea of tolerance here refers to how tolerant a species is to shade. Because shelterwood cutting is built around growing trees in shade, it is not suitable for intolerant hardwood species such as white birch and quaking aspen.
When growing tolerant hardwoods, on the other hand, shelterwood harvests are generally suitable. However, the objective of the management, unlike most softwood species, is the quality of the timber. Different considerations must be made. Depending on the stand of timber, it might be best to use a variation of shelterwood cutting, such as an irregular shelterwood or extended shelterwood. An irregular shelterwood uses the same methodology as a normal shelterwood, but it is done in an uneven-aged stand with more than one age structure, and there is never a total harvest of the canopy. An extended shelterwood, as the name implies, is a normal shelterwood in which the overstory is retained far beyond when it would normally be harvested. This can have the advantage of sparing young regeneration from damage and allowing a shelterwood removal harvest to be combined with a commercial thinning of the understory.
When Should Shelterwood Cutting Be Done?
Shelterwood cutting is best done when a stand reaches or approaches its maximum growth potential. Over the life of a tree, its growth resembles a sigmoid function. Trees grow slowly as seedlings and gradually speed up as they age. As they reach maturity, their growth once more slows until the tree dies. Ideally, a stand should be regenerated no earlier than when growth declines, although financial considerations may change the calculus.
Once it is determined a stand is ready to be regenerated, it is best to plan the harvest for a year with a bountiful seed crop. Many trees alternate between a small and large production of seeds every year, and a harvest done during a good seed year can vastly improve the odds of success.
What Is the Difference Between Shelterwood Cutting and Thinning?
While shelterwood cutting and thinning are both partial harvests, the objective of a shelterwood harvest is the regeneration of the stand. Thinning, on the other hand, seeks to grow residual trees. For this reason, stands that are thinned usually leave more trees, and gaps in the canopy close as residual trees grow. Stands that are cut using a shelterwood harvest have larger gaps in the canopy, and gaps do not easily close, as residual trees are mature individuals that have peaked in growth and have little ability to grow further.
What Is the Difference Between Shelterwood Cutting and a Seed Tree Harvest?
The shelterwood and seed tree systems are similar, but it is a difference of degree. A seed tree cut selects the largest and most well-suited trees from the forest and leaves them for seed production. The residual density of the stand can be as low as only one tree per acre! Unlike a shelterwood system where enough residual stand is left to warrant re-entry into the stand, a seed tree cut essentially sacrifices the trees and leaves no possibility for a removal. Sometimes, trees left for a seed tree can act as valuable wildlife trees for raptors and creatures that live in cavities of older, declining trees.
Is Shelterwood Cutting Right For My Forest?
Unfortunately, silvicultural prescriptions are complicated and nuanced. There is no way a blog post can fully address all the considerations you must make for your property. If shelterwood cutting interests you, contact a local consulting forester and ask for a field visit. You’ll be glad you did.