Minnesota’s black spruce forest type

A brief overview of Minnesota’s black spruce forest type: products & uses, growing conditions, regeneration, silviculture, and pests.

Minnesota’s northern white-cedar forest type

A brief overview of Minnesota’s northern white-cedar cover type: products & uses, growing conditions, regeneration, silviculture, and pests.

Minnesota’s aspen-birch forest type

A brief overview of Minnesota’s aspen-birch cover type: products & uses, growing conditions, regeneration, silviculture, and pests.

Minnesota’s eastern white pine forest type

A brief overview of Minnesota’s eastern white pine cover type: products & uses, growing conditions, regeneration, silviculture, and pests.

Thinnings and woodland stand improvement

Thinned oak stand near Mora, MN. Flickr photo by esagor. Click for original.

Thinnings and timber stand improvement operations are designed to improve the vigor and value of existing forest stands.  There are many ways to do this.  As in choosing the right silvicultural system, choosing the right kind of thinning for your woodland can be somewhat complex.  That decision depends on a number of factors, including site characteristics, stand age, species composition, stand acreage, and landowner objectives.

Thinnings can be precommercial or commercial.  In a precommercial thinning, harvested material can not be sold and is generally not removed from the site.  Precommercial thinnings are made entirely as investments in the future growth of the stand.  Commercial thinnings, on the other hand, yield products that can be sold.  Commercial thinnings sometimes merely break even in the sense of covering harvest costs, but in older stands can be fairly profitable.

This section provides a basic overview of different thinning and timber stand improvement strategies.

Row thinning

Row thinning in red pine near Mora, MN. Flickr photo by esagor. Click for original.

As the name suggests, row thinning means removing trees in rows or strips.  Row thinnings are most often conducted in plantations, where trees are planted in rows.  Row thinnings are relatively efficient.  They also open up lanes for harvesting equipment to enter and move around within the stand, which may not be possible in unthinned plantation stands.  In most plantations, the first thinning is a row thinning.

Selection thinning
Selection thinning involves removal of certain trees based on their characteristics, spacing, and other considerations.  Selection thinning is often used in plantation stands for second or subsequent thinnings.  The advantage of selection thinning is that it allows more flexibility than row thinning, allowing for the removal of low-value trees.  This focuses growth on high-value trees, improving the health and long-term value of the stand.

Selection thinning can also occur in hardwood stands.  However, if not applied carefully, this approach can lead to high-grading, which can damage the stand and severely set back its vigor and long-term value.

Crop tree thinning

Crowns of unthinned (top) and thinned red pine, Cloquet MN. Flickr photo by esagor.

Crop tree thinning involves carefully maximizing the growing space available to the best trees in the stand.  Crop tree thinning is an excellent approach to use while cutting firewood on your property.  Crop tree thinning involves the following steps:

1. Walk through your stand and identify the trees with the greatest potential future value.  These are your crop trees.  Mark your crop trees using flagging tape, spray paint, or some other marker.  “Value” need not mean “timber value.”  You might mark den trees, trees of rare species, or any other kind of tree that you want to thrive in your woodlot.
2. Identify any trees that are in direct competition with your crop trees.  To identify competing trees, don’t look down.  Look UP at the crowns.  Any tree with a crown that’s touching the crown of your crop tree is competing with it.
3. Remove some or all of the competing trees.  Be careful not to overdo it.  If your crop trees have been growing under intense competition for years, they could be shocked and stressed if all trees around them are removed at once.  Consider a multi-stage approach where competing trees are removed over a several-year period.
4. Monitor crown closure after thinning.  Repeat these steps as needed.

High-grading
High-grading involves harvesting only the highest-value trees from a stand and leaving all the rest.  High-grading can severely degrade the health, visual appearance, and long-term value of the stand.  High-graded stands tend to contain suppressed trees of poor form and/or species.  It can take decades for the stand to recover.  Diameter-limit cutting is one common way to high-grade a stand.

Although a partial harvest may seem preferable to a clearcut, in many cases you’d be far better off clearcutting the stand.  Clearcutting will generally lead to vigorous new growth of an early successional stand.  By contrast, high-grading leads to stagnant growth of a low-value stand.

Woodland stand improvement

One approach to woodland stand improvement. Adapted from "Woodland Stewardship: A guide for Midwestern landowners." Click for a larger version.

Woodland stand improvement refers to any treatment designed primarily to improve the composition and condition of an existing stand. Stand improvement treatments require a financial investment in the future of the stand.

There are many different types of stand improvement treatments. One common approach is to kill or remove undesirable species to allow desired species more room to grow. Another approach is a targeted release of the best young trees in a stand. Trees are released by removing competing vegetation.

For more info
Another excellent source of information on Minnesota silviculture, including thinnings and stand improvement, is the North Central Forest Management Guides.

Planting Trees

This page includes information and links about planting trees in Minnesota woodlands.

Planning

Tree planting costs money and is hard work. Good planning is essential. Talk to a local professional forester about species selection, spacing, season and method of regeneration, equipment and contracting options, and other considerations.

Flickr photo by Tim Redpath. Click for original.

Planning for regeneration should begin well before harvesting the site. Thinking ahead may create opportunities for natural regeneration, which can be less costly and every bit as effective planting trees.

Planting stock

Planting seedlings, either bare-root or container-grown stock, is the most reliable way to regenerate a stand, especially for conifers. Bare-root seedlings are the most common. They frequently are designated as 1-0, 2-0 or 2-1 stock, with the first number referring to how many years they were grown in the original nursery seedbed and the second to how many years they were grown in a transplant bed.

Transplants (seedlings that spent a year in a transplant bed) generally have a larger root system and stem diameter than seedlings that were not transplanted. Transplants are recommended for regenerating slow-growing conifer species such as spruce and fir, and for harsh planting sites where survival is likely to be a problem.

Seedling costs vary by tree age, species, and quantity ordered. Transplants survive very well, but are expensive and therefore are not widely used. One- or two-year-old seedlings are less expensive than transplants and are recommended for most hardwood and conifer plantings.

Two kinds of seedlings can be purchased: Bare root and containerized.

Bare root and containerized seedlings. Click either image for a better view.

Bare root seedlings are grown in open air nursery beds. When removed for planting, they are bundled without soil.

Containerized seedlings usually are grown in a greenhouse in containers between 1 and 2 inches in diameter. Some biodegradable containers may be planted in the ground with the seedling in them. Others must be removed from the seedling before it is planted. Container-grown stock can be very useful for dry planting sites or for planting late in the growing season.

Cuttings

Cuttings provide another alternative for artificially regenerating certain tree species. These usually are 8- to 12-inch lengths of tree stems about 1/4- to 3/4-inch in diameter (longer cuttings may be used on drier sites). They are cut during the dormant season from the previous year’s growth of vigorous seedlings or stump sprouts. Cuttings usually have no visible roots, but when buried vertically with just an inch of the stem protruding above ground, they will form roots. Rooted cuttings also may be available for purchase.

Cuttings produce an exact genetic replica of the parent tree. They commonly are used to regenerate poplars, but also can be used to regenerate willow and green ash. Cuttings grow best where the soil remains moist throughout the growing season.

Direct Seeding

Photo by Brian Lockhart. Click for original.

Direct seeding is the process of sowing or planting seeds. In Minnesota, direct seeding is most often used to regenerate heavy-seeded hardwoods such as black walnut, oaks, and hickory. It is also used in some cases to regenerate jack pine or black spruce. In the right situations, direct seeding can be relatively inexpensive and can produce prolific regeneration.

Spacing

When designing a plantation, you need to determine an appropriate spacing between trees. Consider the crown width of trees when they reach a useful size. For example, when growing trees for timber, allocate space so individual trees are just beginning to crowd each other when the trees are large enough to support a commercial thinning. A professional forester can help you determine the correct spacing depending on the species and purpose for the plantation.

The following table shows the number of trees needed per acre for various spacings. To calculate the number of trees per acre for other spacings, multiply the planned spacing (in feet) within rows by the spacing (in feet) between rows and divide that number into 43,560. For example, if trees are to be spaced 8 feet apart within rows and rows are to be 10 feet apart, you would plant 545 trees per acre:

43,560 =  545 TREES PER ACRE
8×10

Number of trees per acre at different spacings:

Spacing (ft)	Trees per acre
4×4	2,722
5×5	1,742
6×6	1,210
7×7	890
8×8	680
9×9	538
10×10	436
11×11	368
12×12	303

Site Preparation

Site preparation often is necessary prior to planting. Its purposes usually are to expose mineral soil and set back competing vegetation. While site preparation can be done with hand tools, this method usually is expensive and vegetation that is cut down may resprout. There are herbicides available for site preparation that may be very effective and economical in some situations. You also can use mechanical methods such as disking, scalping, or trenching. If you use mechanical methods, be careful not to destroy the nutrient-rich organic layer near the soil surface. Often a combination of mechanical and chemical methods is most effective. In some circumstances controlled burning can be used to remove debris from sites and temporarily reduce vegetative competition.

Handling seedlings

The Minnesota Department of Natural Resources packages its nursery trees in a plastic bag inside a wax-lined cardboard box. It recommends the following handling procedures:

1. Protect the box of seedlings from direct sunlight and heat.
2. Plant the seedlings as soon as possible. Seedlings should not be stored for more than three to five days and then only at temperatures of 35° to 45 F.
3. Once you open the package, plant the seedlings immediately. Exposure of tree roots to hot sunlight and drying winds for three to five minutes may be fatal.
4. While planting, keep the seedling roots moist, but do not immerse them in water for more than an hour.
5. If you need to postpone planting for more than three to five days after receiving the trees, remove the seedlings from the container and heel them in a trench.

Heeling in seedlings for temporary storage

To heel-in trees, dig a V-shaped trench in a cool, shady location, deep enough so the earth will cover the entire root system and part of the lower stem. Open the boxes, spread the trees along the sloping side of the trench in two or three layers, pack soil around the roots, and water as necessary to keep the roots moist. Store trees in this manner only as long as they remain dormant.

An even better storage method is to place the seedlings in a refrigerator set at 40 F or slightly cooler.  It is absolutely essential that seedlings be planted before new growth starts to emerge. The sooner you plant the trees after they arrive from the nursery, the better the survival will be.

Planting
The best time to plant is in the spring as soon as the frost is out of the ground. At this time the soil is moist, the climate is somewhat mild, and normally there is ample rainfall. If necessary, container-grown seedlings can be planted later in the growing season. Fall planting usually is less successful because frost heaving may occur, especially on fine-textured or wet soils, and growth regulators in the tree may become imbalanced, leading to top dieback.

Be sure to take good care of seedlings before you plant them. They should be dormant when you receive them (i.e., the buds should not be elongating or flushed). Do not let the roots dry out or freeze.This will likely kill the trees, but since the crown will appear alive (conifers will remain green) for a period of time, you may not realize it. To minimize risk of tree roots drying during shipment, ask nurseries to ship by the swiftest transportation available. If you transport the trees yourself, protect them from wind and sun during transit.

General tree planting guidelines

You may plant trees by hand or machine. Regardless of the method, follow these rules:

1. Plant the tree at the same depth that it grew in the nursery
2. Plant the tree in a vertical, upright position to avoid a crooked stem.
3. Place the roots in the planting hole in a normal position without twisting or bending.
4. Carefully firm the soil around the roots to eliminate air pockets.
5. Plant only when soil moisture is adequate to ensure survival.

Hand planting

Photo by Brian Lockhart. Click for original.

There are two general methods of hand planting. One of these is the hole method. Dig a hole with a shovel, mattock, or grub hoe. It should be large enough to accommodate the tree roots without bending. Place the tree in the hole, distribute the roots evenly, and pack the soil firmly around the roots, covering the root collar. This method usually results in a high rate of survival, but it is slow and is not practical for planting large numbers of trees.

The slit or bar method is preferred when a large number of trees are being planted because it is faster. Insert a spade, planting bar, hoedad or similar tool into the soil and move it back and forth to form a V-shaped slit. Insert the tree seedling into the slit so it will be buried to the root collar or to the same depth the tree was growing in the nursery. (If you err at all, plant slightly too deep rather than too shallow.) Remove the planting bar and reinsert it about three inches behind the seedling. Pull the bar back to firm soil around the roots, then push forward on the bar to seal the top of the planting hole. Push soil into the second slit and press down firmly with your boot to seal the slit. Using this method, you can plant 1,000 to 3,000 seedlings per day, depending on your experience and the condition of the planting site.

This website illustrates proper hand-planting technique.

Tree planting machines
There are many designs for tree-planting machines, but generally they have a coulter that breaks through the soil surface, a V-shaped blade that opens a trench into which the operator places seedlings, and packing wheels that firm the soil around the seedlings. Some newer planting machines have spray attachments for applying herbicides for grass and weed control.

Tree-planting machines work best where terrain is fairly level and the site has been cleared of stumps and logging debris. If you use a tree-planting machine, protect seedlings from the wind and sun so the roots do not dry out. Place seedlings erect in the planting trench at the proper depth and pack the soil firmly around the roots. A three-person crew using a tree-planting machine can plant about 10,000 trees in an eight-hour day.

Protecting planted seedlings from damage

To you, newly planted seedlings are a future forest. To hungry deer, they’re a welcome meal on a cold winter day.

Deer herds in our area are far, far above historic norms. Deer love to browse seedlings, and unless you protect the seedlings well, deer will wipe them all out in the first winter after you plant them. There are a few common strategies to reduce deer browse damage:

Budcapping. The main problem with deer browse isdamage to the terminal leader (the tallest central stem). Stapling an index card over the terminal bud may deter some deer. I’ve heard other landowners talk about using different materials in place of paper once the deer get used to the paper. Other readers may want to suggest other materials?

Click for a better view.

Deer repellents : There are a variety of deer repellent products out there. Some are made from hot chili peppers, some from rotten eggs, some from blood meal (image), and maybe some others. You should be able to find these at garden supply centers.

Again, these have varying rates of effectiveness. But they do seem to work, at least for a while, in most cases. If you care to read more, here are links to two studies of different deer repellent products: Comparison and to a Walnut Council Deer Repellent Study (Illinois).

Fencing: While very effective, this approach quickly gets cost-prohibitive for large areas.

You can read more about reducing deer damage in this 2003 Forest Tree Notes article by Mike Demchik.

Competing vegetation: If you can keep the deer off of your seedlings, you’ll still need to control competing vegetation, especially in old field situations. There are many different ways to approach this, including use of herbicides, mechanical soil disruption (like discing), and more.

This will need to be an ongoing effort–planted seedlings will need several years of vegetation control in order to overtop and outcompete the weeds. You can learn more about controlling competing vegetation in your tree plantings in an Extension publication called Vegetation Management in Forestry and Agroforestry.

Read one family forest owner’s tree planting story on our discussion board.