In Part 1 of Improving Your Woodlot, I wrote about identifying and killing low quality species, low quality formed trees and diseased and damaged trees. However, the woods may still be over populated. This session is going to explain how to manage the tree canopy for increased timber production.
Each woodlot or specific areas of the woodlot is unique with its own characteristics based on soil type, elevation, sight index (direction it faces N-S-E-W), tree species, age, density, and past use or management practices.
Our farm is in the Appalachian hardwood region with 95% hardwoods and 5% hemlocks and white pine. There are three distinct wooded categories. Our best area is the steep hillside with mixed hardwoods, the second area is along Yellow Creek and its flood zones. Our poorest is an area of tree regrowth on spoil banks (Strip mine banks from the 1960’s). Each area has its own unique management needs. The State Service Forester or your Consulting Forester can provide you with an aerial photograph of your woods. The NRCS also has aerial photographs. If you want a quick aerial map of your property, go online to a local interactive weather site and zoom in on your property. Using the aerial map you can identify dense areas of the woods by the heavy canopy as well as the sparse areas.
When you stand under the trees, look up. You are looking into the woodlot canopy. This is what you are managing when you 'release' crop trees. Once leaves are on the trees you want to evaluate the amount of sunlight that is coming through to the under-canopy and ground.
I want to explain some terms I will be using:
Canopy – the upper tree crowns, may refer to an individual tree or the total mass of trees in a woodlot;
Even Aged Woods – woods that are the same age, even though they vary in size. An example might be pine or tree plantations;
Uneven Aged Woods – woods with a large variation of ages and sizes;
Dominant Crown – The large tree crown that generally extends above the canopy and received full sunlight from a above and on the side of the crown;
Codominant Crowns – make up the general canopy level and receive direct sunlight from above but little or no light on the side of the crown;
Intermediate Crown – crowns that find some open spaces in the canopy where it gets direct sunlight on the top but no light on the side;
Suppressed (Overtopped) Crown Trees – trees under the general canopy receiving no direct sunlight. Crowns are short, narrow and sparse;
Shade Tolerant Trees – trees that can grow in the understory of the canopy;
Shade Intolerant Trees – trees that need direct sunlight to grow;
Intermediate shade tolerant trees – trees that grow in the understory, but need direct sunlight to flourish;
Clear Cut – harvesting all trees 2 inches DBH (diameter at breast height) and above;
Selective Harvest – harvesting timber on a selective basis, leaving a sustainable timber inventory for future harvests;
Wolf Tree – a large, spreading crown tree of low timber value.
DBH – Diameter at Breast Height. A measurement taken at 4.5 feet from the base of a tree on the uphill side of the tree. A specific and consistent measurement used to calculate tree growth, wood production, and basal growth.
On our farm, the uneven age timber on our hillsides produces a timber harvest every 15 – 20 years and provides excellent soil protection. This type of selective harvesting produces income to pay taxes and insurance over the years.
The spoil bank regrowth / even aged woods won’t be ready to harvest for 30 – 40 years or once in the lifetime of the owner. Possibly it may be even longer before harvest. When it is harvested, a clear cut will be the best harvest procedure. We may be able to do light thinning cuts over the years to help offset costs.
Example of even-aged woodlot. The trees are different sizes, much like a 4th grade class with kids of all sizes and shapes, the even-aged woodlot will have trees of various diameters.
The goal of this session is to describe Crown Canopy Management. In forest management, we can’t change the soil type, sight index, slope, elevation, rainfall, or even easily change the tree species. However, the one area we can improve to increase the tree’s vigor is the tree’s ability to receive adequate sunlight. Remember the tree’s crown is a large solar collector that produces energy and therefore, tree growth. To increase its ability to produce the maximum amount of growth, the tree needs to capture the maximum amount of sunlight.
The upper canopy consists of three different tree crowns. The dominant crown is the larger crown reaching above the rest of the tree canopies. These crowns are usually 360° full round shape. The codominant tree crown grows and competes for the top space in the crown. In a well stack density woods a codominant crown canopy is the normal. However, the third class is the intermediate crown class. This tree crown finds whatever room is available to grow in the canopy. They generally only have crowns between 50 – 70% of a full crown shape. The size and shape of the crown receiving direct sunlight reduces its potential growth. For example, cherry trees are shade intolerant and need direct sunlight. When walking in your woodlot, you will find a cherry tree that is twisted and turned, bending to shoot up in to open spaces in the canopy. However, cherry trees are not as aggressive as other species and therefore have a tendency to be crowded out of direct sunlight. Usually, you can find a nice, tall, clean (it has no lower limbs or defects) cherry tree that looks like a great crop tree only to find it has less than a 50% crown. Even providing the open canopy space for the tree won’t help it overcome its lost growth potential. It most likely will always be a stunted tree.
These trees are misshapen as they reach for the sunlight.
Tree species have different levels of shade tolerance. This list shows our main tree species and their relationship to direct or indirect sunlight. You should speak with your consulting forester to learn what the shade tolerance is of trees in your specific area.
1. Shade Intolerant – needs direct sunlight
a. Butternut
b. Black Walnut
c. Yellow Poplar
d. Sycamore
e. Aspen
f. Cherry
2. Intermediate Shade Tolerant – trees that grow in the understory, but need direct sunlight to flourish
a. Red Maple
b. Ash – if you have any that survived Emerald Ash Borer
c. White Oak
d. Red Oak
e. Elm
f. Hickory, except Shagbark Hickory
3. Shade Tolerant – Will grow in the understory of the canopy
a. Box Elder
b. Sugar Maple
c. Beech
d. Basswood
e. Shagbark Hickory
Using the crown classes and shade tolerance list, you now are ready to identify crop trees and thin the remaining timber.
Let me use an example from one of our woodlots: I had a group of 15 red oak trees in about a 1000 sq. ft. area. I killed 5 trees due to poor form and defects and 2 additional trees due to poor crowns. I still had 2 trees that needed to be removed. One of the trees was sandwiched between 2 good crop trees – that tree removal was a ‘no brainer’. Then I needed to determine which one of 4 otherwise equal trees I was going to remove. After a week of trying to decide, I just sat down and prayed. I asked God to show me which one I should remove. Later that day, as I walked past the tree group, I saw a gray squirrel run up one of the trees. I watched it disappear into a hole hidden behind leaves. This gave me the answer – an open hole meant possible tree rot. It was an easy decision to kill the tree by girdling it and leaving it for a den tree. The squirrel was happy and so was I.
To help us determine which trees and how many to thin out, we can use the thinning rule of thumb for hardwoods. After we select our crop tree, we need to figure how much room the crop tree needs in the canopy for maximum growth potential. In Ohio, I was taught that you measure the diameter of the crop tree at DBH or 4 ½ feet above the ground on the uphill side of the tree. (There are tree diameter tapes that measure the circumference and provide the diameter. I use a regular tape measure and divide the number by 3. This gives a rough estimate of the diameter that is close enough for me.) This will give you the diameter in inches.
To calculate the amount of space between trees use this formula:
Diameter (inches) x 1.5 = ___ feet to next tree
Example:
I measured the circumference of a white oak as 42”.
Divide 42 by 3 = 14” diameter
14 x 1.5 = 21 feet
I need 21 feet from the base of the white oak I am measuring to the next tree.
Ideally all trees competing in the upper canopy should be 21 feet from the base of your crop tree. As your tree grows in diameter, that distance will increase.
Note: for Sugar Maple management for maple syrup production (a sugar bush) we use a different formula. Diameter x 2 (instead of 1.5)
Here is an example for further explain:
You identify a Red Oak which is 12” DBH (TREE A) as your crop tree.
Formula: 12” x 1.5 = 18 (feet of space needed between trees)
You have a Sugar Maple 8” DBH (TREE B) that is 10 feet away but its crown is not competing in the crown canopy. A sugar maple is shade tolerant and will not compete for sunlight in the canopy.
There is a Cherry 12” DBH (TREE C) also 8 feet away from the Red Oak
There is another Cherry 12” DBH (TREE D) that is 14 feet away from the Red Oak on the opposite side of Tree A and Tree B
You have selected the Red Oak (TREE A) as your primary crop tree. The rule of thumb recommends the nearest competing crown space tree should be 18’ away from the tree base. The Sugar Maple tree is not competing in the crown, so leave it. The Cherry (TREE C) is only 8’ away and competing, so remove it (by girdling, cutting it down). The other Cherry (TREE D) is within the crown competition range but, if there is no other major competition for crown space, leave TREE D. Our crop tree A has at least 67% of the crown space available for growth.
This illustration shows which tree would be removed.
Sometimes, we have two trees similar in DBH, growing side by side or almost from the same space. If the trees have crop tree potential, you may want to leave them both as long as each tree has 2/3 of a full crown in the canopy.
Here are some suggested guidelines:
1. If you aren’t sure whether to keep or remove a tree, leave it. You can always come back and remove it at a later date.
2. Trees 18” DBH are entering the mature stage. If they are healthy and prime crop trees, allow them to grow and become more valuable.
3. Most adults can hug a mature tree. If their hands don’t touch, the tree’s DBH is over 18”.
4. Try not to damage or kill potential young crop trees.
5. Young, immature trees 10 – 16” are the ‘teenagers’ that grow the fastest in the woodlot. Protect future crop trees, especially in uneven aged woods.
6. Some people mark crop trees with surveyor’s tape or use spray pain. Be aware that some spray paint has toxic chemicals that damages tree cell growth.
7. For wildlife, try to leave one or two den trees per acre. You can girdle the tree, but leave it for habitat.
8. Concerning Wolf Trees – in an open field, park, or yard the large, limby wolf tree is beautiful. However, in the woods, the wolf tree produces low value wood. You may get lots of firewood, but they are not crop trees.
9. Wolf Trees shade our large areas, suppressing tree regrowth and production. A wolf tree can occupy up to 15% of an acre. That is the same amount of space 3 – 18” DBH mature, crop trees need to grow.
This wolf tree is an old white oak. 26" DBH and canopy spread of 106 feet. Nothing is growing underneath the tree.
10. It’s OK to leave certain trees. Maybe that special tree is where Dad asked Mom to marry him, where you shot your first deer, for historical reasons, or its natural location.
11. If you get a chance to attend a forest crop tree program that goes through a woodlot, take advantage of it. You will learn a lot.
12. If you can find someone with the American Tree Farm sign, ask them to show their woodlot and what they are doing. Members like to pass good stewardship on to others.
The American Tree Farm System certifies tree farmers who meet forestry standards.
13. Remember falling trees damage potential crop trees but you can see the immediate crown openings formed.
14. When girdling trees and leaving them to die back it is harder to visualize the crown openings being created.
15. You don’t have to it all in one year unless you have an NRCS crop tree contract. So, start out slow – you can always come back and do more.
16. Like I said before, I leave marginal trees, allowing them to grow and produce more firewood.
True Growth Rings:
Each year the tree adds another growth ring. The distance between each year’s rings is half the distance the tree grows in diameter that year. (Remember, the tree grows on each side so the growth is doubled if you measure a ring.)
Foresters have a tool called an increment borer that they use to take a cross section sample for tree growth. Most of us don’t have one of those, so what can we use? When you cut down a tree, look at the growth rings. Measure 1” inside the bark and count the number of growth rings.
Fast growing trees may have as few as 4 rings per inch compared to stunted or slow growing trees that may have 15+ rings per inch. A tree with 4 rings /inch is growing 2” in diameter every 4 years. It can take 15 years for that other tree to increase 2” in diameter. The faster the crop tree reaches maturity the faster it makes money. By implementing TSI/Crop tree management practices, the landowner can help the trees increase the distances between growth rings – and increase its growth. As the tree grows and matures, its crown expands and competes with bordering trees, therefore TSI/ Crop tree management should be part of the 10 – 15 year management plan rotation.
Two example of growth rings. You can easily see the different rates of growth through the years.
My next section will be on saw logs, determining board feet and how to grade out a saw log to increase your income!
Happy Growing!
Bob
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