Thinning hardwood stands

      Advice on how to thin, prune and groom. February 6, 2002

Q.
Assuming that lateral branch growth is not a factor, does thinning hardwood stands to increase diameter growth effect the quality of the lumber sawn from the log at harvest time? Also, does this have an effect on the amount of sap/heartwood in the log? If not, what causes a high percentage of heartwood in a log?

Forum Responses
From contributor A:
Great saw logs are clear (no branches for many years) with tight growth rings (like virgin timber) and straight (not bent from wind and weather). I remove sick trees and those that will never have any worth. Pick what is ripe and you can use. I read that a good stand will have 50 to 75 stems per acre. Here sapwood seems to be about 12 to 15 growth rings, which may be from 3/4 inch to 3 inches. I cut 2 red oaks and a walnut that were downhill from some turkey barns and there was 1/2 inch between the growth rings and sapwood of almost 6 inches. No local woodworkers wanted the wood so I sold it to a big hardwood outfit. I have noticed that the trees around the fields benefit from lime and fertilizer.



There are a whole host of factors that affect stand growth. Maximum height is determined by the quality of the site - thus, fertilization could increase height growth. Diameter is affected by the spacing or density of a stand. Wider spaced stands allow stems to grow more radially. This room also allows branches to grow well. Dense stands force the trees to compete for limited resources (light being the biggie) by growing in height more than diameter.

So, the prescription for good sawlogs? That depends on the order of magnitude you wish to manage. Small woodlots are relatively easy to manage while large ones are more difficult. To achieve maximum potential quality of the stems, you should plant the seedlings well apart (9'x9' should be more than plenty) and begin pruning the lower branches as soon as possible (a tree can stand to have the lower 1/3 of its crown removed). This requires a lot of labour and time. Alternatively you can plant close (say 4 - 6 foot spacing) and thin the stand out once it achieves crown closure (branches touching). This "trains" the trees to grow for height but also allows them to grow to fill the space provided by thinning. Pruning is also recommended to achieve maximum stem quality. Of course this also works for young natural stands. It is generally recognized that if you do not begin active management by the time the stand is 15 to 20 years old, the effects of your effort will not be noticeable.

Fertilization and irrigation are the stuff foresters' dreams are made of. As for the relative percentage of sapwood to heartwood, genetics and about a million other factors go into determining that.



Someone pointed out to me that when selecting cedar (eastern red) for fence posts, the ones with fewer branches and brown as opposed to very green foliage trees will have more heart. Do the fewer limbs, and therefore less food make the bigger heart, or does the bid heart starve the limbs of nutrients and water? I realize cedar isn't a hardwood, but I would think the relationship probably is similar.


I have noticed that the best red cedar grows in the thickest of woods. The more shade the more red.


From contributor R:
Typically, timber stocking levels are measured by basal area. It is the cross-sectional measurements of all the trees in an acre, and is expressed in square feet.

For optimum growth, hardwoods should be between 70-110 sq ft/acre. Higher than that, individual tree growth will slow. Less than that is poor use of the land. These factors increase as the average dbh in the stand increase, but not too dramatically. Softwoods may have an upper end of 180.

Number of trees/acre is not a good measurement. As trees get larger, their basal area increases. Basal area is easily measured using either an angle gauge or a prism. I prefer the angle gauge.

One problem of thinning too hard is epicormic branching. These are buds that are underneath the bark, and are stimulated by sunlight. You may have noticed leaves all along a bole on a tree that has been left behind. This is epicormic branching. Also, stump sprouts are a form of epicormic branching. These most often develop into some form of defect. I can tell when I hit them in a log. I will cut into defect, then cut out on the next cut. Two ruined boards due to careless logging.

Sapwood is dependent on growing conditions and species. If there is insufficient crown on a tree, the amount of sapwood will diminish since sap conduction is reduced. Some trees have relatively little sapwood. Cherry has 10-12 rings of sapwood, while sugar maple has 30-40 rings, while tupelo may have 80-100.

The bulk of the quality in most trees is in the first 16' log. Most species in a normal stand will prune well on their own. This is where the stocking comes in. Too thin and they won't prune well.

For thinning purposes, pick your crop trees, leave them and thin those from the understory. In many stands, they are the same age as the overstory. Choose ones with poor form, quality, or inferior species. Picking the "ripe" ones is a good way to deplete your stand and ruin your genetic quality.

At the end of your rotation, you must consider some method of reproduction. You can use a shelterwood cut, or seed tree cut prior to your final harvest. After sufficient seedling generation, you can have your final harvest.



Picking the "ripe" or the good trees is also called "high-grading". Most of the hardwood sites in the east I have seen have been high-graded. This is how the loggers get their money. Most owners don't know the difference. The remaining trees have the genetics to form poor trees. Repeated high-grading keeps reducing the genetic pool from which the future trees draw upon.


From contributor A:
If the "ripe" trees are the ones making the most seeds, it would seem that its babies are the ones under it. Genetics are there but no light or root system to bring them up. A tree will just live so long and then starts going bad. I understand that every area is different. Here in the Ozarks if you've got oaks you had better take the ripe trees before the borers kill it. Most loggers who high grade a stand destroy what's left and do it no good. I have 200 acres of trees and I thin it in spots so that the 30 ft 10 inch trees have some shelter and a chance for light and food. In virgin forest I have seen oaks in the under story 8 inches across and 50 feet high. It is only when the giants are removed without tearing up the little ones that they will make it. When the big ones do fall on their own you get the next crop to grow. I cut a white oak that was 18 inches at the first cut and over 300 years old. Very fine wood. Don't take the ripe and wait, nature will take over.


From contributor R:
Trees that are in the understory that are the same species are the same age as the overstory. Diameter has no direct correlation with age. A 10" tree can be as old as a 30" tree. Trying to release a small, overgrown old tree is a waste of land and time.

The high grading I have been seeing is economic clearcutting. It is paramount to mining timber. All good merchantable growing stock is removed, but those little understory trees are left to grow. Then you end up with a stand of black birch, gum and red maple with scattered hemlock. It still looks wooded, but the stand is depleted.

My neighbor cut his trees because they were ripe. He now has a stand of goldenrod and multiflora rose. All those smaller understory trees died. He has no regeneration and no prospects of regeneration. It would have been smarter to open the stand up so regeneration could take place before the final harvest.

Trees only grow through crown expansion. If you keep them tightly compacted, their growth is stunted.

Trees will only last so long, as you say. Red oak can grow for 200-300 years, white oak maxes out at 500-600 years, walnut is about 250 years. Maturity will be reached before that, but I haven't seen too many reach maturity lately. Many are cut as soon as they make veneer.



Your county extension service may be able to provide you with additional information. I contacted mine and am now thinning the stand based on crop tree crown release. I have 145 trees I am putting out for bids.

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