Site quality assessment

Regenerating red pine

Managing established red pine stands

• Thinning and stand density
• Prescribed under burning
• Pruning
• Growth and yield
• Rotation age
• Harvesting

Managing for ecological complexity

Pruning

Red pine after pruning (1. lift) up to 9 feet (A. Ek)

Pruning, as part of a red pine production management system, is used to increase the value of red pine sawtimber by promoting growth of clear, knot-free wood in the first log of the tree. Those who implement pruning must generally balance the cost of producing high value red pine logs containing clear wood with maximizing the return on investment.

The simplest and least expensive way to prune red pine in plantations is to plant at high densities (~ 800 trees per acre) and allow trees to self-prune. The natural process of pruning usually occurs as crowns close and lower branches are shaded, fall off, and the wound is closed. Artificial pruning accelerates this process. Increased use of flitch technology whereby veneer is acquired from slicing very thin boards has dramatically increased the importance of pruning. It generally takes about 60 years (depending on site quality, timing of pruning and adequate thinning) to recoup the cost of pruning.

The use of proper technique is critical when pruning. Done improperly pruning is a waste of resources and can injure trees. There are a number of things to consider when pruning red pine. Season of pruning is important; red pine pruning should be done in the late-fall to early-spring, otherwise the bark is loose and can strip away easily from no more than the weight of a saw, damaging the stem. Always retain an adequate live crown ratio by not pruning more than the lower one-third of the live crown and try to keep live branches in the upper half of the tree. Dead branches should always be removed. Prune the branches flush with the end of the branch collar and do not leave stubs. Stubs can be entry sites for insect and disease infestations. Prune only the largest diameter (dominant and co-dominant) trees with the best form because these trees have the greatest potential for return on investment. Avoid pruning trees with numerous branches greater than 2 inches in diameter. Begin pruning when trees reach a dbh of 4 to 6 inches in diameter.

Figure 3. The key to proper pruning is to protect the tree stem and trunk. To avoid tearing the bark and stem wood and to facilitate healing, make a small cut just (known as the wedge or notch) beyond the branch collar. Then make your second cut just beyond the notch from top to bottom. Once the branch has broken free at the notch, make a third cut parallel to and just beyond the branch collar to reduce the length of the stub.

 

Figure 4. Pole size trees (hardwoods 5 to 11 inches and conifers 5 to 9 inches dbh) can be pruned one or two lifts (9 to 17 feet) which results in one or two logs of knot free sawtimber or veneer.

Minimizing pruning costs using natural pruning can be achieved by planting red pine seedlings at high densities (~ 800 trees per acre). The number and size of knots in a sawlog or utility pole is a major factor in determining the value of a tree. Higher plantation densities also encourage straight boles with a minimum of taper. Pruning is typically applied in concert with thinnings in anticipation of stimulated diameter growth.

Pruning may be an important consideration even outside of a production management model. Extensive management objectives may well include production of large quantities of trees with high quality, knot-free timber. Moreover, pruning may be used to promote development of clear boles, which can be characteristic of old-growth conditions. Because spacing in stands managed for something other than intensive production is typically wider than uniform plantations managed for production management, pruning may be required to remove lower branches on potentially high value trees.

Pruning is recommended in stands dominated by the desired species (>60% of trees). However, in mixed-species stands, look for the possibility of exchange of dominance whereby unpruned trees overtake and reduce the growth of pruned trees in the 1-2 years immediately following pruning. A good guideline is to prune all stems in a stand if a change of dominance may occur between pruned and unpruned trees.