Raising the crown

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Lower branches often have to be removed to clear them from traffic, to prune them away from a building or walk, make signs visible that were installed too far off the ground, or open up a desirable view. Shortening or thinning limbs in large trees is preferred over removal because of the negative health impacts of large limb removal. Crown raising does minimal damage to a tree as long as 1) removed limbs are not too large (preferred cut diameter is less than two to four inches), 2) only a few branches are removed at one time, and 3) many branches are not removed from the same spot. The best way to accomplish this is by structurally pruning over time to keep low branches small.

Removing too many low branches shifts future growth to the top of the tree. Wind is stronger there, and with no low branches, crown movement at the top of the tree can not be counter-acted, or damped, by the removed lower branches. Too much raising also causes dysfunctional wood leading to cracks and possibly decay inside the trunk. Removing too many lower branches can result in sunburn on the lower trunk and causes sprouting on the trunk and remaining limbs.

The live crown ratio should be at least sixty percent, meaning that there should be live branches along the upper sixty percent of the trunk to distribute wind stress and develop trunk taper for stability and strength. Some major branches should be left on the lower one-half of the trunk. Similarly, half the foliage on scaffold limbs should originate from secondary branches on the lower two-thirds of these limbs where practical. Lions-tailing is not synonymous with crown raising and is considered inappropriate pruning. Removing up to about fifty percent of the foliage and associated branches from the lower crown on conifers has little impact on subsequent growth and movement in wind. In contrast, thinning the top half of the crown would have a greater effect.

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