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Lower branches often have to be removed to get
them out of the way of traffic, keep them away from a buildings, to make
signs
visible that were installed too far off the ground, let in more light,
open up a desirable view or create a lower trunk free of branches.
This type of pruning does much less damage to a tree than reducing the
canopy size.
It is best done gradually over a period of years.
A trunk could be seriously injured if too many lower branches are removed
at any one time. Discolored wood and possible decay
may begin inside the trunk of an over pruned tree. Removing too many lower
branches can result in sunburn on the lower trunk
and can cause epicormic growth and forces the tree to grow taller.
Ideally half the foliage should originate from branches on the lower two
thirds of the tree. Some major branches should be left
on the lower half of the trunk.
We try to leave small branches on the lower trunk intact for about a year
or more if possible after removing large branches
because they help minimize injury from sudden sun exposure by shading
the trunk. They also speed closure of pruning wounds.
If many branches need to be removed we would recommend that this be done
in two steps. First we thin or drop crotch cut the
largest branches in the lower part of the tree, but leave the small ones
intact. This may provide enough clearance for a year or
so because the branch will often spring upward after removing branches
from the tips. If necessary we would remove all branches
back to the trunk one or more years later. Sometimes more than one large
diameter branch is located at the same point on the
trunk, and both need to be removed to provide clearance. Since removing
both at the same time could initiate a fairly large area
of trunk decay and weaken the tree, we would recommend removing one first
and shortening or thinning the other. We would return
year or more later to remove some or all
of the other branches. The objective is to only remove one large branch
in a cluster on the
trunk at a time.
Raising the canopy on trees with large diameter (greater than half the
trunk diameter measured directly above the branch) low
branches can initiate trunk decay if these large branches are removed.
To prevent this we would recommend thinning them
reducing their length with drop crotch cuts instead of removing them.
This will slow their growth rate, and eventually the trunk will grow to
become larger than the branch. This gives the tree an
opportunity to form the branch defense zone at the base of the branch
thus minimizing trunk decay once it is removed.
When raising the canopy it may be necessary to attend to any structural
pruning that needs to be done to correct defects.
It is inappropriate to simply remove lower branches without correcting
structural problems.
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