Page 318 - Moving the Earth_ The Workbook of Excavation

LANDSCAPING AND AGRICULTURAL GRADING

7.12 THE WORK

Ditching. Ditching on one side of a tree ordinarily does not injure it severely. However, it is best
to keep the cut as far from the trunk as possible, thus reducing the number of roots lost, minimizing
the danger of tearing the trunk, and making the digging easier.
If a hoe or dozer digs within two trunk diameters of the tree, the roots should be uncovered, and
then cut by hand to avoid danger of splitting the trunk while tearing them up.
A close cut weakens the tree’s resistance against a wind that tends to tip it away from the ditch. If
uprooting in that direction would cause it to fall on a building or across a highway, a tree expert
should be consulted about the advisability of providing cable support, Fig. 7.6, or removing some of
the upper branches.

Burial. A tree’s reaction to having its trunk buried varies with its species, health, and the nature
of the dirt. Burial is fatal to the majority if the fill is deep enough or of such a nature that it will
smother the bark and support organisms which will destroy it.
The fill also changes the air and water content of the topsoil and subsoil around the roots. Such
changes may damage or kill the roots directly, or indirectly by changing the nature of the soil population.
The best defense a tree can muster is to put out new roots near the surface. The willow does
this automatically, but the majority of temperate-zone trees do it with difficulty or not at all.
Trunk damage can be avoided by building a stone wall around the tree on the original ground,
at a sufficient distance to allow free air circulation. See Fig. 7.7. The space inside is called the
well. Sometimes the fill is made and part of it dug away by hand to make space for the wall. Or
the wall may be built first, and the dirt placed around it.
The first method is expensive and offers some danger of damaging the tree with the digging
tools. The second is subject to the danger of knocking over the wall while placing fill, or acci-
dentally spilling dirt over it that will fill up the well.
In general, the most satisfactory technique is to build the wall first, and fill the well with easily
removed material such as stones, wood scrap, or crumpled newspaper. Such items will prevent any
appreciable amount of dirt from entering the hole, and are easily taken out when grading is complete.
Sometimes pebbles or crushed-stone collars are used to avoid unsightly or dangerous holes.
These will usually allow sufficient air circulation when new, but are likely to plug up with dirt.

FIGURE 7.6 Temporary tree brace.