Symptoms of Deep Roots
Symptoms Can Vary
The visible symptoms of deep roots can vary widely, and depend
on a number of factors. Of course, the deeper the roots are, the
greater the likelihood of severe problems. Some species are more
tolerant of deep roots than others. Quality of the site (drainage
and aeration) also plays an important role.
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In the most severe cases, deep root systems can lead to
decline and death of the tree, sometimes very quickly. Deep
roots are subjected to greater soil saturation and insufficient
oxygen, and symptoms can be similar to drought stress. Loss
of willow oaks was five times greater when planted six inches
deep. (See Smiley [pdf]) |
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Under less severe conditions, growth will be
slowed and the tree will be stressed. The tree may appear fairly
normal without comparison to a tree with roots at the correct
depth, as the photo of container grown trees shows. (See Fare [pdf])
Live oak trunk caliper and height growth increased more slowly
as planting depth in containers increased. (See Gilman [pdf]) Deep planted trees can have greater defoliation,
chlorosis and leaf curl. (See Wells [pdf])
(photo
by: D. Fare) |
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Symptoms of deep planting may also be delayed in developing
under moderate conditions. There was little response to planting
depth in the first year on green ash and live oak, compared
to subsequent years. The delay in symptom development is likely
related to tolerance of these species to periodically wet soils.
(See Bryan [pdf]) |
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Over time, a tree with deep roots will grow slower and stress will
develop earlier than a healthy tree. Sometimes girdling roots
can develop after deep planting in the landscape and make the
symptoms even more pronounced. Even a mild reduction in growth
will reduce the ecological, economic, health and psychological
benefits provided by the urban forest. |
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The Site Can Make a Difference in Symptom Development
Symptoms Vary Among Species
Tree species vary in tolerance to soil poor conditions. In a study
comparing the effects of deep planting on hypoxia tolerant
and intolerant species, planting 7.6 cm (3 in) below grade
reduced the survival of green ash (F. pennsylvanica) by
about 40% after 3 years and bougainvillea goldenraintree (Koelreuteria
bipinnata) over 90% within only 2 years. (Bryan paper
link) Within two years of installation, one half of deeply-planted
cherries died, while there was no impact on survival of red
maples. (See Wells [pdf]) |
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Tree Stability
Deep root systems increase tree failure rates.
Thirty-three percent of trees with excess soil over the roots
failed, compared to only eight percent of trees without excess
soil over the roots. (See Smiley [pdf])
In a Minnesota study, 73% of the Little Leaf Lindens that
suffered total failure had four inches or more of soil over
the structural roots. Most of these trees also had girdling
roots causing stem compression where the trees broke off. (See Giblin [pdf])
(photo by: T. Smiley) |
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Deep roots have been associated with greater winter injury
in conifers. (See Smiley [pdf])
(photo by: T. Smiley) |
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Adventitious Root Development
Some species have the ability to produce adventitious lateral roots
above existing lateral roots if planted too deep, but these
are the exceptions. Most do not. Production of shallower adventitious
roots could allow a tree to adapt to deep planting.
Four months after bing planted too deeply in a container,
all of the roots above the finger are adventitious roots
formed after planting. (See Giblin [pdf]) (photo
by: E. Gilman) |
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Cathedral Oak™ developed adventitious roots along
the stem above the top-most root present at the initial planting,
but only on very young trees. The ability to develop adventitious
roots was lost as the trees aged. (See Gilman [pdf]) (photo
by: E. Gilman) |
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