Providing Continuing Education for Louisiana Arborists
EFFECTS OF DROUGHT ON URBAN TREES
HOW TO AVOID PROBLEMS
DEATH COMES GRADUALLY TO TREES
When trees die, people assume
that it is because of current environmental stresses.
Research suggests that trees
often die as a result of stresses that occurred years, sometimes decades,
before tree death.
Trees typically continued
growing for up to 20 years after they were injured by some stress, but
the growth rate during those years was substantially lower than before
the stress occurred.
Loss of rigidity in needles
Drooping, wilting, yellowing of foliage
Premature leaf or needle drop
Excessive squirrel damage (especially on oaks)
Twig and branch dieback
Leaf margin scorch and interveinal necrosis on deciduous trees
Browning of needle tips on evergreens
General canopy thinning
Poor growth and stunting
In extreme cases - DEATH
HAPPENS IN A DROUGHT?
A water deficit develops in
Non-woody feeder roots and root hairs are particularly sensitive to drying
and are affected first.
They shrivel and become non-functional. They lose the ability to absorb
The roots can no longer provide sufficient water to the top of the tree.
The tree is forced to draw upon stored resources for survival.
Additionally, many metabolic changes occur which substantially alter the
physiology of drought-stressed trees.
Water during periods of low
Select appropriate site and follow good planting practices.
Where possible, select native plants and match plants to site conditions.
Mulch properly to retain soil moisture.
Prune dead and weakened tissues to avoid secondary problems.
DO NOT PRUNE healthy, living tissue from mature trees during drought periods.
Maintain tree vigor through good cultural practices.
Trees need approximately one
inch of water per week.
Water is best applied at one time as a slow, deep soaking to a depth of
Frequent, light watering is harmful, as it promotes surface rooting, which
can lead to excessive root drying.
The length of time required to deep water will vary according to soil type
and water pressure. Clay soils will require more time than sandy soils.
Use an organic mulch.
"Whole tree" chips are most beneficial. A layer of rich compost
under a layer of chips is especially good.
Try to match mulch to tree type (i.e. hardwood or conifer).
Apply 2-4 inches of mulch evenly, well beyond the dripline of the tree.
Avoid mounding or placing mulch immediately onto tree trunk or root crown
area. Leave about 3-4 inches free of mulch at the base of the trunk.
WORDS ABOUT ROOTS & FOUNDATIONS
Tree roots are often unfairly
blamed for foundation cracking during times of drought. People trying to
sell root barrier products or foundation repair services will often try
to convince home owners that a tree barrier will "protect" their
slab. In most cases, this is faulty information, derived from poor knowledge
of tree physiology.
Most tree roots exist within the top 18 inches of soil. They do not "pull"
water from lower soil levels. In a drought, all soil in an area dries as
the water table drops. If a root system is in place, it sometimes cannot
allow for even settling. It is this uneven settlement which causes slab
cracking - not the tree! Removal of an existing tree can cause even more
settlement problems as the old root system decays and leaves voids in the
If a tree exists close to a newly built house, the roots are usually destroyed
by the construction of the slab.
New tree roots rarely will grow under a building slab. The soil there is
compacted to such a high degree that water and oxygen are not available
to the tree.
Roots growing alongside a slab may exert pressure as they grow in size
over the years, but these roots are normally easy to locate and remove
before becoming a problem.
The best solution? Water your yard regularly. The water will help keep
your soils from shrinking, but it will benefit your drought-stressed trees
Louisiana Arborist Association
P.O. Box 41396
Baton Rouge, LA 70835-1396
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