We are not always fully aware of the impact that heat
has on our trees. The effects of heat damage are more
subtle and appear in many different parts of the plant.
Cold can kill instantly, but plant death from heat is
slow and lingering. The heat damage is always linked to
the lack of water available to the trees. Leaves droop,
chlorophyll production quits, leaves turn white or brown
or fall off, stress moves in and the tree and roots
stops growing, insects and pathogens attack. With
depletion of water and intense heat desiccation elevates
and the growth enzymes deactivate and mortality is
eminent. Plant tissue must contain sufficient amounts of
water to keep their cells turgid and sustain the plants
processes of chemical and energy transport. Other
factors also come into play -- depletion of soil gases,
nitrogen and oxygen, soil pH, lack of nutrients,
increase soil toxins and soil based microbes go into a
dormant mode. All this can screw up a tree's
metabolism. Call it heat/drought stress or summer
scorch, it all comes down to tree mortality.
Watering directly at the roots
with a soaker hose helps conserves water and reduces
evaporation and run off, and the tree becomes more
efficient in water uptake. The lack of water in the root
zone controls the availability of oxygen which is
required for respiration and lack of water can lead to
soil toxin build up and almost total oxygen depletion
and availability.
Hot, dry air movement will have a devastating effect and
cause rapid dehydration. The tree loses water faster
than it can replenish it's water needs. Man-made
structures and asphalt landscapes also increase the heat
and air movement factors.
Light is essential for photosynthesis-providing energy
for growth and development. Light also provides heat,
which affects plant temperature. Day length is also
critical in regulating growth and development. The long
hot, dry days of summer add substantial to heat and
stress and have a profound effect on the tree's
survival.
Our soils are high pH alkaline and this greatly affects
the tree's ability to absorb water and nutrients. With
the lack of soil moisture, soil based microbes go
dormant and toxins increase, creating more problems for
trees.
Trees vary greatly in the ratio and form of nutrients
they need for consistent healthy plant growth. Some
trees tolerate heat and drought better than others and
some adjust to these conditions by simply dropping
leaves, thus reducing photosynthesis and lowering energy
growth requirements, basically shutting down into a
semi-dormant state for preservation of life. Like any
factory, if trees cannot receive the required raw
material to create a finished product, then production
has to slow down, halt or come to total shut down.
Death.
Jim Rediker
(See article "Leaf Scorch")
