We have had a pretty hot and dry summer throughout much of
South Carolina and, although we are seeing some precipitation now, many trees
are showing signs of stress.
Heat, especially combined with drought conditions, can
damage trees in several ways. Most trees grow best in the 75°F to 85°F (24-30°C)
temperature range. Above about 95°F (35°C) photosynthesis becomes less
efficient, using more energy than it creates. Most plants cannot survive
temperatures above 112°F (44°C). At these temperatures enzymes denature,
nucleic acids (DNA and RNA) unravel, and cellular function ceases. Trees can
cool down, most efficiently by transpiration, but this requires water, lots of water!
When temperatures stay high for multiple days, trees feel it!
Trees respond differently to excessive heat and drought.
Some species, like many pines, tulip poplar and sycamore, will drop older
foliage to reduce transpiration loads and water loss. Others, like maples and
many oaks, keep their foliage on but are thrifty with available water so that
many leaves get a scorched appearance, usually around the edges of the leaves. Most
of these trees will look poorly, but should recover once water is available and
temperatures have cooled down.
Water is key to helping trees survive and is most effective
BEFORE the trees are stressed. When weather is hot trees need more water.
Watering in the heat of the day can be wasteful… much of the water is lost to
evaporation so it is better to water in the evening. Avoid watering at the base
of the tree; many of the roots that absorb water and nutrients are at or beyond
the drip line, the ground with foliage directly overhead. Applying fertilizers
can be counterproductive; stimulating new growth will increase the water
requirements of the tree.
Trees are resilient. With a little extra care and the right
weather, stressed trees should come out healthy next spring!
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| Maple leaves showing the scorched symptoms typical of draught or heat stress. Some fungal diseases cause similar symptoms, but usually when it is cooler and wetter. |
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| These oaks are showing signs of stress from the long (more than one week) exposure to temperatures at or close to 100 degrees. |
