Conservation Matters July 2012

The Texas Land, Water and Wildlife Connection

What's really killing Texas trees?

What’s really killing Texas treesAlthough drought is often the cause, trees can die for other reasons besides lack of soil moisture, said Dr. Eric Taylor, a Texas AgriLife Extension Service forestry specialist in Overton.

"Drought is the primary contributor to tree kill, but it may not be exactly the way you might be thinking," Taylor said. "You may find this hard to believe, but relatively few trees likely died directly from dehydration in 2011. Instead, the 2011 drought severely weakened mature trees, making them susceptible to opportunistic pathogens like hypoxylon canker and insects like pine bark engraver beetles."

He said that in most instances, the trees that died in 2011 were already stressed from a number of pre-existing environmental factors such as overcrowding, growing on the wrong site, age, soil compaction, trenching or inappropriate use of herbicides. If not for these factors, a large proportion of the trees that died might have recovered from the drought.

"This is an important concept to remember because our best defense against drought is to promote a tree's health and vigor through proper care and management," Taylor said.

This is not to play down the importance of water to tree health, he said. Water, particularly soil moisture, is critical for all a tree's physiological processes. Trees require water to make and transport food, take in and release carbon dioxide, conduct biochemical reactions, build tissue and more.

"You name it, the tree needs water to do it," Taylor said.

Though moisture stress may be the trigger many trees likely died from insect damage, invasion of fungi and other diseases, and even heat stroke, according to Taylor.

"Much of the recent tree deaths and general decline might also be attributed to the extreme and prolonged heat of 2011," he said. "Extreme temperatures, not only during the day but also in the early evenings and night, have negative impacts to tree physiological processes."

Read the full AgriLife TODAY article for more information.

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