Dry weather has implications for trees
Despite the recent soaking rain across Minnesota, eight-straight
weeks of dry weather could impact tree growth and tree mortality said
Susan Burks, a forest health specialist for the Minnesota Department
of Natural Resources (DNR).
During that eight-week period between July 15 and Sept. 12, rainfall
was four to eight inches below normal throughout most of Minnesota. A
lack of rain is detrimental to a tree's root structure and hurts its
ability to gather much needed water and nutrients from the soil. Burks
said that could affect tree growth, bud production and self-defense.
"The lack of water puts trees under enormous stresses," Burks
explained. "It causes trees to use up their stored food reserves,
which can affect their ability to recover from a drought. Their
defense systems are also weakened by the lack of water, allowing pests
and diseases to move in and cause further damage."
Drought symptoms among tree species vary, but usual signs include leaf
browning (curling, rolling, wilting, yellowing or scorching of leaves)
or leaf loss. The extent of future impacts depends on tree health
prior to the dry weather and the severity of the drought locally.
While a few isolated areas may see tree mortality, most trees across
the state should survive and eventually recover.
"Most of the trees are already shutting down for the season," Burks
said, "but any rain, now, should help trees replenish some of the
nutrients they've lost as they prepare for winter and next spring."
Property owners can help minimize impacts to their trees:
o water trees with a long, slow soaking, using drip irrigation, a
deep-root waterer or soaker hose to percolate down through the roots
o mulch the "critical root zone" four to six inches deep and surround
the tree, 1.5 times the tree's diameter in feet (a four-inch diameter
tree would receive a six-foot ring of mulch).
o do not place mulch up against the trunk
o minimizing other stresses; trees must divide their remaining food
supplies for recovery, maintenance, growth and defense; wounds, root
disturbance, and insect and disease problems can slow recovery.
The drought carryover into September has raised questions about fall
colors. In areas where the drought was severe, fall colors could be
limited because trees may have already dropped their leaves to
conserve energy and their food supply. Burks said soil moisture,
sunlight, temperature, tree health and the timing of the first frost
are the biggest contributors to fall color production.
"As long as the leaves aren't too dry and shriveled, we should get
plenty of fall colors this year," Burks said. "But because the effect
of drought can vary between locations, my suggestion is people should
check ahead before jumping in the car."
Current fall color conditions can be found on the DNR's Web site at