Severe weather taking toll on Minnesota's forest
MINNEAPOLIS Beset by forces from road salt to roaring winds, trees in Minnesota have taken a beating this year, and some foresters think more of the same lies ahead. Straight-line winds and tornadoes have felled an estimated 5,000 trees in Minnea...
Beset by forces from road salt to roaring winds, trees in Minnesota have taken a beating this year, and some foresters think more of the same lies ahead.
Straight-line winds and tornadoes have felled an estimated 5,000 trees in Minneapolis this spring and summer. Hundreds more were toppled in Sauk Centre last Sunday night. In Belview, about 125 miles southwest of the Twin Cities, 70 percent of the small city's trees were destroyed July 1 by a low-level tornado that took out hundreds more across Redwood and Renville counties. Another 1,000 went down near Cambridge during storms that same night.
But as communities clean up the mess and confront the shocking and long-term loss of summer shade, their trees remain vulnerable to many more threats than just wind, including climate change.
Foresters say that in the short term, soil still saturated by snowmelt and heavy rains, too much road salt last winter, rising water tables in some areas, a late-starting and possibly short growing season, and cool, wet conditions favorable for fungi have added to the challenge faced by the state's urban forest.
Gary Johnson, professor of urban and community forestry at the University of Minnesota, said trees sprouted leaves so far behind schedule this spring that they may not be able to accumulate the energy reserves they customarily need to get through the next winter. In many places, particularly in still-soggy southwest and northwest Minnesota, saturated soils are starving trees of the oxygen they need to thrive, he said.
"Regionally, trees are suffering as much as corn and soybeans are," Johnson said. "We're likely to see weaker trees just not making it through to the next season. We will see it next year."
Winds in the range of 60 to 75 miles per hour perform a sort of "selective weeding" by taking down weak trees, said Lee Frelich, director of the university's Center for Forest Ecology. But this year's tornadoes, as well as the derecho -- a wide juggernaut of straight-line winds -- that rolled across central Minnesota July 10, have been more powerful and have toppled mature, healthy trees. And if climate-warming scenarios produce the increases in both severe weather and drought they consistently indicate, trees of all kinds are at risk.
"I think trees are vulnerable to the climate chaos we're in, where we're having more storms, and storms seem to be more intense, " said Katie Himanga, president of the Minnesota Shade Tree Advisory Committee. "We're more likely to get more trees going down."
"Is [severe weather with high wind] more likely to result in tree damage? Absolutely," Johnson said.
Tom Hultquist, chief science officer for the Twin Cities office of the National Weather Service, said it's difficult to tie recent increases in tree-toppling stormy weather to long-term climate trends. While reports of severe weather are on the rise, he noted, that is partly due to more people more actively looking for it. But trees will certainly be vulnerable to increased temperatures in a warming climate, he said.
Frelich and Himanga added that sugar maples, one of Minnesota's emblematic trees, appear to be in trouble both from increased temperatures and from their own popularity. Too many have been planted in narrow boulevards, where they are exposed to road salt they can't tolerate, Johnson said.
But to some foresters, the situation is not so dire. Ralph Sievert, director of forestry for the Minneapolis Parks and Recreation Board, indicated that even without a tornado, the city might see a net loss of about 1,200 trees per year to various causes, with few people noticing. That's despite planting 5,000. But the fact that two tornadoes have hit Minneapolis in three seasons -- after 28 years without one -- "seems unusual," Sievert said. A small tornado in 2009 stripped mature tree cover from several blocks of Portland Avenue South and neighboring streets.
Foresters now cover such losses with many species of trees planted in clumps instead of long rows of the same species. That's one significant effect on the urban forest of both contemporary violent weather and disease, though Himanga said she's concerned that dwindling public funds might also limit how completely damaged urban forests might be replaced. Ken Holman, urban forestry coordinator for the Minnesota Department of Natural Resources, said he believes that conditions across Minnesota have generally been beneficial for trees this year. But his longer view is a little different.
"We're going to continue to experience extremes of weather and damage," he said. "Whether it's disastrous, I think it's really the way things are moving. Personally I believe climate change is going to make these [years] more average years."
Distributed by McClatchy-Tribune Information Services.