Evergreens, with their splash of green in drab Nebraska winters, have become the first to die as historic drought and its shadow, climate change, redefine the trees that can survive the Great Plains' extreme weather.
Nearly 700 pines in Lincoln's iconic Pioneers Park have died since July. Other parks across the state are losing trees, too. In neighborhoods, the deaths are more isolated, as first one tree, than another dies.
Deciduous trees, those that shed their leaves seasonally, are struggling too, but they have more ways to adapt.
The rapid decline of trees, even species believed to be hardy enough to survive in Nebraska, is worrisome given that another hot, dry year may be unfolding.
“If it was that bad in one year, what if we have something similar this year?” said Eric Berg, a community forester with the Nebraska Forest Service. “It's going to be devastating.”
As the drought takes its toll, the Nebraska Forest Service is re-evaluating the recommendations it makes to Nebraskans, Berg said. The revisions are made more difficult by climate change.
“Drought will refine our recommendations, but the greatest challenge is the climate is changing,” he said.
In the past, foresters have considered winter, not summer, as the limiting factor on tree survival in Nebraska. A tree had to survive a temperature plunge from 70 degrees on one day to 15 degrees the next, so foresters recommended northern seed sources, Berg said.
But Nebraska is warming at an accelerating pace, so state foresters have begun looking southward for new tree species. To this end, the Nebraska Forest Service is working with its counterparts in Kansas to develop new recommendations for the Central Plains, Berg said.
If only it were that simple, he added.
Nebraska will continue to see extreme temperature swings even as its climate warms, so foresters aren't sure whether to look north, south or overseas for seed stock.
“I don't think we'll ever get an answer to that,” he said. “The answer is probably going to be more diversity.”
In the broadest terms, the start of this drought has disproportionately claimed evergreens, said Justin Evertson, also a forester with the Nebraska Forest Service.
White pines have been hit worst, and arborvitae aren't far behind.
Spruces have begun to suffer from a combination of drought and humidity. Declines are being seen in green, blue and Norway spruce. The popular and regal scotch pine was already being wiped out by pine wilt.
Evergreens have been especially vulnerable because so few are native to Nebraska.
The aggressive, unattractive red cedar is the closest native evergreen for the Omaha-Lincoln area, Evertson said. And even those trees are beginning to die from drought.
“The way the climate is shifting in eastern Nebraska, we'll have fewer evergreen choices,” he said. “We'll probably continue to lose evergreens at a fairly alarming rate.”
That doesn't mean that people should give up on evergreens or that foresters will stop searching for suitable species, he said. Instead, those planting several trees should weight their selections toward deciduous trees.
“There's a fine line between alerting people to our concerns about drought and trees, but not scaring them,” Evertson said.
“There are so many challenges. If I was the average person looking at this, I'd think, 'Why should I plant a tree?' Trees are hugely important to making our cities livable and attractive.”
Evergreens have been dying faster than deciduous trees because they're less able to cope, said Graham Herbst, also a forester with the Forest Service.
A deciduous tree can drop its leaves when under stress and then bud new ones later. A pine can't drop and later replace needles. Likewise, deciduous trees have a nourishing layer inside their bark that evergreens lack.
White pine, Herbst said, are dying first because their thinner needles are more vulnerable to winter's drying winds.
Eastern Nebraska's humidity encourages disease among evergreens in way that doesn't happen farther west, he said.
The fingerprints of climate change last summer were on the high number of warmer-than-normal nights, climate experts have said. In addition to chronic warmth — the year was the hottest and driest on record in Nebraska — Omaha and other communities set nightly records for warmth.
This is a problem because trees rest at night and replenish lost moisture. If nights are too warm, trees don't have the chance to recover and instead continue to function as if it were daytime, using up water. In the long term, that weakens the tree and makes it more vulnerable to disease and pests.
Like evergreens, deciduous trees are encountering problems, but those tend to be the result of planting or care, Evertson said.
A notable example is the popular river birch.
The species thrives in protected wet environments, but it is often planted in sun-baked, windswept new developments and mulched with heat-absorbing river rock. Individual river birch planted in such conditions are struggling, the foresters said, while others placed in more protected areas, well-watered and properly mulched are doing better.
“Drought is not indiscriminate,” Evertson said. “It takes out trees least acclimated to an area, and it will take out those that are compromised for other reasons.”
Foresters, he said, are learning along with the public.
“Most trees are pretty naturally drought tolerant, that's what has been surprising to me,” Evertson said. “We're going to learn some things as we watch these old soldiers fall.”
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