Brown trees result of sudden temp swing last fall; some might surviveJun 5, 2015 By Andrea Novotny, Staff Writer
Evergreen plants are rugged enough to withstand extreme weather conditions in Wyoming, yet evergreens were among the plants hit the hardest during the rapid temperature change in the fall.
Caitlin Youngquist, a soil scientist at the University of Wyoming Extension office, said the damage had to do with a rapid drop in temperature that took place before trees had "hardened off," or gone dormant for the season.
Temperatures in Riverton were mild late into the fall, but they dropped to minus 18 and minus 21 degrees on Nov. 12 and Nov. 13, causing cells to rupture in plants that had not yet gone dormant.
By the end of November, temperatures rose back to nearly 60 degrees for several days in a row, sucking moisture from leaves that were unable to absorb additional water from the still-frozen soil.
Youngquist said it was this sudden temperature fluctuation that yielded the dramatic damage this winter throughout the Rocky Mountain region.
Some deciduous trees went dormant early enough to be saved from last year's damage, however. Box elders and honey locusts seem to be doing well, for example, and some pines with thicker, "waxier' needles also were spared.
Though the most noticeable damage was to juniper trees and shrubs, other plants suffered too, said Riverton arborist Ron Hammer.
"This is the first year that I've ever seen Siberian elm trees not seed out,' he said.
Siberian elms cast their seeds before sprouting leaves in the spring. This year, there were no seeds, and the leaves appeared only in sparse tufts on many trees.
Hammer noted that ash trees and some fruit trees also were damaged.
Spruce trees showed damage by the end of winter, and Ponderosa pines, noted for their long needles, sustained considerable damage.
Water, don't prune
Winter-damaged trees become more vulnerable to damage from bacteria, fungus, disease or boring insects.
Healthy evergreens are able to push out boring beetles with sap and are better equipped to fight off diseases carried by the bugs, for example, but stressed, damaged and clipped trees become ideal targets.
Tina Russell, a UW extension educator who specializes in forestry, said it may not be possible to determine which trees will survive until early July.
"If you peel back a little bit of the bark, they might still have some green underneath or some fleshy tissue,' she said, describing trees that are likely to recover.
Another way to tell whether a tree will survive is to feel the ends of the branches.
"If there's still green on them, they're still alive, and if there's still some flexibility in their branches or a growing tip, they'll still survive,' she said. "Once they're dead, the wood will become brittle and snap off in your hands.'
Youngquist said the plants may be stunted, but with plenty of deep watering, they can bounce back.
"Many people think that if they have a tree planted in their yard and they're watering the lawn, that that means they're also watering the tree, but it's really important to deep water," she said. "Watering your lawn is not going to be enough to get that water deep down to the roots of that tree."
The amount of water a tree will need depends on the size and type of tree and the type of soil it is planted in. Clay will hold water longer than sandy soil, for example.
"One option is to dig down around the tree without damaging the roots to see how far the water has gone down," Youngquist said.
She warned that pruning may cause further stress to the damaged plants. Late season pruning can be dangerous as well, as it can stimulate growth and prevent plants from entering dormancy in time for winter.
Youngquist said the best way to ensure that plants survive is to do research before planting and choose varieties that are best suited to the local environment.
Still, the exceptional conditions in the fall hurt even native and locally adapted species, including the Rocky Mountain juniper.
Winter watering also is essential in preventing damage, Youngquist said. She recommends watering any time temperatures reach 45 degrees or warmer.
Some garden centers offer anti-desiccation solutions, which can be sprayed on plants to give them a waxy coating that prevents evaporation through the leaves.
Protecting plants from additional drying factors, including exposure to wind and salt used to melt ice on roads and sidewalks, also can minimize damage.
Correction: This story should have said temperatures in Riverton were mild late into the fall, but they dropped to minus 18 and minus 21 degrees on Nov. 12 and Nov. 13, causing cells to rupture in plants that had not yet gone dormant. The correction was made June 8.