Local trees showing signs of spring
It’s still winter in Wyoming, even though the thermometer reads 60 degrees in February.
Trees aren’t privy to the human calendar. Instead, temperature changes signal a change in seasons. As a result, certain species of trees in Buffalo are breaking bud earlier than usual during a warmer-than-usual winter. And a cold snap now could damage vegetation that is beginning to transition out of its dormant state.
Bud break is the first sign of trees transitioning out of winter dormancy to the spring growing season, said Micah Most, agriculture and natural resources educator with the University of Wyoming’s Johnson County extension office. While specific signs of bud break vary by tree species, existing buds that develop in the fall and stay dormant through the winter begin to turn green and swell in size, he said. These buds get squishy and soft, signaling the start of spring growth.
Most said he first noticed buds on a lilac outside of the extension office starting to turn green and transition from their brown, dormant state in January.
“The lilac that’s out here, these flowers developed late last summer and they're all tucked in there inside that bud,” he said. “If they start to break and emerge then we get a cold snap, there won’t be very many flowers because it’ll damage all that tissue.”
Through conversations with extension colleagues around the state, he found a similar trend statewide, though there aren’t yet reports of trees actively blooming, or producing flowers, he said.
Each day in February, as of Feb. 15, had high temperatures above 40 degrees, according to National Weather Service data for Buffalo. January also had unseasonably high temperatures with some single-digit cold snaps around the end of the month. On Monday, the National Weather Service indicated that Johnson County was under a red flag warning, which means wildfire risk is elevated due to low humidity, warm temperatures and strong, gusty winds.
These above-average temperatures are contributing to early bud break in trees, Most said.
Some species tend to break dormancy earlier than others, including trees of the poplar genus, which includes cottonwoods and aspens. Spring blooming bulbs, such as daffodils and tulips, typically emerge and show some growth in March or April in this region. Most said that he has heard reports of some growth in those.
Trees transition into a dormant state in the fall in response to diminishing day length and dropping temperatures, according to Colorado State University extension. On deciduous trees, leaves discontinue chlorophyll production, resulting in changing fall colors. A chemical called abscisic acid forms in the terminal buds at the tips of the stems that connect to leaves, which signals the leaves to drop.
When trees drop their leaves, they are no longer making food and therefore conserving energy throughout the winter. Trees use stored energy during this dormant period and roots continue to absorb moisture.
In addition to warmer-than-average temperatures, this winter is also, so far, lagging in precipitation in Johnson County, especially at lower elevations. The snow water equivalent in the Powder River Basin is at 71% of normal as of Feb. 16, according to the Natural Resources Conservation Service.
Evergreen trees, which retain their needles year round, are adapted to live at high elevations with snowpack, Most said. Wet soil insulated by snowpack aids photosynthesis.
“Water is an important component of that process,” he said. “I think there’s a chance we’re going to see a lot of winter injury.”
That injury, called desiccation, occurs when a coniferous tree lacks needed moisture and needles start to die, turning from green to reddish brown. Wind exacerbates this process by pulling moisture out.
“I think we’ll see some damage to our evergreens around town because it’s been so dry,” Most said.
Deciduous trees are more resilient to dry conditions, because they are not photosynthesizing throughout the winter months, he said.
In Wyoming, there is still a lot of potential winter left to be had. That can be problematic for deciduous trees that are beginning to break bud. Shade trees should be relatively unharmed, but fruit trees may see diminished yields, Most said.
“A healthy tree can pull resources from its root stores to set out another flush of leaves,” he said. “That is very metabolically taxing on the tree, so it’s going to need special attention and care through the rest of the summer, making sure it has enough water to do what it needs to do.”
Landowners concerned about trees on their property this winter can help them by applying a lot of water when temperatures are above 40 degrees, the ground is not frozen and there is no wind or snow cover, according to a University of Wyoming extension publication on winter watering. It’s best to water under the tips of a tree’s branches, because, there, roots are really fine and best able to absorb water, Most added.
“That would be something to prioritize now through the end of the fall is keeping them watered,” he said.
It’s recommended that for every inch of trunk diameter, a tree receives 10 gallons of water. So, a tree whose trunk measures 12 inches in diameter should receive 120 gallons per week. It can be difficult to measure how much water is being applied, but in general, Most said, any water is better than no water.
Gardens with perennial plants could benefit from watering as well, Most said.
“For the most part, they’re not actively photosynthesizing this time of year, but keeping the soil moist helps keep those roots healthy,” he said. Lawns are resilient generally, but where gardeners have invested a lot of money into plant material, whether in trees, shrubs or perennial plants, water will be helpful in the long run, Most said.
“I would guess as we get a little bit later into the spring we’ll maybe even start to see some premature development on some of those species as well,” he said.
SIDEBAR:
HED: Community science opportunities
For Micah Most, agriculture and natural resources educator with the University of Wyoming's Johnson County extension office, early bud break in trees and other vegetation presents an opportunity – data collection.
Phenology is the study of seasons and the timing of recurring biological events in plants and animals. Most said that those who notice bud break on trees or vegetation can email him photos with the location and date noted to mmost@uwyo.edu.
The National Phenology Network also runs a community science initiative called Nature’s Notebook, where users can submit observations to be included in a dataset that tracks the seasonal events of plants and animals in a given area.