Drought-stressed trees face a long-term problem
Northern Minnesota trees were hit especially hard in 2021 when the area set records in temperature and below average rainfall — and trees will be affected for years to come.
BADOURA — Like returning song birds, early signs of spring include the first vibrantly green leaf buds, but long-term effects from last year’s drought may still be taking a toll on trees.
Northern Minnesota trees were hit especially hard in 2021 when the area set records for high temperatures and below average rainfall as the entire state entered the drought warning phase in mid-July. And by July, the Brainerd lakes area found itself in the fourth driest year on record.
Though lawns grew back relatively quickly, trees can take between 2 to 4 years to recover after the stress of a drought, said Rachael Dube, a forest health specialist for the Minnesota Department of Natural Resources’s Division of Forestry.
“Generally, drought-stress trees are less able to resist attack from insects and diseases that wouldn't normally cause serious problems,” Dube said.
From researcher to tree coroner, Dube grew up around the hills of Avon and always found herself in the woods as a child. Finding the forest to be a fascinating place, Dube pursued a degree in forest resources from the University of Minnesota.
“Getting back to my childhood connections to nature, I remember going on hikes with my sister,” Dube said. “We would just go get lost in the woods together, sometimes putting flagging tape behind us like Hansel and Gretel, so we can make our way back. I stumbled on what I now know is … called wolf milk slime mold. It's a really weird name, but to us as young kids it looked like someone had blown out circles of a bright pink bubble gum and just kind of plopped them on the fourth floor.”
Still spending her time amongst the trees, Dube now tracks things such as beetle sightings, oak wilt and state drought projections as she prepares to take care of Minnesota’s forests.
Oak wilt is a deadly disease that affects all species of oaks found in Minnesota and is caused by a non-native, invasive fungus.
“It's not only our lakes, but it's our trees that draw people to this area,” Dube said. “We have so many oak trees in this area that if [oak wilt] got its foothold in this area, it would kill a lot of trees.”
Dube said for people keeping trees in their yard, taking proper care of both old and new trees is essential to their survival.
Newly planted trees need 15 to 25 gallons of water a week for the first 3 to 5 years when the ground is thawed, though watering can be skipped if the area has received more than 1 inch of rain in a week.
“I think proper watering of trees is important,” said Shaun Malady, arborist and owner of Arbor Thrive in Brainerd and St. Cloud. “It's completely different than watering your grass. Trees should be watered deeply once a week. So if we're not getting one inch of rain per week, you should be out there with a hose on a light trickle and giving that tree a good soak once a week.”
With the drought last year, Malady said stressed trees will be more susceptible to diseases this year, even if the tree looked fine last year, the effects may not present themselves until this spring.
“The way the drought affects trees, we don't just see symptoms for the one year that we are in a drought and then it goes away,” Dube said. “We do tend to see symptoms for several years after and it's largely because of opportunistic pests and pathogen populations. They attack drought-stressed trees.”
Signs of drought stress in trees can be seen in the form of wilting, yellowing or scorching of the leaves with some bronzing or browsing around the edges of their leaves. Dube saw trees rapidly drop their leaves last summer as a “kind of a stress response they use to conserve resources.”
Looking at the U.S. Drought Monitor website’s map for Minnesota, most of the state is considered in normal conditions. Looking into the northern third of the state, starting a little bit west of Lake of the Woods County dipping down into the northern half of Cass County and going up into the northern half of the Arrowhead region, those areas are abnormally dry and classified as pre-drought by the U.S. Drought Monitor.
Working with her colleagues, after hearing a meteorologist say they noticed severe droughts come in pairs, they started looking at past historical data.
“Looking back at that past data, I see that there's a good chance that we could be dry again this year,” Dube said. “Unfortunately, the DNR doesn't provide us with a crystal ball for the weather, so we'll have to see what happens this year.”
Over the winter, Dube saw an increase in pine engraver beetle attacks though she believes the area may see an increase in Twolined chestnut borer , a native beetle that attacks weakened oaks of every species in Minnesota that lives in and feeds on the inner bark and cambium, a layer of cells between the bark and the wood.
“Twolined chestnut borer right now, we're kind of estimating that we're still going to see a lot of stress symptoms in oaks, in 2022 and 2023, and thus increase in attacks by that insect,” Dube said. “We potentially won't see that begin to taper off until 2024.”
With her work at the DNR, Dube’s office, outside of the forest, is at Badoura State Forest Nursery where she works to maintain the health of trees. From seedlings to sapling, trees at the nursery are watched over until ready for planting.
The number of fields in production varies by year at the nursery. They have around 80 fields, though some are used for other purposes, they typically have about 25 to 30 fields in production each year.
Each spring, the nursery has its “spring lift” as they prepare trees for sale to the public and state use.
The number of seedlings per bed at the nursery will vary, conifer beds each yield about 30,000 to 40,000 seedlings, hardwood beds each yield about 15,000 to 20,000 seedlings. Most fields have around 20 beds, two of which are used for irrigation lines, so there are often 18 beds growing trees in each field.
As Dube and her team of foresters prepare for regeneration surveys to evaluate newly planted plots and the die-off, they hope for the best but some areas are expected to have mortality rates of about 60%.
Resources for yard tree health may be found at the University of Minnesota Forest Resources Outreach Line. Questions may be emailed to email@example.com , or may be answered through the U of M Extension What’s wrong with my plant bit.ly/3vpQiwG online option.
Resources for forest health issues may also be found at the DNR’s forest stewardship program bit.ly/3vp22Q6 and use bit.ly/39qNt6f to find a local DNR office.
A certified arborist can be found at bit.ly/3vqPhVp .
TIM SPEIER, staff writer, can be reached on Twitter @timmy2thyme , call 218-855-5859 or email firstname.lastname@example.org .