Recurring and prolonged periods of drought are worsening worldwide, triggering a dangerous chain reaction for trees, according to a forest health expert at North Carolina State University.
Trees rely on soil moisture to transport nutrients, cool their leaves and create food through photosynthesis – all vital processes for survival. Drought removes that moisture.
“As soils dry out, trees can no longer take up water fast enough to meet the demands of the canopy ,” said Kelly Oten, an assistant professor and Extension specialist in the Department of Forestry and Environmental Resources at NC State.
This shortage of water, Oten added, can “severely compromise trees,” weakening them and making them more susceptible to structural collapse, weather damage, pest infestations and diseases.
In 2023, for example, southern pine beetles killed an estimated 12.5 million drought-stressed pine trees across nearly 80,000 acres in Mississippi.
Such widespread losses will likely become more common as climate change drives more frequent, intense and prolonged droughts.
Future climate models project that the frequency, duration and severity of droughts will increase globally, with up to 62% of land area facing severe conditions under high-emission scenarios.
In the following FAQ, Oten addresses common questions about the effects of drought on tree health, from identifying the warning signs of stress to implementing recovery strategies.
- What are common signs of drought stress in trees?
- How long can a tree survive without water before it dies?
- Which trees are most vulnerable to drought?
- What are the best drought-tolerant trees to plant?
- How do you save a drought-stressed tree?
- How long does it take trees to recover from drought?
What are common signs of drought stress in trees?
Drought-stressed trees shut down vital functions to conserve moisture, triggering visible symptoms. One of the earliest warning signs of this is leaf wilting.
“Just like an indoor plant that wilts when it goes unwatered, leaves often begin to droop or curl because the tree can’t move enough water from the roots to the canopy,” Oten said.
Trees may also develop leaf scorch – a condition where the edges of their leaves turn brown and crispy – or begin dropping leaves prematurely.
“If you step back and look at the entire tree, the canopy may appear thinner than it did in previous years or the leaves may be smaller than normal,” Oten said.
During periods of prolonged drought, trees sometimes experience twig dieback, when the tips of their branches dry out and die.
Twig dieback is a sign that a stressed tree is entering “survival mode,” according to Oten. By sacrificing its outer twigs, it can prioritize survival over growth until conditions improve.
How long can a tree survive without water before it dies?
Tree survival during a drought depends on numerous factors, according to Oten. That includes tree species and age, soil type and even weather conditions.
Age is probably the most important determining factor, according to Oten. Newly planted trees are by far the most vulnerable during periods of drought.
“When a tree is planted, it either loses much of its root system or is planted with a much smaller root system than the tree needs to thrive, leaving it with a limited ability to absorb water from the soil,” Oten said.
Even a few weeks of hot, dry weather can be enough to cause severe stress or death if a tree isn’t watered regularly during its first year or two after planting, according to Oten.
Mature trees are less vulnerable to drought-related stress because they have more extensive root systems and greater reserves. A mature oak, for example, can often withstand weeks or even months of drought.
Oten noted that while trees can die during the peak of a severe drought from dehydration or starvation, they often die one to three years later due to the combined health impacts of depleted energy reserves, reduced root presence and pest infestations.
Which trees are most vulnerable to drought?
Drought vulnerability varies among tree species based on a variety of factors, including their native habitat, root structure and moisture needs.
Oten said trees that naturally evolve in and prefer moist soils – such as the river birch, tulip poplar, sycamore and black gum – often show drought stress relatively quickly.
These species are adapted to areas where water is typically abundant, meaning they possess few biological mechanisms to conserve water during extended dry spells.
Research shows that urban trees suffer more during droughts than their rural counterparts because they face additional stressors, including soil compaction.
Soil compaction in cities happens when heavy machines, cars and walking crush the air spaces in dirt. This makes the ground hard and dense.
Because of hardened soil, urban trees cannot develop the deep, healthy root systems needed to access water from lower soil layers during a drought.
What are the best drought-tolerant trees to plant and why?
There is no universal list of drought-tolerant trees for homeowners and landowners to reference when thinking about which species to plant on their properties, according to Oten.
Instead, it’s most important to think about location. “Trees that best survive periods of drought are those that are planted on the right site that give that tree the optimal growing conditions it needs,” she said.
Different tree species do best in specific conditions, so it is important to match each one with its corresponding soil type, water access and sunlight exposure so that it thrives, not just survives.
Extension programs nationwide can often help identify regionally adapted trees and plants capable of withstanding numerous challenges, whether it’s drought or deer browsing.
u0022… no tree is drought-proof during exceptionally hot or prolonged droughts.u0022
The NC State Extension Gardener Plant Toolbox, for example, provides a list of more than 190 drought-resistant tree species that can be planted across North Carolina.
Oten said planting a variety of tree species in the landscape is important because it “spreads risk so that a single insect, disease or weather event is less likely to dramatically change your landscape.”
She also reiterated that newly planted trees, even some of the more drought-tolerant species, require supplemental water for the first one to two years while they build their root systems.
“Once established, they’ll be much better equipped to handle dry periods, but even then, no tree is drought-proof during exceptionally hot or prolonged droughts,” Oten said.
How do you save a drought-stressed tree?
Even when a tree has become stressed due to drought, it’s not a lost cause. Oten said homeowners can take several steps to help restore its health.
One of those steps is watering the tree slowly and deeply once every 7-10 days, which according to Oten, is more effective than a light daily sprinkle.
Shallow, frequent watering can cause roots to grow near the surface where they quickly dry out and suffer heat stress. Long, deep watering encourages the development of deeper root systems that can help the trees survive the next dry spell, Oten said.
Oten said applying a 2-4 inch layer of mulch around the tree can also help by conserving soil moisture, moderating soil temperatures and reducing competition from weeds and grass.
“Just be sure to keep the mulch a few inches away from the trunk as to not trap moisture or pathogens against the trunk,” Oten said.
It’s also important to avoid pruning or applying fertilizer, she added. Pruning forces the tree to heal, while fertilizer makes the tree grow fast. Both require water the tree does not have.
Finally, Oten recommended avoiding planting new trees until the drought subsides, and for recently planted trees, providing them with supplemental watering as needed.
“Caring for your tree now can mean the difference between a tree that merely survives and one that thrives for many years,” Oten said.
How long does it take trees to recover from drought?
After a severe drought, Oten said it often takes years for a tree to fully recover. Even when rainfall returns, trees can remain under stress.
“The leaves may perk up and other symptoms may dissipate when rainfall returns, but the rebuilding of the energy reserves and damaged root systems takes time,” Oten said.
Oten added that the recovery timeline is ultimately determined by the severity and duration of the drought alongside the tree’s age and health.
Research shows that it can take up to four years for living trees – mostly oak and pine species – to return to normal growth rates after severe drought.
Young canopy trees, while more susceptible to drought, also recover faster than older trees, returning to pre-drought growth levels in about a year.
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This post was originally published in College of Natural Resources News.
