Trees and Drought: How Do Trees Weather Long Periods of Dry Heat?
Nashville’s environment experiences regular bouts of drought, ranging from mild to severe. When there’s not enough rain over a long period of time, urban trees can suffer from dehydration and its consequences if not watered properly. Some trees are more resistant to drought than others, which is a crucial trait for planting in urban environments, where temperatures tend to be warmer and drier than in surrounding areas. In this article, we’ll look at how trees react to drought conditions, then provide some tips on how to best care for your trees when Nashville’s air is at its driest.
If you’ve recently planted a tree (from NTCC’s tree sale or elsewhere), this information is important for summertime care for young trees that are still getting established! The first three years of a tree’s life in-place are crucial for root establishment, and since droughts can particularly affect young and recently transplanted trees, regular watering is critical in long periods without rain.
Drought Conditions in Urban Areas
Drought conditions occur when there isn’t enough rainfall over a long period of time, which can lead to water shortages in rivers, reservoirs, and in the ground. This affects agriculture, the water supply, and local ecosystems, including the trees that make up a city’s canopy. High temperatures contribute to drought conditions by increasing the evaporation rate of water that is present, reducing the overall amount of available moisture.
Urban places tend to be warmer than surrounding areas due to the heat island effect: the hard materials used for streets, parking lots, and buildings absorb and retain heat and release it slowly, which can prevent a location from cooling efficiently during the warmest parts of the year.
In Nashville, droughts tend to be seasonal, with the most intense ones occurring in the summer and early fall, when rainfall is at its lowest and water demand is at its highest. The frequency and duration of these droughts are increasing as the climate warms, which will have implications for landscapes and tree care.
What Happens to Trees During a Drought?
When there’s not enough water available for trees, they aren’t able to perform normal self-maintenance processes, which can lead to weakened health in individual specimens and the canopy in general.
Trees use water to:
Transport nutrients from the soil through their roots to the upper portions of the tree.
Support photosynthesis, the process that makes energy using sunlight.
Maintain cell structure and stay upright and flexible.
Cool themselves through transpiration (releasing water vapor from their leaves).
When water isn’t available:
Trees close their leaf pores (stomata) to reduce water loss, which also slows photosynthesis.
Growth slows or stops.
Trees must use stored carbohydrates to continue respiration
Leaves may wilt, turn yellow or brown, or fall off.
Prolonged lack of water can lead to weakened defenses, disease, or death.
Signs of Dehydration in Trees
Drought has both short- and long-term impacts on trees, and the effects of drought damage may not show up for a year or two after the weather event. Some symptoms of dehydration will show right away, which can alert us that the tree is in need of water.
In a water deficit, a tree’s signs of immediate stress include:
Wilting, curling, or shriveling leaves
Browned edges of leaves (scorching)
Early-season leaf color change or leaf drop
Trees can avoid damage from drought when watered properly throughout stressful weather.
How to Care for Trees in Drought Conditions
A good regular watering habit is the first line of defense against drought. Healthy, well-maintained trees have more tolerance to stress, and when drought does occur, already weak trees will be among the first to react to the dryness.
In drought conditions, both mature and young trees need water, but the amount and frequency differ because their needs are based on their size, root systems, and ability to store water (overwatering can be just as damaging as receiving too little water). The top three to four inches of soil should be dry before watering.
Mature trees should be watered once every week or two during a drought within the tree’s drip area (under the crown). Big trees have extensive roots that hold moisture and reach deep into the ground; they need a good soak every other week in drought conditions to absorb enough water.
Young and smaller trees should be watered more frequently with less water at a time since they have shallow, small roots that can be damaged easily when overwatered. During drought, watering your tree twice a week for half an hour should keep it hydrated, allowing plenty of time to dry out between waterings.
It's important to pay extra attention during drought periods because years of tree growth can quickly be lost to drought damage in young and mature trees alike. A big, mature tree that gets severely damaged cannot be easily replaced, and it takes decades for a newly planted tree to reach maturity and match an older specimen’s benefits. While younger and smaller trees may not accrue as many seasons as the canopy’s biggest and oldest trees, it still takes several years for them to get established to begin really producing benefits.
Drought-Tolerant Trees
Certain tree species have more drought tolerance than others. These trees may have deep root systems (which can reach deeper groundwater than trees with shallow roots), small leaves, waxy leaves, water efficiency, or sizable roots and trunks.
Some trees that are adapted to withstand periods of drought include:
Many types of oak
Honeylocust
These trees are popular in urban areas due to their ability to tolerate the heat and dry conditions of the built environment. For a longer list of drought-tolerant species, check out this pamphlet provided by the University of Tennessee Extension Office.
Other trees that do well in urban areas in general will struggle in extended dry spells and require more moisture support. Drought-sensitive tree species include:
Maples (except the red maple)
Birch
Linden
Planting Trees in Nashville’s Climate
Although drought is generally caused by large-scale weather patterns, the presence of trees can reduce the severity of drought in a location, especially when those trees are cared for in both good weather and in periods of dryness. Trees keep soil moist and hold it in place, release moisture into the air, and provide cooling shade, all of which help buffer against the effects of drought on local ecosystems and communities.
Check out the Nashville Tree Conservation Corps’ tree sale, where you’ll find a range of drought-resistant tree species along with other species that may need more attention in dry spells.
If you don’t have room to plant a tree at home, volunteer with us or donate a tree for us to plant in a needy spot in the city! Nashvillians can also make a financial contribution to NTCC to help fund our mission to promote, preserve, protect, and plant the tree canopy.
Subscribe to our newsletter for ongoing tips and updates on the care of Nashville’s canopy, and check out our Linktree for more ways to connect with us.