Drought and Trees Explained | Culture & Leisure

Only in mid-June, Texas has already experienced extreme heat and very little rain, with the trend expected to continue.

Anticipation of drought can prompt many thoughts, from water scarcity to increased risk of wildfires. But what do drought conditions mean for our trees?

Drought is defined by a relatively long duration with significantly below normal rainfall, usually occurring over a large area, and Texas is no stranger to drought. According to the US Drought Monitor, in 2011, one of the state’s worst drought years, more than 80% of Texas experienced exceptional drought conditions. This drought killed an estimated 300 million trees, including 5.6 million urban shade trees.

According to Texas A&M Forest Service experts, tree deaths occur during a drought because drought is a major stress on trees.

“A stress is anything that reduces the tree’s ability to function efficiently and grow vigorously,” said Texas A&M Forest Service woodland ecologist Karl Flocke. “Stresses are things that can affect growth, nutrient uptake, the tree’s ability to photosynthesize, and ultimately the tree’s ability to defend itself against environmental conditions and pathogens. These include excessive heat or cold, predation by animals, insects and disease – a number of different things.

Drought alone cannot kill your trees, although it can be the tipping domino of tree mortality and should be cause for concern.

“Most trees usually die from a combination of different stresses,” said Courtney Blevins, an urban forester with the Texas A&M Forest Service. “One of the biggest stresses we see in Texas is drought. When that happens, the stresses build up and secondary pests or diseases can establish themselves in the trees.

Secondary pests and diseases are those that attack a tree that is already stressed by something else, such as a drought or a winter storm. Hypoxylon and most annoying insects are considered secondary pests and diseases, with the exception of the emerald ash borer, which attacks both healthy and stressed ash trees.

Blevins said when a tree is already stressed, these types of insects and diseases will increase — not just during the drought period, but for years after a drought or other significant stress event ends. .

So what happens to trees during a drought? Ultimately, the lack of water causes the trees to photosynthesize less or produce less food, resulting in a lack of nutrients necessary for their survival.

“Plants generate their own food through photosynthesis, and one of the key components of photosynthesis is water,” Flocke said. “Water is necessary for the chemical reactions that create sugars. It is also necessary to help move the necessary materials in the tree and, finally, to use these materials.

Without water, a tree cannot generate sugars and cannot utilize the sugars necessary for tree growth. When this happens, the trees begin to show physical symptoms due to lack of nutrients, usually through their leaves.

“Things to look for on your tree are falling or wilting leaves, small or malformed leaves, yellowing of leaves and browning of leaf tips,” Blevins said. “Some species, such as junipers, can completely turn brown and lose all of their leaves.”

Just because the leaves are starting to fall from your tree doesn’t mean the tree is dead. For smaller trees, you can just use your thumbnail and scrape off some of the smaller twigs – if there’s still green underneath, then the tree isn’t dead. In a few weeks, he can start again. If you are concerned that your tree is dead, contact a certified arborist for professional advice.

The most helpful way to reduce stress on your tree during drought conditions is to give supplemental water, although the amount and frequency of watering will depend on your tree and region.

“Watering will depend on the tree; the size, species and age of the tree as well as the soils you have in your area,” Flocke said. “If you’ve established trees that are well suited to your location, chances are they won’t need any additional water at all. But I would watch them for signs of stress.

If you’re starting to see signs of stress in your trees and the ground under your trees is extremely dry, it’s time to start watering. To test the dryness of the soil, you can take a long screwdriver and stick it in the ground. If the screwdriver doesn’t easily penetrate 6 to 8 inches into the soil, it’s time to water.

“Start by watering the area around the tree canopy,” Flocke said. “Not just at the base of the tree and not just around the edge of the drip line, but water the entire area below the canopy of the tree to the point where water begins to pool and drain. sink to the surface.”

A good guideline for how much water your tree needs is 2 to 3 gallons per 1 inch of trunk diameter.

According to Blevins, a general rule for newly planted trees in the heat of summer is to water them up to three times a week in the absence of rainfall. However, you want to make sure the soil is not completely saturated with water at all times.

Large, established trees may not need a lot of water, but extremely high temperatures and lack of rainfall may justify watering them every two weeks.

When watering your trees, follow any water use restrictions you may have in your area and try to maximize the water you give.

“The most important thing is to avoid watering during the heat of the day because a lot more water is going to be lost to evaporation,” Flocke said. “Either early morning or late evening is the best time to water.”

An easy trick for watering trees during a drought is to try to mimic what a typical summer looks like for your trees, watering every 10 days to two weeks and knowing that it’s okay to failing to follow a set schedule – just like normal summer rain.

Mulching is another way to help your trees deal with drought stress. Mulch is an easy and inexpensive option to help your trees because it conserves water, regulates soil temperature, reduces competition from other plants, and improves soil health.

“In general, apply a layer of mulch no more than 2 to 3 inches deep,” Flocke said. “In reality, the entire area below the canopy could be mulched, but mulching several feet around the base of the tree, being careful not to let the mulch touch the base of the trunk, will help.”

During periods of drought, be extremely careful not to add additional stress to your tree, making it more susceptible to insects and secondary diseases. First, don’t prune your trees unless absolutely necessary.

“What you’re trying to do is reduce the stress on the tree, so pruning, even when you have to, adds stress because you’re hurting the tree,” Blevins said. “If you prune live branches or areas of live leaves from the tree, you remove food and the site where the tree’s root growth hormone is developed, affecting root growth and further stressing the tree. tree at a time when it is already too stressed.”

According to Blevins, the exception to pruning trees during drought is a branch that is completely dead or poses a danger to its environment.

Another common mistake that can be harmful to your trees during a drought is spreading fertilizer.

“Just generally applying fertilizer without knowing if there’s a deficiency is a really bad idea,” Blevins said. “If there’s no nutrient deficiency, it won’t help, and it can actually harm things and make the tree worse.”

During the summer heat, and especially during droughts, he suggested monitoring your trees for symptoms of stress and adding additional water if needed.

“Trees provide tremendous value to us in our landscape,” Flocke said. “Keeping trees, especially near our homes, can help lower overall energy bills, keep us healthier and provide shade at home. If we lose these trees, we potentially lose benefits that have taken decades to accrue.


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