The Drought of 2011: What it means to Central Texas trees

For more than a year now we have had only a few inches of rain. Austin and the surrounding areas and even the entire state are experiencing a severe water deficit. And this isn’t getting any better, as harsher watering restrictions come into play.

No relief yet

What this means is that area trees are under serious stress, and likely will be for the foreseeable future, even as we say goodbye to the triple-digit temper- atures of summer. With the increased restrictions, a lot of trees are not getting any sprinkler water or any supplemental water, which means they are in serious trouble.

By the time the drought in 2009 was over, we’d lost hundreds of trees around the area, including scores of trees in Zilker Park. Many trees appeared to be dead, and we were unsure whether they would re-leaf in the spring. For most of 2010 we were removing dead trees, most of which were pecan trees. Additionally, some live oaks, cedar elms and other species also died and had to be removed.

During these extreme, extensive drought periods, trees that do not have additional water, are in exposed, bare soil areas (no mulch over the root zone), or are in areas that get direct sun on the root zone are extremely susceptible to decline. Radiant heat from the street, driveways, patios and other concrete features can further add to stress.

Stress spares no trees

Many trees turn yellow, many wilt and droop, and the canopies appear thinner and less robust. Trees eventually defoliate and die. All trees go into a semi-dormant state to conserve as much water as possible. Small, absorbing roots die, and then grow back when they finally get rain. Trees with higher water requirements such as maples, box elders, cottonwoods, bald cypress, willows, sycamores, catalpas, silver maples and hackberries are generally the first to die if their water supply dries up or they do not get supplemental water. The tougher native trees in water-stressed settings are the next to go.

In 2009, native pecan trees in the hottest, driest areas such as parks and dry south-facing yards died and defoliated by the hundreds. This was not something we’d seen before. We’d just assumed that these native trees were fairly drought tolerant and could handle the hot, dry summers. What we found was that during three months of 100+ degree temperatures with no rain, all bets were off. Many pecans had 50 or more percent canopy dieback, and we spent a great deal of time in 2010 removing the dead limbs in these canopies.

What you can do to minimize tree stress

So, what can be done?

Water your trees: We recommend that if you are not watering your lawn regularly, you hand water the trees once a week or once every two weeks to help keep them alive. Water only has to get down around 12 inches or so (max) below the surface soil. However, frequency and duration are the important factors during drought summers. The best way to think of it is to mimic rain when you water. Although rainwater is better for trees than chlorinated city water, as it also contains nitrogen, the important thing to note is that it saturates the soil for a prolonged period so the tree can take up enough water to make a difference. If you soak the tree for 15-20 minutes once a week or once every two weeks the frequency will also help.

Protect the root zone: Mulch: A thick layer of mulch, 2-3 inches thick is recommended around the root zone, as far out to the drip line as possible. Mulch helps keep the water in the roots, and also helps insulate the roots from the heat and keeps them cooler. Tree roots are not as deep as many people think. The anchoring woody roots go down typically no more than 2 feet. The small, absorbing roots that are responsible for uptake can typically be found in the top 8-10 inches of soil, in the Austin area they are often much closer to the surface than that.

What to do if damage has occurred

Once severe drought damage has occurred, often the limbs in the upper canopy will die. Once this happens, they will eventually need to be pruned out of the canopy, especially if they are of any size, before they fall. Sometimes we get what we call tip die-back, where smaller diameter twigs die back throughout the canopy. This is often associated with drought conditions, but also with root problems in general.

Water whenever, however you can

Water is obviously the limiting factor. Knowing what species you have and what their water requirements are is also key. Mulching to invigorate the roots and help with water retention is also recommended. Many people I talked to since the last drought had no idea that their trees needed supplemental water. Many people are having to re-think their trees water requirements, and help the trees out a little. It also helps to look up! Is the tree wilting? Losing leaves? Turning yellow? Maybe it’s time to turn on the water!

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