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June 25, 2002
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DESERT BLOOM: Plants Survive the Heat...

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Now, and for the next few months, even people who have lived in Southern Nevada for years will admit - It's hot!

I know that I won't walk out the door without at least a couple of water bottles in hand. And just like us, non-native landscape plants are desperate for every drop of water the irrigation system is emitting. It's a matter of basic survival, right?

Here we are, all of us drinking quarts and quarts of water, sports drink, whatever. Home landscapes with non-native plants look mighty peaked without irrigation. Now, given all this, haven't you ever wondered how native plants, all the creosote bushes, and Joshua trees, and globe mallow flowers, how are they able to survive, year in and year out, with minimal water from nature? And isn't that a good thing, seeing as we've only received one tenth of one inch of rain this entire year!

Well, the fact is that native desert plants are geniuses when it comes to surviving extreme heat, lack of moisture, and very bright sunlight. Truly. Of course, not all desert plants have evolved the same set of strategies to contend with the hostile environment that is summer in Southern Nevada. When you look at the range and variety of plants out in the desert, it's clear that they would have to come up with different mechanisms.

For obvious reasons, the first thing that a lot of us think about a desert is "lack of water", and this is certainly a very big issue for plants. Some desert plants have evolved to deal with water shortages by storing any moisture that might become available. You might have noticed, for instance, that the pads of a prickly pear cactus will shrivel when conditions are very dry, as it's used much of its stored water. When a barrel cactus does this, it kind of looks like a compressed round accordion. After a rainfall, though, it will plump up again, storing water.

Certain plants also develop strategies to avoid losing water in the first place. If you look at the leaves of a lot of desert plants, you'll see that they're often quite small. Cactus are at the extreme of this, where their leaves have shrunken down to the point of just being spines, which don't perform any of the actions of leaves, at all. The leaves of other desert plants, like creosote bush, for example, are small and relatively thick. They might have a waxy coating, too. In this way, water doesn't just boil off in the hot sunshine. Some of the most successful desert natives have even devised a system where many part of photosynthesis takes place at night, when it's cooler. This results in those plants surviving extreme heat and drought, but it's also part of the reason that many desert plants grow quite slowly.

I mentioned that the desert is a hostile environment. Just as we humans can get sunburned, it's possible for a plant to experience excess sunlight, too. At some time you've probably seen dry patches on the leaves of a non-native plant, dry spots that don't seem to be the result of any disease or insect. That can be an indication of sunburn. The same thing can affect trees, which is a reason why many tree trunks are painted white.

Obviously, desert plants can't afford to wait until some kind human comes along to paint their trunks, and they can't risk losing precious leaf tissue to sunburn.

Unlike many plants in cool, moist areas, plants in arid regions like ours aren't trying to capture sunlight. They've had to come up with a variety of innovations to escape some of the sun's most damaging rays. Their leaves might not even look particularly green. A lot of desert plants produce silvery leaves to provide protection against the sun. Sometimes leaves are placed on the plant at an angle. In that way, they don't get hit with so much direct sunlight. Other leaves are covered with hairs, which actually offers some shade to the leaf surface.

Then there are those plants that have come up with a way to escape the hottest, driest growing conditions completely. They grow very quickly in the spring, before it gets too hot. If there's available water, they can go through their entire life cycle during a fairly short period. Then their seeds might remain dormant in the soil for years, until conditions are right again.

The mechanisms that all these desert plants have evolved enable them to survive extreme climate conditions that would kill species from less challenging areas. It points out that when we incorporate natives in our yards, we really don't need to use so much water in order to create a fascinating landscape.

For KNPR's Desert Bloom, this is Dr. Angela O'Callaghan of the University of Nevada Cooperative Extension. Remember - hat and sunscreen.

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