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posted: 8/18/2012 10:54 AM

How the prairie survives a hot, dry summer

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  • Silphium, better known as compass plant, blooms at LeRoy Oakes Forest Preserve in St. Charles.

      Silphium, better known as compass plant, blooms at LeRoy Oakes Forest Preserve in St. Charles.
    Laura Stoecker/Daily Herald

  • The afternoon sun beats down on prairie plants at Tekakwitha Woods in St. Charles. Three species in the genus silphium -- drought hardy native prairie plants -- are well prepared to weather the drought.

       The afternoon sun beats down on prairie plants at Tekakwitha Woods in St. Charles. Three species in the genus silphium -- drought hardy native prairie plants -- are well prepared to weather the drought.
    Laura Stoecker | Staff Photographer

  • Rough hairs on the leaves of a compass plant help retain moisture near the leaf's surface.

       Rough hairs on the leaves of a compass plant help retain moisture near the leaf's surface.
    Laura Stoecker | Staff Photographer

  • Rough hairs on the edges of a compass plant leaf are highlighted by the setting sun. The hairs are on the front and backsides of the leaves as well, giving it a sandpaper-like feeling, and helps retain moisture near the surface of the leaf. Prairie dock, which has broad leaves, also has rough hairs.

       Rough hairs on the edges of a compass plant leaf are highlighted by the setting sun. The hairs are on the front and backsides of the leaves as well, giving it a sandpaper-like feeling, and helps retain moisture near the surface of the leaf. Prairie dock, which has broad leaves, also has rough hairs.
    Laura Stoecker | Staff Photographer

  • Big Bluestem (Andropogon gerardi), nicknamed Turkey Foot, waves in the breeze of an approaching storm at LeRoy Oakes Forest Preserve's Horlock Prairie.

       Big Bluestem (Andropogon gerardi), nicknamed Turkey Foot, waves in the breeze of an approaching storm at LeRoy Oakes Forest Preserve's Horlock Prairie.
    Laura Stoecker | Staff Photographer

 

Robins perched motionless in the shade, bills agape.

Thirsty plants wilted in flower beds, and trees prematurely surrendered their yellowing leaves. Lawns turned brown and prickly, shunned by barefoot kids who fled indoors to play. Grown-ups, too, holed up in air-conditioned houses.

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Everyone, it seemed, was held hostage by the heat this summer. Everything was dying for rain.

Everyone and everything except the prairie.

As the scorching summer of 2012 took its toll on gardens, crops, critters and people, the prairie endured. Its stalwart plants and resilient wildlife have quietly gone about the business of survival. While we are still counting our losses from this summer, a look at the prairie reveals lessons in survival.

The prairie evolved in a climate of extremes. Long-ago summers of searing heat and limited rainfall forged a flora strong enough to withstand the rigors of drought. Wildlife, too, evolved adaptations to the rigors of the changing climate.

What are some of the secrets of the success on the rugged prairie? For starters, take a look at some of the big, bold plants that are in the peak of their flowering this week. Compass plant and prairie dock, close botanical cousins, are classic examples of drought-hardy plants.

You can easily recognize them by their tall flower stalks rising like ships' masts above the prairie sea. In years of abundant rain, the stalks rise eight to 10 feet high to unfurl their bright yellow flowers. In times of drought, the plant conserves energy and the stalks grow shorter.

Going underground

While these species are impressive above ground, it's what's underground that counts in years of drought. A well-developed root system is the foundation of drought-hardiness. Prairie dock, compass plant and many of their hardy comrades develop tap roots that plumb the depths of the prairie earth in search of moisture. In his classic book "Where the Sky Began," author John Madson wrote, "The taproot of an old compass-plant may be as thick as a man's wrist just below the surface of the earth -- and although it may be less than an inch in diameter only three feet down, this main root may drive almost fourteen feet into the earth."

Madson also cites prairie rose among the champions of prairie taproots. One individual rose shrub sent a taproot some 21 feet underground.

While the tap root may be the advance guard, there's much more to the quest for moisture. Prairie plants send an army of lateral roots to infiltrate the soil. Millions of small rootlets extend their reach into crevices, cracks and tiny pores from which water can be extracted.

Several horizons, or layers, of soil can thus be exploited when water is scarce. The lateral roots of myriad plants interconnect underground. This reticulated network makes up the bulk of the biomass, or living material, of the prairie.

Plant ecologists have estimated that up to 80 percent of the total biomass of the prairie is in its root system.

This immense root system not only maximizes absorption of water, it's key to the survival of the conflagrations that sweep across prairie aboveground. Faced with the double whammy of fire and drought, the prairie survives by virtue of its underground reserves.

Maintaining moisture

After going to all the trouble of finding water and escaping the heat of fire, prairie plants face the challenge of losing water in a process called transpiration.

Sometimes referred to as the plant's version of sweating, transpiration involves the movement of water through small openings in the leaves called stomata.

In a feat of physics and chemistry, transpiration pulls water up from the roots while releasing water through the leaves. This can be a good thing, but too much of a good thing is, well, not very helpful under stress.

On a dry, windy day in a drought year, water loss from transpiration may measure in thousands of gallons per acre. With no water to pump up, this results in a net loss that's hard to recover when there's no rain in sight.

Why not close the stomata altogether to prevent water loss? The stomata are also the portals through which gases enter and exit the leaves -- notably, oxygen and carbon dioxide. Controlling all the comings and goings of water and gases is tricky. But prairie plants meet the challenge handily.

Rattlesnake master, a bizarre but cool plant in our native flora, avoids the problematic situation by having sunken stomata. The stomata are below the actual leaf surface, so the plant avoids exposure to desiccating winds. A similar strategy employed by numerous prairie plants is to have more stomata on the undersides of their leaves than on the upper surface -- again dodging the problem of water-stealing wind.

Yet another tactic is to trap moisture on leaves. Find a prairie dock plant along the trail and check out the surface of those giant leaves. "Sandpaper!" is the immediate reaction when people first feel the rough surface. (You'll notice, too, that it's cool to the touch due to the moisture drawn up from the roots several fathoms underground.)

The leaves are covered with rough hairs that retain moisture close to the surface. Their stems, too, sport stubbly hairs. Water-conserving hairs don't have to be rough, however. The downy sunflower is one of many species that have long, soft hairs as water-conserving structures.

Conservative growth

Taking a conservative approach to life also helps to survive times of scarcity. No use going full speed ahead if you're going to run out of steam. Thus, the tallgrass prairie hasn't grown tall this year, and big bluestem grasses are rather small big bluestems, the size of little bluestem (height, I have found, is all relative).

These prairie grasses have found that rather than racing to reach the sky, its better to hang tough. Wait it out. Remain firmly anchored in the earth. The time to crank out the carbs for height and girth is when rain is plentiful. And that's certainly not now.

On the prairie, there was no escaping the blast furnace of summer this year. But the prairie flora and fauna seem to live by the maxim, "This too shall pass." Indeed, droughts have come and gone for thousands of years, and the prairie has not only endured, it has flourished in astonishing beauty.

Incorporating these hardy plants in our landscaping will reduce our use of scarce resources in years of extreme weather conditions.

As Louise Erdrich so eloquently summed up in her essay "Big Grass," it all boils down to this: "Sink deep roots. Conserve water. Respect and nourish your neighbors and never let trees gain the upper hand. Bow beneath the arm of fire. Connect underground. Provide. Provide. Be lovely and do no harm." This is how to survive, and thrive, on the prairie.

• Valerie Blaine is a naturalist with the Forest Preserve District of Kane County. She welcomes your comments, questions, and suggestions. You may contact her at blainevalerie@kaneforest.com.

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