Jerry Wilhelm on Soil, Water, Organisms, and Love

When mid-nineteenth century plough technology finally made “breaking” the tough prairie sod feasible, the extraordinary fertility of Midwestern soil was revealed and the destruction of the prairie immediately got underway. Then modern development and agricultural methods increased the pace, until today only 1/10th of one percent of original, remnant prairie remains in Illinois, with similar tiny percentages for other types of remnant habitats.

Remnant habitat: Why should we care?
Jerry Wilhelm, PhD, co-author of the 4th edition of The Plants of the Chicago Region, says emphatically, “There is nothing we can do for our grandchildren that is more important than to preserve the remnants that are left, and to try to return health to the soil.” The remnants are a font of genetic diversity that exists nowhere else, and healthy soil cools the atmosphere, replenishes the water table, and protects rivers and streams, he explains.

Wilhelm calls remnant lands “the living tissue of the earth,” its original skin. The species diversity found on these tiny parcels of original wild lands is way beyond what can be reproduced in new native plantings, and this diversity is the safety net evolution has provided that allows for calamities to be overcome through redundancies in natural systems. Such redundancies have kept natural systems in balance for millennia, but the webs that they create are being broken as extinctions occur across our flora and fauna in the modern era.

The way we treat soil and water now ignores the natural laws that our very existence depends upon, Wilhelm warns. Healthy soil is replete with organic material, which gives it tremendous water-retention capacity that in turn mitigates the wildly fluctuating climate scenarios we are now experiencing across our landscapes.  Modern agricultural practices and development strip the soil and send it with our rainwater, polluted, into our waterways, rather than keeping soil in place and water where it falls, as has been nature’s way for millennia. Finally, tilling the soil dumps enormous amounts of carbon into the atmosphere, a rarely discussed source of greenhouse gas.


Wilhelm explains that climate change isn’t only about atmospheric CO2. “It’s the whole living system,” he says. The earth’s natural skin is made up of healthy soil that is able to regulate its own temperature, a moderating effect that is transferred to the atmosphere above it. Healthy soil is full of many forms of life and a measure of porosity that allows water to be held in those pores. Water has a special property that allows it to heat and cool only very slowly, so that soil with sufficient moisture does not experience extreme temperature fluctuations.

“Healthy soil contains about 55 percent soil moisture,” Wilhelm says, “which gives it a connection to the thermal mass of the earth below so that its temperature cannot change rapidly. This, in turn, allows the organisms in the soil that depend upon a stable, slowly changing temperature regime to thrive. ”

It is this healthy community of organisms that, in turn, allows the soil to retain moisture and the organisms and roots within it to continue to fix carbon in the soil. When the soil becomes depleted of organic matter, soil moisture drops to as low as 20 percent, Wilhelm says. Then there is not enough water in the system to protect the living organisms, and the system can no longer thermoregulate.

“That presents a real danger,” Wilhelm warns. “It’s what’s wrong with our land. If you look at our region in Google Earth, you will see how high a percentage of our land in Illinois is planted in soy and corn, in commodity-scale agriculture. That soil has lost its organic matter.”

Depleted soils, such as those under commodity agricultural crops, experience “fever and chills,” says Wilhelm. And the atmosphere above those soils does the same. “The commodity farmer has to irrigate to bring the soil moisture up, and that soil is only alive about 90 days per year. Every time the farmer tills, organic matter is lost to oxidation. That means that farmers have to irrigate the soil and when it is not irrigated the temperature of the soil fluctuates wildly.”

Wilhelm adds that we have similar problems with the soil beneath our lawns and paved areas, where little or no water infiltration can occur.

Today’s earth has third-degree burns
“It’s almost as if the whole earth skin has third-degree burns,” he says. “We have to get the organic matter back into the soil. We have to allow perennial grass roots—which go down into the soil up to 15 feet—to grow and die every year. That will replenish the organic matter and bring the soil back to life.

Another soil health problem is compaction, from the depletion of spongy organic matter and the use of heavy equipment. “The more we subsidize, and the more land we put into commodity agriculture, the more compacted the soils become and so when we do get rain, the soil’s ability to absorb the water has been reduced. So, this precious resource simply runs off—causing havoc to downstream neighbors and aquatic systems.”

To Wilhelm, it’s simple: If we don’t put organic matter back into the soil and allow natural thermoregulation to occur, we will keep having broad climate fluxes, we will face extinctions, and we will be in for a very bad time. “Slowly but surely, we have to go in that direction, to preserve the remnants that are left, and to try to return health to the soil. But the remnants are important, you have to have some living tissue, you can’t start it from nothing.”

Why remnants are supreme among native plantings

Among the signs of health on any parcel of open land is the number of native species still present, both plant and animal. Wilhelm says that his co-author on the current book-in-progress, Laura Rericha, has found as many as 26 bee species in her home garden, which hosts an array of native plants. Yet, he adds, Laura has found more than 62 species of bee on Amorpha canescens [lead plant] alone in a remnant prairie; there is no comparison between native gardens whose owners seek to replicate the prairie, and the genuine article.

“You can’t just plant plants and get all our insects back,” Wilhelm says. “Ninety percent of our native insect species live in our remnants. We have over 400 species of bee in our region, but you can’t put them into unhealthy soil [many of our native bees are ground-dwelling, as opposed to the European honey bee]. And you may be able to build a healthy soil, but that bee may be in a remnant 20 miles away. And then, there are so many connections; some of these bees are parasitic on other bees, for example.”

Yet, Wilhelm is not saying we should give up on planting natives in our yards and parks. His own backyard is full of natives and he performs a prescribed burn, simulating the burning native Americans performed for millennia on our wild lands, every year. He encourages everyone to do what they can to plant and preserve native species, and gives solace and encouragement to those working to know and love and support our native flora and fauna.

“What’s important is what is in your heart. There’s a force there. If you’re not doing that, what else are you doing? Tie yourself to something real. When you start trying to restore, you reach a better frame of mind.” Finally, he adds, paraphrasing Rachel Carson, “If you are devoted to nature and love its beauty, you’ll have less of an inclination to destroy it.”

Monica Buckley interviewed Gerould (Jerry) Wilhelm, Ph.D., for this post. Wilhelm is director of research, Conservation Research Institute. He and co-author wildlife biologist Laura Rericha are updating and expanding Floyd Swink and Gerould Wilhelm’s 1994 reference book, Plants of the Chicago Region, to be renamed  Flora of the Chicago Region: An Ecological Synthesis. The new book will include observations on regional fauna and geology in addition to regional flora. It will be published by Conservation Research Institute and the Indiana Academy of Sciences. 

To learn more about native ecosystem function and restoration, go to to read essays by Jerry Wilhelm.

The image of Wolf Road Prairie in midsummer was taken by Dan Kirk of the Illinois Department of Natural Resources.

The image of Jerry Wilhelm leading a group at Wolf Road Prairie was taken by Dave Wacie for the Salt Creek Greenway Association.