Last week the conditions were almost ideal for burning parts of our oak-hickory woods on the Des Plaines campus. I wasn't paying close attention to the possibility of a burn, but I only had to follow my nose to find out for myself. As I walked outdoors from my lab session on Tuesday afternoon, the earthy yet acrid odor of a woodland fire wafted into my nostrils and I saw a smoky haze rising from the woods to the south and east of Parking Lot C. I love the sounds and smells and sights of fire in the woods, so I hustled over to the area where my nose and eyes led me, and indeed, where there was smoke, there was fire...
The leaf litter dominated by the dry and stiff leaves of swamp white oaks (Quercus bicolor), white oaks (Quercus alba), bur oaks (Quercus macrocarpa), and even a few red oaks (Quercus rubra) was crackling in the cool air and sending up little plumes of smoke everywhere the blazing tentacles of the fire snaked through the woods. I marveled at the stark color contrast between the recently burned and unburned areas and the aromatic and complex mixtures of organic scents that tumbled through the smoky air and up my nose. The immediate sensory experience of the fire was invigorating, but so too was the knowledge that this apparently destructive force would lead to so much new growth and rebirth.
Periodic fires in the oak-hickory woodlands are absolutely necessary for healthy oak-hickory woodland ecosystems. Fires tip the ecological balance to favor thick-barked trees like oaks (Quercus spp.) and hickories (Carya spp.) over more fire-sensitive species like maples (Acer spp.). In the absence of fire, faster-growing, shade-tolerant trees proliferate and shade the ground to the point where trees like young oaks cannot grow effectively. One important difference between oaks and maples is that young oaks are shade-intolerant, whereas young maples can grow just fine in deeply shaded woodlands. This is one reason that oaks have evolved secondary compounds, such as tannins, in their leaves. Tannins have antimicrobial properties that allow the leaves to persist in the leaf litter for years before they decompose. Leaves that stick around longer build up fuel loads, and larger fuel loads make fires mores likely to sweep through the woods and kill some of the more fire-sensitive trees, thus increasing light levels on the woodland floor. Maple leaves, on the other hand, decompose much faster than oak leaves.
In this way, fires are part of the necessary maintenance for oak-hickory woodlands. Without fire, the woodlands will change rather dramatically in character and species composition, becoming much less open, more deeply shaded, with a much less diverse understory of plants and woodland wildflowers due to the relative lack of sunlight hitting the forest floor. So as the fires crackled and the smoke went up, I gave thanks to the workers who were managing the prescribed burn that day - and to the oak leaves and their tannins that were providing much of the fuel for the fire.
Today, not a week later, I awoke to a layer of hoary frost gracing the leaves of many of the plants in my native plant gardens at my home. Some of the most beautiful designs were deposited on the leaves of the Sage (Artemisia ludoviciana).
The juxtaposition of the fire and the ice in my recent memory seem to help me appreciate the elemental realities of our tough yet elegant living world. We live on a complex and protean planet where organisms have adapted to the fluctuating realities of the physical world with remarkable ingenuity and resilience. Humans sometimes have an unfortunate tendency to consider themselves separate from the rest of nature - whether due to pure human chauvinism or just learned ignorance of our origins and our ultimate fates. However, when I step back and observe other organisms like the plants around me standing tall and dealing with the winds and the weather - the fire and the ice - I am reminded that I, too, have it within myself to weather most any storm that life presents to me. It's a lesson that helps me contextualize and think about all the challenges that we face in the world. Sometimes we just need to accept what is given, like an oak tree rooted in place. After all, the oaks and the sage are distant kin - long-lost cousins - though our proud lineages diverged long ago in the annals of deep evolutionary time. Maybe I'll spend some more time thinking about how to get in touch with my inner oak. It seems like a good thing to do.
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