I first heard of oak savannas as a high school student while reading a biology textbook. They were described as one of the most endangered ecosystems in the world. I was captivated: globally rare savannas — here in North America? Albeit, without giraffes or elephants…but, still. So, several years later when I had the chance to see one myself while visiting Toledo, OH, I couldn’t resist. The allure of this ecosystem tipped the scales as I sought to call a new place home; now, I live in a house in northwest Ohio that (as far as I can tell) sits on land that used to be oak savanna.
Oak savannas are, fundamentally, zones of transition where oak woodlands and prairies meet. (Technically, there are 3 major types of oak savannas in the US: Southwestern, Calilfornian and Midwestern. As I live in Ohio, however, I plead regional bias and brevity to refer to Midwestern oak savannas as simply “oak savannas” for the purposes of this piece.) As the name implies, they contain oak trees, but scattered across a plain with lots of space and, importantly, light between them.
Oak savannas are born of fire; prior to the 20th century, fires, sometimes set by lightning and, more often, by people, would sweep through these areas, burning back the maples, sumac and sassafras, and allowing oaks, prairie wildflowers and other fire-resistant plants to flourish. Many of these fires were sent intentionally to encourage these savannas, first by the Native Americans in the region, and then later to a lesser extent by settlers.
In spite of their resilience to harsh conditions, in the modern era these ecosystems have become increasingly rare. Only about 0.06 percent of the 50 million acres of historic oak savanna survives today.
As with many transition zones, they support a richer diversity of life than either ecosystem could alone, a phenomena known as the edge effect. In previous eras, they would have been home to large ungulates, like elk and bison, who would have helped keep the forest at bay by eating tree saplings, though now in most places where oak savannas existed, neither of these large animals survive in the wild.
Oak savannas provide good habitat for humans, with lots of sun to grow crops and some trees to provide shade. Therefore, these ecosystems have largely been turned into farms and, more recently, urban/suburban developments (including the one in which I currently live). The remaining savannas have become smaller and more fragmented, giving plants and animals less room to “run” from any stress that may occur in one part of the habitat.
Furthermore, oak savannas are surprisingly fragile when they don’t burn. Without fires, other plants, particularly maples, are able to encroach on these areas, causing the soils to become shadier and wetter and drowning out the sun-loving prairie plants. Invasive species, like autumn olive, buckthorn and multi-flora rose clog the landscape, leaving no sunlight for the goldenrods and purple lupines. Without these oak savanna plants, the birds, butterflies, bees and other animals that have evolved with them over millions of years disappear.
But it’s not all doom and gloom for oak savannas. Many organizations and individuals are working to protect and restore these ecosystems. I spoke with Maureen Bogdanski, Northwest Ohio Preserve Manager with the Ohio Department of Natural Resources, and Benjamin Bomlitz, Restoration Practitioner/Crew Lead for The Nature Conservancy focusing on Oak Openings habitat in Michigan and Ohio, about restoration work in these habitats.
These organizations use cues from the landscape, historical records and satellite imagery to find areas where an oak savanna may have existed. For example, the canopies of oak trees that grow in savannas tend to sprawl out horizontally, luxuriating in the abundance of light. When they grow closely together in a forest, however, they grow straight upwards, fighting with their siblings and cousins for precious sun beams. If you find a big old oak with far-reaching branches in a forest of younger trees, the area may have been a savanna.
Once they find a suitable location, land managers often use construction equipment to move earth, re-channel water and thin trees. Once the big stuff is removed, management of invasives — both native species like maples and non-natives like autumn olive — are controlled using chainsaws and herbicide sprays. When these species are kept at bay, the oak savanna plants are able to fill out the landscape, providing habitat for the insects — like the endangered Karner blue butterfly — and splashing the scenery with a rainbow of colors constantly in rotation from May to October.
To help maintain these habitats, fire or mowing is needed to prevent woody species from encroaching — and fire is the preferred tool. Many of the restored oak savannas, however, are surrounded by farm, industrial or residential areas, and the planning for these burns is challenging. Experienced professionals with years of experience and training, called “burn bosses,” are required to supervise. And if conditions are not perfect, no burning can occur. According to Maureen Bogdanski, these types of restoration efforts are long-term projects; timelines vary depending on the exact goals and starting conditions of the site, but many of the restoration projects she’s working on today won’t be complete within our lifetimes.
Because of the long-term nature of these restoration projects, additional planning is needed to ensure they can survive into the future. According to Benjamin Bomlitz, many organizations, including the Nature Conservancy, are working to ensure that the properties they restore and protect are resilient to climate change. The Nature Conservancy has already seen changes in the temperature and amount of rainfall in the areas that they manage. This means that these regions might not be as hospitable to organisms that live there currently and organisms that previously lived a little further south may actually have a better chance of thriving. It thus becomes increasingly important for them to connect natural areas so that plants and animals are able to migrate as the climate changes.
Even people who don’t own large tracts of land or have decades of time are working to restore these ecosystems. Many restoration organizations with big ambitions and tight budgets rely on armies of volunteers to help them rejuvenate landscapes. People who live in areas that would have supported oak savannas can grow wildflowers that were once widespread in these areas and entire organizations, such as WildOnes, have sprouted up to support them. Even larger institutions, like corporate businesses and universities, have started to convert some of their manicured lawns into tamed versions of these landscapes. While they might not replicate the pre-settlement habitats, they can still support the birds and pollinators that are struggling to hang on in our human-dominated world.
All this effort is vital not only because these ecosystems are intrinsically valuable and support a vast array of life, but also because intact ecosystems play an important role in cleaning our water. The roots of most of the plants that we as humans like to spread across our landscapes — think corn, soy or lawn grasses — have shallow and superficial root structures, and in many cases, we harvest the plants and dig up the soil every year. So soil, and the fertilizers, pesticides and toxic chemicals bound to it, wash out into the lakes and rivers.
“When we alter the landscape, whether it’s for farming, residential, or commercial purposes, we change what the water does and how it percolates from rain down through the soil and ends up into these other rivers and tributaries,” Bomlitz said.
Unlike our typical farm/suburban landscapes, the roots of oak savannas go deep. When water falls on these systems, “this rainwater is percolating through all these different plants and nutrients being uptaken. And even some toxins can be removed.” In essence, Bomlitz said, these upland oak savannas “wash the water,” which helps keep our groundwater, lakes, rivers and, ultimately, drinking water clean.
A few hours after interviewing Benjamin and Maureen, I decided to go to the patch of oak savanna closest to me. I find it just off a bike trail, a few acres sandwiched between a high school and an office park. The mild July afternoon feels hotter without the protection of trees. Almost immediately I spot a Baltimore oriole, a flash of orange among the oak trees. Butterfly milkweeds scream with their bright orange flowers, dripping with bumble bees, beetles, and a myriad of insects that I cannot identify. An iridescent blue butterfly lays open in the afternoon sun, though it flits away when I clumsily attempt to take a picture on my phone. I crush some sweet fern between my fingers, smelling its sweet and spicy fragrance — the summer smell of dry, sunny places. I spot two blue jays fighting over a twig, one puffing his wings out in threat until the other is cowed or decides it’s not worth the effort. The savanna is quiet in the afternoon heat, save for the wind rustling the oak leaves and a lone cicada singing “grong grong grong grong” against the backdrop of nearby road noises. It is a slice of beauty and life that stubbornly continues to exist because of the plants, animals and people who depend on — and love — oak savannas.
Where you can see oak savannas in northwest Ohio:
The author would like to thank Benjamin Bomolitz and Maureen Bogdanski for their generosity in sharing their knowledge about Midwestern oak savannas.