State of Change: Habitat Disturbance in Glen Helen
by Ben Silliman, Glen Helen Land Manager
For the past 100 years, the Glen has made a great recovery from the denuded landscape that it once was.
In the eastern United States, when land is left undisturbed by human activities, woody plants take over. In a sense, you could essentially define an Ohio forest as “land that has not been disturbed by people.” Yet in Ohio, all forests have, to one degree or another, been influenced by anthropogenic forces over the past several hundred years. Consider a contrast: while people are understandably impressed by the size of the great Coastal Redwoods of the western United States – some of which grow to more than 350 feet tall – it is their age that I find most impressive. Some redwoods are 1,500 years old, signaling that their habitat has not been substantially disturbed by humans for many, many generations.
It is important here to make a distinction between natural disturbance and human-caused disturbance. All forests are subject to some degree of natural disturbance, such as from fire, flood, ice, wind, or extreme temperature. The type of disturbance, along with its timing and intensity, acts to sculpt the type of forest you’d find in any given area. These natural disturbances also drive the regeneration of forests, keeping them healthy, alive, and able to provide the ecosystem services we rely on.
For example, eastern deciduous forests naturally have what is called gap disturbance. This is when a large canopy dominant tree falls, and takes out other smaller trees, creating a gap in the canopy. This opening allows sunlight to reach the understory releasing a new crop of trees. This type of disturbance creates a forest with various age classes spread across the landscape like a mosaic, with old trees and young ones, and an opportunity for high biodiversity.
Low intensity ground fires were another important, if lesser known, natural disturbance in our eastern forests. Before European settlement, it is thought that fires burned on dry ridges every six to eight years. This type of natural disturbance helped drive species across communities, and preferenced species that were adapted to low intensity fires (Figure 4) like white oak, instead of thin-barked trees like maples. Combined, natural disturbances shaped what our forest looked like before human intervention.
Now consider human caused disturbance. By removing the natural disturbance of low intensity fire, and by adding in large scale harvest techniques that didn’t mimic natural disturbances, we altered the natural ecosystem processes. (Compare clear cutting of a forest to the smaller scale of selective harvest where just one or two trees are removed.) These disturbances shift forests out of the equilibrium maintained by natural ecosystem processes, and create a new type of forest that is less diverse, less resilient, and frequently more susceptible to invasion by pioneering invasive species.
Glen Helen has experienced myriad human disturbances over the past 200 years. These disturbances have created a mix of forest types with various quality levels. When we read the current forest in Glen Helen, we are able to observe and diagnose these past human disturbances Even though the Glen has existed as a nature preserve for nearly 90 years, we can still today find clues in the forest structure and species composition which suggest what type of disturbances and land management practices occurred in the past.
The northeast portion of the Glen, east of the Fire Road, is a fitting example. The current presence of standing dead Osage orange trees suggests that this area was pastured. Osage oranges were brought to the area to be planted as natural fence rows for livestock operations, and the trees migrated into the pasture because they aren’t palatable to livestock. As the pasture was abandoned these scattered Osages were overtopped by a crop of maple, ash, and cherry trees, which shading them out and eventually killed them. Looking at that part of the Glen you can still see the Osage ghosts of the forest past.
Not only was this part of the Glen denuded of forest cover, the soil there was heavily disturbed by pasturing and grazing animals. This explains directly why today we find no little to no herbaceous layer of wildflowers, but a strong presence of invasive bush honeysuckle. Even though it was 100 years ago, using that area for pasture disturbed the soil so much it essentially set the soil disturbance timeline back to zero, far from the thousands of years that the soils of the west coast redwoods have been able to exist undisturbed. Today, as you walk south along the Talus Trail, you can see how past management practices and disturbances created a stark contrast between what was the “Neff Glen” (the northermost part of Glen Helen, near what is now US Route 68 and State Route 343) and the “Shelden Glen” (the area south of the Neff property, but north of Grinnell Road).
The northern portion of the Talus Trail has a tremendous herbaceous layer, along with many different species of trees and age classes ranging from one-year old to over 200. There is also very little bush honeysuckle.
Once you cross the line into the Shelden Glen you can notice the dense layer of honeysuckle, and no herbaceous layer.
Visit in winter when the leaves are off the honeysuckle and you can see farther into the woods, and it becomes obvious that there are no large canopy trees present, and there is less age diversity among the trees. An aerial photo from 1926 (Figure 2) gives clues as to why these two adjacent areas are so different today. Below the old quarry at the corner of Corry St. and Grinnell Rd., you’ll notice bare eroded ground, which appear to be spoils from the quarry. That is a high soil disturbance which would lead directly to the poor conditions of the forest in that area today. However, when you look just north of the Neff-Shelden line, you see darker grey indicating more tree cover and less disturbed soils. This where we find our amazing display of wildflowers in the spring. Activities (or lack thereof) from a century ago are driving current conditions!
Connecting these disturbances from the past to current forest conditions is important for a land manager. For the past 100 years, the Glen has made a great recovery from the denuded landscape that it once was. In some areas, purposeful recovery efforts like the planting of the red oak and poplar trees helped stabilize the soil and move the ecosystem toward equilibrium. But mostly, it was the removal of anthropogenic soil disturbance that allowed mother nature the time and space to recover.
This is not to say that there aren’t unnatural disturbances still occurring in the Glen. These disturbances may not be as obvious as a clear cut or a forest being converted to agriculture, but they are helping to create a less stable ecosystem. The overabundance of the whitetail deer prevents new trees from growing into spaces left behind by dying old trees. A low diversity of invasive species occupy ecological niches that should be occupied by hundreds of native species. Uncorralled visitation leads to stream bank erosion as people stray from the trail and enter the creeks. Trails both sanctioned and rogue act as vectors for the spread of invasive species. A forest ecosystem is a complex web of life and death, with ebbs and flows of decay and growth. It is so complex that it is impossible for a human land manager to fully control its outcome. What I have learned, by understanding how past conditions have led to present conditions, is that the best thing I can do to ensure success is to remove myself as much as possible, let mother nature be my guide, and maintain as light a touch as possible.
This story first appeared in the Winter 2018 print edition of “In the Glen” Magazine.