The Restorative Power of Ecosystem Disturbance

by Cate Nelson

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I spend many of my days working in conservation destroying things. I’m more likely to be cutting down shrubs, felling trees, removing biomass, burning savannas, and tearing out vegetation than I am to be planting, scattering seed, or nurturing new life. But destruction isn’t the end of the story in an ecosystem. Conservationists introduce disturbance in collaboration with nature’s incredible abilities to create. Our acts of destruction become opportunities for natural systems to generate diverse and resilient landscapes that will sustain native species.

The word conservation suggests protection, preservation. It sounds like pruning, trimming, and other gentle forms of maintenance. But Mother Earth doesn’t treat fragile things nicely. Natural systems have destruction built into them, whether through catastrophic events like floods, fire, and storms, or in more subtle disruptions like rivulets of rain eroding a slope, woodpeckers boring holes in trees, or deer tracing trails through the grassland. In ecology, the intermediate disturbance hypothesis is the idea that moderate levels of disruption are essential for the most stable and most diverse ecosystems. Keep everything all the same all the time, and you’ll find little variety in an ecosystem—the organisms most successful in those very specific conditions will outcompete most everything else. Think about uninterrupted, dark cave lakes with nothing in them but eyeless fish. However, if there’s too much destruction, nothing will be able to get its footing and begin to grow. A good example would be a beaten-down dirt trail—it’s walked upon too much for any brave little seed to take root, so it’s nothing but bare earth.The intermediate disturbance hypothesis encourages conservationists to introduce disturbance—to be moderately destructive—in order to encourage nature to move habitats towards more resilient and diverse communities.

The fellows have recently been doing a lot of work removing smaller trees and shrubs in dense, previously unmanaged forest. These forests have a robust understory, the sort of ecosystem where Hansel and Gretel could easily become turned around. You can’t see for further than a few yards, and it’s hard to maneuver through the branches and bushes. Despite being thickly vegetated, there are relatively few species. Instead, the understory is composed of dense patches of invasive species like black locust and buckthorn, or an overgrowth of aggressive native species like prickly ash and red oak saplings. Forests like these have their place and time, but aren’t always the most desirable ecosystem. Variety is the spice of life, but, because of a lack of management, forests are much more common across the state of Wisconsin than they were prior to European settlement. On the Leopold-Pines Conservation Area, in fact, floodplain forest was historically a rarer biome, as the property was once mostly oak savanna. At the Aldo Leopold Foundation, it’s a priority to return much of the land we conserve to the now-rare savanna ecosystem. Part of that process requires removing some of this woody habitat in order to reconstruct a savanna habitat. The end goal of this project is not the removal of vegetation, but enabling another kind of habitat to become established. Much of our brush removal has been along the boundaries of forested areas. Removing small woody stems at these borders is called “feathering the edge,” and it introduces a gradual shift between forest and prairie. These subtle gradations between forest and savanna will become nuanced edge habitat, with more possibilities for unique and subtle changes in species composition than a hard, harsh treeline isolating a prairie segment. In addition to introducing gradual shifts in habitat, sometimes our brush removal targets connectivity between areas. Many grassland birds abhor the vertical barrier that a dense stand of trees presents. Species like Henslow’s Sparrow won’t fly above a stand of pines, so opening a flyway—an open, minimal-tree region between two prairies—can expand a grassland bird’s usable habitat exponentially.

Another reason to remove undergrowth is that sometimes forests become overcrowded with small saplings, all of them stunted and competing for a chance at sunlight. Removing some of these saplings releases the remaining trees from this stress and competition, and gives them a better chance for living a full, lengthy, and happy life. A few trees are removed in hope of a healthier future forest.

Sometimes, the justification for removing small saplings or bush understories is fuels management: preparing the area for prescribed fire. In a dense patch of forest, the piles of branches and logs could create a huge, hot flame that would scorch standing trees as well as burning through dead ones. In areas where we want to maintain some canopy cover, removing smaller trees or some of the dead wood will protect living trees that we want to preserve. It’s a smaller sacrifice for a greater good.

Prescribed fire introduces disturbance and destruction on the land before, during, and after the burn crackles across the grasslands. In addition to fuels management, preparing for burns requires building burn breaks, which keep the fire burning “within the lines” of the landscape coloring book. Like moats made out of dirt, burn breaks are a zone with little to no flammable material, so they prevent fire from racing outside of the intended unit. Building these burn breaks requires mowing down the grasses, forbs, and vegetation along the burn break, then using industrial leafblowers to expose bare mineral earth. The result is a nearly lifeless stretch of soil. But again, these burn breaks are not the ultimate goal. Our objectives are to promote a healthier savanna, to rejuvenate a floodplain forest, to release nutrients into soil, to push back against invasive species: all hoping to promote land health and growth. It costs some vegetation along the edge of the burn unit order to prioritize the success of vegetation inside the region.

Putting fire on the landscape for conservation is an incredibly destructive process. A wall of flames can consume much of the vegetation, whether green and growing or shriveled and dry. Grasses and forbs turn to ash, and bare earth is exposed. Trees get thermally pruned: their lower leaves, exposed to heat and smoke, shrivel and die. After the burn, the landscape is black, and sometimes even the soil is burning, as small organic particles in the earth can smolder for hours. It initially looks like a charred wasteland, but the end of the burn is not the end of the story. The burning of organic matter releases nutrients like nitrogen, calcium, and magnesium into the topsoil. The bare areas left after fire expose the area to sunlight, permitting the growth of native species whose seeds have lain dormant in the soil for years and were shaded out by other vegetation. Within only a week or so, grasses may begin to poke tender green shoots through the newly fertilized soil, and the prairie begins to come back to life. The next spring, the grassland will burst into glorious life with greater species diversity and renewed vigor. We don’t burn for the joy of destruction. We burn because we have hope in the future and in the next season. We burn because we trust in nature’s resilience and its ability to rebuild. We burn in cooperation with creation.

Ultimately, conservation is not control. My work alone is not what powers and protects a native savanna ecosystem or supports a sandy marsh. Though most of my days may be spent taking away, removing, and disrupting, I’m working in conjunction with natural systems, relying on nature to build and grow in response to my actions. Living out a land ethic means treating the land as part of the community. We work to offer nature an active role in its own maintenance and health. Conservationists are facilitators, not constructors. Our work means little without the intervention and assistance of the ecosystems that we collaborate with. What is a burn without next spring’s blooms? Would felling trees matter if the savanna did not seed into the newly sunlit space that the oak and mulberry left behind? Could removing saplings mean anything if the trees that remained did not rejoice in the resources that become available to them? It’s a joy and a privilege to be able to cooperate with life itself in its cycles of disruption, loss, and most importantly, rebirth.