From Disturbance Comes Resilience

By Ben Sebastian, Land Steward

In late June, a massive storm swept through Bloomington, leaving Monroe County to declare a state of emergency due to fallen debris, power outages, and infrastructure damage. The sudden and intense winds caused several tangles of tree blowdowns at multiple Sycamore Land Trust properties comparable to damage caused by previous tornados. There was enough force to uproot even healthy and well-established trees leaving trunks as tall as city buildings to be strewn about.

Porter West Preserve, June 2024

Two properties that were hit the hardest were the Porter West Preserve and the Amy Weingartner Branigin Peninsula Preserve, which remained closed for the rest of the summer. The Stewardship Crew spent many scorching days meticulously working to clear and reroute trails to get these preserves back to a baseline for the community to feel safe to explore.

If you walked through one of these preserves soon after this storm, the initial reaction to the almost post-apocalyptic damage is likely disheartening. A more positive angle to look at these events is the idea of disturbance and its role in ecological dynamics.

Forest Succession illustrated by Mary Connors

Stage 1: Pioneer Stage

The process of forest succession begins with an introduction of “pioneer species,” generally within 1-2 years from a disturbance. These species are likely from groups like lichens, mosses, and annual grasses and forbs. These populations cultivate until there are changes to environmental conditions such as the soil type, light exposure, and nutrient availability.

Stage 2: Shrub Stage

These changes instigate competition which progresses the area into another successional stage with a composition more proliferate in perennial grasses, forbs, and shrubs which is indicative around 2 to 5 years from disturbance.

Stage 3: Young Forest

Shade-intolerant tree species begin to establish the understory between 3 and 30 years from disturbance.

Stage 4: Mature Forest

Eventually, the forest matures to encompass distinct canopy layers to the point that the environmental conditions and the biodiversity reach what can be described as a stable equilibrium until the next disturbance event.

A forest may be listed as an “old-growth forest” if the system has achieved an assumed equilibrium and is dominated by trees that are over 150 years old. Sycamore Land Trust has had the privilege of owning an 81 acre old-growth forest known as Hoot Woods in Owen County, which has individuals documented at over 350 years old!

Old-growth forest at Hoot Woods. Photo by Chris Fox

These types of forests are seen as the final stage of succession and are rich in community structure to stimulate a web of wildlife niches. These areas are known to be efficient in water filtration and storing greenhouse gasses, with soils dense in nutrients and microbial activity.

The novelty of the ecology that develops within these woods is dependent upon the frequency, type, and severity of disturbance events that take place throughout its growth history. This disturbance pattern will dictate how quickly the forest progresses through successional stages and can even revert the area back to a previous stage depending on the caliber of these events.

Areas that have had long periods without these events become dominated by fewer species of similar ages, leaving the canopy closed enough that shade-tolerant species begin to take over the understory. This more uniform biodiversity leaves these ecological communities to exhibit a lower adaptive resistance (ability to persist) and a lower adaptive recovery (ability to return to pre-disturbance conditions). The forest is now vulnerable to being wiped out by threats such as insects or disease if the proliferate species are those sensitive to this kind of infiltration.

A substantial disturbance provides a chance for other species that may be resistant to this threat type to thrive in this sudden habitat availability. This prevents an ecosystem collapse by assuring that resistant species will survive a potential threat and continue forest function. A distinctly complex forest biodiversity will also display resilience to disturbance events of different types, such as fire.

An effective example of this phenomenon of resilience via disturbance comes from studies of the role of fire in forest dynamics. Native Americans were methodical in prescribed burning practices as a way to control the plant community structure of the land around them. In the 20th century, wildfire suppression policies were put in place that promoted fire exclusion in many of these forests that were adapted to frequent fire disturbances. What followed was the buildup of dead vegetation and proliferation of fire-sensitive species in the understory. These areas now exhibit increased vulnerability to severe wildfire behavior as there is a higher occurrence of an ideal fuel type for the fire to continue expanding.

Climate change effects also contribute to the increasing prevalence of wildfires in the last century due to the rising occurrence of heat waves leaving forest ecosystems to stay drier for longer periods of time. This greatly increases the chances of a spark occurring and intensifies the severity that the fire may reach. This leads to a much higher level of destruction to the ecosystem leaving less capability for the forest to restore itself back to its original ecosystem value. In the 1960s, fire exclusion policies shifted, allowing the use of prescribed fire techniques as a conservation tool to moderate threats against our mature and old-aged forests.

Disturbance events, even those to the extremity of a summer storm, can have an optimistic outlook despite the calamity it can cause. What may be seen as a catastrophe can be viewed as a chance for renascence. The opportunity for resolution in a stagnant system can come from a point of dishevelment. The ability to adjust, improvise, and overcome will test the strength of the foundation in place. And the growth that occurs after such an occasion will redefine its constitution to defend against future threats.

This article is from the Fall 2024 issue of The Twig, “The Indiana Bat Issue.” Read more articles at sycamorelandtrust.org/twig.

Land Steward Ben Sebastian clears the trail at Amy Weingartner Branigin Peninsula Preserve. Photo by Chris Fox