By Jenevra Wetmore
My grandmother was born in 1916 and grew up in a Vermont without possums. The Virginia opossum (Didelphis virginiana), so peculiar in appearance with its naked tale and bare ears, is arguably not very well-suited for a cold climate such as ours. It wasn’t until the 1940s that the possum—North America’s only species of marsupial—made it to southern Vermont. I can guess that my grandmother in Hartland wouldn’t have seen one until the late 40’s or 50’s. I wonder what she must have thought the first time she ran across one. My grandmother, a lifelong nature observer and incredibly inquisitive person, might have wondered what brought the species this far north.
As it turns out, possums have traveled north to Vermont (and beyond) due to habitat destruction, urbanization, and climate change. Warmer winters mean that this marsupial, which dislikes deep snow and temperatures colder than 28 degrees, can now survive in Vermont. Now let’s compare my life to my grandmother’s life. I was born in 1994 and lived down the hill from my grandmother my entire childhood. I knew a Vermont that had possums already, and it didn’t occur to me that they hadn’t always been here until my grandmother told me. My perception of what was “natural” in Vermont was different from my grandmother’s reality.
This phenomenon is actually a common human experience, and has a name: Shifting Baseline Syndrome, or SBS. This term, coined by Professor Daniel Pauly, describes how new generations accept the conditions they are born into without the context or information of past generations. Because our “baseline” of the natural world shifts over time, we do not have a true understanding of how much the natural world has been degraded. This amnesia can take place generationally, as it did with my grandmother and I, or personally when people forget how things used to be in their own lifetimes.
Shifting Baseline Syndrome matters because it affects how we make environmental and conservation decisions today. A good example of this is the gray wolf population in the Western US, particularly in Yellowstone National Park. Colonization meant westward expansion of Europeans, who brought livestock. Colonizers sought to eliminate animals that preyed on their livestock, including wolves, bears, cougars, and coyotes. From the late 1800’s to the early 1900’s predator control was common practice at Yellowstone, including poisoning. Between 1914 and 1926 at least 136 wolves were killed in the park; by the 1940s, wolf packs were rarely reported.
In the mid 1990s the Fish and Wildlife service began reintroducing wolves brought from Canada to Yellowstone. This was a controversial move; many local ranchers and hunters were opposed. In addition to concerns over wolves killing livestock near Yellowstone, some were worried that they would decimate the elk herds. No one remembered a time when they had been part of the ecosystem. Now we know that bringing wolves back stabilized elk populations by stopping the extreme boom and bust population cycles of elk that had been occurring since the wolves left, which resulted in elk starvation. Wolves leveled out the populations, fitting into the ecosystem they belonged to originally.
How can we work to address shifting baseline syndrome? How can we truly understand how the natural world is changing before our eyes, and how it has changed from the past? SBS still needs more research and is a relatively young theory, but the solutions needed seem to be what we humans have been doing for millennium: storytelling. Passing on generational knowledge of what nature looked like even a few decades ago is vital to help young people understand how much things have changed. Studying history to look at old photographs and diaries can help us understand what areas looked like before development, and what animal species were prevalent in the past compared to now.
We can also work to make sure that data on what the world is like now is recorded. Even if you are not a scientist yourself, you can engage in citizen science. Use INaturalist to record sightings of mammals, birds, fish, insects, fungi, and plants. You can use EBird and EButterfly, and participate in amphibian road crossings to record sightings of these specific species.
The natural world here in Vermont has changed so much just in my lifetime. As a child I never worried about ticks or Lyme disease because I never got ticks when I spent time in the woods. Now Vermont’s 3-year average incidence rate for Lyme disease is the second highest in the US.My parents once “tapped out” our sugarbush during the February school break every year, but this spring some people were already making syrup as early as January. The reality of my childhood is now long-gone. It is our responsibility to preserve these memories, and to tell younger generations about the “old” Vermont. If we don’t understand what we have lost, how can we fight for what we have?
The naked tail and ears of possums living in the North Country often get frostbite, which is likely how the possum in this photograph lost the tip of its tail. Photo by Maddy Weiss on Unsplash