This time inspired me to examine the potential for large-scale rewilding on my home continent, where, unlike what was occurred in the EU, rewilding has not been adopted as a major government policy. What happens when places become more "accidentally wild"? Where can we make them more wild? Where can we make space for other beings?

Minnesota, where I live, is the only state in the continental US not to lose its wolf population after the arrival of white settlers. Minnesota's wolves have received lots of national attention since their low point in the 1970s, especially for their spread into neighboring Wisconsin and Michigan. What has gotten less press, however, is the increase in the density of the wolf population.

I followed the work of Yale ecologist Oswald Schmitz, who modeled wolves' contributions to carbon sequestration on Isle Royale, just a few miles east of Minnesota in Lake Superior. Schmitz, working on the assumption that wolf presence on the island reduced the number of moose found that the lower number of moose increased the amount of carbon the forest could capture (from between 0.11 to 0.23 tons per acre).

What are we looking at?

Credit: Minnesota DNR, 2014

1. Biodiversity solutions are climate solutions

   Rewilding is important because it does not view wildlife recovery and reducing carbon emissions as two separate goals. They are both part of restoring function to landscapes. Minnesota's annual carbon emissions are lower because of protections placed on wolves through the Endangered Species Act. Their southward spread and increase in density mean that the state's forests store more carbon in 2026 than they did in 1999.

2. It shows us what happens when we make ourselves smaller

   This is important in a few ways. First off is that the carbon benefits of wolf protection happened accidentally! Allowing the biosphere to operate with greater autonomy, allowing land to exist with less human intervention, has knock-on effects on climate. What else might we see if that approach were taken in other policy areas, deferring to non-humans to carry out their own plans?

3. People and wildlife can thrive together!

   Over 730,000 people live inside wolves' range in Minnesota. Minnesotans are able to sustain a rural economy and one of the healthiest habitats for wolves in the Lower 48. Still, the region is home to commercial logging and mining, small-scale farms, and a massive tourism industry. There are ways for wildlife to exist on a human-populated landscape - things we do, and things they do. This in itself is a whole research agenda: how to live well alongside one another. There is a whole social, cultural, and political fabric behind meaningful carbon policy.

0.64 tons

of carbon per acre per year.

12%

of Minnesota's annual carbon emissions

*I converted DNR observations in each year (in addition to a baseline year from the 1989 wolf census), to Poisson point process models to account for observation bias (canopy cover, distance from roads, and a spatial autocorrelation term were included). I standardized PPM output to a distance of 0 meters from roadways.

**This model included covariates for all kinds of other factors that could account for changes in carbon biomass: plot-level random effects, yearly random effects, spatial autocorrelation, elevation, precipitation, snowfall, temperature, solar radiation, atmospheric carbon fertilization, human population density, change in farm acreage, ecoregion, dominant soil type, the time since a stand had been logged, a stand's protected status, and the kinds of disturbance which occurred at a USFS site during the five year inventory cycle. For more details on model specifics, please feel free to reach out.

If these numbers don't mean much to you, this figure is roughly equivalent to:

That model lets us produce a baseline for the hypothetical degree of carbon sequestration which would occur without wolves. From there, we can see how much of the carbon sequestration we see in the state is attributable to the presence of its wolf population. The results are staggering.

Across their range, from 1999 to 2018, wolves in Minnesota have helped to sequester:

15 million tons

of carbon per year, or

Above- and belowground carbon sequestration attributable to grey wolves in Minnesota

As wolves have recovered in Minnesota, we can model their effects on carbon across the state. The US Forest Service maintains around 17,000 plots in Minnesota, and takes rigorous data on the trees inside these plots every five years. This makes it possible to quantify the change in forest carbon on a five year cycle virtually anywhere in the country. The MN Department of Natural Resources monitored wolves over that same period, also at roughly 5-year intervals.

I used a generalized additive model to model the spatially varied effect of standardized wolf population density* on forest carbon sequestration.**

When we map out these changes, what is especially notable is how much carbon is sequestered in the southern reaches of the wolves' range! These are places where wolves are either just now establishing themselves, or where, while they may have been present earlier on, population numbers have just now gotten space to recover.

These figures may seem large, but they are largely in line with findings by ecologists. Schmitz's figures from Isle Royale capture carbon sequestration in a place where wolves have been present for nearly 80 years, and these figures parallel per-acre values this model produces for the nearby Arrowhead region in Minnesota, where wolves were never extirpated. What the spatial variation in carbon storage suggests is that wolves play a significant role in improving ecosystem health where they are new to the landscape (or at least where they are new to the landscape in large numbers).

Why does any of this matter?

Where else can we rewild?