By analyzing 46 years’ worth of data on bird distributions, collected via the North American Breeding Bird Survey, which included about 400 bird species found within a 250-mile-wide transect stretching from Texas to North Dakota, the researchers have found that the northernmost ecosystem boundary has moved about 365 miles north. Furthermore, the southernmost border has moved about 160 miles north since 1970.
The researchers noted that their findings could help develop an early-warning system that would give land managers decades to prepare for ecosystem shift or collapse, thus allowing them to accommodate or foster the change rather than simply reacting.
These results, published in Nature Climate Change, have also proven that ecological shifts are actually more ordered and predictable than previously thought.
“If we can work toward prevention (of changes), we’re going to save ourselves so much money and time,” said lead author Caleb Roberts, a postdoctoral researcher at Nebraska. “We won’t have to worry about specific endangered species, perhaps, because we will be protecting the system they require.”
Upon collecting and analyzing the 400 bird species from the North American Breeding Bird Survey, the team separated the species into groups based on their body masses. They then searched for gaps in the distribution of the groups.
“All (these breaks) are saying is that there are a lot of animals with the small body size; then there’s a gap with nothing in this middle body size; then you have another group and another group,” said Allen, director of the University’s Center for Resilience in Working Agricultural Landscapes. “And since these reflect the domains of scale in an ecosystem, it’s like a signature — the DNA — of a given ecosystem.”
The researchers were then able to measure how much and how fast each ecosystem shifted north by analyzing the geographic movement of the distinct body-mass signatures throughout the near 50-year period.
The phenomenon of the northernmost boundary shifting more than the southernmost is called “Arctic amplification,” and suggests that climate change is to blame. This shift aligns with other global change drivers like upticks in wildfires, the invasion of woody plants like eastern red cedars, energy development, urbanization, and agricultural land conversion.
“Like most things in ecology, (these shifts) likely have multiple causations,” Allen said. “And I think it’s fairly intractable to try to separate, say, tree invasion from climate change, because it has to do with fire but also with changing climate. All of these things are highly related.”
Roberts noted that grasslands are the most endangered global ecosystem due to woody plant invasion. People can get involved in saving the grasslands by increasing burning and tree removal.
“Those are all things we can do and use the early warning to say, ‘We’re coming to the edge of this grassland’s resilience. It’s about to collapse, especially in our area. What can we do to stop that?’ That’s the kind of power this tool would have,” he said. “You don’t have to wait until it gets to you. You can see it coming and act preemptively.”
“We are working closely with a long list of partners to understand how to navigate these types of transitions and increase the performance of conservation investments,” said Dirac Twidwell, associate professor of agronomy and horticulture. “Large-scale transitions should not be underestimated. Restoring what has been lost has proven extraordinarily difficult when the challenge spans large geographic regions.”
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