North American plant biome resilience ‘hints at mass extinction’

A mass extinction not seen in 13,000 years may be on the horizon due to human activity and climate change, cautions a new study.

The warning comes as the resilience of North American’s plant biomes is declining, suggesting present-day landscapes are ‘primed to herald a major extinction event.’

Scientists analyzed over 14,000 fossil pollen samples from 358 sites across the continent in order to reconstruct the landscape resilience, which is a habitat’s ability to persist or rebound after being disturbed.

The results show that it can take up to three centuries for landscapes to recover, but only 64 percent of biomes are restored to their original state.

The team found that landscapes today are experiencing resilience lower than what occurred at the end of the Pleistocene megafauna and animal extinctions some 12,700 years ago.

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The study was conducted by researchers at the Georgia Institute of Technology, who analyzed 14,189 fossil pollen samples taken from different sites in North America.

The samples were used to determine landscape resilience, such as observing how long certain landscapes existed and how well they bounced back after disturbances such as natural disasters or human destruction.

According to the authors: ‘Our work indicates that landscapes today are once again exhibiting low resilience, foreboding potential extinctions to come.’

‘Conservation strategies focused on improving both landscape and ecosystem resilience by increasing local connectivity and targeting regions with high richness and diverse landforms can mitigate these extinction risks.’

The researchers studied 12 major plant biomes in North America that lived over the past 20,000 years using pollen data from the Neotoma Paleoecology Database.  

The Neotoma Paleoecology Database contains fossil pollen and spores that are found in lake and mire sediments. 

The study used pollen data from five forest types: forest-tundra, conifer/hardwood, boreal forest, deciduous forest, and coastal forest; five shrub/herb biome types — Arctic vegetation, desert, mountain vegetation, prairies, and Mediterranean vegetation; and two no-analog biome types — spruce parkland and mixed parkland. 

Jenny McGuire, assistant professor at Georgia Tech, said: ‘We find that the retreat of North American glaciers destabilized ecosystems, causing large herbivores — including mammoths, horses, and camels — to struggle for food supplies.’

‘That destabilization combined with the arrival of humans in North America to land a one-two punch that resulted in the extinction of large terrestrial mammals on the continent.’

The fossil pollen samples told the team that over the past 20,000 years, forests were able to thrive longer than grassland habitats – 700 years versus 360 years.

However, when disturbed, their ability to re-establish to their previous state decreased to 360 years versus 260 years.

‘These findings were somewhat surprising,’ said McGuire.

‘We had expected biomes to persist much longer, perhaps for thousands of years rather than hundreds.’

The analysis also revealed that  forests and grasslands rapidly transition when temperatures are changing fast, and that the landscapes recover faster when the ecosystem contains high plant biodiversity. 

However, the team also found that not all biomes recover, as the study revealed just 64 percent are capable of regaining their original biome type – but the process can take up three centuries to complete.

And it was Arctic systems that were least likely to recover, the study found.  

‘Identifying the tempo and mode of landscape transitions and the drivers of landscape resilience is critical to maintaining natural systems and preserving biodiversity given today’s rapid climate and land use changes,’ the authors wrote. 

‘However, resilient landscapes are difficult to recognize on short time scales, as perturbations are challenging to quantify and ecosystem transitions are rare.’