The bigger they are, the harder they fall

Vast, rich ecosystems that have existed for millennia could collapse in less than a human lifetime, according to a study published in the journal Nature Communications.

Although they take longer to crumble than smaller systems, simply because stresses take longer to spread across larger distances, the rate is relatively faster; “so a forest that’s 100 times bigger than another forest will take much less than 100 times the time to collapse,” says senior author John Dearing from the University of London.

That includes iconic ecosystems like the Amazon, he adds.

“Once deforestation and global warming stress the forest to the point that it reaches a tipping point, it could be a matter of a few decades before the whole forest shifts into a grassland.

“Other ‘large’ ecosystems like the highly diverse Caribbean coral reefs might take just a few years to turn into much more simple ecosystems with few species.”

Seeking to understand why clear water lakes in China had rapidly turned green, tainted by algal blooms, the group of UK researchers collected data from scientific publications, institutional reports and online databases on how long it takes ecosystems to shift from one state to another.

The 40 natural environments included lakes, coral reefs, marine fisheries and forests, ranging in size from small ponds to the black sea aquatic ecosystem. 

Once they found a relationship between the size of a system and the time it takes to shift states, defined as “the time taken to transition to a stable but functionally different system state”,  the team ran a series of computer models which confirmed this link.

The finding can be explained by the fact that larger ecosystems have subsystems, all containing a richer diversity of species and habitats. Initially, these can provide a buffer against stress, but once a certain threshold has passed, that same diversity can quicken its unravelling. 

It may help explain the rapid spread of uncontrollable bush fires recently seen in Australia. 

It also magnifies concerns about the impact of recent bushfires in the Amazon and the resilience of the Earth’s largest rainforest in the face of climate change – indeed, the authors warn that it could reach a tipping point as early as next year.

“The messages here are stark,” says Dearing.

“It’s yet another warning about the potentially irreversible damage that’s being done to global ecosystems – damage that threatens biodiversity, the food and other ecosystem services that we depend upon, the wellbeing of local communities, and the stability of other interdependent systems, like regional climate.

“And all happening much more quickly than we might think.”

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