Climate Change-Driven Extinction of Alpine Plant Species May Go Undetected

Researchers worry that current methods for tracking extinction could be missing important data about the relative health and distribution of species.

Researchers working in the Austrian Alps warn that current models may be missing the impending extinction of alpine plants that are unable to migrate from or adapt to a warming climate.

While current models tend to look for the mere presence or absence of a plant species as the primary indicator of how well they are adapting to changing climate conditions, a team of scientists at the University of Zurich say that they’re missing important data — namely, the density and age structure of these populations.

“For now, presence or absence at a given location has been the model, but even if you have the presence of the species, it may be doing quite badly,” said evolutionary biologist Frédéric Guillaume, who led the study published today in Nature Communications.  

Guillaume and his team have developed a model that they hope will address this problem, specifically for alpine species that face a unique risk of extinction. Given the inherent limits to their range — constrained to pyramid-shaped mountaintops — and the longevity of alpine plants, they are particularly ill equipped to evolve to warming conditions.

Of particular concern is the age structure of alpine species, which are highly endemic and considered especially vulnerable to climate change. Much like an aging human population, the three alpine flower species and one alpine grass species targeted in the study are failing to produce viable replacements for the aging plants, creating what authors refer to as an “extinction debt.”

“The adults are adapted to a climate of the past, while juveniles must adapt to a new climate,” Guillaume explained. “By producing offspring with genes that were selected in a previous environment, they have a handicap evolving to the current environment.”

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If a critical number of juvenile plants don’t take root, the population thins and faces a “demographic deficit” that could eventually lead to its extinction. And because the alpine species included in the study live for a long time, they will appear in current models even if the population is both aging and thinning.

It is a challenge faced by any plant species with a small or geographically fragmented population, attributes that will make its evolution or adaptation to a changing climate more difficult. In the Alps, this scenario is further compounded by the fact that for these plants, the only way to go is up. They quickly run out of space and options. 

In the best case scenarios put forth by scientists — that warming will be limited to 1 degree Celsius compared to pre-Industrial Age levels — these populations could recover, so long as the warming slows after 2090, according to authors. But, if climate change continues unabated, alpine plants could face mass extinction.

What’s more, it could be a problem that will go undetected until it's too late, as current models cannot see what authors describe as the “invisible extinction debt.”

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This is where Guillaume and his team hope that they might be able to help. While he described their models as “quite data hungry,” requiring large amounts of information to fulfill the parameters, they believe that a more comprehensive model of threatened plant populations could be part of the key to saving them.

“In conservation terms, you can use this data for assisted migration, the facilitation of movements between populations, or to prioritize certain areas over others,” he said. Alternatively, older individual plants will persist in a worsening environment as the demographic decline slowly grows.

In this case, Guillaume added, “you might not see extinction coming.”

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