Plant biodiversity at risk as climate changes #Impact #ClimateChange

A report based on fossilised evidence reveals that plant biodiversity in Europe and North America is changing profoundly as the world heats up.

By mid-century, the woodlands, grasslands and shrubs of Europe and North America will have changed. Scientists have used fossilised evidence from the last 21,000 years to build up a picture of how vegetation responds to climate change. And the message is: it does. And, sometimes, it responds poorly.

“It means that our own grandchildren will encounter largely different landscapes compared to those we know today,” says David Nogués-Bravo, of the Natural History Museum of Denmark in Copenhagen, who led the study. “They will see new species in forests, on prairies and scrublands, while other species that are common in those areas today will be gone.”

Future plant biodiversity

He and colleagues from the UK, the US and Switzerland report in the journal Nature Climate Change that they addressed the big question: what will happen to the plant biodiversity of two continents as the world warms and climates change in response to increasing emissions of greenhouse gases?

The question has been repeatedly addressed by biologists and conservation authorities: their observations, and their simulations of future climate change, have variously shown greater risks of extinction for birds, for mammals, for amphibians and reptiles, and even for trees.

That does not mean that global warming will of itself extinguish species, but it does mean that those wild things already threatened by the expansion of agriculture and the clearing of the forests, or by chemical pollution, or invasive species, or simply by the loss of habitat, will become increasingly at risk as global temperatures rise and climate regimes shift.

But Dr Nogués-Bravo and his colleagues looked not at the future, but at the lessons of the past, preserved in museum and botanic garden archives. They examined fossilised pollens of 100 European plant species found in 546 sites, and 87 North American pollens from 527 places.

From this data, they were able to build up a picture of how vegetation shifted at the end of the last ice age, when the ice sheets retreated and global temperatures rose by 4°C or 5°C, which is about the level of change predicted for this century, unless nations commit to drastic action.

And the message is: climate change alone is not likely to cause outright extinction. But one-third of North American plants and more than half of all European plants may face what conservationists delicately call “increased threat status” because of future climate change.

“We can see that ecosystems were transformed by past
climate changes, for ecosystems both on land and in
waters, and across many regions. Thus we can expect
profound changes throughout the Earth”

That prediction does not include increased threat from a human population likely to reach 9 billion before the end of the century, and a massive expansion of the cities.

The study is concerned with the big picture, and the researchers do not identify the species at risk. But, according to evidence from separate research, Dr Nogués-Bravo told the Climate News Network, some characteristic plants could disappear from their existing homes.

Empetrum nigrum or the crowberry is a mountaintop shrub common across Europe and the US: it survived climate change 10,000 years ago even in the southern Mediterranean and still clings to life on just three summits in the Cantabrian mountains of Spain. Further warming might finish it off.

But even if it doesn’t, it is still at risk, because ski resorts in the same region now attract 200,000 visitors a year. “So several factors contribute to endanger species,” he says.

And in the Central Range of the Iberian peninsula, change, too, is on the way. Ice age relicts such as Scots pine (Pinus sylvestris) and European beech (Fagus sylvatica) still have a foothold, but climate change will favour the more drought-hardy species such as the evergreen holm oak (Quercus ilex ballota) or the Aleppo pine (Pinus halepensis).

Global implications

The research began with evidence from Europe and North America, but the implications for plant biodiversity are global.

“The fossil record gives us a natural model system for studying species’ responses to climate change,” says Jack Williams, professor of climate, people and environment at the University of Wisconsin-Madison, and one of the authors.

“We can see that ecosystems were transformed by past climate changes, for ecosystems both on land and in waters, and across many regions. Thus we can expect profound changes throughout the Earth.”