Global plant species at peril from climate change as habitats shrink

As climate change becomes an ever more major cause of species extinction, changing and frequently diminishing the ​habitats that the plants require to exist, some of the plants that make familiar landscapes unmistakable may not survive by century’s end, scientists say.

Researchers modelled future ranges for many species of vascular plants, a category that includes practically all the world’s plants – those with water- and nutrient-carrying tissues. They analysed more than 67,000 species, almost 18 percent of the world’s known vascular plants.

They showed that between 7% and 16% might lose more than 90% of their range and face a significant danger of extinction. They include the rare California indigenous tree Catalina ironwood or island ironwood, azure spike-moss from a plant lineage stretching back more than 400 million years and about one-third of Eucalyptus species, one of Australia’s most recognisable plant families.

They arrived at their figures by studying millions of records of where plants are found and scenarios of greenhouse-gas emissions in 2081-2100.

A plant’s habitat is not just a location on a map, but the whole set of variables it needs: temperature, rainfall, soils, land use and landscape elements such as shade.One way to think about this is to imagine plants trying to track a moving “climate envelope.” ​As the temperatures warm up, many species can move north or uphill to stay cool enough. But temperature is only half of the story,” Junna Wang, a postdoctoral researcher at Yale University, and ​ Xiaoli Dong, a professor of environmental science and policy at the University of California, Davis, said in a joint comment to Reuters.

Wang and Dong contributed to lead the study published in the journal Science .

In many places, the study found, climate change is causing these combinations to diminish, leaving fewer places where all the conditions that a species needs are still found together.

Movement, or dispersal, for plants normally happens over generations, through seeds or spores ​carried by wind, water, animals or gravity. But when the researchers compared realistic migration to a scenario where plants could reach any new suitable environment, the rates of extinction were fairly similar.If slow mobility were the main concern, then dispersal should be allowed to be infinite, and that should drastically minimise extinction danger. But that is not what we discovered,” Wang and Dong said.

That matters conservation. “If dispersion constraint is the main cause, then measures such as aided migration – physically enabling species to relocate to new places – could eliminate most of the problem. But if climate change is diminishing the quantity of the right habitat on the whole, then simply assisting animals relocate may not be enough,” they added.

The expected impacts differ by region. Extreme cold regions are disappearing and Arctic cold-adapted flora may lose habitat. Drier places like the western United States and Mediterranean-climate areas are likely to see more severe drought, lower soil moisture and more frequent wildfires. Coastline movements towards the pole may be restricted in southern and eastern coastal Australia.

At the same time, local plant diversity could increase across about 28% of Earth’s land surface as species move into newly suitable areas, including parts of the tropics and subtropics where increased rainfall, rather than temperature alone, could make conditions suitable for additional species, the researchers found.

They called it a worldwide reshuffling, with some species vanishing from sections of their historical range while others relocate into new places, but noted local improvements do not suggest plants are doing better overall.

These changes might also result in the creation of “novel communities” – combinations of plants that have not coexisted historically, but would start to meet each other for the first time. What might these exchanges be like? The researchers said they do not know.

Most terrestrial ecosystems are underpinned by plants. They retain carbon, stabilise soils, sustain wildlife and supply food, timber, medicines and other commodities . So changes in plant diversity can cascade through ecosystems and humanity.If vegetation cover decreases because of climate change, ecosystems might absorb less carbon dioxide from the ​atmosphere, which might make warming worse. That produces a feedback loop, in which climate change hurts plants, and decreasing plant cover/productivity, in turn, worsens climate change,” Wang and Dong added.”Ultimately, conserving plant diversity is not just about saving nature for nature’s sake – it is about conserving the ecological systems that underpin human societies,” they stated.