Tropical plants near the equator face an uncertain fate

Tropical plants near the equator are severely threatened by climate change. Scientists at the University of New South Wales report that over the next five decades, it will become too hot for many tropical plant species to germinate.

The researchers analyzed data from the Kew Gardens’ global seed germination database, including nearly 10,000 records for more than 1,300 plant species.

The analysis is the first of its kind to investigate the potential consequences of climate change for such a large number of plant species.

According to study lead author Alex Sentinella, past research has established that animal species near the equator have an elevated risk from climate change.

“The thought was that because tropical species come from a stable climate where it’s always warm, they can only cope with a narrow range of temperatures – whereas species from higher latitudes can cope with a larger range of temperatures because they come from places where the weather varies widely,” said Sentinella.”However, this idea had never been tested for plants.”

“Because climate change is a huge issue globally, we wanted to understand these patterns on a global scale and build upon the many studies on plants at an individual level in their environment.”

The seed germination data examined for the study represented plant species from every continent except Antarctica.

Sentinella explained that the team chose seed data because it was widely available and relevant to the ability of a species to cope with different temperatures.

“With seeds, you can experiment on them quickly, there are a lot of studies about them and importantly, germination directly relates to how a species will survive, because if the seed doesn’t germinate the plant won’t live,” said Sentinella.

“So, we collated the data from the Kew Gardens database, examined all experiments on the same species from the same locations, and then determined the range of temperatures each species could tolerate in order to survive.”

The researchers compared the warmest months from 1970 to 2000 to the temperatures predicted for 2070. The study revealed that global warming will push tropical plants to their maximum seed germination temperatures. On average, the closer a plant is to the equator, the more at risk it is of exceeding its temperature limit by 2070, according to Sentinella.

“These plants could be more at risk because they are near their upper limits. So, even a small increase in temperature from climate change could push them over the edge.”

“The figures are quite shocking because by 2070, more than 20 percent of tropical plant species, we predict, will face temperatures above their upper limit, which means they won’t germinate, and so can’t survive.”

The analysis showed that more than half of all tropical species are projected to experience temperatures which exceed their optimal germination temperatures.

“That’s even worse because if those plants can survive it would be at a reduced rate of germination and therefore, they might not be as successful,” said Sentinella.

“If a seed’s germination rate is 100 percent at its optimum temperature, then it might only manage 50 or 60 percent, for example, if the temperature is higher than what’s ideal.”

Sentinella was surprised to find that climate change would threaten so many tropical species.

“But our most unexpected discovery was that the hypothesis often used for animals – that those near the equator would struggle to survive the impact of climate change because they have narrower temperature tolerances – was not true for plants.”

“We found that regardless of latitude, plant species can germinate at roughly the same breadth of temperatures, which does not align with the animal studies.”

It is possible for some plants to adjust to warming temperatures over time, but it is difficult to predict which ones could survive.

“The problem with the quick change in temperatures forecasted, is that some species won’t be able to adapt fast enough.”

“Sometimes plants can migrate by starting to grow further away from the equator or, up a mountain slope where it’s cooler. But if a species can’t do that it will become extinct.”

“There are almost 400,000 plant species worldwide – so, we would expect a number of them to fail to germinate between now and 2070.”

“Ideally, we would be able to conserve all ecosystems, but the funding is simply not there. So, our findings could help conservation efforts target resources towards areas which are more vulnerable. We also hope our findings further strengthen the global body of research about the risks of climate change.”

“Humans have known about dangers of climate change for decades and we already have the answers to tackle it. So, hopefully our study will help encourage people and policy makers to take action now.”

The study is published in the journal Global Ecology and Biogeography.

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By Chrissy Sexton, Earth.com Staff Writer