The threat of climate change for tropical plants.

Tropical plants closest to the equator are most at risk from climate change because they are expected to become too hot for many species to germinate in the next 50 years, researchers at UNSW discovered.

Their study analyzed nearly 10,000 records of more than 1,300 species from Kew Gardens’ global seed germination database.

The research, published in the magazine. Global Ecology and Biogeography Recently, he was the first to analyze the global impact of climate change on such a large number of plant species worldwide.

Lead author Alex Sentinella, UNSW Ph.D. The researcher said that previous research had found that animal species closest to the equator would be at greater risk from climate change.

“The idea was that because tropical species come from a stable climate where it is always warm, they can only cope with a narrow range of temperatures, while species at higher latitudes can cope with a broader range of temperatures because they come from places where the climate varies a lot, “Sentinella said.

“However, this idea had never been tested for plants. Because climate change is a huge problem globally, we wanted to understand these patterns on a global scale and build on the numerous individual plant studies in their environment”.

Seeds a key indicator of survival

The researchers examined seed germination data from the Millennium Seed Bank Partnership Data Warehouse, hosted by Kew Royal Botanic Gardens in London, to quantify global germination temperature patterns.

They analyzed 9,737 records of 1,312 plant species from all continents except Antarctica, and excluded agricultural crops.

Mr. Sentinella said they chose the seed data because it was widely available and relevant to a species’ ability to cope with different temperatures.

“With seeds, you can experiment with them quickly, there are many studies on them and, most importantly, germination is directly related to how a species will survive, because if the seed does not germinate, the plant will not live” , said. .

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

The researchers also examined weather data for the same locations as the plant species used in the study.

They analyzed the current temperature, the average temperature of the three warmest months from 1970 to 2000, and predicted the temperature by 2070.

The researchers then compared the temperatures the plants were now experiencing with the temperatures predicted for 2070.

Tropical plants to reach or exceed temperature limits

The study found that tropical plants do not have tighter temperature tolerances, but were at greater risk from global warming as it would bring them closer to their maximum seed germination temperatures.

Sentinella said that, on average, the closer a plant was to the equator, the more risk it would run of exceeding its temperature ceiling by 2070.

“These plants may be at higher risk because they are close to their upper limits. Therefore, even a small increase in temperature due to climate change could push them to the limit,” he said.

“The numbers 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 will not germinate and therefore cannot survive.”

Mr. Sentinella said the researchers also found that more than half of tropical species are expected to experience temperatures above their optimal germination temperatures.

“That is even worse because if those plants can survive it would be at a reduced germination rate and therefore they may not be as successful,” he said.

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

Sentinella said she was surprised to discover 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 have a hard time surviving the impact of climate change because they have closer temperature tolerances, was not true for plants,” he said.

“We found that regardless of latitude, plant species can germinate at approximately the same temperature range, which is not in line with animal studies.”

The researchers also found that 95 percent of plant species at latitudes above 45 degrees are expected to benefit from warming, because environmental temperatures are expected to approach the species’ optimal germination temperatures.

Findings to Help Focus Conservation Efforts

Sentinella said it was possible for some plants to evolve slowly at increasing temperatures, but it was difficult to predict which ones would survive.

“The problem with the rapid change in predicted temperatures is that some species will not be able to adapt quickly enough,” he said.

“Sometimes plants can migrate by starting to grow further away from the equator or, on the side of a mountain where it’s colder. But if one species can’t do it, it will become extinct. There are almost 400,000 species of plants worldwide, so we would. ” hope some of them won’t germinate between now and 2070. “

Sentinella hopes the researchers’ findings will help conserve plant species threatened by climate change.

“Ideally, we could conserve all ecosystems, but funding just doesn’t exist. Therefore, our findings could help conservation efforts to target resources to areas that are more vulnerable,” he said.

“We also hope that our findings further strengthen the global body of research on the risks of climate change. Humans have known about the dangers of climate change for decades and already have the answers to address it. Therefore, we hope that our study will help. to encourage people and policy makers must take action now. ”