Climate change threat to tropical plants

Date:
July 2, 2020
Source:
University of New South Wales
Summary:
Half of the world's tropical plant species may struggle to germinate
by 2070 because of global warming, a new study predicts.



FULL STORY ========================================================================== Tropical plants closer to the equator are most at risk from climate
change because it is expected to become too hot for many species to
germinate in the next 50 years, UNSW researchers have found.


========================================================================== Their study analysed almost 10,000 records for more than 1300 species
from the Kew Gardens' global seed germination database.

The research, published in the journal Global Ecology and Biogeography recently, was the first to look at the big picture impact of climate
change on such a large number of plant species worldwide.

Lead author Alex Sentinella, UNSW PhD researcher, said past research
had found that animal species closer to the equator would be more at
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," Mr Sentinella said.

"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." 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 patterns in
germination temperature.

They analysed 9737 records for 1312 plant species from every continent
except Antarctica and excluded agricultural crops.

Mr Sentinella said they 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," he said.

"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 also examined climate data for the
same locations as the plant species used in the study.

They looked at current temperature -- the average temperature of the
warmest three months from 1970 to 2000 -- and predicted temperature
for 2070.

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

Tropical plants to hit or exceed temperature limits The study discovered tropical plants do not have narrower temperature tolerances but were
more at risk from global warming, because it would bring them close to
their maximum seed germination temperatures.

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

"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," he said.

"The figures are quite shocking because by 2070, more than 20 per cent of tropical plant species, we predict, will face temperatures above their
upper limit, which means they won't germinate, and so can't survive."
Mr Sentinella said the researchers also found that more than half of
tropical species are expected to experience temperatures exceeding their optimum 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," he said.

"If a seed's germination rate is 100 per cent at its optimum temperature,
then it might only manage 50 or 60 per cent, for example, if the
temperature is higher than what's ideal." Mr Sentinella said he 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," he said.

"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." The researchers also found 95 per cent of plant species
at latitudes above 45 degrees are predicted to benefit from warming,
because environmental temperatures are expected to shift closer to the
species' optimal germination temperatures.

Findings to help target conservation efforts Mr Sentinella said it was
possible for some plants to slowly evolve to increasing temperatures,
but it was difficult to predict which ones would survive.

"The problem with the quick change in temperatures forecasted, is that
some species won't be able to adapt fast enough," he said.

"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."
Mr Sentinella hopes the researchers' findings will help to conserve
plant species under threat from climate change.

"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," he said.

"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."

========================================================================== Story Source: Materials provided by University_of_New_South_Wales. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Alexander T. Sentinella, David I. Warton, William B. Sherwin,
Catherine
A. Offord, Angela T. Moles. Tropical plants do not have narrower
temperature tolerances, but are more at risk from warming because
they are close to their upper thermal limits. Global Ecology and
Biogeography, 2020; DOI: 10.1111/geb.13117 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200702100414.htm

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