Some tree leaves will fall 3-6 days in advance by end of century due to climate change: Study
Berlin: A large-scale study of European trees suggests that the leaves of trees between the tropics and the polar regions of the Earth will start to fall in advance by three to six days by the end of the 21st century rather than lengthening by one to three weeks as current models have predicted.
The scientists, including those from the University of Munich (LMU) in Germany, said earlier studies had predicted that the shedding of leaves from these temperate trees will get later under the ongoing climate crisis.
They said early observations also supported this idea since warming caused leaves to stay on the trees later over recent decades, driving increased growing season length that could help to slow the rate of climate change.
However, the current study, published in the journal Science, showed that this trend might be reversed as increasing photosynthetic productivity begins to drive earlier autumn leaf fall or senescence.
According to the researchers, the results build on growing evidence that plant growth is limited by the ability of tree tissues to use and store carbon.
While changes in the growing-season lengths of temperate trees greatly affect global carbon balance, they said future growing-season trajectories remain highly uncertain since the environmental drivers of autumn leaf senescence are poorly understood.
Autumn leaf-shedding at the end of the growing season in temperate regions is an adaptation to stressors, such as freezing temperatures, the scientists explained.
While a common assumption is that alleviating a warmer climate could allow leaves to persist longer and consume more atmospheric carbon, the researchers said the role of photosynthesis in governing the timing of leaf senescence has not been widely tested in trees.
In the current study, the scientists used long-term observations from dominant Central European tree species from 1948 to 2015, and experiments designed to modify carbon uptake by trees, to evaluate related impacts on senescence.
"Accounting for this effect improved the accuracy of senescence predictions by 27 to 42 percent and reversed future predictions from a previously expected 2- to 3-week delay over the rest of the century to an advance of three to six days," the scientists wrote in the study.
The data revealed that increased growing-season productivity in spring and summer due to elevated carbon dioxide, temperature, or light levels can lead to earlier -- not later -- leaf senescence.
This is likely because roots and wood cease to use or store leaf-captured carbon at a point, making leaves costly to keep, the study noted.
The model built by the researchers forecasted the possibility of slight advances, no delays, in autumn leaf-dropping dates over the rest of the century.
According to the scientists, the results "substantially lower our expectations of the extent to which longer growing seasons will increase seasonal carbon uptake in forests".
However, they said the universality of this pattern in other forest types remains unknown.
The researchers believe it is important to implement such growing-season length constraints in other models that do not consider these dynamics.
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US VP JD Vance says Lebanon not part of ceasefire, calls it ‘misunderstanding’
Budapest/Washington: US Vice President J D Vance has said that Lebanon was never included in the ceasefire understanding with Iran, describing the confusion as a “legitimate misunderstanding”.
Speaking to reporters before departing from Hungary, Vance said, “I think the Iranians thought that the ceasefire included Lebanon and it just didn’t. We never made that promise.”
He stressed that the United States had not included Lebanon in the scope of the ceasefire at any stage.
His remarks come amid continued Israeli strikes in Lebanon, where more than 200 people were reported killed, even as ceasefire talks between Iran and the US move forward.
Vance said Israel had “offered … to check themselves a little bit in Lebanon because they want to make sure that our negotiation is successful”.
He warned that if Iran allows the situation in Lebanon to affect the negotiations, it could derail the talks.
“If Iran wants to let this negotiation fall apart in a conflict where they were getting hammered over Lebanon, which has nothing to do with them and which the United States never once said was part of the ceasefire, that’s ultimately their choice,” he said.
