Researchers in New Zealand say they've identified extensive changes in the growth patterns and timing of the planet's tree leaf activity in the last few decades.
Their findings, a first global assessment of changes in the seasonal pattern of vegetation activity, could signal significant ecological and atmospheric consequences, they say.
Those seasonal patterns of the timing of leaf emergence, growth, and death -- known as leaf phenology -- are influenced by environmental cues including temperature and rainfall.
However, scientists at the University of Otago point out, they can also be influenced by the concentration of atmospheric CO2.
Changes in the environmental and atmospheric cues have been tied to early leaf emergence in North America and Europe, but other parts of the world, particularly in the Southern Hemisphere, have been less studied, they say.
"For the first time, we have shown that equally severe changes have occurred over large regions of Africa, South America and Australia," study leader Steven Higgins explains. "Overall we found that the phenological signature of 95 percent of the Earth's land mass has altered with 54 percent changing substantially.
Such drastic changes could present higher extinction risks for some animal species that depend on the particular timing of leaf phenology cycles, he says, noting there have already been such occurrences in the Northern Hemisphere.
For examples, he says, "several bird species have already experienced population losses due to the effective seasons moving out of sync with their life-cycles, and similar changes have been reported for insect pollinators and even large mammals such as deer," he says.
In addition, leaf changes will probably have significant influence on the stability and functioning of ecosystem, along with impacts on the carbon and energy exchange between the Earth's surface and its atmosphere.
It could also have unforeseen effects on global agriculture, the researchers report in the journal Nature Climate Change.
For the study the researchers analyzed satellite data on world vegetation coverage and character gathered between 1980 and 2012.
The techniques developed for such analysis offer a direct and sensitive way for measuring changes in how our planet's land surface is "breathing," Higgins says.
"We now have a tool that will be useful for both monitoring ongoing change and measuring the reliability of early warning indicators of catastrophic ecosystem state changes," he says.
