A century of warming has extended the annual growing season of hardwood by a month on average, researchers studying them in northwest Ohio have said .
In the research they said has implications for how well different types of trees will cope with future climate change, scientists from Ohio State University compared recent observations to detailed notes a local farmer began taking in the 19th Century.
Between 1883 and 1912, farmer Thomas Mikesell made meticulous notes on local tree growth, precipitation and temperature in his home town of Wauseon, Ohio.
The planet has warmed by 1.1C since the industrial revolution about 200 years ago with most of that occurring in recent decades. Researchers say Mikesell’s observations are a near unique pre-warming dataset to compare with modern times.
Lead author Prof Kellen Calinger-Yoak who travelled to Wauseon herself in Spring and Autumn between 2010 and 2014, to monitor seven different species of hardwood said that leaves stayed on trees about 15% longer than they did in Mikesell’s day.
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“Things are not the way they used to be – they are profoundly different. An entire month of growing season extension is huge when we’re talking about a pretty short period of time for those changes to be expressed,” said Prof Calinger-Yoak.
Species responded to warmer temperatures in different ways – most kept their leaf colour longer into Autumn but some budded early.
The implications of the longer growing period are unknown.
Trees are important in sucking planet-warming carbon dioxide out of the atmosphere, and the researchers said a longer growing period probably meant they did more of that. However, they warned that higher, fluctuating temperatures may also stress trees in ways so far unknown.
Species reacted differently to higher temperatures. Prof Calinger-Yoak said that suggested more species-specific research was needed with regard to the role of tree-planting in limiting climate change.
“When we’re thinking about a relatively low-cost mitigation strategy, planting a whole bunch of trees that suck CO2 out of the air is a really good strategy, but to promote those activities you also have to have evidence of the level of benefit you’d derive from it,” she said.
Story was adapted from the BBC.