Bloomin’ Early

It’s become a hallmark of a warming climate: All across Europe and North America, farmers, gardeners and biologists are reporting that fruit trees and flowers are blooming earlier in the year. Scientists who study “phenology” – the link between climate and life cycles – have confirmed the trend by combing through record books going back hundreds of years. But similar historical data has been largely lacking from nations south of the Equator. A new study of fruit trees in South Africa, however, is one of the first to document how climate change is affecting flowering in the southern half of the globe.

The southwestern Cape of South Africa has become well known for its bountiful orchards full of apple, pear and cherry trees. To see if these trees are flowering earlier than they used to, Stefan Grab and Alessandro Craparo of the University of the Witwatersrand examined data collected by two large growers between 1973 and 2009. In particular, they charted flowering dates for three popular varieties of apple — Golden Delicious, Sayaka, and Granny Smith  — and one kind of pear, named Bon Chrétien. They also assembled temperature and rainfall records.

Overall, they found that the trees – which typically flower in October — are blooming about 6 days earlier than they did 37 years ago, they report in Agricultural and Forest Meteorology. On average, flowering dates have been advancing by 1.6 days per decade – while average spring temperatures have increased by 0.45 degrees Centrigrade per decade. Looking ahead, they predict that the trees will bloom about 3.6 days earlier for every degree rise in temperature. That’s less than advances seen in Germany, where blossoming dates have moved up 5 days per degree, but comparable to trends seen for cherry trees in Japan.

Rising temperatures alone may not explain the shift, the researchers note. It also correlates with changing rainfall patterns. This “combined role of temperature and water availability” is “likely complex,” they add, and highlights the need for researchers to consider both factors when evaluating how species and ecosystems may respond to a warming climate. David Malakoff | January 20, 2011

Source: Grab, S., & Craparo, A. (2011). Advance of apple and pear tree full bloom dates in response to climate change in the southwestern Cape, South Africa: 1973–2009 Agricultural and Forest Meteorology, 151 (3), 406-413 DOI: 10.1016/j.agrformet.2010.11.001

Image © Tamara Kulikova