Wild Holly, Mistletoe, Spread With Warmer Winters

December 7, 2005

Christmas greenery is bringing festive color to new parts of Europe as holly and mistletoe growing in the wild begin to take root outside of their traditional ranges.

Two recent studies suggest that a trend toward milder winters in northern Europe is likely tied to the spread of these plants, which are common decorations during the winter holidays.

The research shows that holly is heading north across Scandinavia, while mistletoe is scaling snowy alpine slopes.

Common holly (Ilex aquifolium), a spiky-leaved, red-berried evergreen, has advanced across southern Scandinavia and northern Germany in recent decades, according to researchers.

The shrub has increased its range by 75 miles (120 kilometers) in Germany and 80 miles (130 kilometers) in Denmark since the 1940s, says Gian-Reto Walther, a vegetation ecologist at the University of Hanover in Germany.

"In Norway the northward range expansion is about 30 kilometers [19 miles]," Walther added. "There are also new occurrences along the Swedish coast."

A study published earlier this year in the journal Proceedings of the Royal Society B compared the plant's current distribution in Scandinavia and Germany with records from 1944.

On the Move

The team found that holly, which can stand winter freezes down to minus 4°F (minus 20°C), has been spreading as temperatures rise due to climate change.

"Climate stations included in our study have experienced an average temperature rise of approximately one degree Celsius [1.8°F] in the coldest month," Walther said.

This finding is in line with figures from the Intergovernmental Panel on Climate Change based in Geneva, Switzerland. The panel has documented an average temperature increase of 1 to 1.2°F (0.6 to 0.8°C) per decade in northern Europe since the 1970s.

The distribution of some plants—especially evergreen, broad-leaved woody species—is strictly limited by climatic factors, Walther says.

Continued on Next Page >>


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