Autumn reds disappearing as global warming blurs boundaries between the seasons

Michael Day in Milan

Last Updated: 11:01am BST 08/10/2008

The vibrant palette of autumn is draining away from Europe's woodlands, as global warming continues to blur the boundaries between seasons, scientists have warned.

Researchers at the Italian Meteorological Society have observed less gold, copper and red foliage in the country's woodlands, and linked this to rising temperatures and extended springs and summers.
'Colours are fading because the temperature difference between night and day is getting smaller'
A similar warning has come from the Veneto region's forestry department.
The developments in Italy mirror concern elsewhere in Europe - and the Northern Hemisphere. The US Department of Agriculture has just begun funding a study into claims that the northern states' famed Fall colours are also fading away with climate change.
"I'm in the forests and woods every day," said Dr Giustino Mezzalira, a forestry expert and director of agricultural research for Italy's northern Veneto region, told the Telegraph, "and in recent years, we just haven't seem seen the same beautiful colours that we used to see.
"Something is clearly happening to make the colours less vivid. The wood is a living organism that tries to adapt to the climate, and change in climate is the cause. We really need to study and understand what's happening.

"But I think that, as in the United States, the colours are fading because the temperature difference between night and day is getting smaller and smaller."
In the US, researchers at the University of Vermont have just received $45,000 grant from the Department of Agriculture to monitor the situation following fears that famous autumnal displays in its woodlands are losing their splendour.
This group's research will also focus on temperature. Like Dr Mezzalira, the Vermont researchers suspect that the summer-like conditions that increasingly prevail in September and October, with a diminishing gap between day and night-time temperatures, is causing the woodland's palette to fade.
Botanists believe that brilliant leaf colours associated with autumn are promoted by cold nights followed by warm, sunny days; in the absence of such conditions, the trees probably continue to produce the green pigment chlorophyll as if it were still summertime.
"The leaves are telling how the climate is changing," said Dr Luca Mercalli, president of the Italian Meteorological Society.
In the alpine Aosta Valley he is measuring whether temperatures are changing in the area's forests and examining what effects such changes might be having. He has already found evidence linking less colour and higher temperatures.
His team is studying various woodland locations, starting in April this year and going right through to November, and comparing the results with previous years. The researchers are even measuring numbers of every single leaf on some branches.
"The preliminary data confirms what we suspected regarding the temperature," he told La Repubblica newspaper. "The rising temperatures are provoking an elongation of the vegetative season.
"The leaves are sprouting earlier by 15 days or more. So the spring is arriving earlier, while the leaves are staying put in autumn."
As a result the of the continuing heat and sunlight, the green pigment chlorophyll, which gives leaves their colour is not draining away so quickly in autumn to reveal the minor pigments, such as anthocyanins, that give trees their seasonal red, gold and copper hues.
This means that more leaves are dropping off later in November cold snaps before they have had the chance to change colour.
Dr Mercalli said that, in addition to robbing us of one of nature's most beautiful spectacles, the fading of autumn woodlands highlighted potentially disastrous environmental changes that were taking place.
"The temperatures are continuing to rise and nature is obviously reacting. Unfortunately mankind is doing very little about it," he said.