Subject: GL:  in _Nature_:  Growing season extended in Europe

25 February 1999
Nature 397 , 659 (1999)

Growing season extended in Europe

Changes in phenology (seasonal plant and animal activity driven by
environmental factors) from year to year may be a sensitive and
easily observable indicator of changes in the biosphere. We have
analysed data from more than 30 years of observation in Europe, and
found that spring events, such as leaf unfolding, have advanced by
6 days, whereas autumn events, such as leaf colouring, have been
delayed by 4.8 days. This means that the average annual growing
season has lengthened by 10.8 days since the early 1960s. These
shifts can be attributed to changes in air temperature.

Nature subscribers can view full text at http://www.nature.comews/mediarel/mr1999/mr9937.htmlraindisorder.asp

BBC report:

Wednesday, February 24, 1999
Spring comes early

    Spring is arriving earlier in Europe.  A study of trees has
found that they are unfolding their leaves six days earlier than
they did in the 1960s. The autumn shedding of leaves has also
been delayed by about five days.

    German scientists looked at data from the International
Phenological Gardens (IPG), a Europe-wide network of sites where
genetically identical trees and shrubs have been grown in
parallel for 40 years. This allowed them to track changes such
as leaf unfolding, flowering, leaf colouring and leaf fall.

    Annette Metzel and Peter Fabian, at the University of Munich,
showed that the onset of spring was sensitive to climatic change.
Depending on the species, Spring is up to six days earlier for
each degree increase in winter air temperature, and Fall occurs
5 days later.  An 11-day average increase in Europe's growing
season fits with other studies and mirrors satellite data from
1981 to 1991.

    Dr Metzel said the changes that were taking place were likely
to be beneficial in the short-term.

    "It means more oxygen for example, it means better wood
supply, and concerning the climate change debate it means that
Europe's forests will provide more carbon sinks to soak up carbon
dioxide," she told the BBC.

    "After the UN global climate change summit in Kyoto last
year, all countries are trying to build up existing carbon sinks
and develop new ones."

Water supply

    However, Dr Metzel said the longer growing seasons would put
greater strain on already limited water resources, especially in
southern Europe.

     "An earlier and longer growing season, and higher tempera-
 tures, will all increase problems of water supply. And with
higher temperatures, the evaporation of the plants will increase
too.  If precipitation stays at the same level, and temperatures go up,
there might be less water to go around."

Global warming

    An increase in temperature is just one of the factors which
trees and other plants will have to contend with if the Earth
continues to warm as predicted.  Increases in atmospheric carbon
dioxide and changes in rainfall will also have a major impact.

    Scientists are uncertain as to the overall effect of global
warming on plant life. On the one hand, raised carbon dioxide
should "fertilise" plants. On the other hand, high temperatures
will also extend the range and life cycles of certain pests.