Global warming has plants on the move

In response to Earth's warming temperatures, plants in the Alps are 
seeking higher ground, according to a study comparing today's flora 
to vegetation earlier in the century.

"Our data indicate that even small differences of temperature...can 
induce [plant] migration up a mountain," Austrian researcher 
Georg Grabherr and his colleagues at the University of Vienna write 
in a letter in the June 9 NATURE.

In 1992, the researchers counted the number of species and estimated 
the abundance of primarily flowering plants above 3,000 meters on 26 
mountains in western Austria and eastern Switzerland. They compared 
their data to the same figures from the early and middle 1900s.

Species richness on these mountains has increased during the past few 
decades, thanks in part to the steady upward climb of vegetation, 
Grabherr says. Not only do former residents of the nival zone, the area 
above about 2,000 meters, move up, but former alpine plants ascend to 
the nival region.

"We were very surprised by that"  he says. Historical documents showed 
no alpine plants above the nival zone.

Nine common species have ascended the mountains at the rate of 1 to 4 
meters per decade--somewhat slower than the investigators had expected. 
The mean annual temperature has increased 0.7¡C since the early 1900s; 
because mountain air cools about 0.5¡C every 100 m, the vegetation 
should have moved 8 to 10 m per decade. Why it didn't is unclear.

If global temperatures continue to increase, some mountain plants may 
have nowhere to go, the researchers point out. Global warming "may cause 
disastrous extinctions in these environments" Grabherr and his 
colleagues warn.

Science News, Vol. 145, No. 25, June 18, 1994