RESPONSES TO NATURAL CLIMATIC VARIATION AND EXPERIMENTAL WARMING IN 2TUNDRA PLANT-SPECIES WITH CONTRASTING LIFE FORMS - CASSIOPE-TETRAGONAAND RANUNCULUS-NIVALIS
U. Molau, RESPONSES TO NATURAL CLIMATIC VARIATION AND EXPERIMENTAL WARMING IN 2TUNDRA PLANT-SPECIES WITH CONTRASTING LIFE FORMS - CASSIOPE-TETRAGONAAND RANUNCULUS-NIVALIS, Global change biology, 3, 1997, pp. 97-107
Two circumpolar tundra plant species, the evergreen dwarfshrub Cassiop
e tetragona and the perennial herb Ranunculus nivalis, were studied at
Latnjajaure in northern Swedish Lapland during three consecutive grow
ing seasons (1993-95) as a contribution to the ITEX programme. Open-to
p chambers (OTCs) were used in a passive heating experiment, and the p
erformance of the plants in unmanipulated controls was correlated with
climatic fluctuations among the years. Phenological, vegetative, and
reproductive variables were measured. In both species phenological res
ponses were controlled mainly by ambient air temperature. In the everg
reen C. tetragona vegetative growth was controlled mainly by the influ
x of global solar radiation and was not temperature-dependent, whereas
the opposite applied in the herbaceous R. nivalis. Vegetative growth
in C. tetragona was rather stable among years as well as between treat
ments, whereas it was strongly influenced by annual climate in R. niva
lis. Both species increased their reproductive success with increasing
temperature, but R. nivalis was also radiation-dependent in this case
, probably because of its green, photosynthetic nutlets. Ovule number
in R. nivalis increased steadily in the experimentally heated plots du
ring the study in response to the constant temperature amelioration ab
ove the ambient. At the community level, evergreen C. tetragona seems
to have low competitive ability under warmer conditions. The situation
for vernal low-growing herbs like X. nivalis is more complex; despite
a strong positive response to increased temperature, they may exhibit
decreased reproductive success if overgrown by a vigorous graminoid c
anopy.