Clone members of each of three altitudinal populations (910-1590 m) of two ecologically important
snow tussocks (Chionochloa macra and C. rigida) reciprocally transplanted to four sites (10-1590 m)
in 1960 were further subdivided and re-reciprocally transplanted to the same four sites in 1974 and
their subsequent growth and flowering behaviour followed over two seasons.
Interpopulation differences in stature and growth rates remained distinct after the 14-year
intervening period, reinforcing earlier evidence for some genetic control of these characters.
In contrast, the flowering of each population at each site had converged towards that of the
resident plants, which indicated some adjustment to the critical threshold temperature for flowering.
Interpopulation differences in flowering behaviour could not, therefore, be strictly controlled
genetically as had been previously assumed.
No interpopulation differences emerged as a result of 14 years of preconditioning in diverse
environments. Furthermore, the preconditioning had a negligible effect on the subsequent perfor-
mance of each population in a wide range of temperature environments.
Distinct differences in growth rates between a lowland coastal population of C. rigida and its
alpine counterparts appear adaptive, suggesting differentiation of a lowland ecotype.
The high degree of physiological plasticity inherent in all populations of snow tussock studied
may have its origin in the climatically diverse post-Pleistocene period when genotypes with maximum
flexibility may have been selected preferentially. Since then, probably as a result of expansion of
snow tussock grasslands within the last millenium, local adaptive variants have evolved.