The effects of temperature variation on germination and seedling growth in populations from different altitudes of Eucalyptus pauciflora were investigated by means of experiments in controlled environments and under natural conditions in the field.
Germination and seedling growth showed no statistically significant variation in optimum temperature according to altitude. On the other hand, there was strong evidence of differential resistance to freezing temperatures whereby seedlings from high-altitude seed proved considerably more resistant than those from low-altitude seed. This was reflected, to a certain extent, in the survival of reciprocal transplants over winter.
The relative uniformity of temperature optima suggested that in the field germination and early seedling growth would occur later with increasing altitude, thus bearing out casual field observations. The marked altitudinal variation in tolerance to low temperatures suggested that natural selection may have operated under the influence of winter temperature gradients to bring about adaptive changes related to altitude of occurrence.