Conclusions

Contrary to expectation, the photosynthetic performance of alpine plants hardly sets limits to growth, and the respiratory demand for growth and maintenance takes advantage of thermal acclimation. Current evidence suggests that alpine plants are not carbon limited, a conclusion supported by the results of a long term in situ CO₂-enrichment experiment (see Atmospheric influences). The two major limitations for growth and biomass production of natural alpine vegetation are low night temperature and the length of the growing season both limiting growth and carbon investment. It comes as a great surprise that, if the comparison is based on the time available for growth (the growing period), the seasonal biomass production of closed alpine vegetation in humid mountains does not differ from that in any other humid climate, including the tropical lowlands.

As anywhere else on the globe, growth and biomass production of alpine vegetation can be stimulated (see Plants and climatic stress).

So why are alpine plants so small? Some alpine species belong to the smallest higher plants on earth (Fig. 1). The most plausible explanation is that they are small "by design", not by any inability or stress. By staying small and closely attached to the ground they capture the warmth provided by solar radiation that they need for growth (see Dynamic mountain climate). Evolution has selected alpine dwarfism as a way to cope with an otherwise unbearable environment. The photosynthetic and growth performance of these small alpine plants illustrate that this morphological adaptation is very successful.