A Growth Analysis Technique for Assessing Habitat Severity in Tundra Regions

Abstract

The results are reported of growth experiments carried out over three seasons on the sub- Antarctic island of South Georgia. The values obtained for relative growth rate, net assimilation rate and leaf area ratio for oats, radish and turnip are discussed and contrasted with values reported for temperate sites. A hypo- thesis is put forward to explain the consistent depression of Rw and FA whilst the intermittent depression of Ea is linked with Warren Wilson's theory of the inhibiting effects of sugar accumulation. The usefulness of this technique in ecological applications is examined with particular reference to tundra regions. water and nutrient status of the growing medium, and genotype may be considered as the most important. If measurements of productivity are made in natural communities growing in situ it is usually difficult to assess the relative importance of each of these factors in determining the results, since native species are suitably adapted to the prevailing conditions. Investigations of such communities, especially those in temperate and tropical regions, are further complicated by the complexity of their species composition and range of life forms. In this respect there has been an increasing interest in alpine and polar regions where natural assemblages are comparatively simple in regard to community structure and number of species, particularly phanerogams. Bliss (1962a, 19626, 1966), Scott and Billings (1964), Dennis and Johnson (1970) and Svoboda (1972) have provided much basic information on plant productivity in various habitats of these cold regions, but it has proved difficult to isolate the degree of importance of each of the factors deter- mining growth. A method for eliminating some of the variables associated with plant growth in Arctic environments was attempted with some success by Warren Wilson (1966a). He grew both native and alien species in untreated local soils and a non-limiting medium (vermiculite) and was able to estimate to some degree the limiting effects of natural soils and the maxi- mum production possible during short test periods under the local climatic regime. Extending this technique Lewis and Greene (1970) carried out experiments both in sub- Arctic Greenland and on the sub- Antarctic island of South Georgia using crop plants as phytometers grown in non-limiting vermiculite. Their results indicated that the choice of site, and therefore of micro-climate, had a considerable effect on the amount of growth and that the local soils were deficient in nutrients, at least with regard to the alien species. They emphasized the importance of using a standardized technique in such phytometric experiments, particularly when they are being repeated in different geographical regions and in different seasons.