Different plant growth-forms such as tussocks and rosettes, were selected as micro ecosystems in an area in which these structures were spatially isolated from each other. These growth forms are important during winter since they serve to regulate temperatures, which is important to invertebrate animals. This was shown with intensive temperature recordings in winter, correlated with numbers of animals. Plant growth-forms are more important in young bare areas where there are fewer plants to provide shelter, than in older areas, where a denser vegetation cover affords more possibilities for shelter. Such differences can be expected to influence the abundance as well as the occurrence of animals during the development of a community.