The abundance of heterotrophic flagellates, ciliates and naked amoebae was measured in 8 sites covered with different vegetation (beech, birch, beech-birch, birch-oak-beech, grass) from January to April 2001. The results were analysed by a suite of mathematical techniques, together with data on bacteria, fungi, nematodes, microarthropods, and the composition of forest litter and field layer, available from parallel research. The population levels ranged between 4.02 and 795 × 103, 28 and 1010, 35 and 1170 g–1 litter dry wt for flagellates, ciliates and amoebae, respectively. Temporal changes in the microbiota appeared to be affected by progressive winter cooling followed by a spring increase in temperature, and influenced by habitat characteristics and a complex multivariate interplay among ecosystem components. The population abundance in winter (January-mid March) was higher than in spring (late March–April) for all protozoa. Amoebae showed minimum values in March, followed by considerable recovery in April. However, ciliate values dropped slightly between March and April, whilst flagellate values steadily decreased throughout the whole research period, suggesting that the spring growth of ciliates and flagellates might have been arrested by increased predation and/or competition. Statistical analysis revealed a number of significant relationships between the protozoa studied and other ecosystem components. These relationships were indicative of the conditions studied and may, therefore, be useful for future reference. The results highlighted the complexity of transient multivariate interactions of protobiota in forest litter, suggesting that any interpretations of the population dynamics must take account of a full range of both temporal and spatial factors.