Influence of herbivory on caesium turnover in a forest ecosystem

The effect of herbivory by bank vole ( Clethrionomys glareolus) and moose ( Alces alces) in relation to litterfall in a boreal forest is analysed. The main purpose is to estimate the relative importance of these processes for the transfer of caesium-137 to soil. Biomasses of litterfall and food consumption were selected from different forest biotopes. The analysis of the input and output of caesium-137 in the vole and moose populations is based on mass balance calculations for caesium-137 in steady state conditions. From this assessment, herbivory appears to be within an order of magnitude of litterfall. With due regard to the lower caesium level in litterfall than in living plant tissue, transfer of radioactive caesium by herbivory is seen to be even higher in comparison to that by litterfall, than apparent from the corresponding transfer of organic matter. In addition, the availability of caesium-137 from animal excrements is expected to be high and fast, which further emphasises the relative importance of herbivory feed-back from vegetation to soil.