Effect of fertilisation on ¹³⁷Cs in understory spruces on a dryish pine site

¹ Finnish Forest Research Institute (METLA), Parkano Research Station, 39700 Parkano, Finland
² Radiation and Nuclear Safety Authority (STUK), P.O. Box 14, 00881 Helsinki, Finland

Abstract

Undergrowth spruces (Picea abies) in a pine stand in Finland were studied in 1997, 13 years after refertilisation with NPK. The aim of the study was to quantify the effect of NPK fertilisation on the distribution of radiocaesium (¹³⁷Cs) and dry mass in the trees. Biomass functions for different tree compartments were derived by means of regression analysis. Radiocaesium contents in the different tree compartments were calculated using plot-specific biomass values and ¹³⁷Cs concentrations. Fertilisation decreased the ¹³⁷Cs concentration in each of the compartments by 73-92 %. In the control spruces, the ¹³⁷Cs concentrations were highest in the stem bark, needles and branches of the upper half of the crown (2455-3443 Bq kg^-1 DW) and in the dead branches (2882-4408 Bq kg^-1 DW). These concentrations were double those in the lower half of the crown irrespective of the fertiliser treatment. The needles and branches in the lower half of the crown contained 58-62 % of the tree biomass and 56-60 % of the ¹³⁷Cs. Changes in the relative vertical distribution of ¹³⁷Cs in the trees due to fertilisation were small. The total ¹³⁷Cs content of the trees correlated with the biomass and diameter of the trees.