Size and efficiency of Scots pine (Pinus sylvestris L.) assimilation apparatus

The aim of the study is to analyse the size and efficiency of assimilation apparatus of Scots pine (Pinus sylvestis L.) using the site index model for unthinned pine stands (Model Pinus). The size of the assimilation apparatus was regarded in terms of mass of the twigs covered with needles (Ugc) and Mass of needles (lc). It reaches maximum values at the age of 20-25 years, then dynamically decreases to the age of 50 years, stabilizes between 50 and 80 years and from the age of 85 to 120 years again shows a mild increasing trend. The maximum mass of twigs covered with needles is from 40 (BON34) to 20 (BON26) t/ha, while mass of needles - from 25 (BON34) to 13 (BON26) t/ha. The minimum weight is from 18 (BON34) to 16 (BON26) t/ha and from 13 (BON34) to 11 (BON26) t/ha, respectively. The efficiency of the assimilation apparatus determined as the dependence of the current volume increment on in the dependence on mass of twigs covered with needles (W-Ugc) or mass of needles (W-lc) is dynamically increasing and at the age of 45 years it reaches the maximum and then shows a downward trend to the age of 120 years. At the culminating point of these features, they are similar for all site indices and range from 0.83 to 0.88 m(3)/t (W-Ugr) and from 1.23 CO 1.31 m(3)/t (W-lc).