The keeping back the atmospheric precipitations of vertical direction is the important manifestation of biomass of forest stands which take part not only by influencing their production but also of circulation of water in the forest ecosystem. The common rule of law connected with the interception are from the main part known from the sooner done researches. Today it is necessary to locate the research for solving the detailed problems and the relations of the interception; and stand biomass belong to it. The research of this relation was deomstrated in the period of years 1981 till 1983 in a spruce stand of 60 years of age, of first bonity and of full canopy. On the experimental plot with the area 127.4 m2 of the told stand the precipitations under canopy were measured and on their basis the interception of the stand was counted and determined the other relations. The trees of the experimental plot were divided to highgrowing, growing in the canopy and under it. After the measuring of interception was finished these trees were felled and the analysis of their biomass was done. The measurements showed that the biggest interception have the trees growing under canopy, the middle values reach the trees growing in the canopy and the lowest ones the trees overgrowing the canopy. The average index of the leaf area in experimental plot is 14.4. The highest index of the leaf area have the trees growing in the canopy 17.81, overgrowing in 14.57 and undergrowing 10.1. The high degree of interception by the last category is influenced also by shade of trees of both remaining tree classes. These experiences give the theoretical presumptions for their practical application during pruning and thinning of spruce stands in the forests with the watermanagement destination where one of the aims is to do the suitable arrangements for the safe receipt of maximal possible amount of precipitation water into soil for the infiltration and forming the necessary provisions of disponible water.
