The Use of Mineral Nutrients for Biomass Production by Young Birch Stands and Stands Vitality in Different Forest Growing Conditions

The data of field studies about mineral nutrient content in the biomass components of young birch stands (9-15 years old) in different forest growing conditions and soil types have been analyzed. In forest growing conditions on fertile soils (ASG, TSC and SP) the total amount of biomass produced by young birch stands divides into fractions as follows: stem wood 51.8%-59.5%; branch wood 9.8%-12.4%; foliage 5.7%-6.8%; stump wood and roots 25%-30%. In forest types on lean soils (TP) the same indices are 32.3%-41.8%, 18.2%-24.2%, 13.2%-16.1% and 26.8%-27.4%, respectively. The stand performance closely correlates with the basic nutrient (P, N, K, C and Mg) availability in forest soils. In lean typicpodzol soils (TP) the content of mineral nutrients is no higher than 20%-48% of that in more fertile soils (ASG, TSC and SP). In young birch stands the take-up of mineral nutrients from 0-40 cm soil layer for developing the above-ground biomass makes a fairly small proportion of the total: up to 4.8%-6.2% for P; 4.9%-12.2% for N; 1.1%-4.1% for K; 11.6% for Ca; 0.8%-7.7% for Mg; in leaner soils the same indices are P 0.1%-0.4%, N 1%-1.5%, K 0.2%-0.6%, Ca 0.1%-0.9%, Mg 0.1%-0.8%, respectively. The analyses of pest damages in young birch stands confirm a hypothesis that the degree of pest damage depends on the stand vitality as described by the site index.