Long-term biomass production and nutrient uptake of birch, alder and willow plantations on cut-away peatland

The leafless above-ground biomass production of planted silver birch (Betula pendula), downy birch (Betula pubescens), grey alder (Alnus incana), indigenous willows (Salix triandra and Salix phylicifolia) and an alder-willow mixture growing on a cut-away peatland area in Central Finland was investigated during a period of 18 (willows) or 19 (birches and alders) years. Biannual fertilization of the birches (0, NPK) and alders (0, PK) and annual fertilization of the willows (NPK1, NPK2) were continued for 10 years. S. phylicifolia had the highest yield (123 t ha⁻¹). The yield of the fertilized downy and silver birch was 112 t ha⁻¹ and 108 t ha⁻¹ respectively, and that of fertilized grey alder 85 t ha⁻¹, and alder S. triandra mixture 93 t ha⁻¹. The mean annual increment of willow was highest at the age of 10 years (S. phylicifolia 7.9 t ha⁻¹ a⁻¹; S. triandra 5.6 t ha⁻¹ a⁻¹). NPK-fertilization increased the 19-year biomass production of downy and silver birch by 14 and 29 t ha⁻¹ respectively and PK fertilization that of alders by 25 t ha⁻¹. The alder plantations bound more N, P, K, Ca and Mg per unit leafless biomass produced after 10–11 growing seasons than the silver birch and downy birch plantations. The silver birch used more N, K and Ca, but similar amounts of P and Mg per unit leafless biomass produced than the downy birch. S. triandra used more N, P, K and Mg per unit biomass produced than S. phylicifolia and both birch species.