摘要 : During the last decade, more than 400 000 ha of agricultural land was abandoned in Estonia. Such areas are often characterized by rapid natural afforestation with silver birch, which has led to an increase both in the woodland are... 展开 During the last decade, more than 400 000 ha of agricultural land was abandoned in Estonia. Such areas are often characterized by rapid natural afforestation with silver birch, which has led to an increase both in the woodland area and in the area of silver birch stands. However, many bioenergetic aspects related to birch stands growing on arable land are still poorly understood. The main aim of the present study was to investigate the above-ground biomass production, nutrient (NPK) accumulation, and foliar characteristics of young silver birch stands on abandoned agricultural land. Five 8-year-old stands of silver birch growing on different soil types were included in the study. The density of the studied stands varied from 3060 to 36 200 trees per ha and their above-ground biomass varied from 6.0 to 22.91 DM ha~(-1). The largest share in the above-ground biomass of the birches (59-80%) was from the stems. The mean stem mass of the birches ranged from 0.29 to 1.79 kg, and the mean total above-ground biomass ranged from 0.36 to 3.03 kg. The leaf area index for the studied stands varied from 1.21 to 4.64 m~2m~(-2), being the highest for the stand of medium density. Mean single leaf area varied from 9.4 ± 0.2 to 15.4 ± 0.3 cm~2, leaf weight per area varied from 61.1 ± 0.4 to 77.5 ± 0.5 g m~2, and specific leaf area varied from 13.2 ± 0.1 to 16.8 ± 0.1 m~2 kg~(-1). However, no significant differences were found between stand density and the foliar characteristics. There was a strong positive correlation between soil nitrogen concentration and leaf nitrogen concentration (R = 0.92); regarding phosphorus concentration, the corresponding correlation was weak (R = 0.52) and regarding potassium concentration, no significant correlation was found. The amount of nitrogen accumulated in the above-ground part of the silver birch stands varied between 42.4 and 145.8 kg ha~(-1), the amount of phosphorus, between 5.9 and 27.9 kg ha~(-1), and the amount of potassium, between 7.2 and 78.6 kg ha~(-1). The N:P:K ratios for the foliage were comparable. It is evident that the proportion of nitrogen and phosphorus are close to optimum, while the N:K ratio was lower than optimum value in all cases. 收起