Long-term Effect of Weed Control on Survival and Growth of Silver Birch Planted on Arable Land

The effects of competing vegetation and weed control methods (fibreboard mulch, herbicide) on the survival and growth of silver birch (Betula pendula Roth) were analysed based on 20-year data from a field experiment established in Central Finland. The growth of birches was equivalent to that on the most fertile forest sites in Finland. Herbicide treatment did not reduce the total vegetation cover but it decreased the coverage of grasses and increased that of forbs. After 20 years, the average stem volume on the herbicide-treated plots was 38% higher than on the control plots (148 m(3)ha(-1) vs. 10(7) m(3)ha(-1)). The increase in volume was mainly due to reduced seedling mortality (24% vs. 43%). Weed control increased seedling height during the first seven years, but did not significantly affect seedlings' final height or diameter. The mean stand volume (123 m(3) ha(-1)) and mortality (31%) on mulched plots did not differ from the other treatments. Weed control did not affect seedlings' biotic or abiotic damage and most foliar nutrient concentrations.