Long-term effects of site preparation on growth in Scots pine

Abstract

Effects of soil scarification on long-term site productivity up to 70 years, and soil content of carbon (C), nitrogen (N), and macro nutrients, were studied in five site preparation experiments, established between 1922 and 1965 on Scots pine ( Pinus sylvestris L.) heathland, on poor sandy sediments. The soil was inverted by spade, hoed, harrowed or ploughed. All scarification methods disturbed close to 100% of the soil surface, the most radical treatments to a depth of approximately 20 cm. Some of the experiments had an inadequate original design. However, by comparing the experiments some general characteristics were found. Site productivity measured as top height was higher on scarified plots than on control plots ( P < 0.05), indicating that long-term site productivity was improved by scarification. Total C and N contents in soil were 6–41% and 16–30%, respectively, lower on scarified plots compared with control plots. On scarified plots, all mineral elements analysed showed equal or lower contents in the organic layer, including the field layer, ground layer, organic debris, and humus. Total contents of P, Mg and S in mineral soil samples from 60–100 cm depth were higher on scarified plots than in corresponding samples from control plots. On the two burned plots analysed, total C content in the soil was 2 and 31% lower than on controls, and total N content 10% higher and 63% lower. The results suggest that the risk for decreased long-term productivity on poor Scots pine sites caused by mechanical scarification methods used today are negligible.