Articles | Volume 11, issue 22
Research article
27 Nov 2014
Research article |  | 27 Nov 2014

Forest conversion to poplar plantation in a Lombardy floodplain (Italy): effects on soil organic carbon stock

C. Ferré, R. Comolli, A. Leip, and G. Seufert

Abstract. Effects of forest conversion to poplar plantation on soil organic carbon (SOC) stocks were investigated by sampling paired plots in an alluvial area of the Ticino River in Northern Italy. According to land registers and historical aerial photographs, the two sites were part of a larger area of a 200 yr old natural forest that was partly converted to poplar plantation in 1973. The soil sampling of three layers down to a depth of 100 cm was performed at 90 and 70 points in the natural forest (NF) and in the nearby poplar plantation (PP) respectively. The substitution of the natural forest with the poplar plantation strongly modified soil C stock down to a depth of 55 cm, although the management practices at PP were not intensive. After calculation of equivalent soil masses and of SOC stocks in individual texture classes, the comparison of C stocks showed an overall decrease in SOC of 5.7 kg m−2 or 40% in consequence of 37 years of poplar cultivation.

Our case study provides further evidence that (i) spatial heterogeneity of SOC is an important feature in paired plot studies requiring a careful sampling strategy and high enough number of samples; (ii) land use changes through tillage are creating a more homogeneous spatial structure of soil properties and may require the application of dedicated spatial statistics to tackle eventual problems of pseudo-replicates and auto-correlation; (iii) short rotation forests are not properly represented in current reporting schemes for changes of SOC after land use change and may better be considered as cropland.

Short summary
In a paired plot design we studied the effect on soil organic carbon stocks of the transformation of a natural forest in the Po Valley in northern Italy into a short rotation poplar plantation 37 years ago and observed a reduction by 40% or 5.7 kg m−2 over the plowing depth of 55cm. A dedicated sampling scheme and application of spatial statistics was needed to proof this change because the homogenization effect of plowing created a spatial auto-correlation.
Final-revised paper