Effects of plantation forest species on soil properties

Abstract

Large scale afforestation of grasslands has occurred in New Zealand. Detailed investigation of changes in soil properties over time following establishment of different tree species is necessary to understand the impacts of this land-use change on soil nutrient dynamics and availability. A field trial was established in 1999 comprising 4 replicate plots of three commercial tree species (Pinus radiata, Eucalyptus nitens, Cupressus macrocarpa). Soil samples were taken from each plot prior to tree planting and after 5 years growth (2004). Analyses of samples taken in 1999 showed that the topsoil (0-5 cm) had a low pH (5.1), with low to medium levels of total carbon (5.01%), nitrogen (0.43%), phosphorus (630 mg/kg), sulphur (510 mg/kg) and exchangeable base cations (7.52 cmolc/kg). Results for comparison between samples taken in 1999 and 2004 revealed a decrease in total C, N, P, S and exchangeable Ca and Mg confined to the 0-5 cm soil depth. The reductions were generally greater under P. radiata than E. nitens and C. macrocarpa. In contrast, inorganic and plant available Olsen P levels increased under all species. These findings confirm that afforestation of grassland has a major short-term impact on soil properties and processes.