Effects of plantation forest species on soil phosphorus

Rationale Recent large-scale afforestation of pastoral farmlands represents a major land-use change in New Zealand (Chen et al., 2003). The area under short-rotation plantation forestry (mainly radiata pine (Pinus radiata)) doubled from 0.9 to 1.8 million ha (c. 7% total land area) between 1985 and 2005 (Davis, 1998). Most of the established forests were planted on hill country areas developed under pastoral farming, where significant accumulation of organic matter and associated nutrients (nitrogen [N], phosphorus [P], sulphur [S]) occurred in these soils as a consequence of fertiliser inputs (Binkley and Högberg, 1997). This change in landuse was attributed to a combination of declining returns from pastoral farming and the expectation of increased future returns from forestry (Davis, 1998). In addition to the potential economic benefits associated with the establishment of conifer plantations, development of forestry in grassland areas may help to restore degraded lands and control soil erosion, especially in hill and high country areas (Davis, 1998). There is evidence from studies conducted in New Zealand that there are short and medium term effects associated with the change in land use from grassland to forest such as increased phosphorus availability (Chen et al., 2008). It is commonly believed that conifers degrade soil fertility in various ways, although there has been little consistent scientific evidence for this (Binkley, 1995). However, there is evidence from studies conducted in New Zealand that there may be some short term beneficial effects associated with the change in land use from grassland to forest such as increased phosphorus availability (Davis and Lang, 1991; Belton et al., 1995; Chen et al., 2008). Most afforestation studies carried out to date in New Zealand have focused on the influence of radiata pine on soil properties and processes, and have involved paired site comparisons at one point in time, commonly 15-20 years after forest establishment (Chen et al., 2000; Chen et al., 2008).