Nutritional characteristics of soils on an inferred chronosequence. A comment on Laliberté et al. (2012)

1. We question the reasoning of the authors who claim that their evidence strongly supports a longterm ecosystem development model in which phosphorus (P) is the factor that leads to the regression phase of the succession. Parent material, relief (topography and drainage) and climates (past and present) are key factors that were not considered sufficiently or critically. 2. Their choice of P as the most important factor determining the direction of the succession overlooks other likely critical determinants of primary productivity on sandy soils such as the supply of water and nutrients other than P, particularly trace elements on calcareous soils. 3. The use of crop species as phytometers to determine which nutrients were limiting the primary productivity of native species at each site inevitably raises significant problems of interpretation. 4. Synthesis. The main problems with the paper (Laliberté et al. 2012) are (i) that the large differences in soil parent material between the dune systems and other factors make the sites of doubtful use for chronosequence work and, (ii) that errors arise in the discussion of nutritional characteristics because important literature has been overlooked. The paper exemplifies a larger problem where modern long-term chronosequence work tends increasingly to overlook the need for sites to be chosen which minimize changes in all the soil-forming factors other than time as expounded by Jenny (1941).