Early stages of podzolization under Corsican pine (Pinus nigra Arn. ssp. laricio)

To assess the effects of the plants on pedogenesis, two arboreal species, Corsican pine(Pinus nigra Am. ssp. laricio) and silver fir (Abies alba Mill.) were compared. We observed that at the base of the largest Corsican pines, patches of bleached soil occur on top of the A horizon. These eluviated areas lie at the outlet of wide bark channels through which the stemflow reaches the ground. in addition, an apparently less bleached material, in the shape of collars, is present around the big roots that collect and conduct the stemflow into the soil. On the contrary, patches and collars are absent in the soil under firs. To understand the role of the two species in the formation of the bleached material, throughfall, stemflow and forest floor solutions were collected for pine and fir. For pine, the stemflow moving along a wide bark channel was collected separately. All these solutions plus the rainfall were obtained and analysed seasonally for 1 year. Also, a number of profiles were excavated in the vicinity of the trunk base of pines and firs. Two profiles were selected for sampling and for the attendant analyses. The results indicate that under silver fir, the processes induce in the formation of an A horizon. The Corsican pine, on the other hand, in 50 years, has been able to produce, even if in small areas, a separate pedogenic process responsible for the bleaching of an existing A horizon. Because the bleaching process is at an initial stage, the chemical differences between the E material and the surrounding A horizon are small. Nevertheless, the E material is poorer in organic matter and in the most mobile inorganic elements than the A horizon. The presence of E material exclusively at the trunk base of the pines is due to the strong acidity of the stemflow - about 30-times higher than that of the fir. The most evident differences between the soils under pine and fir concern the features more directly related to the dynamics of the soil organic matter. Mineral assemblage, which needs longer time for its evolution, is very similar in the two soils; nonetheless a small amount of pedogenic smectite has been recognized in the E material. (C) 1998 Elsevier Science B.V.