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Background and aims: Pioneer plants may improve the ecological restoration of degraded ultramafic areas by plant-soil interaction processes. In this study, we assess the effect of the pioneer actinorhizal tree C. terminale (Casuarinaceae) on the recovery of plant communities and soil functions on degraded tropical ultramafic sites. Methods: Soil and plant samples were collected along a tree-age gradient in two degraded ultramafic sites in Sabah (Northern Borneo, Malaysia): a Technosol and a Leptosol. Chemical composition of plants and soils, and biological activity of soils were assessed at both sites. Plant colonisation was assessed by plot vegetation surveys. Results: An improvement in soil fertility parameters (pH reduction from 8.5 to 6.8, an increase in the concentrations of several nutrients and enhanced soil enzyme activities) was observed along the C. terminale age gradient. However, plant cover and diversity was only improved around mature trees at the site that was not impacted by mining. Conclusion: C. terminale promotes the recovery of several soil functions, mainly related to the storage and recycling of N, P, K, S. Besides plant-soil feedback, other environmental factors (i.e. exposition to sunlight, drought) may play an important role on revegetation of ultramafic soils. [ABSTRACT FROM AUTHOR]

Splash is an essential process in interrill erosion because it detaches soil fragments front their substrate and transports them. However, splash measurements are difficult to interpret and relatively little is known about the influence of particle characteristics on the spatial distribution of splash. The objective of this work is to study the splash distribution of different size fractions for aggregated soils. We used a recently proposed theory for spatial distribution by splash to interpret experimental data on the radial distribution of soil fragments splashed by simulated rainfall. A laboratory device with five concentric rings was used to determine average splash lengths for 16 fragment size fractions (0.05 to >2000 μm) of rout soils. Sieved soil (3- to 5-mm size fraction) was exposed to simulated rainfall at 29 mm h-1 and with a time-specific kinetic energy of 252 J m-2 h-1. We interpreted the measured masses of fragments splashed into the different rings using an approximate solution of the exponential splash distribution theory applied to the experimental design. We demonstrated that the theory is valid for hulk aggregated soil as well as for individual fragment size fractions. The derived average splash lengths ranged from 4 to 23 cm, depending on the fragment size and soil. Splash lengths were greatest for soil fragments of 100 to 200 μm, and decreased for finer and coarser size fractions. Comparison of these findings with physically-based theory suggests that the coarser fragments, 50 to 2000 μm, are transported as single airborne particles, whereas the smaller ones. <50 μm, are transported in groups in splash droplets. This interpretation is consistent with observations reported in the literature. [ABSTRACT FROM AUTHOR]