Rock dust as a restoration measure for acidified forests: from mineral to helicopter

In the Campine, the main forest area of Flanders, acidifying nitrogen deposition is exceeding the critical load for decades. Consequently, many forests have acidified soils. Soil acidification has negative effects, including the leaching of base cations (Ca, Mg, K), which lower forest vitality and productivity. To assure the continued delivery of ecosystem services by forests, soil restoration has to tackle the root of the problem, i.e. the acidity and low base saturation. Rock dust (RD) application is a potential remedy to supply base cations to acidified systems. These silicate powders are by-products of mining with a high nutrient content and acid neutralizing capacity. RD weathers slowly, but the slow release is an advantage over liming and soluble fertilisers that may deteriorate ecosystem health. RD application is well studied in agriculture but research in forestry is in its infancy. The aim of the project is to evaluate RD types and particle sizes as a measure to restore acidified sandy forest soils. We will set up lab experiments of accelerated RD weathering to quantify acid neutralizing and fertilising dynamics. Subsequently, field trials in the forest with RD amendment will be performed in comparison with conventional lime and fertiliser treatments, and response in terms of soil nutrient status and seedling growth will be monitored. Finally, long-term effects of rock dust will be evaluated by assessing soil and tree growth responses to realworld RD applications.