Impact of grazing on the input of organic matter and nutrients to the soil in a grass-encroached Scots pine forest

Abstract

In the Netherlands, grazing is used as a measure to counteract grass-encroachment in Dutch pine forests. A 7-year experiment with moderate and heavy grazing intensities versus non-grazed control situations was performed to evaluate the impact of grazing on nutrient cycling in these forest ecosystems. In this paper, changes in organic matter and nutrient input to the soil compartment due to grazing are quantified. Grazing resulted in a 50% reduction of grass shoots, which was partly caused by a lower biomass production (35%). Grass root production and input also decreased by about 30%. Total litter input in the pine stand was only reduced by 20%, due to the lack of impact on tree litter input. The relative contribution of pine litter to the total litter input increased from about 30 to 40%. Grazing also reduced the input of nutrients, but reduction was not equal for all nutrients. Changes in nutrient input were not a result of changed nutrient concentrations in litter, but were due to shifts in the relative contribution of different litter types. Potassium was most reduced (30%) and reduction was mainly due to biomass consumption, while the input of N and P (20–23% reduction) was mainly affected by decreased production of grass roots and shoots. The input of Ca was least affected by grazing: 10% reduction. Reduced input of fresh litter and nutrients and an increased contribution of pine litter may result in lower decomposition rates and presumably decreased nutrient availability. This may affect biomass production and nutrient cycling through the grass layer.