Grazing as a measure to reduce nutrient availability and plant productivity in acid dune grasslands and pine forests in The Netherlands

Abstract

Grazing by large herbivores is applied as a management tool to counteract encroachment of tall grasses in species-rich vegetation. Its effects on soil organic matter and nutrient dynamics were studied in two ecosystems with acid sandy soil: a coastal dune grassland and an inland pine forest. Grazing resulted in a 2–6 fold reduction in standing crop and in 1.5–4.1 times reduced plant productivity. Plant nutrient stocks (uptake plus storage) were 1.3–2.4 times lower under grazed conditions. Root biomass was hardly affected in the coastal dune site, but significantly decreased in the forest site by a factor of 1.6. This reduction in nutrient stocks may be caused by the strong reduction in ‘available’ nutrients, such as NH 4, NO 3, K and N released through mineralisation, together with a potential reduction in nutrient storage in the plant and, in the case of lower root biomass, uptake capacity. Changes in stocks of soil organic matter and N-total were only detectable in the dune site, where the amounts of organic matter prior to grazing were very low, and not in the forest site with high initial stocks of soil organic matter. This study suggests that grazing may reduce nutrient availability by 50% in acid sandy habitats. In this way grazing will improve light conditions for short species and reduce the competitive abilities of the dominant species. The reduction in N-availability caused by grazing may also more or less compensate for the high atmospheric N deposition in the study area.