Soil nitrogen concentrations have been rising for decades and in combination with growing wild ungulate populations poses great threats to the regeneration of mixed temperate forests. Rock dust could be a solution to the negative effects of nitrogen in the long run, but it could also work counterproductive.
Nitrogen, although an essential nutrient for plant growth, currently is causing problems in the Dutch ecosystems. Due to a high atmospheric deposition, nitrogen causes acidification and eutrophication. These changed acidic conditions and nutrient availability favors certain vegetation communities, especially coniferous or fast-growing species. In addition, temperate broad-leaf forests have difficulty regenerating on more acidic soils and in mixed forests have a hard time competing with conifers.
To improve the current degraded soil, different measures can be taken like applying slow- or fast-releasing fertilizers. By adding fast-releasing fertilizers like lime, acidic soils can drastically improve in a short period of time. However, this rapid release can cause nutrient leaching and unwanted fast-growing species can dominate the system. Therefore, slow-release fertilizers like rock dust are more efficient in the long-term. By slowly releasing minerals and recharging the buffer capacity, the soil quality will improve generally, the system is more resilient to acidification caused by the atmospheric nitrogen deposition and probably there are fewer risks of nutrient leaching.
Wild ungulates have an important function in a forest, controlling their environment via browsing or trampling. However, in the northern hemisphere, their densities have grown significantly in recent decades creating problems in different natural systems. For instance, their browsing preference for deciduous trees over coniferous species causes great pressure on the broad-leaf tree regeneration in mixed temperate forests. In addition, due to a lower soil quality caused by atmospheric deposition and fewer minerals, the general food quality is lower as well, increasing the browsing pressure on these tree species even more. By adding rock dust, the soil quality would improve, raising the food quality as well. However, it is suggested that this improved quality will also further increase the browsing pressure.
We aim to understand the effects of rock dust application on forest regeneration and its subsequent effect on the wild ungulates in the Veluwe region in the Netherlands. To monitor these effects, we will collect leaf- and litter samples and analyse camera trap data to see the effects of rock dust on the system. We expect that the general soil- and leaf quality will slowly improve over time, which will make the system more resilient. However, broad-leaved tree species treated with rock dust will probably be exploited more intensively by wild ungulates which will hamper their natural regeneration.
The results will provide a better understanding on how slow-releasing fertilizers affect mixed temperate forests, especially how wild ungulates respond to the improved quality which can be used to better help conserve mixed temperate forests, its biodiversity and make them more resilient to e.g. climate change.