Dutch nature and biodiversity are being threatened by issues such as desiccation, fertilisation, acidification and fragmentation. The Dutch government has been outlining measures to improve the environment since the end of the eighties in the last century. Even now, more than twenty years later, neither spatial cohesion nor environmental quality are good enough to maintain biodiversity. This means that the Netherlands is not complying with either the European Commission’s standard for the maintenance of bio diversity or Natura 2000. Further measures are required, such as switching to a more sustainable form of agricultural management.
Some of these issues are more significant than others in the struggle to achieve the required spatial and environmental quality. Two-thirds of Dutch nature reserves, for example, are below standard in relation to at least one factor. Undue nitrogen deposition is a major problem for most of the reserves, while almost all wetlands are labouring with desiccation. As a rule, insufficient spatial cohesion is an additional problem for these nature reserves. Measures undertaken in relation to soil acidity have, for the most part, resolved acidification problems.
As part of the annual Environmental Balance report of the PBL Netherlands Environmental Assessment Agency, Alterra has researched the quality of Dutch nature reserves. This research has been carried out in relation to four risk factors which together in equal measures determine the quality of the nature reserves:
- The quantity of nitrogen which deposits from the air onto nature reserves and results in fertilisation. The maximum amount before plant species disappear has been determined. This is the critical deposition level. If this level is breached then the problem is recorded on a map.
- The degree of soil acidity. In the past, sulphur emissions resulted in ‘acid rain’, which acidified the soil. The degree of soil acidity, which is deduced from what has been taken up by the vegetation, is compared with what the vegetation actually prefers. If the soil is too acidic, the corresponding areas are recorded on a map.
- The ground water level is only relevant when it causes problems for vegetation sensitive to it. The levels are compared to the level which conforms to the ideal conditions for this vegetation. If groundwater level is too low, then this level is also recorded on a map.
- The spatial cohesion of nature reserves has been researched in regards to eighty species listed in the Habitats Directive’s Annexes II and IV and Annex I of the Birds Directive. This spatial cohesion was determined by the LARCH model. Reserves where the cohesion for one or more species is deemed insufficient were, once again, recorded on a map.
The four maps of the problem reserves have been joined together into one overview map. Reserves with only one problem can be found throughout the Netherlands. This is also true for reserves without problems. The nature reserves situated on sandy soil such as in the centre of the Netherlands, dunes but also isolated areas in the east typically have problems with excessive nitrogen deposition. In wetlands, such as marshes and moorlands, the problem lies in most cases with low ground water levels. Reserves in the east suffer from insufficient spatial cohesion. In these areas natural habitats can be too small or too isolated to sustain a sustainable population of protected species. There is no nature reserve where all four of the risk factors are present.
The completed research project clearly illustrates that the spatial and environmental conditions required in order to maintain Dutch biodiversity and to comply with the standards set by the EU are often not being met. In consequence, some nature reserves, including those categorised as Natura 2000 sites, are still nowhere near able to properly conserve habitats and species. Further measures should be put in place in order to satisfy the goals stipulated in part by the EU’s Habitats and Birds Directives. These measures can be enacted in both the field, for example by building robust connections between large and small nature reserves, and at the source, for example by preventing the emission of nitrogen (ammonia and nitrate). A solution could also lie in a more sustainable form of agricultural management, but this would require a fundamental shift in European agricultural policy.