The forts and dikes of the Defence Line of Amsterdam are home to various remarkable plants and animals. This stems from the fact that they were constructed from dune sand with a top layer of clay. In contrast to the surrounding area, dune sand is low in nutrients.
This poor soil forms a good basis for meagre, grassy, herbaceous vegetation of high botanical value. This attracts many insects and spiders who, in turn, serve as dinner for birds or amphibians, for instance. Good examples of the great value of nature in these areas are the rare blue field madder (plant) and the Brown Argus butterfly. The trees and bushes provide mating, nesting, resting and feeding spots for birds, small mammals, insects and amphibians.
Once a year history comes alive at the Fort near Krommeniedijk. In early spring, part of the polder is flooded on purpose. Thus, the ‘principle’ behind the Defence Line of Amsterdam – inundation - is made visible. The event attracts hundreds of people, but also many meadow birds and migratory birds. Here you can see large gatherings of European golden plovers, lapwings, black-tailed godwits, ducks and geese. In 2014 a Defence Line visitor centre will open at the Fort near Krommeniedijk that will focus on nature and the landscape.