Changes in Biodiversity: Lower Organisms, Vegetation and Flora

Biodiversity is a framework concept, referring to the variety of life on Earth, and in this sense the concept is neither measurable nor quantifiable. However, specific features of biodiversity, e.g. species richness of taxonomic groups can be quantified. Circa 2% of the total number of identified species on Earth, roughly 35,000 species of plants and animals, live in the Delta, comprising roughly 25,000 species of animals (and among them 18,000 insects), and more than 10,000 plants, and among them ca. 1,400 higher plants (seed-plants or Spermatophyta). For a few hundreds of species the Delta has a (great) international significance, and this counts in particular for waterfowl (Chapter 19) (www.mnp.nl/natuurcompendium).

In this chapter data will be given on the historic changes in the biodiversity of aquatic and terrestrial organisms, mainly plankton, aquatic macro-invertebrates, aquatic macrophytes and terrestrial vegetation of higher plants. The changes in the vegetation of the Biesbosch wetland are highlighted in a case study, because this national park is one of the few areas in the Delta where the flood-plain vegetation is allowed to flourish unrestrained, hence mimicking a semi-natural succession of flood-plain vegetation, developing under almost non-tidal conditions. Some notes on the human use of rushes, reeds and willow trees will close this chapter.