Plant richness patterns in agricultural and urban landscapes in Central Germany—spatial gradients of species richness

Urban areas are generally inhabited by greater numbers of plant species than rural areas of the same size. Though this phenomenon is well documented, scientists seem to be drawn to opposing views when it comes to explaining the high ratio of alien to native plants. Several ecological concepts claim that in cities, alien species displace native species. However, several studies show that both species groups increase proportionally. Another view tries to correlate the high species number in urban areas to the heterogeneity of the urban landscape. This correlation seems to be evident but still needs to be tested. Most of these findings stem from studies performed on large or intermediate scales using data from official databases. We wanted to confront existing findings and opinions with our study comparing a typical urban with an agricultural landscape section on a local scale. Our results support the view that plant species richness is higher in cities than in surrounding rural areas, partly because of a high rate of alien species brought into cities by humans. However, this species richness stems from an increase in alien as well as native species. Higher species richness is supported by a highly varying landscape structure mainly caused by anthropogenic land use.