At regional to global scales there is strong evidence of declines
in species diversity in non-urban ecosystems accompanied by
increases in exotic species (Sax & Gaines, 2003; Muller & Bornstein,
2010). Research on urban biodiversity however, shows that there
are increases in biodiversity in cities due to invasive species as well
as human interventions in planting horticultural species (Marris,
2011). Unlike in non-urban habitats where Sax (2002) and Brown
and Peet (2003) found that native and exotic diversity are often
positively correlated, suggesting that where species richness has increased (Sax & Gaines, 2003), urban floristic diversity often comes
at the expense of the native landscape.