Biodiversity can be defined as the variability among living organisms, from tiny insects to tall trees, from all sources including among other things, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and ecosystems.

When evaluating biodiversity particular value is given to native species and natural habitats (i.e. species and habitats which can be shown to be present in Ireland or in the Phoenix Park for a very long period).  This approach considers more recent arrivals (plants and animals) as being of low interest. 

The Phoenix Park has ongoing management measures that are sensitive to biodiversity.  Such measures include wildlife sensitive grass management, allowing trees to die naturally within conservation zones and the minimal use of chemicals and fertilizers.  Further measures will continue to be introduced in line with the proposals in  the Phoenix Park Conservation Management Plan 2008 and best practice.