Addo's vegetation is remarkable because in a relatively small area, five of South Africa's biomes are found.

Much larger parks such as Kruger National have only one biome. Biomes can be defined as the major communities of the world, classified according to their predominant vegetation and characterised by adaptations of organisms to that particular environment. Biomes are characterised by a similar association of species, comparable climates, and consistent soil types.

The original Addo-Elephant area is mainly covered by subtropical thicket (also known as valley bushveld), characterized by impenetrable Spekboom. It was this vegetation that protected the last remaining elephant and buffalo from being wiped out by hunters.

The Zuurberg Mountains harbour deep wooded kloofs and streams. In the exposed higher altitude areas, grassland and fynbos are found. Moving inland over the mountains the area around Darlington Lake turns to succulent Karoo-type (arid semi-desert) vegetation known as Noorsveld. On the seaward side of the original elephant section the Woody Cape section contains a remarkable display of coastal dune-fields and coastal grassy plains. Moving east the Alexandria Forest is an excellent example of pristine temperate forest.