I have 1,612 verified observations on iNaturalist between Auckland and Whangarei documenting 552 species (mostly invertebrates) covering forest, freshwater, intertidal and marine habitats. I don’t take many photographs of plants. Of these observation 96 or 17% of species were introduced. Here is a break down showing areas where I have found more or less introduced species:

Hauturu Aotea Tawharanui East Auckland Waitakeres Hunua Ranges Rangitoto / Motutapu / Motuihe Motukorea Mungatapere
Observations 206 149 141 197 77 94 71 33 159
Species 86 84 86 120 57 64 52 25 83
Introduced 6 12 8 35 1 4 11 4 9
Percent introduced 7 14 9 29 2 6 21 16 11

I expected the restored and protected islands in the Hauraki Gulf to have a smaller percent of introduced species. I think the high number of introduced species (compared to the Waitakeres and the Hunua Ranges) reflects the islands farmed history with islands like Motukorea and Motutapu still dominated by kikuyu. The larger and older the forest the more indigenous biodiversity.