The invasion of non-native epiphyte Platycerium bifurcatum in Auckland’s urban forest canopy

New Zealand has been subject to extensive plant introductions since the 1840s leading to c. 2700 naturalised plant taxa including 500 serious environmental weeds. To date, non-native plant invasions in New Zealand have not included epiphytic invasions in forest canopies. Numerous records indicate non-mediated naturalisation of individuals of the non-native epiphytic fern Platycerium bifurcatum have been made; further, recent survey work on urban epiphytes identified a number of juveniles across the Auckland isthmus. To investigate the extent of P. bifurcatum naturalisation across Auckland we identified 30 mature plants of varying sizes that had been planted across the Auckland isthmus on both public and private land using iNaturalist NZ. A further 46 mature plants were identified during field surveys and whilst driving between field sites. All adult plants were measured and all publicly accessible walls and trees for up to 100 m around each plant were checked for juvenile plants. We recorded 104 juvenile (naturally established) plants; all but 19 had at least two publicly accessible adults within 100 m. Platycerium bifurcatum is establishing on trees with fissured or cracked bark-types and on scoria walls. Where large, fertile specimens of P. bifurcatum occur within 100 m, and suitable surfaces are available, this non-native epiphyte is successfully establishing in Auckland’s urban forest canopy. The potential for this non-native epiphyte to spread into native forest ecosystems is not assessed in this study; however, key risks are highlighted along with suggested next steps to monitor and potentially control P. bifurcatum before this fern can invade.