Taxonomic Notes
The Kermadec Islands Rhopalostylis were initially described as an endemic species R. cheesemanii based on fruit and seed characters (de Lange et al. 2005). Sykes (1977) treated R. cheesemanii as a variety of the Norfolk Island R. baueri until further investigation by de Lange et al. (2005) relegated the Kermadec plant into full synonymy with R. baueri (thus rendering it indigenous to the Kermadec Islands).
Justification
Rhopalostylis baueri is a tree indigenous to Norfolk Island and Aotearoa / New Zealand, where it occurs on the Kermadec Islands (Raoul Island). The species is considered abundant on Raoul Island, and on Kermadec Islands it is no longer considered threatened. The only major risk to the species is volcanic eruptions, as Raoul Island volcano is extremely active. On Norfolk Island Rhopalostylis baueri is very localized and confined to the Norfolk Island National Park. There is no urgent threat to the species other than possible threat of volcano eruption and the fact that regeneration is limited by seed predation by rats, and serious weed issues. Volcanism is part of this palms ecology, however, should the volcano erupt in a way that the population is eradicated on Raoul Island then most of the population would be lost and the species could become Endangered in a short time frame. It is assessed as Near Threatened.
Geographic Range Information
This species is indigenous to Aotearoa / New Zealand where it occurs on the Kermadec Islands (Raoul Island), as well as on the Norfolk Island group (Norfolk Island). Distribution map is generalised.
Population Information
No accurate population estimate for this species is known. Sykes (1969, 1977) noted it was extremely uncommon due to goat browsing pressure with most trees, saplings and seedlings occurring as epiphytes on tree ferns (Alsophila kermadecensis, A. milnei) or on cliff refugia. However, following the eradication of feral goats (Capra hircus) in 1984 (Parkes 1984) the species rapidly spread from these sites across the island, and it is now commonly found in all forested habitats except the absolute coastal fringe forest on Raoul Island (29.38 km2). The population is still recruiting and expanding its range and at most sites comprises numerous seedlings, subadults and adults.
Habitat and Ecology Information
Rhopalostylis baueri is abundant throughout the two main forest associations of Raoul Island dubbed ‘dry’ and ‘wet’ forest by Oliver (1910). Ranging from near sea level to the island’s summit Moumoukai (516 m asl). It is, however, still more common in the ‘wet’ forest where it is a common understory tree, although in a few places such as along ridge lines and along ravines, especially toward the ravine heads (de Lange 2023) it can form part of the canopy. In some locations, Rhopalostylis baueri forms the dominant subcanopy almost to the exclusion of other species. It co-associates with Metrosideros kermadecensis, Melicytus ramiflorus subsp. ramiflorus, Piper excelsum subsp. psittacorum and in the upper portion of the island Coprosma acutifolia and Ascarina lucida var. lanceolata.
Threats Information
On the Kermadec Islands Rhopalostylis baueri was once threatened by feral goat browsing and seed predation by rodents (Oliver 1910, Sykes 1969, 1977, Parkes 1984). Feral goats once rampant on Raoul Island, were eradicated in stages from 1937 to 1984 (Parkes 1984) and rats in 2002 (de Lange and Havell 2009). From the 1960's onwards R. baueri rapidly recovered from browsing pressure and spread across the island (Sykes 1993, Sykes and West 1996). R. baueri is now an abundant component of most of the forested portions of Raoul Island (de Lange 2023). Within the Kermadec Islands part of this species' range it is no longer considered threatened and is currently listed as ‘At Risk / Naturally Uncommon’ by the New Zealand Indigenous Vascular Plant Threat Listing Panel (de Lange et al. 2018). The only major risk to the species is volcanic eruptions, a risk which all Kermadec biota face as Raoul Island volcano is extremely active.
On Norfolk Island Rhopalostylis baueri is confined to the Norfolk Island National Park (6.5 km2) where aside from a small stand (Palm Glen) it is found as widely scattered specimens. Regeneration is limited by seed predation by rats, and serious weed issues, especially from Psidium cattleianum and Schinus terebinthifolius.
Use and Trade Information
This species is occasionally cultivated in Aotearoa / New Zealand.
Conservation Actions Information
Provided Raoul Island remains predator free Rhopalostylis baueri is unlikely to be threatened there. The only major risk to the species is volcanic eruptions, a risk which all Kermadec biota face as Raoul Island volcano is extremely active. For example, it has erupted at least five times since eruptions were first documented from there in the 1830's (Gentry 2013). Natural events aside the main risk to the species, and indeed all the island’s biota, is the potential for new incursions of pest species – as such it is imperative that biosecurity measures currently in place are maintained. During the sars-cov-2 outbreak the resident rangers on Raoul Island were evacuated back to Aotearoa / New Zealand (2020) and since that time there has not been a continuous human presence on the island. This is a risk as the island is frequently visited by boats / ships and illegal landings could be a source of new diseases / pest incursions.