The Escarpment Mine on the Denniston Plateau has been tentatively approved by the Environment Court, subject to suitable mitigation plans. One of the issues that may be under consideration is what to do about the site’s population of the Sticherus tener umbrella fern.
Sticherus tener has a conservation ranking in New Zealand of Nationally Critical. That is as rare as you can get without being extinct.
Destroying a population of a species so threatened in New Zealand has to be weighed against the economic benefits of the proposed mine. Of course, the Denniston area’s natural values are far greater than this one fern species. A factor in any consideration specific to Sticherus tener is that it is common in Australia. In that context, it is similar to the white heron or kōtuku (Ardea modesta), which graces our $2 coins. The white heron is also Nationally Critical in New Zealand, but Secure Overseas. Would New Zealanders accept a development destroying part of the white heron population in New Zealand?
Our paper detailing the status of Sticherus tener in New Zealand has just been published. Sticherus tener was known in New Zealand only from one 1980s record from Fiordland. Department of Conservation staff have recently made additional records from Fiordland. Furthermore, Te Papa’s botanists realised that some of the plants in the Stockton and Denniston areas are actually Sticherus tener.
Our paper also recognises Sticherus urceolatus in New Zealand for the first time. Sticherus urceolatus is closely related to Sticherus tener, and also is Nationally Critical in New Zealand while being common in Australia. Sticherus urceolatus occurs at Stockton (but not Denniston), near Takaka, and apparently in Fiordland.
Populations of Sticherus tener and Sticherus urceolatus in the northern South Island had previously been mistakenly attributed to Sticherus flabellatus. We now believe that Sticherus flabellatus does not occur in the South Island, but it is common in the northern North Island. When the Denniston population was erroneously attributed to Sticherus flabellatus, an issue for the proposed mine was the destruction of a population at the southern limit of a species common in New Zealand. The correct identification of the Denniston population as Sticherus tener, Nationally Critical in New Zealand, makes the conservation implications for the proposed mine more serious.
It was an internet photo that first alerted me to the possibility of Sticherus at Denniston being more complicated that everyone thought. I was trying to find more information about Denniston for our 2012 field work surveying for the then-undescribed Gleichenia inclusisora tangle fern; this Naturally Uncommon species also occurs at Denniston. I came across a report containing a photo from Denniston labelled “Sticherus flabellatus”. I was immediately sure that the photo did not show Sticherus flabellatus, but instead some other species of Sticherus. However, determining the correct identity as Sticherus tener took several more months. This involved a revision of existing herbarium specimens from the northern South Island that were labelled “Sticherus flabellatus” (all actually either Sticherus tener or Sticherus urceolatus), DNA sequencing, and field work to visit the sites ourselves.
Interestingly, the Forest and Bird-organised BioBlitz of the Denniston Plateau in 2012 did not detect Sticherus tener. That this medium-sized fern was missed by such a concerted effort to document the area’s biodiversity is a cautionary indicator of how difficult it is to make well-informed land management decisions.