This guest blog is for keen botanists or anyone who wants to know more about the endemic L’Esperance groundsel that was mentioned in the last post and is listed as a plant ‘under threat’. For this blog I have handed the reigns over to resident DoC botanist Peter to talk about his visit to L’Esperance Rock with Warren, and the full story on the genus Senecio in the Kermadecs:
There are two endemic Senecio known from the Kermadecs, the so called Kermadec fireweed (Senecio kermadecensis) and the L’Esperance Rock Groundsel (Senecio lautus subsp. esperensis) both are listed as “Threatened/Nationally Critical”.
In the case of Kermadec fireweed it is threatened by loss of habitat and competition from weeds. That species was once common on Raoul Island and the Herald Islets but by the 1960s was all but extinct on Raoul. This is still pretty much the case today.
In 2009 material was taken back to New Zealand to grow and all of this soon succumbed to the water and soil borne pathogen Phytophora. On Raoul plants persist around the Accommodation House because DOC staff look after them – otherwise attempts to naturalised it on the island have been largely unsuccessful. On the Herald Islets Senecio kermadecensis is still locally common, though it does seem to be in decline on the Meyers.
Anyway, on these islands it is consistently associated with sea bird nesting grounds and we strongly suspect that it is dependent on these birds for nutrients, habitat creation and dispersal. As these birds are only just colonising Raoul Island again (following the rodent/cat eradication) it may be some time before conditions are suitable for it to thrive on Raoul.
Of concern is the spread of blue billy goat weed (Ageratum houstonianum) a common garden plant in New Zealand that was deliberately naturalised on Raoul in the 1940s and which has rapidly spread across the island and onto the Meyers. It too is a daisy, and it is easily spread by wind, bird and humans. It grows in exactly the places Senecio kermadecensis grows and it is faster growing.
On our recent field work we have seen Ageratum outcompeting Senecio on the Meyers. We also noted that Ageratum was absent from Napier, Nugent, Dayrrel and North Chanter – islands with large populations of Senecio kermadecensis. Hopefully they stay that way, though we suspect it is only a matter of time before the Ageratum colonises there. Currently there is no realistic way to control this weed.
L’Esperance Rock groundsel seedlings sharing turf with a stingless member of the nettle family Parietaria debilis © P de Lange
The L’Esperance Rock groundsel is endemic to L’Esperance Rock where it has not been reliably reported from since 1988. The photo shows seedlings growing with Parietaria debilis (a stingless member of the nettle family). Today we managed to access the rock and found many 100s of plants in an area of less than 1 hectare (much less) along the main summit ridge. Being a spring annual we were lucky to see it and we mainly saw tiny seedlings and a few subadults. Old stems of it indicate that in good conditions it may get 1 metre tall.
This plant is threatened by its small area of occupancy – which although natural, is so small it could easily be wiped out. Also in the past its habitat had been occupied by a small emergency fuel hut where aviation fuel was kept by helicopter pilots as a stop over refuel station for trips to Raoul.
In 1988 concerns had been expressed over this fuel dump as fuel was seen to be leaking into the Senecio habitat. Today we found no such hut and no old fuel barrels lying in the crater (these had been reported in 1988). As far as we can tell the hut was destroyed by Cyclone Bune in late March 2011 and we assume the old leaking barrels were washed away as well.
Aside from these two Senecio we have seen no other Senecio during our visit and I would be very surprised to see S. scaberulus there as this is a clear cut New Zealand endemic mostly confined to Northland. Of course ragwort had been recorded from Raoul and eradicated but this plant is now treated as Jacobaea vulgaris rather than Senecio jacobaea.
