Homalium rubrocostatum is an endemic shrub of the north-western part of Grande Terre in New Caledonia. This species is known from 3 massifs: Kopéto, Paéoua and Boulinda. It is found in shrubland and humid forest on ultramafic substrates at an altitudinal range of 200-900 m asl. The main threat is presented by ongoing mining development in Kopéto, uncontrolled bushfires at Boulinda and potentially by future mining projects at Boulinda and Paéoua. Extraction projections for the coming 25 years could lead to a 50% reduction in the impacted subpopulations. Homalium rubrocostatum is assessed as Endangered (EN) under criterion A4c with an inferred population reduction of more than 50 % over three generations (75 years) starting in 1970 and projected to 2045; and under criteria B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v) with the number of threat-defined locations estimated to be four, a continuous decline of all concerned subcriteria and extent of occurrence (EOO) and area of occupancy (AOO) are respectively estimated to be of 67 km² and 20 km².

Geographical area

Homalium rubrocostatum is an endemic shrub of the north-western part of Grande Terre in New Caledonia. This species is known from 3 massifs: Kopéto, Paéoua and Boulinda

Population

Population size is unknown. Field surveys emphasized mostly isolated plants. Mining extraction projections for the coming 25 years could lead to a 50% reduction in the impacted subpopulations and thus contribute to the potential reduction of the total population size.

Habitat

Homalium rubrocostatum is found in shrubland and humid forest on ultramafic substrates at an altitudinal range of 200-900 m asl.

Threats

The main threat is presented by ongoing mining development in Kopéto and is linked to habitat damage by uncontrolled bushfires. This species can also be potentially impacted by future mining operations in Paéoua and Boulinda as well as bushfires at Boulinda (pers. comm. Veillon). New Caledonia contains 20 - 30% of the world’s nickel resources and has experienced intense mining activities since the late 19th century which has generated soil erosion (1.2% of bare ground mapped by SPOT5 in 2007). Based on the distribution of metal-rich soils and site accessibility, these threats are predictable and planned (there was a rise in nickel production from 60,000 to 200,000 tonnes per year between 2013 and 2015). Additionally, uncontrolled bushfires sweep across New Caledonia each year, especially during the dry season (an average of 20,000 ha of land is burnt each year, with dramatic peaks of 70,000 ha). Lowest parts of ultramafic areas are particularly exposed to such risk.

Conservation

Homalium rubrocostatum is protected by legislation in Province Nord and Province Sud, but does not occur in any protected area. It is recommended to collect an herbarium specimen to confirm the Paéoua and petit Boulinda subpopulations. This species would benefit from ex-situ and in-situ emergency conservation actions. It is proposed to monitor the known populations and to preserve a viable population within delimited perimeters in Kopéto. It would be moreover advised to conduct propagation tests in order to assist future planting operations.

Bibliography

L'Huillier L.; Jaffré T. and Wulff A. 2010. Mines et Environnement en Nouvelle-Calédonie : les milieux sur substrats ultramafiques et leur restauration.

Morat, P.; Jaffré, T.; Tronchet, F.; Munzinger, J.; Pillon, Y.; Veillon, J.-M. and Chalopin, M. 2012. Le référentiel taxonomique Florical et les caractéristiques de la flore vasculaire indigène de la Nouvelle-Calédonie [The taxonomic database « FLORICAL » and characteristics of the indigenous flora of New Caledonia]. Adansonia sér 3(34) , p.177-219.

Endemia.nc 2016. Faune et Flore de Nouvelle-Calédonie.

Wulff AS, Hollingsworth PM, Ahrends A, Jaffré T, Veillon J-M, L’Huillier L, et al. 2013. Conservation Priorities in a Biodiversity Hotspot: Analysis of Narrow Endemic Plant Species in New Caledonia.

Experts

Assessor(s): Tanguy, V., Veillon, J., Amice, R., Barrière, R., Chambrey, C., Fleurot, D., Lannuzel, G.

Reviewer(s): Vandrot, H.

Contributor(s): Wulff, A.

Facilitator(s): Chanfreau, S., Tanguy, V.