Taxonomy

endemique
protegee
UICN

Synonyms

Blackwellia polystachya Vieill.

Red List Status -

Critically Endangered (CR) , assessed in 10/09/2015

Protected species -

in Northern Province , in Northern Province

Homalium polystachyum is a narrow endemic tree restricted to the north-west of Grande Terre in New Caledonia. Within that genus, Homalium polystachyum is a discrete taxonomic entity. It is is found in shrubland and humid forest on ultramafic substrate at an altitudinal range 450-550 m asl. The main threat is linked to on-going mining activities on Tiébaghi area. Extraction projections in the coming 25 years leads to the extinction risk of the main sub-population. Homalium polystachyum is therefore considered as Critically Endangered (CR) with criteria A4c and a 80% estimated reduction of population within 25 years.

Geographical area


Homalium polystachyum is a narrow endemic tree restricted to the north-west of Grande Terre in New Caledonia, only known from two localities :Tiébaghi and Ile Art from a single herbarium specimen which dated from 1975.

Population


Mature individual population size is not precisely known, but based on information from experts, it is estimated for Tiébaghi sub-population, which seems to be the largest, around 1000 mature individuals.

Habitat


Homalium polystachyum is found in shrubland and humid forest on ultramafic substrate at an altitudinal range 450-550 m asl.

Threats


The main threat is linked to on-going mining activities on Tiébaghi area. Extraction projections in the coming 25 years leads to the extinction risk of the sub-population. New Caledonia contains between 20 - 30% of the world’s nickel resources. Intense mining activities since the late 19th century have 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 (rise in nickel production from 60,000 to 200,000 tons per year between 2013 and 2015). Ile Art may be severely damaged by uncontrolled bushfires. A fire outbreak could affect the entire sub-population.

Conservation


Homalium genus is protected by legislation but does not occur in any protected area. Through a partnership in 2015 with IAC (Institut Agronomique néo-Calédonien) and SLN (Société le Nickel) a monitoring program was set-up but only a few seed collection has been made so far. This species would benefit from in-situ and ex-situ emergency conservation actions. It is recommended to ensure the follow-up of existing populations and to preserve viable populations on delimited areas on Tiébaghi. It is moreover advised to realize multiplication tests in order to design a replant program and to prospect actively Ile Art.

Bibliography


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

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.

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.

Experts


Assessor(s): Tanguy, V., Veillon, J., Amice, R., Barrière, R., Fleurot, D., Gailhbaud, P., Garnier, D., Suprin, B.

Reviewer(s): Vandrot, H.

Contributor(s): Wulff, A.

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


Geographical distribution