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Homalium acuminatum

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Taxonomy [top]

Kingdom Phylum Class Order Family
PLANTAE TRACHEOPHYTA MAGNOLIOPSIDA VIOLALES FLACOURTIACEAE

Scientific Name: Homalium acuminatum
Species Authority: Cheeseman
Common Name(s):
English Rarotonga Homalium
Taxonomic Notes: The claim of endemic status for Homalium acuminatum is complex but the current author of draft Cook Islands flora, W.R. (Bill) Sykes states that he is maintaining H. acuminatum as endemic. Believing that for any threat assessment a conservative approach needs to be called for we have accepted this status for now.

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2014
Date Assessed: 2011-03-29
Assessor(s): de Lange, P., Martin, T. & McCormack, G.
Reviewer(s): Sayer, C.
Justification:
Homalium acuminatum is the dominant endemic tree of the upper river terrace and slope forest of the central Island mountain range of Rarotonga. In that area it also extends down along the river terraces coming within 0.5 km of the sea in a few places along the southern side of the island. It is also occasionally seen within the start of the cloud forest (c. 500 m asl). Although it is one of the most abundant of the islands endemics, and populations seem stable at present, at some sites (especially along the northern and eastern side of the island, and especially in some of the more intensively settled parts of the island), weeds such as the introduced vines mile-a-minute (Mikania micrantha), balloon vine (Cardiospermum grandiflorum), balsam pear (Momordica charantia), passion fruit (Passiflora maliformis, P. rubra), and the merremia vines (Merremia peltata, M. tuberosa) are a long-term threat. Currently there are no measures in place to control these vines which rapidly smother the indigenous vegetation and play havoc with the canopy of damage forest. Currently we consider that Homalium is still too common to qualify as threatened but it is a species which needs to be monitored to ensure that the species remains stable as the population may be in slow decline in the weedier lowland habitats.

Geographic Range [top]

Range Description: Homalium acuminatum is endemic to the island of Rarotonga (67 km2), Cook Islands.
Countries:
Native:
Cook Islands (Cook Is.)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: There is one population, found throughout the hill and mountain ranges on the island of Rarotonga (4,535 ha).
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Homalium acuminatum is a widespread, abundant, and typically dominant canopy tree of upper riverine terraces, slope and lower cloud forest habitats. It reaches its greatest abundance within the upper valley and slope forests of the central ranges of Rarotonga.
Systems: Terrestrial

Use and Trade [top]

Use and Trade: There is no trade in this taxon. Although the wood is used locally for some buildings and for cultural purposes, felling of Homalium acuminatum for timber is thought to have a minimal impact on this species.

The wood is very rarely used nowadays, as  it is very hard and difficult to work. Timber from H. acuminatum can be found in a few very old buildings (Gerald McCormack pers. comm. 2011).

Threats [top]

Major Threat(s): While Homalium is still the most widespread and abundant endemic tree species on the island it is potentially threatened by the spread of naturalised vines. The most serious of these vines are mile-a-minute (Mikania micrantha), balloon vine (Cardiospermum grandiflorum), balsam pear (Momordica charantia), passion fruit (Passiflora maliformis, P. rubra), and the merremia vines (Merremia peltata, M. tuberosa) all of which are aggressively colonising the habitats of Homalium.

Although we have no proof that Homalium is directly threatened by these vines, our observations within the lowland range of this species, which go back to 2000, suggest these vines are impacting on the species by smothering the canopy of the trees thereby not only killing the foliage but making trees top heavy and so susceptible to toppling. The impact of these vines has notably worsened since 2005 when we assume their seed was widely dispersed through the forest following five back to back cyclones.

A very slight decline in the range of Homalium is inferred from its scarcity on lower slopes and alluvial terraces along some parts of the northern and eastern portion of the main central range of Rarotonga.

Conservation Actions [top]

Conservation Actions: No conservation measures are currently in place.

Citation: de Lange, P., Martin, T. & McCormack, G. 2014. Homalium acuminatum. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 26 November 2014.
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