Trochetiopsis erythroxylon 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Magnoliopsida Malvales Malvaceae

Scientific Name: Trochetiopsis erythroxylon (G.Forst.) Marais
Common Name(s):
English St Helena Redwood, Redwood
Melhania erythroxylon (G.Forst.) Aiton
Pentapetes erythroxylon G.Forst.
Trochetia erythroxylon (G.Forst.) Benth.

Assessment Information [top]

Red List Category & Criteria: Extinct in the Wild ver 3.1
Year Published: 2016
Date Assessed: 2015-06-16
Assessor(s): Lambdon, P.W. & Ellick, S.
Reviewer(s): Clubbe, C.P.
Contributor(s): Cairns-Wicks, R.
The last wild St Helena Redwood tree (Trochetiopsis erythroxylon) died in the 1950s. Small numbers of cultivated specimens have been replanted in wild situations since the 1980s, but many of these have fared poorly and no recruitment has been observed.
Previously published Red List assessments:

Geographic Range [top]

Range Description:The Redwood is endemic to St Helena, South Atlantic Ocean. It is no longer found in the wild but is cultivated in several places on the island.

Much uncertainty surrounds the original wild range of the species. Melliss (1875) reported wild trees at High Peak and Diana’s Peak, and since these locations hold the last fragments of indigenous cloud forest, it has often been assumed that the species belonged to this community. However, recent plantings in high altitude locations have not succeeded; repatriated individuals are vulnerable to strong winds and do not thrive in the very damp climate. It may therefore be significant that Melliss reported the plants to be found “in the glens”, perhaps instead suggesting a preference for the sub-montane belt between 550 and 700 m altitude. This zone appears to fit with the last known wild location, below High Peak at the head of Peak Dale Gut. Banks (1896) also asserted that they “refuse the highest ridges” and Roxburgh (see Beatson 1816) noted them “on moderately high hills”. On this assumption, it could be speculated that the range extended over parts of the upper mid-altitude zone of St Helena, particularly in sheltered valleys and on richer soils.
Countries occurrence:
Regionally extinct:
Saint Helena, Ascension and Tristan da Cunha (Saint Helena (main island))
Additional data:
Estimated area of occupancy (AOO) - km2:0
Number of Locations:0
Lower elevation limit (metres):550
Upper elevation limit (metres):700
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Although a number of trees were present in gardens during the late 19th Century, the cultivated stock appears to have died-out and it is thought that the last wild tree at Peak Dale was the only surviving plant by 1950 (Cronk 2000). All extant specimens are now derived from seed collected from this individual. Cronk guessed that the cultivated population numbered around 60 plants in 2000, and it is likely that the total is approximately the same today.
Additional data:
Number of mature individuals:0

Habitat and Ecology [top]

Habitat and Ecology:Even the basic ecology of the Redwood is now difficult to reconstruct, presenting a considerable obstacle to further conservation. Roxburgh (see Beatson 1816) reported it to be a “middling-sized tree”. Plants today are slender, rarely exceed 3 m in height and usually do not survive for more than 20 years. It is quite possible that the typical growth form was stronger and more robust in the past, and the hard, red wood once used for construction purposes must have been harvested from much older specimens than those currently known (Cronk 1983). Flowering may occur throughout the year under favourable conditions, and the large, pendent blooms produce copious pollen and nectar. They are visited by a wide range on insects and are also self-fertile. Seed set is usually good but severe predation from mice (Mus musculus) occurs in many places. The seed is moderately large and heavy with no obvious means of dispersal, though it is possible that it was once taken and distributed by forest birds which have long since died-out.
Movement patterns:Not a Migrant

Threats [top]

Major Threat(s):

The extinction of the Redwood from natural habitats was, primarily, almost certainly a result of deforestation. Following the establishment of a permanent colony on St Helena by the East India Company in 1659, the middle altitude zone of the island was rapidly cleared to make way for pasture and the forests were felled for timber and fuel. Feral pigs (Sus domesticus), which were then prevalent on the island, were probably responsible for uprooting large numbers of seedlings. By the mid 18th Century only small fragments of the original native woodlands remained, and these had vanished almost entirely by the early 1800s. With the exception of a few preserved stands of Gumwood (Commidendrum robustum (Roxb.) DC.), no descriptions have survived  of the original vegetation of this zone. It is known that Redwood timber was much sought after and the bark was used for tanning.

Today, there are considerable challenges in preserving the remaining vestiges of the species. All extant individuals are derived from a single tree. This severe genetic bottleneck appears to have resulted in serious inbreeding depression, with many rearing attempts failing because the plants die as saplings or exhibit severely retarded growth. It is also possible that the Redwood once formed specific mycorrhizal associations which have now been lost, and this could also impair survival. The adults are susceptible to pests and diseases, particularly Vine Weevils (Otiorhynchus sulcatus Fabricius), and seed predation by mice (Mus musculus) is rife at some seed orchards. However, there is considerable variation in vigour between individuals, and small numbers grow into reasonably strong, shrubby trees exceeding two metres in height.

Conservation Actions [top]

Conservation Actions:

Experiments involving artificial selection have demonstrated that the health of the population can gradually be improved by careful manipulation (Rowe, 1995). Interspecific crosses between T. erythroxylon and the related Dwarf Ebony (Trochetiopsis ebenus Cronk) also produce fertile offspring with greatly increased vigour, and this could offer a possibility to accelerate the removal of deleterious alleles. A limited programme of back-crossing hybrids to T. erythroxylon parents has been conducted by Rebecca Cairns-Wicks. Thus far, F3 plants have been obtained, a few of which display very convincing redwood-like phenotypes, and maintain substantially increased growth rates (R. Cairns-Wicks pers. comm. 2014).

However, in order for such efforts to be successful, operations must be long-term and conducted on a much larger scale, as the small numbers of plants currently managed are very prone to accidental losses. In addition, it is important to preserve the genetic material from as many of the older plants as possible to avoid selective processes from further eroding the gene pool. Careful records of all crosses must be maintained so that genetic provenance can be traced.

A management plan has been produced (Cairns-Wick 2007), on which the above summary is based, but there are several barriers to achieving the goals. These include a lack of finances, local expertise, facilities and training. Furthermore, the short life cycle of today’s plants requires reasonably intensive efforts to replenish and increase the population. The situation is currently precarious: the ongoing programme is minimal, and periodic loss of trained staff and reallocation of budgets on St Helena could lead to further gaps, with serious consequences. As a safeguard against such problems, some seed has been placed in long-term storage, both on St Helena and at Kew's Millennium Seed Bank in the UK.

Citation: Lambdon, P.W. & Ellick, S. 2016. Trochetiopsis erythroxylon. The IUCN Red List of Threatened Species 2016: e.T30560A67371983. . Downloaded on 20 September 2018.
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