Aloe dichotoma Masson

Taxonomy
Scientific Name
Aloe dichotoma Masson
Higher Classification
Monocotyledons
Family
ASPHODELACEAE
Synonyms
Aloe dichotoma Masson var. dichotoma , Aloe dichotoma Masson var. montana (Schinz) A.Berger, Aloe montana Schinz, Aloe ramosa Haw., Rhipidodendron dichotomum (Masson) Willd., Rhipidodendrum dichotomum (Masson) Willd.
National Status
Status and Criteria
VU A3ce
Assessment Date
2005/09/23
Assessor(s)
W. Foden
Justification
Climate change models project a 36% decline in range in 100 years, assuming dispersal into newly suitable areas. Patterns of modelled declines have been supported by field and repeat photo studies. However no colonization of newly suitable areas has yet happened. Without dispersal, the models predict a 73% decline in 100 years, qualifying the species as EN.
Distribution
Endemism
Not endemic to South Africa
Provincial distribution
Northern Cape
Range
From Nieuwoudtville east to Olifantsfontein and northwards to the Brandberg in Namibia.
Habitat and Ecology
Major system
Terrestrial
Major habitats
Desert, Nama Karoo, Succulent Karoo
Description
On north-facing rocky slopes (particularly dolomite) in the south of its range. Any slopes and sandy flats in the central and northern parts of range.
Threats
Main threats include climate change, harvesting and trampling by livestock. Damage by baboons, scale insects and fungus has been observed, but none of these seem to cause mortality.
Population

There is a large amount of morphological variation between populations. Genetic studies show that there is much genetic variation between populations. Degree of interbreeding between populations is unknown, but large dispersal distance and bird pollinators make genetic exchange seem likely. The population is declining due to mortality of individuals in northern subpopulations.


Population trend
Decreasing
Notes
This assessment is based on the assumption that the species will be able to migrate into new areas which become suitable for it due to climate change. To achieve this, the species would have to migrate southwards at 2.6km/yr and increase its mean altitude by 1.6m/yr. This is unlikely, but we have been conservative in our assessment (as well as in our choice of climate change prediction models). A no-migration scenario gives a 78% decline in 100 years and the species' status would therefore be Endangered. This is a vital flagship species for climate change impacts on biodiversity. It is also likely to be a keystone and umbrella species. This species is not likely to be more sensitive to climate change than others. Foden's study has shown that this species is a useful indicator of climate change and that, because modelled and actual mortality are shown to be relatively similar, the modelled future range shifts need to be seriously considered (Foden 2002, Foden et al. 2007). We have assessed this species based on the modelled future range shifts.
Assessment History
Date
Taxon assessed
Status and Criteria
Citation/Red List version
2009Aloe dichotoma MassonVU A3ceRaimondo et al. (2009)
Bibliography

Foden, W. 2002. A demographic study of Aloe dichotoma in the succulent Karoo: are the effects of climate change already apparent? , University of Cape Town.


Foden, W., Midgley, G.F., Hughes, G., Bond, W.J., Thuiller, W., Hoffman, M.T., Kaleme, P., Underhill, L.G., Rebelo, A.G. and Hannah, L. 2007. A changing climate is eroding the geographical range of the Namib Desert tree Aloe through population declines and dispersal lags. Diversity and Distributions 13:645-653.


Raimondo, D., von Staden, L., Foden, W., Victor, J.E., Helme, N.A., Turner, R.C., Kamundi, D.A. and Manyama, P.A. 2009. Red List of South African Plants. Strelitzia 25. South African National Biodiversity Institute, Pretoria.


Van Wyk, B.-E. and Smith, G. 2003. Guide to aloes of South Africa. (2nd ed.). Briza Publications, Pretoria.


Citation
Foden, W. 2005. Aloe dichotoma Masson. National Assessment: Red List of South African Plants version 2013.1. Accessed on 2014/04/18

Comment on this assessment Comment on this assessment
Distribution map

(c) W. Foden

(c) W. Foden


Search for images of Aloe dichotoma on iSpot