Pterocarpus angolensis 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Magnoliopsida Fabales Fabaceae

Scientific Name: Pterocarpus angolensis DC.
Common Name(s):
English Bloodwood Tree, Mukwa

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2018
Date Assessed: 2018-02-21
Assessor(s): Barstow, M. & Timberlake, J.
Reviewer(s): Beech, E.
Pterocarpus angolensis is a widespread timber tree. It is native to southern Africa where it grows from Angola and Namibia, east to Tanzania and Mozambique. The species is also found in South Africa and Swaziland. The species is able to persist as a suffrutex, for a number of years developing its root system until it can rapidly shoot up into a large tree or sapling, which aids the species survival against herbivores, frost and fire. Across parts of its range the largest and most mature trees are at risk from over exploitation for timber causing decline in some subpopulations outside of protected areas and sometimes inside protected sites due to both legal and illegal logging activity. In areas of extraction the size structure of subpopulations has become truncated, with smaller trees (often under 30 cm dbh) being much more common than those of larger size. This reduces the amount of seed being produced by the population. There is concern over the impact this might have on regeneration at some sites. Further investigation is needed to establish the extent to which this threatens the future viability of the species. Despite these threats to the species a large population of Pterocarpus angolensis is likely to remain across its range as not all trees are exploitable due to defects or being small in size. The species also has a large extent of occurrence of over 5 million km2. The persistence of the species in a suffrutex stage and its ability to colonise exposed landscapes are also to its benefit. Pterocarpus angolensis is globally assessed as Least Concern. It is recommended that there is better use of the information available to guide the management of the harvest of the species and that current harvest plans for the species are better implemented.
Previously published Red List assessments:

Geographic Range [top]

Range Description:Pterocarpus angolensis is a native to Southern Africa. The species is widespread in the Miombo woodland of the region and is present in Angola, Botswana, The Democratic Republic of the Congo, Malawi, Mozambique, Namibia, South Africa, Swaziland, Tanzania, Zambia and Zimbabwe. The species is also planted within Kenya (Takawira-Nyenya 2005). The species is found from sea level up to 1,820 m asl (Conservatoire et Jardin Botanique de la Ville de Genève and South African National Biodiversity Institute 2018), though its elevational range varies from country to country. The species has an estimated extent of occurrence of over 5 million km2. Based on the occurrence of the species in the Miombo ecoregion the species could have an area of occupancy (AOO) of up to 2.5 million km2 (J. Timberlake pers. comm. 2018).
Countries occurrence:
Angola; Botswana; Congo, The Democratic Republic of the; Malawi; Mozambique; Namibia; South Africa (KwaZulu-Natal, Limpopo Province, Mpumalanga); Swaziland; Tanzania, United Republic of; Zambia; Zimbabwe
Additional data:
Upper elevation limit (metres):1820
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Pterocarpus angolensis is currently experiencing population decline in some parts of its range. Some subpopulations are in decline due to over exploitation of commercially viable trees to timber. There is a decline in mature individuals to timber and in some areas small trees are also being opportunistically logged (Schwartz et al. 2002, Shackleton 2002, Therrell et al. 2002, Graz 2004, Caro et al. 2005, Mojeremane and Lumbile 2016). In areas of timber harvest, the recruitment of seedlings can be poor (Schwartz et al. 2002, Mojeremane and Lumbile 2016). Commercially utilisable stands of P. angolensis are now scarce across much of its range. The extraction of P. angolensis for timber has created a truncated diameter-size class profile in some subpopulationsIn these sites there are very few trees exceeding the minimum harvestable diameter (MHD), which varies from country to country. Therefore, in Tanzania where the MHD is 60 cm there are few trees larger than this (Caro et al. 2005) and in South Africa and Namibia trees exceeding 35 to 40 cm dbh (Shackleton 2002, Graz 2004) are increasingly uncommon as this is the MHD here. This is reducing the number of seed bearing individuals (Schwartz et al. 2002, Therrell et al. 2002, Caro et al. 2005). It can take a tree from 85 to 100 years to reach a minimum harvestable diameter (Therrell et al. 2002). Despite the loss of large individuals there are still large numbers of trees of around 20 cm dbh and those larger trees which are not suitable for timber due to irregularities in the trunk.

In Msaginia Forest Reserve, Tanzania, where the species is logged in 15 ha survey site there was an estimated 3.67 mature individuals/ha (Schwartz et al. 2002). This was a decline from an estimated density of 11.4 trees/ha prior to logging. The study also predicts that over the next 100 years only 2.1 trees/ha will reach MHD but across this 100 year period population density will decline to 0.3 trees/ha. This will lead to economic extinction of the species (Schwartz et al. 2002). This represents an observed decline of 67.6% in the commercially exploitable trees in the survey site and a potential decline of 97.37% of commercially exploitable trees within the region.

Subpopulations are also at risk of decline due to the fungal diseases mukwa blight (Fusarium oxysporum) which often effects individuals in Zimbabwe. Some will also be at risk from habitat conversion (Takawira-Nyenya 2005). In protected areas there can be a lack of recruitment. A survey found no recruitment of trees within 20 m of parent trees (Caro et al. 2005). The impact these risks have on the species' population overall is not known but is anticipated to be low.

The decline estimates given above are not representative of the total decline in population size but instead describe the decline in the commercially valuable part of the P. angolensis population. Pressure on the species is variable but concentrated on trees that produce good quality planks and timber with straight trunks. This means a population of non-commercially valuable trees will always be retained. It is a secondary species that can grow in fallows or clearings and can be common here. The ability for the species to persists in a suffrutex stage means regeneration in ideal conditions can be rapid. Therefore, across its range the population shows uneven population density and overall populations size is considered to be large, if in decline.
Current Population Trend:Decreasing
Additional data:

Habitat and Ecology [top]

Habitat and Ecology:Pterocarpus angolensis is a large tree species, growing to over 20 m in height. The species grows within deciduous and Brachysteig woodland and wooded grassland. It is most common in Miombo woodland and can be dominant on savanna. The species grows best in open, exposed area hence it often occurs as individual trees in agricultural and settled spaces (Geldenhuys 2013). Within Tanzania the species can also grow on coastal plains (Takawira-Nyenya 2005). The species is highly resistant to fire and tolerant of drought but only mildly tolerant to frost.

Often for the first 10 years of the species life it cycles between being a small seedling until the dry season where the individual dies back to a suffrutex stage. At which point the species expends energy expanding its root system. Once root architecture is strong enough and other growth conditions amiable a true stem is sent up which then grows to maturity. From this point it takes 15-20 years to flower (Goldsmith and Carter 1992) and up to 35 years to begin producing fruit. Fruiting occurs before leaf flushing and always at the beginning of the rainy season. Fruit is not dispersed over large distances (Schwartz et al. 2002). Trees can live to be over 100 years if experiencing ideal growth conditions (Takawira-Nyenya 2005) and in some sites this is the time taken to reach a harvestable diameter (Therrell et al. 2002). In Tanzania the species has growth rate of between 5.5 and 8.5 mm a year while the majority of surveys suggest growth rate is slower at 2- 4 mm a year (Therrell et al. 2002, Shackleton 2002, Graz 2004). The species is pollinated by insects and its fruits are wind dispersed.

Use and Trade [top]

Use and Trade: Pteorcarpus angolensis is one of the most valuable timbers within southern Africa. The wood is resistant to insects making it ideal for the construction of boats, doors and windows. The timber is utilised for carpentry, furniture manufacture and parquet floor tiles (Takawira-Nyenya 2005). It is the most utilised timber within the region for woodcarving (Shackleton 2002). The extensive use of this wood on national and international markets has caused it to become depleted from some areas. Schwartz et al. (2002) states the species is currently being harvested at a rate in Tanzania that is could reach 'economic extinction'. The number of large harvestable trees is also declining rapidly due to harvest outside of protected areas (Caro et al. 2005). There is scarce trade data available for this species, it is reported that 5,000 m3 are exported from Zambia. The biggest importers of the timber are Thailand and China.

This tree can also be used for medicinal purposes. The bark is astringent and used to treat diarrhoea, menstruation, skin complaints, nose bleeds, headaches and stomach aches. The root can also be applied to treat fever, malaria and gonorrhoea. The roots may also be pounded into a powder and used to make a dye. This powder may also be combined with some fats to make a cosmetic pomade in some parts of the range (Takawira-Nyenya 2005).

Leaves may also be collected from the plant for use as animal fodder. The tree can be planted for shade, soil conservation and as an ornamental.

Threats [top]

Major Threat(s): The species is overexploited for its timber which has caused many local populations to become diminished. This exploitation endangers those large trees that are of harvestable size (Takawira-Nyenya 2005). The current harvest of the timber is unsustainable one study showed that if current rate of timber extraction (5.6% per annum) continued in Northern Province, South Africa, all exploitable timber would be gone within the next 30 years (Desmet et al. 1996). Big trees are now rarely seen and there are not thought to be enough small trees to replace these, immature trees are even being harvested to bridge the gap in some (but not all) places (Geldenhuys 2013). The reduction in large trees reduce the amount of seed being produced (Shackleton 2002) but the impact this has on the potential viability of the tree in the future is not currently known.

The species is intrinsically threatened by its poor germination (Boaler 1966) and low seedling survival rate (Takawira-Nyenya 2005). Seedlings will often be browsed by animals putting them at risk and both trees and seedlings are damaged by elephants within the region. The species is also threatened by a fungus (Fusarium oxysporum) that causes dieback known as Mukwa blight or mukwa dieback (van Wyk et al. 1993).

Conservation Actions [top]

Conservation Actions: This species is known from at least 10 ex situ collections (BGCI 2018a). The species is assessed as Vulnerable in Malawi, when considering wild populations (BGCI 2018b) and Vulnerable in Namibia and Zimbabwe when considering the species as economic entity (Golding 2002). However in Zimbabwe the species as a whole is considered at low risk of extinction (Hyde et al. 2018) and within South Africa the species is assessed as Least Concern (Foden and Potter 2005). Within many range countries P. angolensis is a protected species, for example in South Africa the species may only be harvested by those who have submitted and carry permits (Shackleton 2002). It is found within Katavi National Park and Msaginia Forest Reserve in Tanzania (Schwartz et al. 2001) and many other protected areas within its range. Despite this within some of these protected areas the species can still be logged and still at risk from extinction (Caro et al. 2005). It is essential that the current information gathered for the species is employed in the conservation of the species and to generate understanding of the potential of its sustainable use. Harvesting quotas for different areas should be established, off take from the wild better monitored and better implementation of agreed management practices especially in over exploited areas.

Citation: Barstow, M. & Timberlake, J. 2018. Pterocarpus angolensis. The IUCN Red List of Threatened Species 2018: e.T33190A67802808. . Downloaded on 24 September 2018.
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