Barwood (Pterocarpus erinaceus)

Datasheet

Description

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Barwood (Pterocarpus erinaceaus) tree, habit

Barwood (Pterocarpus erinaceus) inflorescence

Common names

Barwood, black camwood, kosso, African kino, African rosewood, African teak, Gambian kino, keno, madobia, Senegal rosewood, West African kino,West African rosewood [English]; kino de Gambie, palissandre du Sénégal, santal, ven, vène, santal rouge d’Afrique, hérissé [French]; afrikanischer Kinobaum [German]; Pau de sangue [Portuguese]; afrikanskt kino [Swedish]; krayie, kpatro [Ghana]; keno, kino [Gambie]: bani, banuhi [Fulfulde (Burkina Faso)]; gwani, n'gueni [Bambara]; tolo [Djerma]; bu natombo [Gourmantché]; noega, noeka, pempelaga [Moré]; ban [Sérer]; ven, yirk [Wolof]

Species

Pterocarpus erinaceus Poir. [Fabaceae]

Related feed(s)

Description

Barwood (Pterocarpus erinaceus Poir.) is a tropical tree from West and Central Africa that has long been a major source of fodder and timber in its native range. In the late 20th century and early 21th century, the overexploitation of this slow-growing species and the reduction of its habitat by land conversion has led to the significant decline of its once large population. The tree has now disappeared in certain regions and was listed as an endangered species in 2018. The current rate of exploitation is considered unsustainable and threatens the survival of the species in the wild (Barstow, 2018).

Morphology

Pterocarpus erinaceus is a medium-sized tree up to 15 (-25) m in height with a rounded, open crown. The branches have long shoots that bend downwards. In good conditions, barwood has a straight, cylindrical and branchless bole up to 10 m in height. Under poorer conditions, the bole is often twisted, fluted and low-branched. The trunk can be up to 75 (-100) cm in diameter, slightly buttressed. The bark surface is greyish brown to blackish in colour, fissured and scaly. The inner bark is yellowish brown, with reddish streaks, and it exudes a reddish translucent gum on slashing. The twigs are densely hairy when young. The leaves are alternate, imparipinnately compound with (5-) 7- 11(-15) leaflets. The leaves are borne on 3–7 cm long petioles, with hairy pinnae, (7-) 10-17 (-22) cm long. The leaflets are thick-papery, usually alternate, veined, hairy when young, ovate to elliptical in shape, (4-) 6-11 cm long × (2-) 3-6 cm broad, and brownish in colour. The inflorescence is an axillary or terminal panicle 7–20 cm long. The flowers are bisexual, golden yellow in colour, papilionaceous, in shape with a standard almost circular, up to 15 mm × 13 mm, wings up to 13 mm long, and keel up to 10 mm long. The fruit is a straw-coloured, circular, flattened, indehiscent, 1-2 seeded pod, 4–7 cm in diameter. The pod has a papery, finely veined wing with wavy or plaited margin. The seed-containing portion bears prickles. The seeds are smooth, reniform, flat to slightly thickened, 10 mm long× 5 mm wide, red to dark brown in colour (Duvall, 2008). The Pterocarpus genus is named after its winged ("pteros") fruit ("carpos") (Orwa et al., 2009).

Utilization

Pterocarpus erinaceus is a multipurpose tree. In Sahelian countries, barwood is mainly used as fodder for animals and is crucial to the livelihoods of the herders and farmers (Duvall, 2008). The leaves are cut, dried and used to feed livestock in the dry season. In Mali, 1400 tons of leaves were sold in the capital each year (CITES, 2015). Barwood foliage is browsed by wild animals like deers during the dry season (Barstow, 2018).

Barwood is internationally valued for its timber. It provides finely grained harwood, dark pink-brown in colour that is used as a substitute for the highly priced and protected rosewood (hence the name African rosewood) to make furniture, decorative panels, flooring and household utensils. The logging and trade of barwood - often illegal - increased significantly in the early 21th century to meet a growing demand, particularly from China (Barstow, 2018).

Barwood yields a resin that is used to dye fabrics. The wood is a source of charcoal. In Ghana, the species is widely exploited for fuelwood and charcoal production (Dumenu et al., 2016). Many parts of barwood are reported to be used in ethnomedicine to treat infections, diarrhea, fever etc. Barwood is a N-fixing tree that improves the soil. It has potential as a an ornamental tree (Duvall, 2008).

Distribution

Pterocarpus erinaceus is native to West and Central Africa. It occurs in openland, woody savanna and dry forest but it can be found on the margins of dense forest or in humid coastal savanna. Its extent has been estimated to exceed 2 million km². It is found in Benin, Côte d'Ivoire, Central African Republic, Gambia, Ghana, Guinea, Guinea-Bissau, Mali, Niger, Nigeria, Senegal, Sierra Leone and Togo (CJB-SANBI, 2017). Its presence in Liberia and Chad needs to be confirmed (Duvall, 2008). Barwood and African locust bean (Parkia biglobosa) are believed to be the main components of the remnants of the former dense Sudanian forest (Orwa et al., 2009). The range of Pterocarpus erinaceus is currently decreasing due to overexploitation and land conversion (see Environmental impact).

Barwood is found from 200 to 1030 m altitude (CJB-SANBI, 2017). It grows where average annual temperature is 15–32ºC, but it is tolerant of temperatures over 40ºC. Pterocarpus erinaceus is tolerant of drought and can survive 6-9 month-long dry seasons. It can grow on poor shallow soils, gravelly and lateritic soils, often on foothills. It is resistant to fire and quickly re-establishes after fire (Orwa et al., 2009; Aubreville, 1950 cited by CITES, 2015).

Forage management

Yields and carrying capacity

Fresh forage production from Pterorcarpus erinaceus was estimated at 4.5 t/ha/year in Mali at the end of the 1990s (van Houten, 1997). The carrying capacity of barwood as fodder is disputed. An early estimate, based on yield and animal requirements, was that 1 ha of barwood could support 24 TLU (Tropical Livestock Unit: cattle = 0.70, sheep and goats = 0.10) during the 3 dry months when animals require supplementation (van Houten, 1997), but this figure was since revised drastically down to 0.03 to 0.08 TLU/ha/year using a model based on biomass production (Sèwadé et al., 2017).

Cultivation

Pterorcarpus erinaceus is easy to propagate by planting nursery-raised seedlings or rooted cuttings. The seeds require to be soaked in tepid water during 18-24 h or in sulfuric acid during 30-60 min and then rinsed thouroughly before sowing in pots or in nursery beds (Roussel, 1996). Germination occurs within 6–10 days. Watering twice a day is necessary. Seedlings soon develop a deep taproot, which must be pruned frequently, 6 weeks after seed sowing and then every 3 weeks afterwards. After outplanting, the rate of survival is high but growth is slow. If seedlings are planted to establish woodlots, a 5 x 5 m spacing is recommended. For fodder production the spacing should be 1 x 2 m (van Houten, 1997).

Barwood is a slow-growing tree that may require up to 100 years to reach full marchandizable size. Two minimum diameters for sustainable merchandization of timber have been determined: 35 cm in the Guinean and Sudanian zones and 65 cm in the Sahelian with a rotation of 20 years (Segla et al., 2016).

Management of barwood for fodder production is based on the copppicing ability of the tree which is high. Barwood was reported to resprout readily when cut at a height of 50 cm at the end of the rainy season and to remain green in the dry season. Uncut trees lost their leaves during the dry season. Cutting at ground level was detrimental for coppicing (van Houten, 1997).

Environmental impact

Endangered species

In spite of its large area of distribution, the population of barwood is in decline and was put in the IUCN Red List of endangered species in 2018 (Barstow, 2018). Three major causes for this decline have been identified: exploitation for fodder and timber, and land conversion. Due to the combination of these threats, some local populations of Pterorcarpus erinaceus have already disappeared and it is predicted that the total number of barwood treeswill decrease by over 50% within the next 100 years (Barstow, 2018).

Use for fodder

In the Sahelian region, the overexploitation of barwood foliage for fodder is the historical reason for its disappearance. In Mali, in the region of Bamako, it wa estimated in the 1990s that 7500-8000 t/year of barwood fodder were needed to feed local sheep, and about 1500 t/year of fresh foliage were sold in the Bamako markets. In spite of efforts to regulate its exploitation and to create barwood-based fodder banks, the severe and frequent lopping of this species has since resulted in its disappearance in the Bamako area (van Houten, 1997; Barstow, 2018).

Exploitation for timber

Barwood timber is an excellent alternative to rosewood, and the demand for African rosewoods on the international timber market has led since the 2000s to massive logging, much of it illegal. There was a 15-fold increase in exports between 2009 and 2015, driven by Chinese demand. In 2014 alone, about 1 million barwood trees were logged to be exported to China (CITES, 2016; Barstow, 2018). Extraction for timber in Gambia, Benin and Côte d'Ivoire exhausted existing stocks with a population decline of 80%, and similar rates of decline are suspected in Nigeria and Sierra Leone (Barstow, 2018). It has been proposed to list all populations of barwood on the appendix II and III of CITES to increase attention on the trade of this species, and to help blocking shipments of illegally harvested and traded barwood (CITES, 2016).

Land conversion

The decline of the barwood population is also linked to the increasing urbanization of its area of extent, as land is converted to new infrastruture such as human habitat, roads and dams (Barstow, 2018, CITES, 2016).

Reafforestion

In order to alleviate the decline of the species, there are attempts at reafforestation of the savanna and at establishing stands (CJB-SANBI, 2017).

Pioneer species

Barwood has the potential to become a dominant tree species in wooded savanna habitats but often its growth and range are reduced. It is considered a pioneer on fallow lands as it is able to fix N from the atmosphere (Duvall, 2008).

Nutritional aspects

Nutritional attributes

Pterocarpus erinaceus foliage contains a moderate amount of protein, about 15% DM on average, ranging from 7 to 22% DM, depending on the season and maturity stage. Its fibre content is rather high, with an ADF value about 41% DM, and particularly a high lignin content of 15% on average.

Potential constraints

Barwood foliage contains condensed tannins in variable amounts, from nearly absent to up to 6% DM, which is the limit above which they can have a negative impact on ruminant health (Okunade et al., 2014; Isah et al., 2015; Njidda et al., 2017).

Ruminants

The leafy branches of Pterocarpus erinaceus are browsed or lopped to feed livestock. Barwood foliage is - or used to be - the most important source of fodder for goats, sheep and cattle during the long dry season in the Sahel, when almost all the other sources of forage have dried up (van Houten, 1997). It is heavily cropped by herdsmen for their livestock during the dry season in Nigeria (Achonwa et al., 2017) and lopped forage is traded as sheep fodder in Mali (van Houten, 1997). Livestock keepers rely heavily on Pterocarpus erinaceus trees in the woodlands of the Sudanian zone (Duvall, 2008). Like other fodder trees, Pterocarpus erinaceus foliage contains moderate amounts of protein, but its OM digestibility is relatively low (Njidda et al., 2017). Consequently, it is recommended to use it as a fodder supplement with low quality forages rather than as a sole forage.

Intake and digestibility

In a study carried out in Burkina Faso, Pterocarpus erinaceus ranked third after Afzelia africana and Kaya senegalensis in terms of browsing preference by cattle, and farmers also ranked it third as a cattle fodder (Ouédraogo-Koné et al., 2006). In Nigeria, two trials with male goats gave different results. A first study with 5 tree species found that Pterocarpus erinaceus ranked second after Afzelia africana (Isah et al., 2015), but it came last of 6 species - Afzelia ranking first again - in another experiment (Okunade et al., 2014), possibly because it contained much more condensed tannins (5.8% DM) than in the first experiment (0.7%) while Afzelia wcontained less than 1% condensed tannins in both trials.

The OM digestibility assessed by the gas production method was 53% (Njidda et al., 2017).

Sheep

In Burkina Faso, barwood leaves offered in place of cottonseed cake to growing sheep resulted in a lower daily weight gain (59 vs 96 g/d) probably because a lower protein intake: 86 vs 136 g/d (Ouédraogo-Koné et al., 2009)

Goats

Several trials with goats have been conducted in Nigeria. Barwood leaves offered as a sole forage to growing goats slightly increased daily weight gain (33 vs 24 g/d) when compared to natural grass hay fed alone. When the leaves were offered at various levels (0 to 100%) in addition to hay, it increased daily weight gain up to 25% (24 to 56 g/d) in the diet but no more until 75% (Olafadehan, 2013). When barwood was offered as a fodder supplement to threshed sorghum forage, it increased the total DM intake and slightly the daily weight gain (34.5 g/day) compared to the diet with sorghum alone (0.95 g/d) (Isah et al., 2015). These positive results were obtained because barwood leaves bring high protein amount to a poor quality forage which allowed a higher total diet digestibility and nitrogen utilization.

Rabbits

Information on the utilization of Pterocarpus erinaceus leaves in rabbit feeding is very scarce in the international literature (September 2019). Since this forage is widely used for ruminant feeding, it should be suitable for rabbits. It seems to be appreciated by growing rabbits even as sole feed, but addition of a concentrate in the daily ration is useful (Ayoade et al., 1998). The calculated digestible energy content is about 7.3 MJ/kg DM and protein digestibility is only 57% (Lebas, 2016), a situation which justifies the supplementation with a concentrate to obtain optimum performance in growing rabbits.

Nutritional tables

Tables of chemical composition and nutritional value

Barwood (Pterocarpus erinaceus), aerial part, fresh

Avg: average or predicted value; SD: standard deviation; Min: minimum value; Max: maximum value; Nb: number of values (samples) used