Acacia mearnsii de Wild.
Syn.: Acacia mollissima auct., not Willd.
Acacia decurrens var. mollis Lindl.
Black Wattle, Acacia Negra, Acacia Noir, Schwarze Akazie, Gomboom
Source: James A. Duke. 1983. Handbook of Energy Crops. unpublished.
- Folk Medicine
- Yields and Economics
- Biotic Factors
Tree of economic importance in South and East Africa, Rhodesia, India, and Rio
Grande do Sul area of South America etc. for tanning of soft-leather. Ranging
from 3054 percent tannin in dried bark. Wood furnishes badly needed fuel and
building material in some areas. Trees not only provide tannin and fuel, but
also add nitrogen and organic material to improve the soil. Bark is used for
wood adhesives and flotation agents (Duke, 1981a). The pulp is suitable for
wrapping paper and hardboard. Some regard it as an attractive ornamental.
Sometimes used for erosion control on poor sloping soils unsuitable for
agriculture. Densely packed plantations are effective in preventing further
erosion on 50° slopes. Some farmers claim that tobacco and vegetable yields
are doubled in rotating with the black wattle. In places it is regarded as a
"green cancer", spreading vigorously as a weed (NAS, 1980; Little, 1983).
Products are often used in folk medicine as styptics or astringents (Duke,
Black wattle bark contains (-)-robinetinidol and (+)-catechin; the biflavonoids
(-)-fisetinidol-(+)-catechin (2 diastereoisomers),
(-)-robinetinidol-(+)-catechin and (-)-robinetinidol-(+)-gallocatechin;
triflavonoids and condensed tannins. The heartwood is rich in
(+)-leucofisetinidin (mollisacacidin) together with (-)-fisetinidol,
(+)-fustin, butin, fisetin, butein, and biflavonoid condensates (tannins)
Tree 6 to 20 m tall, 10 to 60 cm in diameter; crown conical or rounded; all
parts except flowers usually pubescent or puberulous; stems without spines or
prickles; leaves bipinnate, on petioles 1.52.5 cm long, with a gland above;
rachis 412 cm long with numerous raised glands all along its upper side;
pinnae in 830 pairs, pinnules in 1670 pairs, linear-oblong, 1.54 mm long,
0.50.75 min wide; flowers in globose heads 58 mm in diameter, borne in
panicles or racemes, on peduncles 26 mm long; pale yellow and fragrant; pods
gray-puberulous, or sometimes glabrous, almost moniliform, dehiscing, usually
310 cm long, 0.50.8 cm wide, with 314 joints; seeds black, smooth, elliptic
or compressed ovoid, 35 mm long, 23.5 mm wide; caruncle conspicuous; areole
3.5 mm long, 2 mm wide. Seeds 66,000 to 110,000/kg (Duke, 1981a).
Can be crossed with Acacia decurrens, hybrids show more sterility than
parents. Meiosis is regular, with no gross cytological abnormalities, and
sterility may be due to gene differentiation between species. There is little
geographic overlap in the native Australian ranges of the species, and there
are differences in phenology (flowering; seedset). Most of the characters that
vary among the species are quantitative. The development of black wattle
strains or of hybrids with enhanced vigor, better quality bark, outstanding
stem form, or resistance to insect pests and disease would benefit the wattle
industry. Assigned to the Australian Center of Diversity, black wattle or cvs
thereof is reported to exhibit tolerance to drought, laterite, and poor soil
(Duke, 1981). For an Acacia, it is relatively tolerant to frost, and its
growth is slowed by high temperatures. (2n = 26.)
Native to Southeast Australia (Victoria to New South Wales and southern
Queensland) and Tasmania. Introduced and cultivated widely for afforestations.
See Sherry (1971) for details.
In Kenya grows on or near Equator at altitudes of 2,0002,800 m, is well
adjusted to the climate of East Africa. Grows well at 30°S Lat. in South
America on rolling terrain at altitudes of 5070 m. Thrives on poor, dry soils
but favors deeper, moister, more fertile soils. In Australia, black wattle may
occur on soils derived from shales, mudstones, sandstones, conglomerates, and
alluvial deposits. In Kenya on podsols, krasnozems, sandy hills, lava flows or
on mixtures of lava and contemporaneous volcanic tuffs and breccias. In South
America, grown on red clay or sandy soils that have suffered from severe
erosion and soil depletion (ferruginous clay loams with little or no free
silica). In East Africa grows where annual rainfall is 1,0411,321 mm, (about
75% between April and September). On the equator where black wattle is grown
in South America, the rain pattern is nearly opposite, mean annual temperature
range is 1723°C; there is little seasonal variation, but considerable
diurnal variation. At higher altitudes in South America, frost is a risk and
heavy snows may break tree limbs. Tannin content varies inversely with
precipitaton. Ranging from Warm Temperate Dry through Tropical Thorn to
Tropical Moist Forest Life Zones, black wattle is reported to tolerate annual
precipitation of 6.622.8 dm (mean of 6 cases=12.6), annual mean temperature of
14.727.8°C (mean of 6 cases=2.6°C), and pH of 5.07.2 (mean of 5
cases = 0.5).
Propagation by seed is easy. Seeds retain their viability for several years.
For germination seed are covered with boiling water and allowed to stand until
cool. This cracks the hard outer coat and facilitates germination. Seeds may
be broadcast or sown in rows on any barren site. Usually they are sown about 5
cm apart in seedbeds, and are transplanted after 36 months. In South America,
fields are usually plowed and harrowed in April or May. Seedlings are set out
MayNovember, but usually in winter, JuneAugust, after a rain. Plants are
spaced 2 m each way, at rate of 2,500/ha. Propagation by cuttings is almost
impossible without mist. Air layering is more promising. Two types of farmers
grow acacia: the tanner or business man plants 200 ha or so entirely to black
wattle, usually one section at a time so that he can plant and harvest within
the same year and continue year after year; the farmer plants half or less of
his land to black wattle and the rest to crops such as corn, beans, maniac,
sugarcane, other vegetables, or pasture. He plants 26 hectares of acacian
each year and thus evenly distributes work and production. Oxen may be useful
for plowing, but most work is by hand. Usually only plows and hoes are used in
Cultivation. Intercrops may be grown the first year during which trees grow
about 45 m in height, and about 2.5 cm in diameter (Duke, 1981).
Trees provide bark 510 years after seeding (avg 7). Bark is stripped from
lower part of tree, then tree is felled, the remaining bark removed, and tree
and bark are cut into 1 m lengths. Thoroughly dried bark is arranged in bales
of 75 to 80 kg when ready for transportation. Tanning power improves by 1015%
in bark carefully stored for a season. Percent tannin does not differ between
barks harvested in dry and wet seasons. However, the amount of bark on trees
may be less on poor than on rich soils. Tannin runs about 2535% per kilo of
dried bark, on either poor or rich soil. Acacia bark may be sold as baled
bark, or bark powder. Dried bark may go first to commercial bark processors
where it is ground or shredded in a hammermill, then sold in 40-kg sacks. Bark
powder is sold in 60-kg sacks. Liquid extract is sold in 300-kg wooden
barrels. In Rio Grande do Sul an estimated 5,000 MT of liquid extract is
produced annually (Duke, 1981a).
Except for some mangrove species, black wattle in pure stand produces more
tannin per hectare than most tanniniferous plants. In South Africa
well-managed have produced the equivalent of 3 MT/ha tannin, about twice the
average, when grown in rotations in excess of 12 years. One 7-yr-old tree
produces 35 kg of dried bark. Twelve trees produce 1 cu m of firewood. The
wood of debarked trees is dried and used for mine timbers, pulpwood, and fuel.
Moisture loss is rapid in first 4 weeks after felling, then much slower. Wood
weighs 708.7 kg/cu m. One tree can produce up to 10 cwt of bark or about 5 cwt
stripped. One ton of black wattle bark is sufficient to tan 2,530 hides, best
adapted for sole leather and other heavy goods; the leather is fully as durable
as that tanned with oak bark. One ton of bark yields 4 cwt of extract tar.
Destructive distillation of the wood yields 33.2% charcoal, 9.5% lime acetate,
and 0.81 methyl alcohol. As a source of vegetable tannin, black wattle shares
with quebracho and chestnut a large portion of the world market for vegetable
tannins. According to Sherry (1971), plantation grown wattle in South Africa,
Rhodesia, Tanzania, Kenya, and Brazil supplied about 38% of world demand for
tannin. South Africa was the largest producer, with annual output of 72,000 MT
of ca 120,000 MT on the world market. Eucalyptus grandis produces more
wood than wattle, but it is inferior for fuel and charcoal. At one time in
South Africa, 56% of the proceeds from wattle was from bark, the balance from
timber (Duke, 1981a).
An efficient N-fixer, it is reported to annually yield 2128 MT/ha wet leaves
containing 245285 kg N. If we put the information in our cultivation
paragraph and our yields paragraph, we find the improbable 2,500 plants per
hectare, with 12 producing 1 m3 firewood, suggesting a potential of more than
200 m3/ha for 7 year old trees, suggesting annual yields of ca 30 m3/ha. NAS
(1980a) reports annual thickwood production of 1025 m°3/ha and bark production
of 0.84.0 MT. The dense wood (sp. grav. = 0.70.85) 3,5004,000 kcal/kg
(oven-dry Indonesian specimens 4,650 kcal/kg), its ash content ca 1.5%. The
charcoal (sp. grav. = 0.30.5) has a calorific value of 6,600 kcal/kg, with an
ash content of 0.4%.
The most serious disease is disback, caused by Phoma herbarum. Other
fungi attacking black wattle include: Chaetomium cochliodes,
Daldinia sp., and Trichoderma viride. In Rio Grande do Sul,
disease and insects cause about 20% loss of trees. Principal insects attacking
Brazilian wattle are Molippa sabina, Achryson surinamum, Placosternus
cyclene, Eburodacrys dubitata, Neoclytus pusillus, Oncideres impluviata,
Oncideres saga, and Trachyderes thoracica. Ants, termites, and
borers are the most damaging. The sauva ant which attacks the leaves is fought
constantly with arsenicals and carbon disulfide. Nematodes reported on this
species include Meloidogyne arenaria, M. incognita acrita, and M. javanica (Golden, pers. commun. 1984).
Complete list of references for Duke, Handbook of Energy Crops
- Duke, J.A. 1981a. Handbook of legumes of world economic importance. Plenum
- Little, E.L. Jr. 1983. Common fuelwood crops: a handbook for their
identification. McClain Printing Co., Parsons, WV.
- NAS, 1980.
- N.A.S. 1980a. Firewood crops. Shrub and tree species for energy production.
National Academy of Sciences, Washington, DC.
- Sherry, S.P. 1971. The black wattle (Acacia mearnsii de Wild.).
University of Natal Press. Pietermatitzburg.
Last update December 16, 1997