Aucoumea klaineana
Aucoumea klaineana is the only species of the genus Aucoumea within the family of balsam tree family ( Burseraceae ). The wood, with the trade names Gabon mahogany, okoume (Belgium, Germany, France, Netherlands), Gaboon and Gabon ( Germany ), angouma, Okaka, angum, ongoumi, moukoumi, Zouga is used as veneer and makes about 90 % of timber exports from Gabon.
- 5.1 Literature
- 5.2 Notes and references
Description
Vegetative characteristics
Aucoumea klaineana grows as a medium-sized tree that can reach heights of growth of up to 50 meters (in rare cases up to 60 meters). The trunk is cylindrical with a diameter at breast height 110-240 cm. The Board roots reach up to 3 meters high. The trunk is limbless up to 2/3 of its length. The bark is between 0.5 and 2.0 centimeters thick, and from gray to orange - brown color. Lenticels occur and are highly resinous, fibrous and reddish-pink to reddish color. The crown is open.
The alternate arranged leaves are pinnate. The rachis is up to 40 centimeters long and bears 7-13 leaflets up to four centimeters long Fiederblattstielen. The leathery leaflets are at a length of 10 to 30 centimeters and a width of 4-7 cm ovate to oblong. with a rounded base, tapered at the top and smooth edge. Stipules absent.
Generative features
Aucoumea klaineana is dioecious getrenntgeschlechtig ( dioecious ). The lateral or terminal, paniculate inflorescences have a length of up to 30 centimeters. Male inflorescences contain up to five times more flowers than the female.
The unisexual flowers are fünfzählig double perianth. The five hairy green sepals are lanceolate, with a length of up to 5 millimeters. The five whitish petals are spatulate hairs on both sides and long at a length of 5 to 6 mm. The flower tube has bilobed nectary. Male flowers contain ten stamens and a rudimentary stamp. Female flowers contain ten staminodes and a superior ovaries with columnar stylus and head -like scar.
There are about 5 inches long and 3 inches wide, fünfklappige fruit capsules formed with one seed per flap. The egg-shaped seeds are surrounded by a stone cells interspersed with endocarp and extended into a 2 to 3 inches long and about 0.5 inches wide wings. The seeds germinate above ground ( epigeal ) with round, fleshy cotyledons.
The chromosome number is 2n = 26
Occurrence and risk
The natural range of Aucoumea klaineana enough western and central Gabon, on the continental Equatorial Guinea in the south to in the Republic of Congo. In the Congo, but finds the tree only in the Chaillu and Mayombe mountains. Some small holdings can be found in northern Cameroon close to the border with Gabon. A small natural occurrence in Nigeria, on the border with Cameroon is not confirmed.
The altitudinal distribution ranges from sea level to altitudes of 600 m In rare cases, specimens have been found up to 1400 meters.
Aucoumea klaineana is particularly common in old secondary forests and grows like in communion with Sacoglottis gabonensis. The strongest competitor is Macaranga monandra .. The distribution area of the species is limited by the precipitation. You need 1200-3000 mm of precipitation per year with a dry season, which is not longer than three months. The location should be in full sun. Okoume loves acidic, nutrient-rich soils as Arenosols or Ferralsols, but also tolerates nutrient-poor, sandy soils.
Okoume was also elsewhere grown for timber, larger artificial existence are in addition to Gabon and Cameroon in the Ivory Coast, smaller stocks in the Republic of Congo, the Democratic Republic of Congo, Ghana and Madagascar. Even outside of Africa in Indonesia and Malaysia as well as in Suriname and French Guiana, there are experimental cultivation.
In the Red List of Threatened Species IUCN Aucoumea klaineana is because of the heavy usage and slow growth as "vulnerable " = " at risk " rating.
Wood
Okoume makes about 90 % of timber exports from Gabon. Main importer is France, followed by Israel, Japan and Italy. The freshly cut wood is light pink and is in the aging progressively darker and browner. The sapwood has a gray tone and comes with no sharp separation over into the heartwood. The grain is usually straight. Occasionally, but also occurs slightly wavy grain. The wood is very soft and reached the Janka hardness test 240 Janka.
Okoume wood is relatively rarely used as solid wood, but usually processed for veneer. It's good verleimbar and can also be nailed well. The use of wood is limited to interiors, since it is not very durable. The wood has a silica content of about 0.12 to 0.16 percentage so that blades are relatively dull quickly in its processing.
System
Aucoumea klaineana is the only species of the monotypic genus in the family Aucoumea the balsam tree family ( Burseraceae ). There she is in the tribe Bursereae, more precisely in subtribes Boswelliinae, which summarizes the genera Aucoumea, Beiselia, Frankincense (Boswellia ), Triomma and Garuga.
However pollenmorphologische study from 2008 showed a close relationship to the genera Bursera and Commiphora, which jointly subtribes Burserinae form, so that the classification is questionable in the Boswelliinae.