Aucoumea klaineana
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Aucoumea klaineana |
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| Aucoumea klaineana | ||||||||||||
| Pierre |
Aucoumea klaineana is the only plant species in the genus Aucoumea within the balsam tree family(Burseraceae). The wood , with the trade names Gabon-Mahogany , Okoumé (in Belgium, Germany, France, the Netherlands), Gaboon and Gabon (Germany), angouma, okaka, angum, ongoumi, moukoumi, zonga, is used as veneer and makes up about 90% of wood exports from Gabon .
description
Vegetative characteristics
Aucoumea klaineana grows as a medium-sized, evergreen tree with an open crown that can reach heights of up to 50 meters (in rare cases up to 60 meters). The trunk is cylindrical with a chest height diameter between 110 and 240 centimeters. The buttress roots reach up to 3 meters high. The trunk is knotless up to about half its length. The bark is between 0.5 and 2.0 centimeters thick and gray to orange-brown in color and it flakes off in larger scales, plates. Lenticels appear and are very resinous , fibrous and pink-red to reddish in color.
The alternate leaves are pinnate unpaired . The rachis is up to 40 centimeters long and has between 7 and 13 leaflets on stems up to four centimeters long. With a length of 10 to 30 centimeters and a width of 4 to 7 centimeters, the leathery leaflets are ovate to oblong, with a rounded base, a pointed upper end and a full edge. Stipules are missing. The young leaves are reddish.
Generative characteristics
Aucoumea klaineana is dioeciously segregated (functionally diocesan ). The axillary or terminal, paniculate inflorescences have a length of up to 30 centimeters. Male inflorescences contain up to five times more flowers than female ones.
The unisexual flowers are five-fold with a double flower envelope . The five hairy, green sepals are egg-shaped with a length of up to 5 millimeters. The five yellow-whitish petals are spatulate with a length of 5 to 6 millimeters and hairy on both sides. There is a disc with five bilobed glands. Male flowers contain ten stamens with hairy stamens and a rudimentary pistil . Female flowers contain ten small staminodes and a top permanent ovary with columnar pen and head-like scar .
Brownish, about 5 centimeters long and 3 centimeters wide, five-lobed, -part and club-shaped capsule fruits (opening drupes ) with one seed per valve are formed. The fruits open, divide at the base. The egg-shaped seeds are surrounded by an endocarp interspersed with stone cells and extend into a 2 to 3 centimeter long and about 0.5 centimeter wide wing. The seeds germinate above ground (epigeic) with round, fleshy cotyledons .
The number of chromosomes is 2n = 26.
Occurrence and endangerment
The natural range of Aucoumea klaineana stretches from western and central Gabon over the continental Equatorial Guinea in the south to the Republic of the Congo . In the Congo, however, the tree is only found in the Chaillu and Mayombe Mountains. Some small stocks can be found in southern Cameroon close to the border with Gabon. A small natural occurrence in Nigeria , on the border with Cameroon, has not been confirmed.
The altitude distribution ranges from sea level to altitudes of 600 meters. In rare cases, specimens have been found up to 1400 meters.
Aucoumea klaineana is mainly found in old secondary forests and likes to grow in association with Sacoglottis gabonensis . The strongest competitor is Macaranga monandra . The range of the species is limited by the precipitation. It needs between 1200 and 3000 mm of precipitation per year with a dry season that is no longer than three months. The location should be full sun. Okoumé loves acidic, nutrient-rich soils such as Arenosols or Ferralsole , but also tolerates nutrient-poor, sandy soils.
Okoumé was also grown elsewhere for wood extraction, larger artificial stocks can be found in Gabon and Cameroon in the Ivory Coast , smaller stocks in the Republic of the Congo, the Democratic Republic of the Congo , Ghana and Madagascar . There are also experimental crops outside of Africa in Indonesia and Malaysia as well as in Suriname and French Guiana .
In the IUCN Red List of Threatened Species , Aucoumea klaineana is rated as "vulnerable" because of its heavy use and slow growth.
Wood
Okoumé accounts for around 90% of Gabon's wood exports. The main importer is France, followed by Israel, Japan and Italy. The freshly cut wood is light pink and becomes increasingly darker and browner as it ages. The sapwood has a gray shade and merges into the heartwood without any sharp separation . The grain is usually straight. Occasionally, however, a slightly wavy grain occurs. The wood is very soft and reaches 240 Janka in the Janka hardness test .
Okoumé wood is used relatively rarely as solid wood, but is usually processed into veneer . It is easy to glue and is also easy to nail. The use of the wood is limited to indoor spaces as it is not very durable. The wood has a silica content of about 0.12 to 0.16%, so that saw blades become dull relatively quickly during processing.
Systematics
Aucoumea klaineana is the only species of the monotypic genus Aucoumea in the balsam tree family (Burseraceae). There it is in the tribe Bursereae, more precisely in the sub- tribus Boswelliinae, which summarizes the genera Aucoumea , Beiselia , Weihrauch ( Boswellia ), Triomma and Garuga .
A pollen morphological investigation from 2008, however, showed a closer relationship to the genera Bursera and Commiphora , which together form the sub-tribus Burserinae, so that the classification into the Boswelliinae appears questionable.
literature
- JLCH van Valkenburg: Aucoumea klaineana . In: Dominique Louppe, Andrew Oteng-Amoako, Martin Brink (eds.): Plant Resources of Tropical Africa . tape 7 , (1): Timbers 1. PROTA, 2008, ISBN 978-90-5782-209-4 , pp. 82–86 ( limited preview in Google Book Search).
- Andrew Duncan, Gwen Rigby: The Hobby Carpenter - Woodworking Technique . Orbis, Munich 1984, ISBN 3-572-00763-1 .
Web links
- Okoumé on materialarchiv.ch, accessed on November 4, 2016.
- Aucoumea klaineana at Useful Tropical Plants, accessed November 13, 2018.
- Okoumé (PDF; 4.6 MB), from ATIBT - Association Technique Internationale des Bois Tropicaux, accessed on November 13, 2018.
Individual evidence
- ↑ Aucoumea klaineana - data sheet for commercial timbers at DELTA .
- ^ E. Dounias: Sacoglottis gabonensis . In: Gaby Schmelzer, Ameenah Gurib-Fakim (Ed.): Plant Resources of Tropical Africa . tape 11 , (1): Medicinal plants 1. PROTA, 2008, ISBN 978-3-8236-1531-6 , pp. 493–494 ( limited preview in Google Book Search).
- ↑ Aucoumea klaineana in the endangered Red List species the IUCN 2009. Posted by: L. White, 1998. Retrieved on December 15 of 2009.
- ↑ Aucoumea klaineana. In: Contribution to an evaluation of tree species using the new CITES Listing Criteria. UNEP World Conservation Monitoring Center, January 10, 2006, archived from the original on September 29, 2007 ; Retrieved December 15, 2009 .
- ↑ Martin Chudnoff: Tropical Timbers of the World . Handbook No. 607. USDA Forest Service, 1984 ( online [PDF; accessed December 15, 2009]).
- ↑ Duncan et al., P. 198.
- ↑ Mats Thulin, Bjorn-Axel Beier, Sylvain G. Razafimandimbison, Hannah I. Banks: Ambilobea, a new genus from Madagascar, the position of Aucoumea, and comments on the tribal classification of the frankincense and myrrh family (Burseraceae) . In: Nordic Journal of Botany . tape 26 , 2008, p. 218-229 , doi : 10.1111 / j.1756-1051.2008.00245.x .