in Australia, in the midst of the southern hemisphere winter. Tannin The bark of various Australian species, known as wattles, is very rich in tannin and forms an important article of export; important species include A. pycnantha (golden wattle), A. decurrens (tan wattle), A. dealbata (silver wattle) and A. mearnsii (black wattle). Black wattle is grown in plantations in South Africa and South America. The pods of A. nilotica (under the name of neb-neb), and of other African species, are also rich in tannin and used by tanners. In Yemen, the principal tannin substance was derived from the leaves of the salam-tree (Acacia etbaica), a tree known locally by the name qaraẓ (garadh). A bath solution of the crushed leaves of this tree, into which raw leather had been inserted for prolonged soaking, would take only 15 days for curing. The water and leaves, however, required changing after seven or eight days, and the leather needed to be turned over daily. Wood Some Acacia species are valuable as timber, such as A. melanoxylon (blackwood) from Australia, which attains a great size; its wood is used for furniture, and takes a high polish; and A. omalophylla (myall wood, also Australian), which yields a fragrant timber used for ornaments. A. seyal is thought to be the shittah-tree of the Bible, which supplied shittim-wood. According to the Book of Exodus, this was used in the construction of the Ark of the Covenant. A. koa from the Hawaiian Islands and A. heterophylla from Réunion are both excellent timber trees. Depending on abundance and regional culture, some Acacia species (e.g. A. fumosa) are traditionally used locally as firewoods. It is also used to make homes for different animals. Pulpwood In Indonesia (mainly in Sumatra) and in Malaysia (mainly in Sabah), plantations of A. mangium are being established to supply pulpwood to the paper industry. Acacia wood pulp gives high opacity and below average bulk paper. This is suitable in lightweight offset papers used for Bibles and dictionaries. It is also used in paper tissue where it improves softness. Land reclamation Acacias can be planted for erosion control, especially after mining or construction damage. Ecological invasion For the same reasons it is favored as an erosion-control plant, with its easy spreading and resilience, some varieties of acacia are potentially invasive species. At least fourteen Acacia species introduced to South Africa are categorized as invasive, due to