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''Vachellia drepanolobium'', commonly known as whistling thorn, is a swollen-thorn
acacia ''Acacia'', commonly known as the wattles or acacias, is a large genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of nam ...
native to East Africa. The whistling thorn grows up to 6 meters tall. It produces a pair of straight spines at each node, some of which have large bulbous bases. These swollen spines are naturally hollow and occupied by any one of several symbiotic ant species. The common name of the plant is derived from the observation that when wind blows over bulbous spines in which ants have made entry and exit holes, they produce a whistling noise. Whistling thorn is the dominant tree in some areas of upland East Africa, sometimes forming a nearly monoculture woodland, especially on "" soils of impeded drainage with high clay content. It is browsed upon by giraffes and other large herbivores. It is apparently fire-adapted, coppicing readily after "top kill" by fire. Whistling thorn is used as fencing, tool handles, and other implements. The wood of the whistling thorn, although usually small in diameter, is hard and resistant to termites. The branches can also be used for kindling, and its gum is sometimes collected and used as glue. The ability to
coppice Coppicing is a traditional method of woodland management A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the ''plurale tantum A ''plurale tantum'' (Latin for "plural ...

coppice
after cutting make it a possibly sustainable source for fuel wood and charcoal. Conversely, whistling thorn also has been considered a weed of rangelands, and a bush encroachment species.


Symbiosis with ants

Like other acacias, whistling thorns have leaves that contain tannins, which are thought to serve as deterrents to herbivory. Like all African acacias, they are defended by spines. In addition, whistling thorn acacias are myrmecophytes that have formed a Mutualism (biology), mutualistic relationship with some species of ants. In exchange for shelter in the bulbous spines (domatia) and nectar secretions, these ants appear to defend the tree against herbivores, such as elephants and giraffes,J.R. Goheen, and T.M. Palmer,"Defensive Plant-Ants Stabilize Megaherbivore-Driven Landscape Change in an African Savann

Current Biology,Available online 2 September 2010.
as well as herbivorous insects. At one site in Kenya, three ''Crematogaster'' and one ''Tetraponera'' ant species compete for exclusive possession of individual whistling thorn trees: ''Crematogaster mimosae'', ''Crematogaster sjostedti, C. sjostedti'', ''Crematogaster nigriceps, C. nigriceps'', and ''Tetraponera penzigi''. Ants vary in their level of mutualism with whistling thorn trees. The most common ant symbiote (~ 50% of trees), ''C. mimosae'', has the strongest mutualistic relationship, aggressively defending trees from herbivores while relying heavily on swollen-spines for shelter and feeding from nectar produced by glands near the base of leaves. (See also: ''Crematogaster peringueyi''.) Because the ants compete for exclusive usage of a given tree, some species employ tactics to reduce the chance of a hostile ant invasion. ''Crematogaster nigriceps'' ants trim the buds of trees to reduce their lateral growth, thereby reducing chances of contact with a neighbouring tree occupied by a rival colony. ''Tetraponera penzigi'', the only species which does not utilise the nectar produced by the trees, instead destroys the nectar glands to make a tree less appealing to other species. The symbiotic relationship between the trees and the ants appears to be maintained by the effects of browsing by large herbivores. At a site in Kenya, when large herbivores were experimentally excluded, trees reduced the number of nectar glands and swollen spines they provided to ants. In response, the usually dominant ''C. mimosae'' increased their tending of parasitic sap-sucking insects as a replacement food source. In addition, the number of ''C. mimosae''-occupied trees declined while twice as many become occupied by ''C. sjostedti'', a much less aggressive defender of trees. Because ''C. sjostedti'' benefits from the holes made by boring beetle larvae, this species facilitates parasitism of trees by the beetles. As a result, the mutualistic relationship between whistling thorn trees and resident ants breaks down in the absence of large herbivores, and trees become paradoxically less healthy as a result.


Gallery

Image:Acacia drepanolobium and Crematogaster nigriceps @ Ngorongoro Aug2009.jpg, ''Crematogaster nigriceps'' ants in defensive demeanor. Note the absence of leaves except at the swollen thorns. File:Acacia drepanolobium MHNT.BOT.2011.3.97.jpg, ''Vachellia (Acacia) drepanolobium'' - MHNT File:Vachellia drepanolobium seed pods.jpg, ''Vachellia (Acacia) drepanolobium'' seed pods. File:Acacia drepanolobium.jpg, ''Vachellia (Acacia) drepanolobium''. File:Vachellia drepanolobium aka Whistling Thorn on the western slopes of Kilimanjaro Jan 2017.jpg, ''Vachellia (Acacia) drepanolobium'' growing in red volcanic soil on western slopes of Mount Kilimanjaro


References


External links

{{Taxonbar, from1=Q15544744, from2=Q1953932 Vachellia, drepanolobium Myrmecophytes Flora of Northeast Tropical Africa Flora of East Tropical Africa Flora of the Democratic Republic of the Congo