Question: What type of vegetation is in the central part of the country where Ussa is located?

full_context: Document 1: Ukum: Ukum is a Local Government Area of Benue State, Nigeria. It has an area of and a population of 216,930 at the 2006 census.
Document 2: Misau: Misau is a Local Government Area of Bauchi State, Nigeria. Its headquarters are in the town of Misau. It was founded by Hamman Mangan who ruled as an unofficial King for a period of 25 years at around 1850 AD.
Document 3: Sahara: To the north, the Sahara skirts the Mediterranean Sea in Egypt and portions of Libya, but in Cyrenaica and the Maghreb, the Sahara borders the Mediterranean forest, woodland, and scrub ecoregions of northern Africa, all of which have a Mediterranean climate characterized by hot summers and cool and rainy winters. According to the botanical criteria of Frank White and geographer Robert Capot-Rey, the northern limit of the Sahara corresponds to the northern limit of date palm cultivation and the southern limit of the range of esparto, a grass typical of the Mediterranean climate portion of the Maghreb and Iberia. The northern limit also corresponds to the 100 mm (3.9 in) isohyet of annual precipitation.
Document 4: Sahara: The desert comprises much of North Africa, excluding the fertile region on the Mediterranean Sea coast, the Atlas Mountains of the Maghreb, and the Nile Valley in Egypt and Sudan. It stretches from the Red Sea in the east and the Mediterranean in the north to the Atlantic Ocean in the west, where the landscape gradually changes from desert to coastal plains. To the south, it is bounded by the Sahel, a belt of semi-arid tropical savanna around the Niger River valley and the Sudan Region of Sub-Saharan Africa.
Document 5: Gurara: Gurara is a Local Government Area in Niger State, Nigeria, adjoining the Federal Capital Territory. Its headquarters are in the town of Gawu.
Document 6: Geography of Nigeria: With the Intertropical Convergence Zone (ITCZ) swinging northward over West Africa from the Southern Hemisphere in April, heavy showers coming from pre-monsoonal convective clouds mainly in the form of squall lines also known as the north easterlies formed mainly as a result of the interactions of the two dominant airmasses in Nigeria known as the Maritime tropical (south westerlies) and the Continental tropical (north easterlies), begins in central Nigeria while the Monsoons from the south atlantic ocean arrives in central Nigeria in July bringing with it high humidity, heavy cloud cover and heavy rainfall which can be daily occurrence lasting till September when the monsoons gradually begin retreating southward to the southern part of Nigeria. Rainfall totals in central Nigeria varies from 1,100 mm (43.3 in) in the lowlands of the river Niger Benue trough to over 2,000 mm (78.7 in) along the south western escarpment of the Jos Plateau.
Document 7: Chad: Chad has several regions: a desert zone in the north, an arid Sahelian belt in the centre and a more fertile Sudanian Savanna zone in the south. Lake Chad, after which the country is named, is the largest wetland in Chad and the second - largest in Africa. The capital N'Djamena is the largest city.
Document 8: Nigeria: Everything in between the far south and the far north is savannah (insignificant tree cover, with grasses and flowers located between trees). Rainfall is more limited, to between 500 and 1,500 millimetres (20 and 60 in) per year. The savannah zone's three categories are Guinean forest-savanna mosaic, Sudan savannah, and Sahel savannah. Guinean forest-savanna mosaic is plains of tall grass interrupted by trees. Sudan savannah is similar but with shorter grasses and shorter trees. Sahel savannah consists of patches of grass and sand, found in the northeast. In the Sahel region, rain is less than 500 millimetres (20 in) per year and the Sahara Desert is encroaching. In the dry north-east corner of the country lies Lake Chad, which Nigeria shares with Niger, Chad and Cameroon.
Document 9: Babassoua: Babassoua is a village in the Lobaye region in the Central African Republic southwest of the capital, Bangui and near the border with the Democratic Republic of the Congo.
Document 10: Ussa: Ussa is a Local Government Area in Taraba State, Nigeria. Its headquarters are in the town of Lissam (). Ussa borders the Republic of Cameroon in the south; the Donga River forms its northern boundary. Ussa was created in 1996 during the regime of ″General Sani Abacha″ after an earlier attempt failed in 1983, Aticwo (kpambo), Rufu, Lumbu, Fikyu, Acha, Kpambo Puri, are some of the district council within Ussa<.ref>www.kuteb.tripod.com
Document 11: Geography of Nigeria: Nigeria, like the rest of West Africa and other tropical lands, has only two seasons. These are the dry season and the rainy season. The dry season is accompanied by a dust laden airmass from the Sahara Desert, locally known as Harmattan, or by its main name, The Tropical Continental (CT) airmass, while the rainy season is heavily influenced by an airmass originating from the south atlantic ocean, locally known as the south west wind, or by its main name, The Tropical Maritime (MT) airmass. These two major wind systems in Nigeria are known as the trade winds.
Document 12: Takum: Takum is a Local Government Area in Taraba State, Nigeria. Its headquarters are in the town of Takum, it is created out of Wukari local government in 1975, at . Takum borders the Republic of Cameroon in the south, Ussa Local Government to the west, Donga Local government to the north, District within Takum are Abuja, kwambai, jenuwa, Rogo, Dutse, Kashimbila, Bete, Chanchanji, Bika.
Document 13: Sahara: To the south, the Sahara is bounded by the Sahel, a belt of dry tropical savanna with a summer rainy season that extends across Africa from east to west. The southern limit of the Sahara is indicated botanically by the southern limit of Cornulaca monacantha (a drought-tolerant member of the Chenopodiaceae), or northern limit of Cenchrus biflorus, a grass typical of the Sahel. According to climatic criteria, the southern limit of the Sahara corresponds to the 150 mm (5.9 in) isohyet of annual precipitation (this is a long-term average, since precipitation varies annually).
Document 14: Bassa, Plateau State: Bassa is a Local Government Area in the north of Plateau State, Nigeria, bordering Kaduna and Bauchi States. Its headquarters are in the town of Bassa at.
Document 15: Ughelli South: Ughelli South is a Local Government Area of Delta State, Nigeria. It is made up of six Urhobo kingdoms namely: Ughievwen, Arhavwarien, Effurun Otor, Eghwu, Okparabe and Olomu. Otu Jeremi is the headquarters of Ughelli South LGA.
ground_truth: savannah
sub_queries: Ussa >> country Answer: Nigeria
What type of vegetation is in central Nigeria ? Answer: savannah