Patterns of Plant Diversity in Uganda

BS 55 331 Patterns of plant diversity in Uganda James Kalema and Remigius Bukenya-Ziraba Kalema, J. & Bukenya-Ziraba, R. 2005. Patterns of plant diversity in Uganda. Biol. Skr. 55: 331-341. ISSN 0366-3612. ISBN 87-7304-304-4. For its size, Uganda has a high number of species due to the country’s varied habitats, altitude and the fact that it is located at the confluence of six of White’s phytochoria. However, its level of endemism is low as it shares many of its species with neighbouring countries. Unfortunately, a large portion of these habitats has been destroyed or modified, mainly through human activity. We review species richness, endemism and levels of threat of the county’s vascular plants and pro vide information on recent work in Uganda’s wetland and dryland areas as well as that from the forest ecosystems. A total of 30 taxa were registered as new records for the country and three for the entire East African flora area. These new records are of very rare species and many of them are of high conservation importance. The dryland ecosystems in particular support a rich flora in which is nested some globally threatened and range restricted species. It is expected that more surveys of such habitats will lead to more new records. It is important that some of the wetlands in the country be accorded some conservation status and protection in order to conserve the diversity of plants they harbour. James Kalema, Department of Botany, Makerere University, P.O. Box 7062, Kampala, Uganda. Fax 256 41 531061 E-mail: jimskalema@hotmail. com Remigius Bukenya-Ziraba, Department of Botany, Makerere University, P. O. Box 7062, Kampala, Uganda. Fax 256 41 531061 E-mail: [email protected]/[email protected] Introduction country occurring either as lowland, mid-alti tude, or high-altitude forests. The drylands Uganda has a diversity of habitats supporting a occur in the areas of less rainfall in the north, rich and varied flora. The habitats may be while wetlands are mainly along the shores of divided into three broad categories: forests, the larger lakes. The factors that influence veg wetlands and drylands. Figure 1 shows the etation diversity and distribution include geol detailed vegetation types in the country. Lang ogy and soils, climate, altitude, fire, and dale-Brown et al. (1964) mapped the vegetation human influences. of Uganda and recognized a total of 22 vegeta The country’s natural flora has six of White’s tion types based on dominance and common (1983) phytochoria that converge here includ ness. These broadly include heath and moor ing the Lake Victoria regional mosaic, Sudan- land, forest, forest-savanna mosaic, thicket, ian regional center of endemism, Somalia- woodland, savanna, steppe, bushland, swamps, Masai regional center of endemism, Afromon- and post-cultivation communities. The forests tane archipelago-like regional center of are concentrated in the western part of the endemism, Guinea-Congolia /Sudania 332 BS 55 regional transition zone, and the Guineo-Con- documented and little is known about their golian regional center of endemism. Uganda original extent of cover but these vegetation has considerable significance as far as species types have probably been less destroyed as they richness is concerned although there are only tend to occur on less fertile soils and now cover few national endemics as it shares many with more area (about 42%) of the country (Fig. 1). other countries in the region. Its location in The whole range of habitats have had their East-Central Africa accords it floral characteris species composition altered through anthro tics of East Africa and those of West Africa pogenic influences. They have been modified, (Howard 1991). The number of native vascular degraded and impoverished by way of selective plants so far described is 5406 (Davis et al. removal of some species that are preferred for 1994) of which 70 (1.29%) are endemic. Out socio-economic purposes. This overexploita of the 70 endemics, three are globally threat tion of some species has led to significant ened: Afrothismia winkleri (Engl.) Schltr. (Bur- reductions in their population making them manniaceae) and Diospyros katendei Verde. more rare, and changed the community struc (Ebenaceae) are “Critically Endangered” while ture. Another remarkable change has been Euphorbia bwambensis S. Carter (Euphor- fragmentation of the habitats thus turning the biaceae) is “Vulnerable”. According to the originally vast expanses of natural vegetation IUCN Red Eist of threatened plants of 2000, estate into mere patches. Fig. 1 shows how the Uganda has got 43 species of plants that are remaining forest habitats, for example, have globally threatened (Hilton-Taylor 2000). been fragmented. They occur as islands in a The vegetation of Uganda has undergone sea of degraded and converted area. This changes in a number of aspects including destroys habitat connectivity and continuity, extent of coverage, species composition, conti which in turn affects such ecological processes nuity and connectivity, all of which have been as dispersal, increases the edge effects and ren reduced through the times under the influ ders management more difficult. Some of the ence of human actions (see Struhsaker 1997). dryland and forest ecosystems are represented In Uganda, the original extent of forest cover in the protected area network in the country as age is estimated to have been 103,400 km2 shown in Fig. 2 but the wetlands are not. (44% of the country). By 1984 it was only 7400 Relatively more botanical research has been km2 corresponding to 7% of the original cover carried out in the forest than in wetland and age (Davis et al. 1994) and today it is estimated dryland habitats of Uganda in the recent past. to be only 4063 km2 (4% of the original cover). This study emphasized the later two ecosystem Fig. 1 shows areas of degraded forest and those types with a view of getting current informa that have been converted to farmland. Most of tion on their contribution to the conservation these were either forested or covered in dry of Uganda’s flora today. It is through such sur land vegetation. Hamilton (1984) and Eang- veys that patterns of distribution of taxa can be dale-Brown (1960) estimate that ca 20% of better understood and this is vital for planning Uganda’s land surface was covered by other and designing of conservation strategies. tree-rich vegetation such as woodland, includ ing much of the Karamoja area which today is impoverished. Wetlands today occupy only Methods 13% of Uganda’s surface area (NEMA 2000). For assessing the species richness, the sources Drylands - here used to include grasslands of information we used included Davis et al. woodlands, scrub, shrubland - have been less (1994), various floras of the Tropical East BS 55 333 /\J International boundary /\/ Boundary for floral regions Vegetation/ Land use types Broadleaved Tree Plantation Woodland Small - scale farming Coniferous Plantation Bushland Large - scale farming Tropical High Forest Ml Grassland Built-up Area Degraded Forest Wetland Open Water Source: National Biomass Study, Forest Department Fig- 1 The vegetation and land-use types in Uganda. The four floral regions in which the country is divided are indicated asUl,U2, U3 and U4. 334 BS 55 Protected Areas National Parks Forest Reserves Wildlife Reserves Animal Sanctuaries Communal Wildlife Areas Fig. 2. The protected areas of Uganda. Note that some of the National Parks consist of forest. BS 55 335 Africa region, and Phillips et al. (1999). The These were a total of 55. Overall, the floral global threat levels were obtained from the region U2 registered the highest proportion of 2000 IUCN Red List of threatened plants new species (66%) followed by U1 (21%), U3 which is available on the IUCN website (7%) and U4 had the lowest (6%). (www.iucn.org). Endemism was assessed from The new records came mostly from the floral the geographical distribution information pro region U2 (Appendix 1). The particular areas vided in the Flora of Tropical East Africa in this floral region from which they were (FTEA). The new records were obtained from recorded are Bwindi (Impenetrable) National both published and unpublished work of other Park and Budongo Forest for the forested collectors of Ugandan plants as well as that areas while in U1 the main contributors were from our own collections that were made dur Kidepo Valley National Park, Ajai Wildlife ing the period of August 2000 to December Reserve and Murchison Falls National Park for 2001. In our surveys, we inventoried vascular the savanna areas (also see Kalema 2003). plants in wetland and dryland Important Bird Kidepo is located in White’s (1983) Somali- Areas (IBAs). Our study areas varied in size Masai Regional Centre of Endemism character and the sampling effort was allocated in rela ized by very dry conditions, a unique feature in tion to the size of the study area and the level the country. This coupled with the remote of habitat heterogeneity which itself was mea nature of the area makes it a good candidate sured from the number of Langdale-Brown et for encountering new records. The Ajai and al. (1964) vegetation types. Murchison areas tend to have Central and West African floral affinities thus having species occurring at their eastern limit of their range. Results and discussion Many of these new records are undoubtedly The areas of wetland and dryland surveyed very rare species at least at national level (also together cover an area of 10,628 km2 repre see Namaganda 2003, Namaganda & Kalema senting only 4.5% of the country’s total area. 2003). However, the last five species in Appen Nonetheless, we encountered 1038 species in dix 1, namely Flaveria trinervia, Nicandra physa the wetlands and 1448 in the drylands.

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