Mburo

A(i)Site contains one or more globally threatened species, B(iii)Site contains an exceptional number of socially, economically or culturally valuable species

Lake Mburo National Park qualifies as an IPA under criterion A(i) as it supports a globally important population of Rhynchosia crispa, a range-restricted Ugandan endemic species which has been assessed as endangered (EN) (Wheatcroft in press), and Rhipidoglossum bilobatum, a species currently assessed on the IUCN Red List as Vulnerable. It also contains 10% of useful plant species on the national species checklist thus triggering criterion B(iii).

Lake Mburo National Park (LMNP), the smallest grassland national park in Uganda, covers an area of 378 km2. It is situated in the three districts of Mbarara, Kiruhura and Isingiro in the U2 floristic region, in the southwestern part of Uganda. It is in the drier part of Uganda known as the cattle corridor, which stretches from northern Tanzania through Uganda to Ethiopia (Tweheyo et al. 2012), and is surrounded by livestock ranches (Blösch 2002). It lies along the Kampala–Mbarara road, 40 km east of Mbarara town, and is the park closest to Kampala.

The park has significant populations of wild animals residing on the surrounding public land. Accordingly, a wider Lake Mburo Conservation Area (LMCA) is recognized that includes both the core LMNP and adjoining parishes, recognizing the need to work with local communities to achieve conservation goals (UWA 2015; Nyamukuru 2019).

Lake Mburo IPA is botanically important, with at least 529 species of vascular plants recorded, a number higher than even larger-sized similar habitats in Uganda, owing to diversified vegetation types (Kalema 2005). It is the only protected area where the range-restricted Ugandan endemic species Rhynchosia crispa (EN) is known from (Rotton et al. in press). This species is a decumbent or sometimes erect herb 10-18 cm tall, with several shoots from a woody rootstock (APD 2022). The only other recorded localities for this very rare species are Rushozi Dam and Kashari, Moko Range, also in Ankole region. Its presence at the Rushozi Dam and Kashari sites is from old records of 1957 and 1969 respectively. In the park, the species was first recorded in 2001 from Acacia-Pappea wooded grassland - (Kalema #1765; Kalema 2005). Both Rushozi and Kashari sites now appear to be heavily transformed, hence LMNP is the only secure site and could even be the only extant site for this species. It is assessed as Data Deficient (Contu 2012). Also present in the LMNP IPA is Rhipidoglossum bilobatum, a globally Vulnerable (VU) orchid (Gereau et al. 2019). Known from 8 Ugandan sites but should qualify as >1% global population, possibly >5% national population.

The only known Ugandan record of Equilabium (Plectranthus) longipes is from LMNP, collected in Acacia wooded grassland in 2001 (Kalema #1752; Kalema 2005). This species is otherwise known from Kenya, Rwanda, Tanzania, Ethiopia and Eritrea (Paton et al. 2009). It is also Uganda’s only known site for Indigofera vicioides subsp. rogersii collected from an open hilltop of Loudetia kagerensis on stoney ground in 2001 (Kalema #1624; Kalema 2005).

Lake Mburo IPA contains 109 (10%) useful plant species on the national species checklist, exceeding the 3% threshold and so triggering criterion B(iii). The site is ranked the 9th most species-rich site for useful plants within the IPA network. It significantly holds the highest number of Crop Wild Relatives (CWR) of all sites (11 spp., 13%), of which 6 species are only found at this site. A total of 40 species are unique to this site within the IPA network, predominantly food (26 spp., 5%) and medicinal (24 spp., 3%) species.

The present-day vegetation in LMNP has resulted from a combination of factors, including climate, soil, fire, grazing, construction of cattle kraals and cutting trees for firewood and charcoal, besides other human activities (UWA 2015). Significant changes have resulted from these factors. For example, the grass Cymbopogon nardus is steadily increasing, especially from the north, owing to overgrazing and frequent burning (Ayorekire 1999).

LMNP exhibits a semi-arid savanna climate with minimum annual rainfall ranging from 400 mm in the southeast to 700 mm in the west. The park and its environs are drier than the surrounding region, lying in a rain shadow caused by the Kabula hills (UWA 2015). Rainfall is bimodal, occurring mainly from March to May and between September and November, with an intervening long dry season between May and August and a shorter one from December to February. The mean maximum temperature is ca. 27.5°C and the mean minimum is 15°C (UWA 2015).

LMNP contains a mosaic of habitats including rock outcrops, open grassland (mainly in the flat, wide valleys), wooded grassland, thicket, Acacia woodland, gully and riverine forest, and swamp. This variety of habitats gives it a high diversity of plants and animals for its size (Birdlife International 2023). The savanna grassland forms a continuous community of grass cover with scattered trees, the dominant tree species being Acacia hockii (Kalema 2005,UWA 2015). Acacia hockii has increased in abundance over the years (Nyamukuru et al. 2019), reportedly taking up many areas including well-drained hill sides and low-lying hill tops which were previously much more open and provided good grazing areas for wildlife.

The most dominant vegetation type in this region is Dry Acacia Savanna (Wooded Grassland or Woodland) (Kalema 2005). This largely occurs on the elevated parts of the park. Dominant grass species Cymbopogon nardus, Brachiaria decumbens, Panicum maximum, Hyparrhenia filipendula and Themeda triandra, with the aforementioned Acacia hockii being the dominant tree. There is also Moist Acacia Savanna with Acacia polyacantha the dominant tree, and the main grasses being Chloris gayana, Cymbopogon nardus, Brachiaria decumbens and Panicum maximum. There is also grass Savanna, which is open grassland with only very scattered trees. This vegetation type occurs mainly in the eastern and central parts of the park on the higher elevations with thin soil cover on the hilltops, with Loudetia kagerensis, Sporobolus pyramidalis, Themeda triandra, Hyparrhenia spp., Sporobolus stapfinus and Kyllinga (Cyperus) sp. being dominant. Communities with Impeded Drainage represents a fourth vegetation category found within this IPA (Langdale-Brown et al. 1964). In Mburo, these occur in low-lying areas, and they support the grasses Echinochloa pyramidalis, Leersia hexandra and Cynodon dactylon, often growing with Acacia gerrardii, sometimes growing as woodlands. Fifthly, there are wetlands of Cyperus papyrus Swamp. These line most of the southern border of the park and all the lakes (Kalema 2005). Sporobolus spp., Echinochloa pyramidalis and Cyperus spp. dominate seasonal swamps, while Cyperus papyrus and Typha spp. dominate permanent swamps.

The west of LMNP contains dry gully forests located between interlocking hill spurs. These are dominated by Combretum molle. Narrow belts of riverine forests, about 50 m wide, line the western fringes of Lake Mburo and the River Rwizi (Kamugisha et al. 1997), the dominant trees being Markhamia lutea, Vepris nobilis, Ficus spp. and Phoenix reclinata.

LMNP area is underlain by two major Pre-Cambrian rock systems: an older Basement Complex and a younger Karagwe-Ankolean rock system. These have been overlain, since the Pleistocene, by sediments, mainly swamp deposits and alluvium (Kamugisha et al. 1997). The Basement Complex comprises acidic and highly metamorphosed igneous rocks, principally Pre-Cambrian granites and gneisses (Government of Uganda 1967). The soils are mainly ferrallitic soils of sandy type and occasionally sandy loam soils can be found in valleys. The steep slopes are mainly dominated by laterite soils (Government of Uganda 1967).

Lake Mburo was gazetted as a National Park in 1986 with an area of 650 km2 which was later reduced to 370 km2 (UWA 2015). Despite the decrease in size, the large animals’ home range did not reduce as they continued migrating into private land, competing with livestock for pasture, water and salt in addition to transmission of diseases and causing crop destruction. This bred human-wildlife conflicts, with communities (Tweheyo et al. 2012, Amanya 2015, Kembabazi et al. 2024), which appear to be increasing despite (some interventions Braczkowski et al. 2020).

The immediate neighbours of the park mostly derive their livelihood from livestock rearing. Many of these have large herds on small pieces of land, with inadequate water resources and grazing pasture. Despite the fact that during the dry season, most of the cattle keepers request to be given permits to access water in the park, they still illegally graze their cattle in the park even when they have been granted excess permits for only water. Many households are moving away from strict dependence on cattle-keeping, with many beginning to adopt a more sedentary form of mixed farming, rearing livestock and also growing some crops (Ayorekire 1999). Animals, notably buffalo and hippo, raid their crops and livestock farms (Tweheyo et al. 2012). Illegal tree felling mainly for firewood and charcoal is also reported as a major threat to biodiversity conservation in this IPA.

Wildfires which are set frequently within and around the park are also reported to be a key challenge to resource conservation in the park as it has been affecting the quality of habitat. The cool fires, arising from low fuel, are believed to lead to the germination and regeneration of Acacia spp., while more frequent fires destroy native seeds leading to the emergence of unpalatable species (UWA 2015). Periodically, fire has been used in LMNP as a management tool to provide fresh forage for wildlife and to avoid outbreaks and spread of uncontrolled wildfires that would even impact park property. However, no fire management plan is in place to guide more appropriate and effective burning practices in the park. The resulting impact of fires in LMNP is believed to have caused the long-term negative ecological changes being experienced.

Acacia hockii is reported to have aggressively invaded previously open spaces affecting animal species abundance and distribution in the park thereby impairing tourism activity. Community groups have been mobilised and engaged to uproot the A. hockey trees and shrubs, but the exercise has been done mechanically and haphazardly with no research and monitoring component to understand the impact of its removal both on flora and fauna (UWA 2015).

Non-native invasive (alien) species also occur within and outside the park. Notable among these is Lantana camara, a notorious shrubby invader known to spread prolifically if not controlled (Barahukwa et al. 2023). Elsewhere, Eichhornia crassipes (water hyacinth) is an invasive water weed that has been sighted along River Rwizi. This has the potential to invade all the lakes within the Lake Mburo ecosystem. There is need for mapping the extent and monitoring the spread of these two invasive species. Pockets of congress weed (Parthenium hysterophorus) has also been reported around the campsites and road tracks and could potentially spread further if not eradicated or controlled.

Lake Mburo qualified as a Key Biodiversity Area KBA), triggered by the occurrence of Red-faced barbet (Lybius rubrifacies), a bird species assessed as Near Threatened (NT) (Plumptre et al. 2017). The Lake Mburo- Nakivale ecosystem is a Ramsar site which is an Important Bird Area, particularly important as a breeding area for the regionally endemic shoebill (Balaeniceps rex, VU) and contains important habitat for the papyrus yellow warbler (Calamonastides gracilirostris, VU). The park also hosts a number of migratory birds both palaearctic and continental birds (BirdLife International 2023). LMNP is the only park with significant populations of impala, eland, topi and Burchell’s zebras in Uganda.

Lake Mburo National Park, surrounded by livestock ranches, is a critical biodiversity site in this area of intensive pastoral activity. The park plays an important role in provisioning, regulatory and supporting services in this cattle corridor where water availability is key to community livelihood and their socio-economic activities. Lake Mburo and River Ruizi are pivotal in the provision of water in the general landscape. The wetlands fringing these water bodies play an important function in water filtration, improving water quality for use further downstream.

The Lake Mburo IPA is a reservoir of germplasm for crop wild relatives. It is therefore important for crop breeding programmes and the development of varieties with desirable traits such as drought resistance, especially as global and local climate continues to change. There is some local hunting for bushmeat and harvesting of plants for medicinal purposes. Mystroxylon aethiopicum, known locally as “omuboro”, is a tree believed to have aphrodisiac properties and is much sought after (UWA 2015). This also provides the potential for ecotourism at this IPA.

Assessed by:

Kennedy Mukasa, Makerere University Herbarium

James Kalema, Makerere University Herbarium

Samuel Ojelel, Makerere University Herbarium

Iain Darbyshire, Royal Botanic Gardens, Kew

Haley Gladitsch, Royal Botanic Gardens, Kew

Florence O'Sullivan, Royal Botanic Gardens, Kew

Date of first assessment: 18th Nov 2024

Reviewed by:

Aggrey Rwetsiba, Uganda Wildlife Authority