Tiwai

A(i)Site contains one or more globally threatened species, B(ii)Site contains an exceptional number of species of high conservation importance, C(iii)Site contains nationally threatened or restricted habitat or vegetation types, AND/OR habitats that have severely declined in extent nationally

The Tiwai Island IPA qualifies under the criteria A (i) as it contains twenty globally threatened species as well as B (ii) containing several species of significant conservation value. Additionally, the IPA qualifies under criteria C(iii). It is the largest inland island in the country and constitutes part of the intact remnant of the low moist tropical evergreen forest in Sierra Leone, a habitat that is nationally restricted. The region is a mosaic of gallery and swamp forest supporting high species diversity of over 700 plants, at least one of them, Millettia leonensis, is endemic to Sierra Leone.

The Tiwai Island Important Plant Area (IPA) contains a remnant of the West African Tropical Rainforest (Saidu et al., 2022). It is situated on the border between the Kenema District in the Eastern Province and the Pujehun District in the Southern Province of Sierra Leone (Google Earth, 2025). According to the Tiwai Island Wildlife Sanctuary (TIWS, n.d.), the island is surrounded by eight communities in two chiefdoms: Mapuma, Ngjema, and Segbema in Koya Chiefdom (Kenema District), and Kambama, Sahun, Naihun, Jenneh, and Boma in Barri Chiefdom (Pujehun District). This site is situated approximately 15 km southwest of Potoru, about 300 km southeast of Freetown, and roughly 35 km from the Liberian border (Fimbel, 1994, Google earth, 2026).

Tiwai Island, the largest inland rainforest island in Sierra Leone, is located within the Moa River, a few km northwest of Gola West (Oates et al., 1990), covering approximately 12 km² (1,200 hectares; Saidu et al., 2022). The name Tiwai means "large island" in the Mende language. It was recognized in the late 1970s as a critical habitat for wildlife protection, and ecological research and the first community-led conservation commenced on Tiwai Island in the early 1980s (Oates et al., 1990). The humid tropical lowland ecosystem gets up to 3,200 mm of rainfall annually and is home to unique group of fauna, including the Olive Colobus (Procolobus verus) and the Pygmy Hippo (Choeropsis liberiensis) (Oates et al., 1990).

The island's vegetation is classified as tropical moist evergreen forest with a mosaic of gallery forests, palm forests, and inland swamps (Holdridge 1947, Fimbel 1994). Tiwai lies within the Guinean Forests Biodiversity Hotspot, designated by Conservation International. Previous studies have estimated that the island hosts over 700 vascular plant species, approximately 20% of which are globally threatened, with several endemic to Sierra Leone (Oates, 1999). About 60% of the island consists of the mature forest (25 years old), while 30% is regenerating secondary forest as a result of historical anthropogenic agricultural operations that declined during the 1980s (Oates et al., 1990; Kolp et al., 2008).

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Tiwai Island represents one of the remaining sites of lowland evergreen forest in Sierra Leone, supporting more than 700 species of plants. A comprehensive botanical survey conducted in 2003 by the late Prof. Ake Assi and Prof. Aiah Lebbie documented 695 plant species, including 282 voucher specimen collections housed in the National Herbarium. The study identified 20 globally threatened species, 26 previously uncollected species in Sierra Leone, and 103 taxa yet to be assessed by the IUCN.

Notable globally threatened taxa include Dactyladenia smeathmannii (EN), Dactyladenia hirsuta (EN), Eugenia liberiana (EN), Millettia leonensis (EN), Hemandradenia chevalieri (EN), Milicia regia (VU), Okoubaka aubrevillei (EN), etc. The first Sierra Leonean records from Tiwai include Cyperus blepharoleptos, Ruthalicia longipes, Combretum aphanopetalum, Vernonia conferta, Culcasia seretii, and Raphia mannii. The rediscovery of Tiliacora dinklagei, last collected in 1944, further emphasizes the island’s urgent conservation and the need for continued research.

The island is dominated by widespread West African species such as Monanthotaxis mannii, Heterotis rotundifolia, Piptadeniastrum africanum, Parinari excelsa, and big lianas of Landolphia hirtusa of about 104 cm in diameter (Fanny Massally pers. obs.). Other common taxa include Xylopia aethiopica, Anthostema senegalense, Osodendron altissimum, Nauclea latifolia, Alchornea cordifolia, and Uapaca guineensis.

The dominant canopy tree species of the moist evergreen forest at Tiwai are Heritiera utilis, Brachystegia leonensis, and Parinari excelsa. Additional habitats include swamp forest, forest regrowth and secondary forest, and farm bush, which is often dominated by the invasive shrub Chromolaena odorata (Klop et al., 2010).

The island topology is at a low elevation of about 85 - 120 m above sea level with an average annual temperature of about 27°C. Annual rainfall average is about 3,000 mm, with a wet climate and a dry period lasting from December to March (Klop et al., 2010). In some specific habitats, rainfall can exceed 3,200 mm annually. The soils at Tiwai Island are highly sandy, strongly acidic, and have poor mineral nutrients (Oates et al., 1990), typical of the West African humid tropical lowland forest zone.

All protected area management in Sierra Leone including Tiwai island are overseen by the National protected Area Authority, which is the main governmental agency for protected areas in Sierra Leone. The Tiwai Island Wildlife Sanctuary is locally managed by the Tiwai Island Administrative Committee (TIAC), including representatives from the eight surrounding communities, the Environmental Foundation Agency (EFA), government agencies, Njala University, and conservation bodies essential for its protection. The sanctuary forms part of the UNESCO World Heritage site, as the Gola-Tiwai Complex, and is currently classified under the IUCN Category IV (habitat/species management area).

Even though few studies have reported anthropogenic pressures, including poaching, forest fragmentation, swamp modification for rice cultivation, deforestation, and agricultural expansion, in addition to climate change in the past (Saidu et al., 2022, Fanny Massally pers. obs.), there is no forest cover loss has been detected inside the Tiwai Island sanctuary between May 2024 and April 2025 (WFP, 2025)

Recent analysis highlights an ongoing decline in forest cover linked to charcoal production and farmland conversion in the Southern Province, particularly around the sanctuary (Stevens et al. 2025). Historically, similar land-use anthropogenic pressures in the 1970s led to the clearing of 30% of Tiwai’s original forest. To prevent recurrence of land degradation, management must ensure robust protection with community-led efforts, to ensure Tiwai’s continued protection.

Tiwai Island provides a range of ecosystem services that sustain both wildlife and the local communities, including cultural, supporting, provisioning, and regulating services. Many of the plant species on the island provide direct benefit to the human communities; they are used for food, source of local traditional medicines, or as local materials.

The island mosaic of forest habitats offers support to diverse fauna communities, including Pygmy Hippos (Choeropsis liberiensis), several primate species, birds, and insects. The Pygmy Hippos, which are a globally threatened species, depends on the island's dense riparian vegetation for shelter and forage. A dietary study identified ten plant species consumed by this species, included Ipomoea alba, Ipomoea batatas, Theobroma cacao, Pteridium aquilinum, Cucurbita pepo, Urena sp., Digitaria eriantha, Hibiscus esculentus, Corchorus olitorius, and Geophila obvallata (Saidu et al., 2022). These include wild and cultivated taxa, highlighting the animals' use of natural and anthropogenic food sources. Frugivorous primates, like the western white-and-black colobus (Colobus polykomos), eat mostly fruits, seeds, and young leaves, especially from leguminous plants (Fabaceae). They play a critical ecological role by dispersing seeds and maintaining forest regeneration (Dalsilva, 1994).

Tiwai forest contributes to regulating services such as predator and prey regulation to maintain ecosystem balance, water retention, and microclimate regulation. The forest also holds high cultural significance and spiritual historic value to the Mende people who use plants from Tiwai in ceremonies and rituals.

Gabriella Hoban, Royal Botanic Gardens, Kew

Fanny Massally, Royal Botanic Gardens, Kew

Date of first assessment: 24th Apr 2025

Xander van der Burgt, The Royal Botanic Gardens Kew

Mr. Tommy Garnett, Environmental Foundation for Africa