Synsepalum muelleri

(Kupicha) T.D.Penn., Pennington in Gen. Sapotac.: 249 (1991)

093F347D-DD12-5C27-B551-9F012D1C0C1D

• Vincentella muelleri Kupicha in Candollea 33 (1): 37, fig. 4 (1978); Kupicha in Sapotaceae Flora Zambesiaca 7(1): 228 (1983).

The botanical importance of the Chimanimani foothills: an Important Plant Area

The high Chimanimani Mountains have long been renowned for their high botanical endemism, particularly associated with the extensive outcrops of nutrient-deficient quartzites (Wild 1964; van Wyk and Smith 2001; Timberlake et al. 2016b; Wursten et al. 2017; Cheek et al. 2018). Much less well known is the botanical importance of the low elevation foothills of these mountains (c. 300–1200 m elevation, mainly below 1000 m), particularly to the south and east of the massif. This area has extensive stands of low altitude moist evergreen and semi-deciduous forest that, whilst now much fragmented, still represent the largest extent of this highly threatened habitat type in Mozambique.

The area of particular interest stretches from the lower valleys of the Rusitu and Haroni Rivers of Zimbabwe, the Makurupini area on the Zimbabwe-Mozambique border and the Maronga, Zomba and Mpunga communities of Mozambique. The botanical diversity of the Haroni-Rusitu-Makurupini region has been documented in an unpublished checklist of 787 species, compiled from a range of expeditions made between 1955 and 1998 (Timberlake 1999). Recent survey and inventory work in the Mozambican portion of this area, excluding Makurupini, documented 532 plant species (Timberlake et al. 2016a).

The forests vary in species composition and in the relative extent of evergreen versus deciduous components; the species composition in the Mozambican portion of these forests is discussed in detail by Timberlake et al. (2016a). Of particular interest botanically are the mostly evergreen forests and riverine fringes of Haroni-Makurupini, Maronga and the southwestern-most part of Zomba (Thekeza Forest). Amongst the dominant trees, these areas support what is potentially the largest population globally of Maranthes goetzeniana (Engl.) Prance. This species is often locally dominant in Maronga and also extends to Thekeza (Timberlake et al. 2016a).

Although of relatively low species richness compared to lowland forests in other parts of tropical Africa, the Chimanimani forests support a number of rare and threatened plant species. For example, the spectacular herb Streptocarpus acicularis I.Darbysh. & Massingue is so far known only from a single collection from along the Mevumozi River near Maronga (Darbyshire and Massingue 2014). Vepris drummondii Mendonça is largely restricted to the Haroni-Makurupini-Maronga forests except for an outlier population on nearby Mt Pene in Zimbabwe; it was encountered at low abundance in forests at Maronga in 2015 (I.D., pers. obs.). There is also a population of the globally Endangered wild coffee Coffea salvatrix Swynn. & Phillipson, or “mukofi” coffee, in the Maraumi Forest of Zomba and this species may occur more widely in this forest belt. Other range-restricted forest species include Afrocanthium ngonii (Bridson) Lantz and Englerina swynnertonii (Sprague) Polhill & Wiens.

These forests also support species that are nationally rare for Zimbabwe and/or Mozambique, including some interesting outlier populations. For example, Ficus mucuso Welw. ex Ficalho and Raphidiocystis chrysocoma (Schumach.) C.Jeffrey, West African species that are known in the Flora Zambesiaca region only from these forests, and Dianella ensifolia (L.) DC., a species of horticultural importance with an Indian Ocean distribution, on the African continent known in the wild only from the Chimanimani, Mabu and Ribáuè mountains of Mozambique. It is locally frequent at Maronga (Timberlake et al. 2016a). Also of interest is a dwarf, small-leaved species of Podocarpus (Podocarpaceae) that grows frequently along the rocky margins of forest rivers and streams at low elevations and also extending up into the higher mountains. This species has previously been placed within one of the two South African species P. elongatus (Aiton) L’Hér. ex Pers. (Farjon 2017) or P. latifolius (Thunb.) R.Br. ex Mirb. (Burrows et al. 2018) but it is quite possibly a distinct taxon – further taxonomic and molecular phylogenetic studies are required to confirm its placement. It is apparently also known from the Mafinga Mountains of Northeast Zambia which are also partially quartzitic (J. Timberlake, pers. comm.).

The forests are interspersed with extensive areas of miombo woodland, dominated by Brachystegia (most frequently B. spiciformis Benth.) and Uapaca species. Whilst important ecologically, the miombo does not contain high numbers of rare or threatened plant species. Of greater botanical significance is the presence of three other vegetation types within this mosaic:

1. Low elevation outcrops of nutrient-deficient quartzites, usually associated with light woodland dominated by Brachystegia microphylla Harms. These outcrops are most frequent in the Makurupini-Maronga area but also extend further east. They support an interesting rock flora including the endemic Ficus muelleriana C.C.Berg, a tiny fig that climbs on the rock faces, and Otiophora lanceolata Verdc., a locally abundant endemic shrublet. Aloe ballii Reynolds, including its two varieties var. ballii and var. makurupiniensis Ellert (both Vulnerable), is a delicate grass aloe restricted to quartzite slopes along the Zimbabwe-Mozambique border. Other range-restricted and/or scarce species of this habitat include Sclerochiton coeruleus (Lindau) S.Moore, Gutenbergia westii (Wild) Wild & G.V.Pope and Sericanthe chimanimaniensis Wursten & de Block ined. (see Burrows et al. 2018). Where quartzite outcrops along rivers and streams, the endemic grass Danthoniopsis chimanimaniensis (J.B.Phipps) Clayton can be locally frequent.

2. Seasonally wet grasslands, which occur in small scattered areas within the forest-woodland mosaic. These support an interesting, though not diverse, herb flora including the recently resurrected species Crepidorhopalon flavus (S.Moore) I.Darbysh. & Eb.Fisch. whose range is centred on the southern Chimanimani foothills (Darbyshire et al. 2019), and Mesanthemum africanum Moldenke, a Chimanimani endemic mainly found in the high mountains but which occurs at much lower abundance in these lowland wet grasslands (Timberlake et al. 2016a).

3. Swamps and lowland watercourses that are fringed by large stands of the striking tree Pandanus livingstonianus Rendle. Whilst fairly widespread, this tree has very isolated and localised populations and is thought to be threatened by habitat loss (Beentje 2009). The Zomba Centro Swamp is particularly important for this species.

The entirety of this area falls within the Chimanimani Trans-Frontier Conservation Area (TFCA), in part within the core TFCA, i.e. the Chimanimani National Park of Zimbabwe and Chimanimani National Reserve of Mozambique, and in part within the TFCA buffer zone. This buffer zone includes the Maronga, Zomba and Moribane Forest Reserves in Mozambique (see Müller et al. 2005). Lowland habitats within the core TFCA are largely intact, with only small areas of human encroachment at present. However, threats are severe within the buffer zone including within the Forest Reserves. Large areas of forest have either been cleared or degraded for subsistence agriculture, using fire to clear the undergrowth once the large trees have been felled. Excessive burning prevents forest regrowth and impacts other key habitats. Regular burning also encourages the continuing spread of the invasive South American shrub Vernonanthura polyanthes (Spreng.) A.J. Vega & Dematt. (syn. V. phosphorica (Vell.) H.Rob.; see Timberlake et al. 2016a; Sukhorukov et al. 2017) and this species is now mono-dominant over many hectares of disturbed, former forest habitats in the Chimanimani foothills, out-competing native species and preventing regeneration of natural habitats and encroaching into forest margins (Timberlake et al. 2016a). A further threat is the impact of mining for gold along some of the major rivers that flow from the massif, which pollutes the watercourses and denudes vegetation along their margins, as is clearly visible on satellite imagery on Google Earth. Conservation action is urgently needed in the TFCA buffer zone. Ongoing work with communities to attempt to better balance livelihoods with biodiversity conservation is ongoing, led by the Micaia Foundation (http://www.micaia.org), and this has led to the establishment of community conservation areas in the Maronga, Zomba and Mpunga communities of Mozambique (Timberlake et al. 2016a). However, there is still much work to be done to secure the future of the biodiversity within the TFCA buffer zone.

Applying the Important Plant Areas (IPA) criteria as revised by Darbyshire et al. (2017), the Chimanimani foothills qualify as an IPA under criterion A – presence of threatened species – with 17 criterion A taxa, of which 12 currently meet the threshold for criterion A(i) – presence of globally threatened species (see Table ​Table2).2). This site will also qualify under IPA criteria B(ii) – exceptional number of species of high conservation importance, and C(iii) – presence of nationally threatened or range restricted habitat, due to the large extent of threatened lowland moist forest. The lowland forest and the high massif are combined together in the two Important Bird and Biodiversity Areas for Chimanimani, which are divided along the international boundary (BirdLife International 2019a, 2019b). However, in botanical terms, the species assemblages are markedly different between the Chimanimani foothills and the high massif (albeit with a mid-elevation transition zone) and the threats and conservation issues that the two areas face are also markedly different. With this in mind, we consider it most useful to recognise the Chimanimani foothills as an IPA in their own right, with the high massif recognised as a separate IPA. In doing so, this also helps to draw more attention to the importance of the Chimanimani foothills as a site of global importance for biodiversity and in urgent need of conservation action.