612 H. J. Ndangalasi and N. J. Cordeiro


FIG.1 (a) The East Usambara Mountains, Tanzania, showing the known locations of Cola porphyrantha and Gigasiphon macrosiphon (Table 2), and (b) the area of forest in the central and southern East Usambara Mountains. Amani Nature Reserve is the largest block of forest, extending from Mbomole south to Gereza and east to Mashewa, not including the enclave of Shebomeza. The polygon is the area surveyed for the two tree species. All forest fragments are unprotected and are managed by local tea estates.We have not provided precise localities of the plots or of the two species because of the potential for their exploitation. The Tanzania map was developed using Platts et al. (2011) for the Eastern Arc Mountain blocks, and the background data were from Stamen Design, under a CC BY 3.0 license, and OpenStreetMap, under an Open Data Commons Open Database License.


Although a cultivated collection was made from Amani in 1937 (Brenan, 1967), there were no further wild records of it from there until we found it near Amani in 2003. Currently, G. macrosiphon is known from the same forest fragment in the East UsambaraMountains as C. porphyrantha.Two ma- ture trees of G. macrosiphon were thought to survive in this fragment in 2003. As the subpopulations of both of these taxa have not been


assessed for almost 2 decades in the East Usambara Mountains and given their globally threatened status, con- servation assessments are imperative. To locate mature trees and any seedling and sapling recruitment, we surveyed the forest fragment that was known to harbour both species as well as neighbouring forest fragments of varying sizes. We also assessed threats (e.g. tree cutting, encroachment, direct use of tree species) in all sites that we surveyed, to help us identify conservation strategies that could promote the survival of both of these taxa.


Study area


The East Usambara Mountains rise from the coastal pene- plain to 1,501 m (Platts et al., 2011), with forest starting at c. 250 m and being continuous to 1,100–1,200 min some places (Fig. 1). Mean rainfall is 2,000 mm per year and is


seasonal, with long periods of rain during late March–May and short periods of rain during October–November; proximity to the Indian Ocean induces orographic rainfall in most months (Hamilton & Bensted-Smith, 1989). The mean annual temperature is c. 24 °C. Loss of original forest cover in the East Usambara


Mountains is estimated to be .50% (Newmark, 1998), dri- ven largely by deforestation and habitat fragmentation as a result of the establishment of sisal and tea estates during the colonial period, dating back to the late 1800s (Hamilton & Bensted-Smith, 1989; Newmark, 2002). On the submontane plateau, at 800–1,100 m, extensive tea plantations dissect the forest in the central and southern regions of the East Usambara Mountains. Numerous forest fragments of varying sizes are surrounded by tea and, in some cases, subsistence cultivation (Fig. 1). Most of these fragments have no protected status, lying outside Amani Nature Reserve (8,380 ha) and Nilo Nature Reserve (6,025 ha) in the south and north, respectively. Comparable to trends in earlier decades (Hamilton & Bensted-Smith, 1989; Newmark, 2002), resource extraction, such as timber harvesting, and encroachment for subsistence agriculture continue to threaten both unprotected and protected for- ests in the East Usambara Mountains (Tanzania Forest Conservation Group, 2017).


Oryx, 2024, 58(5), 611–617 © The Author(s), 2024. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605324000462


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