Conservation status of newly discovered subpopulations of two globally threatened tree species in the East Usambara Mountains, Tanzania HENRY J. NDANGALASI * 1 , 2 and NORB E RT J. CORDEI R O 3 , 4 , 5 , 6
Abstract Two globally threatened tree species, the Critically Endangered Cola porphyrantha (Malvaceae) and the Endangered Gigasiphon macrosiphon (Fabaceae) are nar- rowly distributed in Kenya and Tanzania. In Tanzania, both species were first located in an isolated, unprotected forest fragment in the East Usambara Mountains in the early 2000s. As no assessment of these subpopulations had been made since then, we surveyed the forest fragment as well as nearby unprotected forest fragments. In contrast to the early 2000s when only five and two mature trees of C. porphyrantha and G. macrosiphon, respectively, were located, we found 18 and five mature trees of these species. We did not find either species in intensive surveys of seven neighbouring unprotected forest fragments but we located a single G. macrosiphon beside a river close to one of the unprotected fragments. Gigasiphon macrosiphon was also previously known from two sites in Amani Nature Reserve in the East Usambara Mountains, but recent surveys, including our own, failed to relocate these sub- populations. Because of heavy anthropogenic disturbance in the one site where the two species still occur and their general absence from adjacent forest, we are working with the local community to protect the isolated fragment. Additionally, in situ planting of locally grown seedlings of both species is being supported by Amani Nature Reserve.
Keywords Cola porphyrantha, Critically Endangered, Eastern Arc Mountains, endemic, forest fragmentation, Gigasiphon macrosiphon, rarity, Tanzania
Introduction P
lant diversity and endemism are exceptionally high in the Eastern Arc Mountains of Tanzania and Kenya
(Lovett, 1998; Burgess et al., 2007), which are part of the Eastern Afromontane Biodiversity Hotspot (Mittermeier
*Corresponding author,
hjndangalasi@gmail.com 1Department of Botany, University of Dar es Salaam, Dar es Salaam, Tanzania 2IUCN Species Survival Commission Eastern Africa Plant Red List Authority 3Department of Biology, Roosevelt University, Chicago, Illinois, USA 4Negaunee Integrative Research Science & Education, The Field Museum,
Chicago, Illinois, USA 5Centre for Functional Biodiversity, School of Life Sciences, University of
KwaZulu-Natal, Scottsville, Pietermaritzburg, South Africa 6IUCN Species Survival Commission
Received 22 June 2023. Revision requested 20 September 2023. Accepted 4 March 2024. First published online 15 October 2024.
et al., 2004). However, the forests in the Eastern Arc ranges are under severe threat from deforestation, habitat fragmentation and resource extraction, such that, together with other forests in this hotspot, they are considered one of the most threatened sites globally (Brooks et al., 2002). Conserving these forests is therefore a priority. This is es- pecially true of tropical African plant species, of which over a third are threatened by extinction (Stévart et al., 2019). Of the 13 mountain blocks that make up the Eastern Arc
Mountains, the East Usambara Mountains in north-east Tanzania are amongst the best studied in terms of trees and other plants (Hamilton & Bensted-Smith, 1989; Iversen, 1991; Burgess et al., 2007). The East Usambara Mountains harbour 16 endemic tree species (R. E. Gereau, unpubl. data, 2024) and .20 near-endemic tree species (Iversen, 1991; Burgess et al., 2007). Despite the extensive bo- tanical coverage (reviewed in Hamilton & Bensted-Smith, 1989), new tree species (Cheek, 2002; Dawson & Gereau, 2010; Gosline et al., 2019) and new subpopulations of restricted-range species (Dawson & Gereau, 2010) continue to be discovered in the East Usambara Mountains. Here we document the distribution, relative abundance and con- servation status of two globally threatened tree species that we have studied since their initial discovery in an un- protected forest remnant of these mountains. Cola porphyrantha Brenan (family Malvaceae) is cate-
gorized as Critically Endangered on the IUCN Red List (Luke et al., 2018) and Gigasiphon macrosiphon (Harms) Brenan (family Fabaceae) as Endangered (Gereau et al., 2023). Cola porphyrantha was first described from a type specimen collected in 1978 from the Shimba Hills, Kenya, with additional records coming from one other coastal for- est in Kenya (Cheek, 2007). There was also a collection made in the Shimba Hills in 1968. In Tanzania, the species was found in 2000 at an altitude of 950 m in an unprotected forest fragment in the East Usambara Mountains (Cheek, 2007). Approximately five mature individuals were reported then, and the habitat was described as heavily affected by human activities. Gigasiphon macrosiphon is known from three coastal forest sites in Kenya and from four disjunct sites in Tanzania, in two Eastern Arc Mountain ranges (one site in the East Usambara Mountains and two in the Udzungwa Mountains) and one on the Rondo Plateau in Lindi Rural District (Luke & Verdcourt, 2004;Ngumbau et al., 2020; Gereau et al., 2023). The earliest specimens of this species in the EastUsambaraMountainswere initially re- ported from Amani in 1906–1912 (Luke & Verdcourt, 2004).
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (
http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited. 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
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140
