206 T. Wacher et al.
line transect surveys conducted in the core of the Reserve during 2011–2019. Our aim was to determine how the pres- ence of livestock, artificial water sources and bush fires af- fects the distribution of wild ungulates. With oryx (Duthie et al., 2018), addax and ostrich reintroductions underway and steps taken to support the dama gazelle in the Reserve, we use evidence from the surveys to recommend management actions to ensure that both conservation and livestock sector objectives are achieved.
Study area
The study area is in the central Ouadi Rimé–Ouadi Achim Reserve, Chad (Fig. 1). The nearest towns are Arada (80 km to the east) and Biltine (117 km to the east-south-east). The habitat is Sahelian grassland on flat grey soils overlain in a few places by vegetated fixed dune formations. Altitude des- cends from 400 m in the east to 374 m in the west of the 70-km wide study area. The shallow gradient on flat land creates diffuse run-off along broad seasonal drainage lines (locally called ouadis). There are no significant hills or rocky outcrops, but vegetated low dunes form a belt of un- dulating sandy substrates across the centre of the study site. The mean temperature is 35 °C (range 21–47 °C) in the
hottest month, May, and 22 °C (9–37 °C) in the coolest month, January. In the driest month, April, relative humid- ity averages 9%(1.7–27.5%), and 72%(27.8–99.9%) in the most humid month, August. The annual passage of the Intertropical Convergence Zone creates a single wet season during July–September, with occasional dust storms as winds change from north-easterly, bringing humid air from the south-west. Mean annual rainfall at the study site during 2017–2020 was 190mm(139–273mm). Typically, there are no natural water sources in the study area for 9 months of the year, but following rainstorms, which are often local in distribution, small temporary water holes last for a few days or weeks. Within the ouadis, longer-lasting chains of shallow, temporary lakes (called rahads) may form, which typically measure 50–100 m across. In the east of the study area some of these have been artificially enlarged to create so-called hafiris, providing water for increased num- bers of livestock and locally prolonging the period of grazing pressure and human occupation further into the dry season (Fig. 1). The grasslands are dominated by annual grasses, of
which Aristida mutabilis Trin. & Rupr., Aristida funiculata Trin. & Rupr., Dactyloctenium aegyptium (L.) Willd., Schoenefeldia gracilis Kunth., Cenchrus biflorus Roxb. and Brachiaria sp. (Trin.) Griseb are important for ungulates. On sandy soil the perennial Panicum turgidum Forssk. is also important, but now appears to be less abundant than formerly (Gillet, 1961; JN, pers. obs., 2007–2020). Following rain, the legume Indigofera colutea (Burm f.)
FIG. 1 Location of the study area in the Ouadi Rimé-Ouadi Achim Reserve, Chad, and details of the line transect and reconnaissance zones in the study area. We used eight core line transect routes in 2015–2019 (solid lines) and four reconnaissance transect routes in 2017 (dashed lines). An additional seven line transects were interleaved simultaneously in parallel to the primary route in 2019 only (dotted line). Natural water hole depressions that have been artificially enlarged (hafiris), major drainage lines (ouadis) and main access routes to the release site of the scimitar-horned oryx Oryx dammah are also shown.
Merrill (selected by gazelles and oryx) forms dense local patches, and stands of the bushy perennial Chrozophora brocchiana (Vis) Schweinf. are characteristic of drainage de- pressions. The bitter melon Citrullus colocynthis (L.) Schrad. is widespread, and the water content of its leaves and fruit is important for wildlife and livestock. Following the short growing season, from late September the grasses and herbs desiccate to form dense, dry hay and the land becomes vulnerable to fire. Shade is provided mainly by desert date trees Balanites aegyptiaca (L.) Delile, growing as widely scattered individ- uals or in small thickets, and less commonly by Acacia tortilis (Forssk.) Hayne, which often indicate seasonal water collection points. On some soil types scattered stands of shrubbier Capparis decidua (Forssk.) Edgew. and Boscia senegalensis (Pers.) Lam. predominate.
Oryx, 2023, 57(2), 205–215 © The Author(s), 2022. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605321001629
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
