Gazelle–livestock interactions 213
significant environmental harm is not always clear (Turner, 2000). In the Reserve, during the dry season the presence of a well can be perceived at distances of up to 5–10 km by pro- gressive thinning of ground cover, increasing density of dry livestock dung, tracks and signs of trampling, and increased dust in the air. Contrary to this, previous research measur- ing primary production around well sites in the Ferlo of Senegal based on satellite data reported no loss of vegetation biomass around wells, which may be associated with persist- ence of unpalatable vegetation (Hanan et al., 1991; Rasmussen et al., 2018). Negative effects such as soil impaction and re- ducedwater infiltration have been detected at higher livestock grazing densities (Hiernaux et al., 1999). Site-specific features such as soil type, vegetation community and particularly the effective livestock stocking rates and management patterns around focal points determine the impact of livestock grazing on the natural habitat. In the Ouadi Rimé–Ouadi Achim Reserve, our findings show that high stocking rates, associated with artificial water points, lead to spatial exclusion of wild ungulates. This has implications for conservation planning.
Assuming that despite the low precision, our estimates of livestock numbers are nevertheless broadly representative, the livestock numbers in the Reserve are typical for the re- gion. The mean observed stocking rate across all surveys was 0.12 tropical livestock units/ha, with a maximum of 0.26 units/ha in some wet seasons (Table 1). This is compar- able to rates of 0.15–0.20 units/ha reported from other (un- protected) areas of the Sahel (De Leeuw & Tothill, 1990; Miehe, 1997;Hein &Weikard, 2008). In the Reserve, the pas- toralist economy has access to c. 95%of all ungulate biomass and associated primary productivity. Distribution of dorcas gazelle populations (and likely other wildlife) is limited by this anthropogenic disturbance and pressure on available resources. An agro-economic case study in the Sahelian Ferlo of Senegal estimated an optimal livestock stocking rate (to maximize profit margins) of 0.09 units/ha; slightly below the estimates for environmentally sustainable and actual observed stocking rates (Hein & Weikard, 2008; Weikard & Hein, 2011). The observed mean stocking rate in the Reserve (Table 1) exceeds this economically optimal stocking rate and is at or above the estimated ecologically sustainable maximum. Therefore, managing stocking rates not to exceed current levels, and ideally slightly reduce them, could be beneficial to the pastoralist economy as well as wildlife conservation. Spacing and management of water points are critical to
managing stocking rates. The waterpoints that most affect livestock distribution in the study area are hafiris (Fig. 1). It is likely that outside the study area, boreholes and wells have a similar influence in other parts of the Reserve, where these water sources are also critical for livestock. Water resource development is a key issue in the Sahel, often associated with disruption of traditional well ownership
and creating social tensions (Cotula, 2006). In view of the ob- served livestock stocking rates in the Reserve, we believe that an effective conservation zone could be established by ensur- ing no further development of water resources or use of mo- bile bladder reservoirs takes place within a designated 8,000 km2 core area (c. 10% of the Reserve), focused on the survey blocks in this study. The size of this core area is scaled to match ecological conditions for livestock andwildlife in a his- torically arid and drought-prone region, and considers the impact of climate change (Fremantle et al., 2013). Manage- ment within the conservation zone should aim to avoid fur- ther increase in livestock density and control fire, both of which would benefit pastoralist communities and support biodiversity conservation. Improved livestock management is also needed in the remaining 90%of the Reserve. The sup- port and active involvement of local communities are vital for this stratified approach to succeed. To reduce potential opposition to what may be perceived as the creation of a large zone from which local people are excluded, the conser- vation plan should specify that livestock grazing may con- tinue in the core zone, but no further water resource development or settlement should take place. The objectives of this management regime are to support biodiversity conservation and habitat sustainability, manage fire risk, improve veterinary care and promote the role of the conser- vation core zone as a grazing reserve supporting the much larger surrounding area. To track the effect of future conservation and livestock
management strategies, ongoing ground surveys with monitored law enforcement and modern aerial survey techniques (Lamprey et al., 2020) will be needed. Satellite tracking of dorcas gazelles could confirm the movement patterns and requirements of this species implied by our study. This would be particularly valuable if coordinated with formal study of livestock management practice and movements. Ongoing productivity and veterinary health as- sessments would confirm progress in the livestock sector. Our finding that the Ouadi Rimé–Ouadi Achim Reserve
holds globally important populations of the dorcas and dama gazelles, in addition to the ongoing reintroduction of oryx (Duthie, 2018;Mertes et al., 2019) addax and ostrich populations (Sahara Conservation Fund, 2019, 2020), high- light its unique value in supporting Sahelian biodiversity. This study provides evidence for management steps needed to achieve national conservation and development goals in a complex social environment and ecosystem. Our recom- mendations aim to ensure that at least 10% of the Reserve continues as a protected area of IUCN category IV (IUCN, 1994) or higher and is managed as such, with management strategy and actions distinct from a sustainable development area (Locke & Deardon, 2005).
Acknowledgements We thank the Government of Chad, its Ministry of Environment and Fisheries and the Direction de la
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
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