Across the globe, human-induced pressures are in large part causing losses in biodiversity. Protected areas (PAs) are key conservation tools, but in the face of biodiversity loss their ecological effectiveness is increasingly contested. In East Africa, there are wide and varying PA networks, yet some of these have faced severe declines in large mammal populations over the last decades, with habitat loss and direct exploitation being identified as the main drivers thereof. Giliba et al. (2022) aimed to understand and assess the ecological effectiveness of PAs in western Tanzania, specifically in the Katava-Rukwa Ecosystem (KRE). The authors investigated changes in land use and population density of six large mammal species over time and across different protected areas and conservation categories, from unprotected to strictly protected areas.
Six surveys from 1991 to 2018 were analysed by the authors, involving remote sensing and aerial wildlife surveys to understand the spatial and temporal patterns of cropland cover and change across the protection categories. They investigated the population densities of six target species: elephant, buffalo, giraffe, zebra, topi, and hartebeest, and the distribution of these species across protection categories, land use types, and different environmental variables.
Giliba et al. (2022) observed that during the survey period, cropland increased from 3.4% to 9.6% on unprotected land and from less than 0.05% to just under 1% on protected land. Among most of the target species, their density decreased in the entire landscape, but these declines often began several years before observed cropland expansion, as was the case with buffalo densities. The authors were able to model species preferences and showed that the target species preferred the national park over less strictly managed PAs, and generally preferred being away from croplands. Both environmental and human variables such as land cover, distance to rivers, distance to houses, and the protection category of the area had an impact on the distributions of the target species.
The authors determined that land use change was a large driver of loss in mammalian megafauna. In the KRE, between 1991 and 2018, cropland cover significantly increased in three of five protection categories, and there was a high level of encroachment in areas where there were fewer restrictions to human resource use. While the game reserves and forest reserves saw relatively small land use change over, cropland expansion directly bordering protected areas such as Katavi National Park, and expanding into others, represented the demands placed on the landscape by humans.
The impacts of this expansion were clearly seen in large mammal distributions, as cropland expansion was linked with wildlife declines in these areas. However, habitat loss was not yet identified as a key factor in wildlife declines, potentially due to the time lag of extinction debt. All target species were observed to prefer areas distant to croplands and preferred the Katavi National Park compared to less protected areas, likely because of their higher restrictions on resource use and hunting. Therefore, the type of protected area had a strong influence on wildlife distributions and density. Therefore, Giliba et al. (2022) recommended that direct impacts in the form of threats to wildlife and cropland expansion in the KRE should be proactively removed, to allow for more wildlife dispersal areas and migratory corridors, improve species survival, and maintain biodiversity.
Read the full paper by Giliba et al. (2022) here.