Human Impacts on Drylands

Global evaluation of current and future threats to drylands and their vertebrate biodiversity

Drylands cover about 42% of the earth’s terrestrial surface, support unique and endemic species, and provide key ecosystem services to a third of the global human population. Yet drylands are often overlooked in broad conservation frameworks and development priorities. Drylands are especially sensitive to increasing human land-use pressures through land conversion due to extensive agriculture and alternative energy sources, overgrazing, invasive species, and climate change ­­– pressures that are expected to intensify in the coming decades. It is estimated that up to 20% of drylands are already degraded or at risk including considerable water declines in natural lakes and groundwater, threatening desert ecosystems and human social environments. Therefore, there is an urgent need to evaluate current and future threats to drylands and their vertebrate biodiversity. In this research, we evaluated the degree of protected area coverage in drylands compared to non-drylands, the current status of anthropogenic threats to dryland vertebrate biodiversity, and the impact that projected future human land-use pressures will have on drylands under different climate and socioeconomic pathways.

We found that drylands are considerably less covered by the global network of protected areas compared to non-drylands. Only ~12% of total drylands are covered by protected areas compared to non-dryland regions with ~21% coverage. Moreover, the most arid dryland regions, which are home to unique and diverse plant and animal species, are the least protected. Also, when considering protected areas managed mainly for biodiversity protection – a considerably smaller proportion of drylands are protected. Less than 5% of all dryland subtypes are found in protected areas designated as categories I-IV. This is true in drylands across all continents.

Drylands contain a rich diversity of unique and endemic plant and animal species. Therefore, we evaluated the distribution and threat status of terrestrial vertebrate species – amphibian, bird, mammal and reptile species with 50% or more of their global ranges in drylands. We found that most dryland species have less than 10% of their ranges protected, which is likely insufficient habitat for maintaining viable populations (Fig. 3). Worse still, many vertebrate species have no overlap with protected areas at all, including dryland endemic species (found nowhere else). Additionally, many species are listed as threatened by the IUCN Red List (categories Critically Endangered (CR), Endangered (EN) and Vulnerable (VU)).

We further explored threat types currently affecting dryland species. The largest and most notable anthropogenic threat to vertebrate groups in drylands is agriculture, as reported in other regions. Other prevalent threats in drylands include timber and plant harvesting (e.g., harvesting plants and trees for commercial, recreational and subsistence uses), threats from invasive species and disease, and infrastructure development.

Overall, most dryland vertebrate species are inadequately protected and therefore require more attention in the context of global targets of biodiversity protection, especially due to the vulnerability of drylands to land-use threats and to projected future increasing human pressures. We evaluated cropland, rangeland, pasture and urban land-use pressures in drylands currently and under future climate and global socioeconomic change scenarios (i.e., shared socioeconomic pathways, SSPs). We found that natural dryland habitats are perilously threatened by projected human population growth, land-use and climate changes (Fig. 5). Alarmingly, by 2100 drylands are projected to experience some degree of land conversion in 95–100% of their current natural habitat due to urban, agricultural and alternative energy expansion. This is also true under very optimistic scenarios that aim to reduce global agricultural land coverage and promote progressive climate policies. These trends greatly threaten the future integrity of dryland systems with important implications for biodiversity conservation, especially considering that the vast majority of dryland habitats and species are not adequately protected. At the same time, drylands provide unique opportunities and considerable scope for achieving conservation and biodiversity goals, including the expansion of protected area networks and incorporating stricter forms of protection.

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