Woody plant encroachment and the ecology of vector-borne diseases.
Abstract
Vector-borne diseases (VBDs) impact human and animal health globally, and their ecology and transmission are affected by human-caused ecosystem and biome transitions. Woody plant encroachment (WPE), a top driver of biome and land cover transitions in grasslands and savannas of the world, greatly changes abiotic conditions, vegetation and animal populations and communities. Although these effects mirror mechanisms by which other ecosystem and land cover changes influence VBD ecology, few studies have evaluated if WPE expands distributions and increases the transmission of VBDs. We develop a conceptual framework for WPE effects on VBDs by synthesizing key literature on these topics and on impacts of land cover change on diseases broadly. We also present examples of WPE systems from two continents illustrating documented and likely effects on VBD systems, and we outline a prospectus for future research evaluating such effects. This synthesis highlights the potential for WPE to increase the transmission of VBDs world-wide. WPE's effects on landscape composition, local vegetation, abiotic conditions, and vector and host resources, interactions and population and community processes, likely impact VBD distributions, transmission and health outcomes. Much additional research is needed on topics like the effects of WPE management on health risks associated with VBDs. Synthesis and applications. Woody plant encroachment (WPE) is drastically changing grasslands and savannas world-wide. Its well-documented influences on abiotic conditions (e.g. temperature and humidity), vegetation and wildlife are having previously underappreciated effects on the ecology of vector-borne diseases, likely increasing spatial distributions and transmission of diseases. Management to reduce WPE is ongoing in much of the world due to its degradation of ecosystem services like biodiversity, livestock production and water quality and quantity. The ecosystem disservice of elevated disease risk in humans, wildlife and domestic animals should be an additional consideration when making land management and policy decisions related to WPE.