Savanna Biome

by

Michael J. Hill

• LAST REVIEWED: 29 November 2022
• LAST MODIFIED: 29 November 2022
• DOI: 10.1093/obo/9780199830060-0043

Introduction

The savanna biome represents the complex of vegetation made up of grassland with trees in varying densities and arrangements that occupies the transition zone between forests and grasslands. Whereas the lay observer could usually identify a forest or grassland, the savanna biome would provide a challenge, greatly influenced by the scale of observation, since it is characterized by high variability in density, arrangement, clumping, and structure of grassland and trees. The large-scale savannas of the world are quite different on the major continents of Africa, South America, and Australia, and they are distributed in smaller, highly variable arrangements and formations in North America and Eurasia. The nature and stability of the savanna biome has received increasing attention because of its perceived dependence on disturbance by fire and herbivory to maintain tree-grass balance and because some savannas are biodiversity hotspots. Evolution of savannas is thought to be associated with a lower CO₂ world where tropical grasses gain advantage from highly efficient photosynthetic systems and fire and grazing control woody encroachment. As a result, there is great interest in the effect of higher atmospheric concentrations of CO₂ on the evolution of the tree-grass balance in the savanna biome. The explorer botanists of the early twentieth century paid significant attention to the neotropical and peri-Amazonian savannas of South America with their extraordinary biodiversity. In the 1980s, the West African savannas became the terrestrial focus of the genesis of remote sensing of land systems and the development of the Normalized Difference Vegetation Index (NDVI) as a global monitoring tool. During the early to mid-twentieth century, many temperate savannas were heavily converted to agriculture in the New World, and a similar trend is now continuing and potentially accelerating in the tropical savannas of South America and Africa. The Australian tropical savanna has remained largely intact as it is generally too arid for agricultural conversion. As a result, it has become increasingly important to conduct ecological and process studies on tree-grass ecosystem function across spatial scales. Tropical tall grass-tree systems in Asia tend to have been extirpated by dense human activity but have also been treated differently in vegetation classifications and so do not clearly appear in global land cover maps. There has been limited attention paid to these systems in the literature. With global population and food demand potentially ballooning in the twenty-first century, accelerated conversion of savannas is likely to intensify both concerns about decline in ecosystem function and competition for ecosystem services that will necessitate a significant expansion in integrated, interdisciplinary research, sophisticated modeling and future scenario development, and research on restoration ecology and amelioration of land degradation. This article maintains a balance between historical articles and books that address biogeography, landscape ecology, and ecophysiology in savannas in traditional ways less commonly applied now and newer articles and books that reflect expanded understanding of climate, atmosphere, anthropogenic disturbance, and theories about factors that control the grassland-savanna-forest ecotone. These newer studies also reflect rapid expansion in capability to handle very large quantities of spatially explicit data and apply these data to modeling across scales.

General Overviews

The savanna biome has been the subject of a number of books and broad overviews. In the landmark Ecosystems of the World series Bourliére 1983 provides a comprehensive overview, Tothill and Mott 1985 provides global treatment of savannas, and the ecology of tropical savannas is covered in Huntley and Walker 1982, but none of these books are currently in print. Mistry 2000 provides an integrated treatment of the ecology and human use of the savanna biome. Furley 2016 provides a recent highly accessible short overview of savannas that is a good introduction to the topic. Another succinct and current overview of the savanna biome is provided in Hutley and Settlefield 2019. Scogings and Sankaran 2020 provides the most comprehensive recent coverage of the savanna biome with detailed coverage of biogeography, woody vegetation, and animal interactions. From a process perspective, Solbrig, et al. 1996, from the Springer Ecological Studies series, provides a broad ecological treatment. The measurement of water and CO₂ fluxes, vegetation dynamics, modeling, and remote sensing of tropical savannas is comprehensively covered in Hill and Hanan 2011. Briske 2017 provides a systems perspective of savannas as part of the global rangelands.

• Bourliére, Francois, ed. 1983. Tropical savannas. Ecosystems of the World 13. Amsterdam: Elsevier.

  A book in the landmark Ecosystems series that describes the ecology of tropical savannas, including vegetation, the components of the trophic pyramid, and disturbances.

• Briske, David D. 2017. Rangeland systems: processes, management and challenges. Cham, Switzerland: Springer Open.

  DOI: 10.1007/978-3-319-46709-2

  A contributed volume that covers global rangelands, including all of the savanna biome from a systems perspective. It has seventeen chapters in three sections covering processes, management, and challenges that highlight problems such as climate change, invasive species, and human and livestock impacts.

• Furley, Peter A. 2016. Savannas: A very short introduction. Very Short Introductions 477. Oxford: Oxford Univ. Press.

  DOI: 10.1093/actrade/9780198717225.001.0001

  This short book of 155 pages and seven chapters introduces the reader to the concept of “savannas” and discusses their formation, vegetation, fauna and microbes, human interactions, recent changes, and future trajectories.

• Hill, Michael J., and Niall P. Hanan, eds. 2011. Ecosystem function in savannas: Measurement and modeling at landscape to global scales. Boca Raton, FL: CRC.

  A contributed volume with twenty-seven chapters in seven sections covering biogeography and ecology, carbon water, and trace gas fluxes, remote sensing of chemistry and structure, patch to landscape scale processes and modeling, regional carbon dynamics, continental and global modeling, and coupled human-natural systems.

• Huntley, Brian J., and Brian H. Walker, eds. 1982. Ecology of tropical savannas. Ecological Studies 42. Berlin: Springer-Verlag.

  Relatively succinct and broad overview of vegetation and plant ecology of the global savannas and dry forests that briefly touches on most issues surrounding biogeography, ecology, and vegetation dynamics.

• Hutley, Lindsay B., and Samantha A. Setterfield. 2019. Savanna. In Encyclopedia of ecology. Vol. 2. Edited by Sven Erik Jørgensen and Brian D. Fath, 623–633. Oxford: Elsevier.

  Comprehensive chapter providing a succinct and current overview of the savanna biome including definition and occurrence, driving factors of structure, tree-grass dynamics, biomass, productivity and threats.

• Mistry, Jay. 2000. World savannas: Ecology and human use. Harlow, UK: Pearson Education.

  Provides a relatively comprehensive overview of global tropical savannas, including those in western, eastern, and southern Africa, Australia, South America, and Southeast Asia. It does not cover temperate savannas of North America.

• Parr, Catherine L., Caroline E. R. Lehmann, William J. Bond, William A. Hoffmann, and Alan N. Andersen. 2014. Tropical grassy biomes: Misunderstood, neglected, and under threat. Trends in Ecology & Evolution 29:205–213.

  DOI: 10.1016/j.tree.2014.02.004

  Highlights the evolution and diversity of tropical grassy biomes, including the distinction between natural and anthropogenic systems, and emphasizes the need for further research on origins, global change effects, carbon sequestration, biodiversity, vulnerability, degradation, and the future for large mammals.

• Scogings, Peter F., and Mahesh Sankaran, eds. 2020. Savanna woody plants and large herbivores. Hoboken, NJ: John Wiley & Sons.

  A contributed volume with twenty-one chapters in four sections covering detailed biogeography, evolution and dynamics of herbivores and herbivory, woody plant characteristics and interactions with herbivores, and a synthesis of savanna dynamics and future trajectories

• Solbrig, Otto T., Ernesto Medina, and Juan F. Silva, eds. 1996. Biodiversity and savanna ecosystem processes: A global perspective. Ecological Studies 121. Berlin: Springer.

  Examines savannas from the perspective of species and interactions with moisture and nutrient availability, fire, and herbivory.

• Tothill, John C., and John J. Mott, eds. 1985. Ecology and management of the world’s savannas. Farnham, UK: Commonwealth Agricultural Bureau.

  Reports the proceedings of the International Savanna Symposium held in Brisbane in 1984.