Savanna Biome

by

Michael J. Hill

• LAST REVIEWED: 06 May 2016
• LAST MODIFIED: 27 November 2013
• 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 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 CO₂world where tropical grasses gain advantage from highly efficient photosynthetic systems and fire and grazing control woody encroachment. The explorer botanists of the early 20th 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-20th century, many temperate savannas were heavily converted to agriculture in the New World, and a similar trend is now continuing and potentially accelerating in 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 for 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 21st 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.

General Overviews

The savanna biome has been the subject of a number of 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. Solbrig, et al. 1996 is from the Springer Ecological Studies series and provides a broad ecological treatment. Mistry 2000 provides the most accessible and integrated current treatment of the ecology and human use of the savanna biome. The current status of measurement of fluxes and vegetation dynamics, modeling and remote sensing of tropical savannas is comprehensively covered in Hill and Hanan 2011. Shorrocks 2007 covers the animal and plant life, interactions and dynamics of African savannas in some detail. Furley 2007 provides a concise recent review of tropical savannas that includes treatment of plant biology, savanna biogeography and tree-grass coexistence and is a good initial introduction to the wider literature.

• 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.

• Furley, Peter A. 2007. Tropical savannas and associated forests: Vegetation and plant ecology. Progress in Physical Geography 31:203–211.

  DOI: 10.1177/0309133307076107

  A concise recent review of vegetation and ecology of tropical savannas.

• 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 Press.

  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 covers touches on most issues surrounding the biogeography, ecology, and vegetation dynamics.

• 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 west, east, and southern Africa, Australia, South America, and Southeast Asia. It does not cover temperate savannas of North America.

• Shorrocks, Bryan. 2007. The biology of African savannahs. Biology of Habitat series. Oxford: Oxford Univ. Press.

  DOI: 10.1093/acprof:oso/9780198570660.001.0001

  Initially compares savannas on different continents and explores the reasons for their existence, as well as describing the processes and functions in the savannah ecosystem. For the most part, the book is focused on description of animals and vegetation and their interaction in African savannas.

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

  DOI: 10.1007/978-3-642-78969-4

  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.