Summary (Savannas)

By
J.I. House & D.O. Hall
Division of Life Sciences, King's College London


	SUMMARY
	Tropical savannas (including grasslands) form one of the world’s most extensive biomes covering 27.6 Mkm². These areas are experiencing significant population pressure and land use changes, and are vulnerable to rapid land degradation. This will have large impacts on global NPP predictions and climate change, thus it is important to improve our understanding of them. The proportion of trees and grasses is highly variable in space and time, yet very little is understood about the complex dynamic processes and interactions controlling them. There is a great paucity of even basic data for these highly heterogeneous ecosystems as relatively few studies have been carried out in this biome in the past. Additionally there is a need for large-scale syntheses of existing data to improve knowledge and understanding. Some are now underway, and it is becoming increasingly clear that these areas have a greater productivity, higher biodiversity and larger impact on global carbon cycles than previously realised (Long et al, 1989; Solbrig et al, 1996, Scholes & Hall, 1996). The current best estimate for productivity ranges from 733 to 1426 g (DM) /m²/yr for different savanna formations (Scholes & Hall, 1996) with an average around 1078 g (DM) /m²/yr, and total annual production in savannas and grasslands at 29.7 Pg (DM)/yr (about a quarter of global NPP), although several authors have shown the data these calculations are based on are underestimates (e.g. Long et al, 1989, 1992).
	ACKNOWLEDGEMENTS
	Many thanks to Bob Scholes (CSIR, South Africa), Xavier Le Roux (INRA, Clermont-Ferrand, France), Jonathan Scurlock (ORNL, USA) and Joe Scanlan (Department of Natural Resources, Queensland, Australia) for providing information and making corrections to the manuscript. Dale Kaiser & Sonja Jones (ORNL, USA) for calculating tropical % of the Olson et al (1983) "grasslands" category. Sadly, David Hall passed away in August 1999 before this chapter was published. His knowledge and love of savannas was only surpassed by his eagerness to learn and teach.

REFERENCES

	Table 1: Previous estimates of area, biomass and NPP of savannas and grasslands
	Table 2: Broad plant functional types found in African savannas (from Scholes et.al., 1997)

Table 3: Biomass reported for tropical grasslands and savannas

	Table 4: Primary production reported for tropical grasslands and savannas
	Table 5: Biophysical properties, fluxes and efficiencies
	Figure 2: The relationship between total NPP and aboveground NPP

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