Abstract
The relationship between grass production and the quantity of trees in mixed tree-grass ecosystems (savannas) is convex for all or most of its range. In other words, the grass production declines more steeply per unit increase in tree quantity at low tree cover than at high tree cover. Since much of the economic value in savannas is ultimately derived from grass, and the main mechanism controlling the tree-grass balance is dependent on the production of grassy fuel for fires, this non-linearity has the effect of creating two savanna configurations. One has a low tree density and supports a viable grazing enterprise, while the other has dense tree cover and a frequently non-viable grazing enterprise. The non-linearity is suggested here to have two main sources: the geometry of the spatial interaction between tree root system and grasses, and the effect of differing phenology (the time course of leaf area exposure) on the acquisition of water and nutrients. The existence of the non-linearity reduces the resilience of the generally-preferred “open” configuration, and increases the resilience of the less-desirable “closed” configuration.
This is a preview of subscription content, log in via an institution.
Buying options
Tax calculation will be finalised at checkout
Purchases are for personal use only
Learn about institutional subscriptionsPreview
Unable to display preview. Download preview PDF.
References
Anderies, M., M. A. Janssen and B. H. Walker (2002), ‘Grazing Management, Resilience and the Dynamics of a Fire Driven Rangeland’, Ecosystems 5, 23–44.
Aucamp, A. J., J. E. Dankwerts, W. R. Teague and J. J. Venter (1983), ‘The Role of Acacia karroo in the False Thorveld of the Eastern Cape’, Journal of the Grassland Society of Southern Africa 8, 151–154.
Beale, I. F. (1973), ‘Tree Density Effects on Yields of Herbage and Tree Components in Southe-west Queensland Mulga (Acacia aneura F. Meull.) Scrub. Tropical Grasslands 7, 135–142.
Belsky, A. J., S. M. Mwonga, R. G. Amundson, J. M. Duxbury and A. R. Ali (1993), ‘Comparative Effects of Isolated Trees on Their Undercanopy Environments in High and Low Rainfall Savannas’, Journal of Applied Ecology 30, 143–155.
de Villiers, G. du T. (1981), ‘Net Rainfall and Interception Losses in a Burkea africana-Ochna pulchra Tree Savanna’, Water SA 7, 4–25.
Donaldson, C. M. and D. M. Kelk (1970), ‘An Investigation of the Veld Problems of the Molopo Area. 1. Early Findings’, Proceedings of the Grassland Society of Southern Africa 1, 27–32.
Groot, J. J. R. and A. Soumare (1995), Root Distribution of Acacia seyal and Sclerocarya birrea in Sahelian Rangelands’, Agroforestry Today 7, 9–11.
Knoop, W. T. and B. H. Walker (1984), ‘Interactions of Woody and Herbaceous Vegetation in Two Savanna Communities at Nylsvley’, Journal of Ecology 73, 235–253.
le Houerou, H. N. (1984), ‘Rain Use Efficiency: A Unifying Concept in Arid Land Ecology’, Journal of Arid Environments 7, 213–247.
Rutherford, M. C. (1980), ‘Annual Plant Production-precipitation Relations in Arid and Semi-arid Regions’, South African Journal of Science 76, 53–56.
Scholes, R. J. (1988), Response of Three Semi-arid Savannas on Contrasting Soils to Removal of the Woody Component. PhD thesis, University of the Witwatersrand, Johannesburg.
Scholes, R. J. (1993), ‘Nutrient Cycling in Semi-arid Grasslands and Savannas: Its Influence on Pattern, Productivity and Stability’, Proceedings of the XVII International Grassland Congress (pp. 1331–1334). Palmerston North: International Grasslands Society.
Scholes, R. J. (1997), ‘Savanna’, in R. M. Cowling, D. M. Richardson and S. M. Pierce, eds., Vegetation of southern Africa (pp. 258–277). Cambridge: Cambridge University Press.
Scholes, R. J. and S. Archer (1997), ‘Tree-grass Interactions in Savannas’, Annual Review of Ecology and Systematics 28, 517–544.
Scholes, R. J., P. G. H. Frost and Yuhong Tian (2002), ‘Canopy Structure in Savannas along a Moisture Gradient on Kalahari Sands’, Global Change Biology (in press).
Scholes, R. J. and D. O. Hall (1996), ‘The Carbon Budget of Tropical Grasslands, Savannas and Woodland’, in A. I. Breymeyer, D. O. Hall, J. M. Melillo and G. I. Agren, eds., Global Change: Effects on Coniferous Forests and Grasslands (pp. 69–100). SCOPE 1996. New York: John Wiley.
Scholes, R. J. and B. H. Walker (1993), An African Savanna: Synthesis of the Nylsvley Study. Cambridge: Cambridge University Press.
Trollope, W. S. W. and A. L. F. Potgieter (1985), ‘Fire Behaviour in the Kruger National Park’, Proceedings of the Grassland Society of Southern Africa 2, 17–23.
van Noordwijk, M., G. Lawson, A. Soumare, J. J. R. Groot and K. Hairiah (1996), ‘Root Distribution of Trees and Crops: Competition and/or Complementarity’, in C. K. Ong and P. Huxley, eds., Tree-Crop Interactions: A Physiological Approach (pp. 319–364). Walingford: CAB International.
van Wilgen, B. W. (1986), ‘A Simple Relationship for Estimating the Intensity of Fires in Natural Vegetation’, South African Journal of Botany 52, 384–385.
Walker, B. H., D. Ludwig, C. S. Holling and R. S. Peterman (1981), ‘Stability of Semi-arid Savanna Grazing Systems’, Journal of Ecology 69, 473–498.
Walker, B. H. and I. Noy-Meir (1982), ‘Aspects of the Stability and Resilience of Savanna Ecosystems’, in B. J. Huntley and B. H. Walker, eds., Ecology of Tropical Savannas (pp. 556–609). Berlin: Springer.
Walker, J., R. M. Moore and J. A. Robertson (1972), ‘Herbage Response to Tree and Shrub Thinning in Eucalyptus populnea Shrub Woodlands’, Australian Journal of Agricultural research 23, 405–410.
Walter, H. (1971), Ecology of Tropical and Subtropical Vegetation. Edinburgh: Oliver & Boyd.
Author information
Authors and Affiliations
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 2004 Kluwer Academic Publishers
About this paper
Cite this paper
Scholes, R.J. (2004). Convex Relationships in Ecosystems Containing Mixtures of Trees and Grass. In: Dasgupta, P., Mäler, KG. (eds) The Economics of Non-Convex Ecosystems. The Economics of Non-Market Goods and Resources, vol 4. Springer, Dordrecht. https://doi.org/10.1007/1-4020-2515-7_3
Download citation
DOI: https://doi.org/10.1007/1-4020-2515-7_3
Publisher Name: Springer, Dordrecht
Print ISBN: 978-1-4020-1864-0
Online ISBN: 978-1-4020-2515-0
eBook Packages: Springer Book Archive