, Volume 56, Issue 1, pp 9–15 | Cite as

Ecological strategies in a Patagonian arid steppe

  • Alberto Soriano
  • Osvaldo Sala


The vegetation in the Coironal arid steppe consists of grasses and shrubs. The objective of this paper was to test Walter's hypothesis that woody vegetation and grasses compete for water in the upper layers of the soil, but woody vegetation has exclusive access to a source of water at deeper levels.

Analysis of root profiles and patterns of leaf and soil water potential led us to accept the hypothesis for this arid steppe. Additional information on phenology and on the ability of the major grass species to respond to watering permitted to identify two ecological strategies corresponding to grasses and shrubs. Grasses behave as opportunists having always leaves ready to grow as soon as water becomes available. They have a shallow root system and are able to respond very rapidly to increases in soil water availability. In contrast, woody species have a clear-cut periodic pattern of growth and dormancy. They possess thick horizontal roots running below 35–40 cm and utilized water stored in lower layers of the soil.

A diagrammatic model summarizes the role of periodic and opportunistic species upon water circulation in the ecosystem. The effect of changes in the proportion of the two groups upon water dynamics is also discussed.


Arid steppe Competition Ecological strategy Life form Patagonia Root system Water relations 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Böhm, W., 1979. Methods of Studying Root Systems. Springer-Verlag, Berlin. 188 pp.Google Scholar
  2. Cabrera, A. L., 1971. Compositae. In: M. N. Correa, (ed.). Flora Patagónica, Vol. VII. Colección INTA. 451 pp.Google Scholar
  3. Clark, R. E., 1977. Internal cycling of 15nitrogen in shortgrass prairie. Ecology 58: 1322–1333.Google Scholar
  4. Evenari, M., Schulze, E. D., Kappen, L., Buschbom, U. & Lange, O. L., 1975. Adaptive mechanisms in desert plants. In: F. J., Vernberg, (ed.). Physiological Adaptations to the Environment, pp. 111–129. Cambridge Univ. Press, Cambridge.Google Scholar
  5. Forrester, J. W., 1961. Industrial Dynamics. MIT Press, Cambridge, Mass. 464 pp.Google Scholar
  6. French, N. & Sauer, R. H., 1974. Phenological modeling in grasslands. In: H. Lieth, (ed.). Phenology and seasonality modeling. Ecological Studies, Vol. 8, pp. 227–236. Springer-Verlag.Google Scholar
  7. Grime, J. P., 1979. Plant Strategies and Vegetation Processes. Wiley, Chichester. 222 pp.Google Scholar
  8. Grime, J. P., 1982. The concept of strategies: use and abuse. J. Ecol. 70: 863–865.Google Scholar
  9. Hall, C. A. S. & Day, J. W., 1977. Systems and models: terms and basic principles. In: C. A. S., Hall & J. W., Day, (eds.). Ecosystem Modeling in Theory and Practice: An Introduction with Case Histories, pp. 6–36. John Wiley, New York.Google Scholar
  10. Nicora, E. G., 1978. Gramineae. In: M. N. Correa, (ed.). Flora Patagónica, Vol. III. Colección INTA. 563 pp.Google Scholar
  11. Sala, O. E. & Lauenroth, W. K., 1982. Small rainfall events: an ecological role in semiarid regions. Oecologia 53: 301–304.Google Scholar
  12. Scholander, P. F., Hammer, H. T., Bradstreet, E. D. & Hemmingsen, E. A., 1965. Sap pressure in vascular plants. Science 148: 339–346.Google Scholar
  13. Soriano, A., 1952. El pastoreo en el territorio del Chubut. Rev. Arg. Agr. 19 (1): 1–20.Google Scholar
  14. Soriano, A., 1956a. Los distritos florísticos de la Provincia Patagónica. Rev. Inv. Agr. 10: (4): 349–347.Google Scholar
  15. Soriano, A., 1956b. Aspectos ecológicos y pasturiles de la vegetación patagónica relacionados con su estado y capacidad de recuperación. Rev. Inv. Agr. 10 (4): 349–372.Google Scholar
  16. Soriano, A., Alippe, H., Sala, O. E., Schlichter, T., Movia, C., León, R., Trabucco, R. & Deregibus, V., 1976. Ecología del pastizal de Coirón Amargo (Stipa spp.) del sudoeste de Chubut. Academia Nacional de Agronomía y Veterinaria, Buenos Aires, Argentina 30 (11): 1–28.Google Scholar
  17. Soriano, A., Sala, O. E. & León, R. J. C., 1980. Vegetación actual y vegetación potencial en el pastizal de Coirón Amargo (Stipa spp.) del SW de Chubut. Bol. Soc. Arg. Bot. 19: 309–314.Google Scholar
  18. Soriano, A., 1983. Deserts and semi-deserts of Patagonia. In: N. E., West, (ed.). Temperate Deserts and Semi-deserts, pp. 423–459. Elsevier Scientific Publishing Company, Amsterdam.Google Scholar
  19. Spanner, D. C., 1951. The peltier effect and its use in the measurement of suction pressure. J. Exp. Bot. 2: 145–168.Google Scholar
  20. Walker, B. H., Ludwig, D., Holling, C. S. & Peterman, R. M., 1981. Stability of semi-arid savanna grazing systems. J. Ecol. 69: 473–498.Google Scholar
  21. Walter, H., 1964. productivity of vegetation in arid countries. The savannah problem and bush encroachment after overgrazing. In: The Impact of Man in the Tropical Environment. IUCN Publ. NS. 4: 221–229.Google Scholar
  22. Walter, H., 1968. Die Vegetation der Erde in öko-physiologischer Betrachtung. Gustav Fischer Verlag. Stuttgart. 1001 pp.Google Scholar
  23. Walter, H., 1971. Ecology of tropical and subtropical vegetation. Oliver & Boyd, Edinburgh.Google Scholar
  24. Woodmansee, R. G., Vallis, I. & Mott, J. J., 1981. Grassland nitrogen. In: E. W. Clark & T. Rosswall, (eds.). Terrestrial Nitrogen Cycles. Stockholm Ecol. Bull. 33: 443–462.Google Scholar

Copyright information

© Dr W. Junk Publishers 1983

Authors and Affiliations

  • Alberto Soriano
    • 1
    • 2
  • Osvaldo Sala
    • 1
    • 2
  1. 1.Departamento de Ecología, Facultad de AgronomíaUniversidad de Buenos AiresBuenos AiresArgentina
  2. 2.PROSAG (CONICET)Buenos AiresArgentina

Personalised recommendations