Plant Ecology

, Volume 150, Issue 1–2, pp 97–114

From snapshot information to long-term population dynamics of Acacias by a simulation model

  • Kerstin Wiegand
  • David Ward
  • Hans-Herman Thulke
  • Florian Jeltsch


The African Acacia species A. raddiana is believed to be endangered in the Negev desert of Israel. The ecology of this species is not well understood. The main idea of our study is to learn more about the long-term population dynamics of these trees using snapshot information in the form of size frequency distributions. These distributions are highly condensed indices of population dynamics acting over many years. In this paper, we analyse field data on recruitment, growth, and mortality and use an existing simulation model of the population dynamics of A. raddiana (SAM) to produce contrasting scenarios of these live history processes that are based on the analysed field evidence. The main properties of simulated as well as observed tree size frequency distributions are characterised with Simpson's index of dominance and a new permutation index. Finally, by running the SAM model under the different scenarios, we study the effect of these different processes on simulated size frequency distributions (pattern) and we compare them to size distributions observed in the field, in order to identify the processes acting in the field. Our study confirms rare recruitment events as a major factor shaping tree size frequency distributions and shows that the paucity of recruitment has been a normal feature of A. raddiana in the Negev over many years. Irregular growth, e.g., due to episodic rainfall, showed a moderate influence on size distributions. Finally, the size frequency distributions observed in the Negev reveal the information that, in this harsh environment, mortality of adult A. raddiana is independent of tree size (age).

Acacia raddiana Individual-based Negev desert Pattern and process Permutation index Rare recruitment SAM Size frequency distributions Spatially-explicit simulation model 


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  1. Ashkenazi, S. (1995) Acacia trees in the Negev and the Arava, Israel: A review following reported large-scale mortality. Hakeren Hakayemet LeIsrael, Jerusalem (in Hebrew, with English summary).Google Scholar
  2. Belsky, A. J., Amundson, R. G., Duxbury, J. M., Riha, S. J., Ali, A. R. & Mwonga, S. M. 1989. The effects of trees on their physical, chemical, and biological environment in a semi-arid savanna in Kenya. J. Appl. Ecol. 26: 1005–1024.Google Scholar
  3. Belsky, A. J., Mwonga, S. M., Amundson, R. G., Duxbury, J. M. & Ali, A. R. 1993. Comparative effects of isolated trees on their undercanopy environments in high-and low-rainfall savannas. J. Appl. Ecol. 30: 143–155.Google Scholar
  4. Bendel, R. B., Higgins, S. S. & Teberg, J. E. 1989. Comparison of skewness coefficient, coefficient of variation, and Gini coefficient as inequality measures within populations. Oecologia 78: 394–400.Google Scholar
  5. Boulos, L. 1983. Medicinal plants of North Africa. Medicinal plants of the world. Reference Publications Inc., Algonac, Michigan, USA.Google Scholar
  6. Coe, M. & Coe, C. 1987. Large herbivores, Acacia trees and bruchid beetles. S. Afr. J. Sci. 83: 624–635.Google Scholar
  7. Coughenour, M. B., Ellis, J. E. & Popp, R. G. 1990. Morphometric relationships and developmental patterns of Acacia tortilis and Acacia reficiens in Southern Turkana, Kenya. Bull. Torrey Bot. Club 117: 8–17.Google Scholar
  8. DeAngelis, D. L. & Huston, M. A. 1987. Effects of growth rate in models of size distribution formation in plants and animals. Ecol. Modell. 36: 119–137.Google Scholar
  9. Dixon, P. M., Weiner, J., Mitchell-Olds, T. & Woodley, R. 1987. Bootstrapping the Gini coefficient of inequality. Ecology 68: 1548–1551.Google Scholar
  10. Dublin, H. T. 1995 Vegetation dynamics in the Serengeti-Mara ecosystem: the role of elephants, fire, and other factors. Pp. 71–90. In: Sinclair, A. R. & Arcese, P. (eds), Serengeti II: Dynamics, management, and conservation of an ecosystem. Chicago University Press, Chicago.Google Scholar
  11. Ehleringer, J. R., Cook, C. S. & Tieszen, L. L. 1985. Comparative water use and nitrogen relationships in a mistletoe and its host. Oecologia 68: 279–284.Google Scholar
  12. Glasser, G. J. 1962. Variance formulas for the mean difference and coefficient of concentration. Journal of the American Statistical Association 57: 648–654.Google Scholar
  13. Gourlay, I. D. 1995a. Growth ring characteristics of some African Acacia species. J. Trop. Ecol. 11: 121–140.Google Scholar
  14. Gourlay, I. D. 1995b. The definition of seasonal growth zones in some African Acacia species-a review. IAWA J. 16: 353–359.Google Scholar
  15. Grice, A. C. 1984. The demography of the leguminous shrubs Acacia victoriae, Cassia nemophila and C. phyllodinea in semiarid south-eastern Australia. PhD Thesis. Macquarie University, North Ryde, Australia.Google Scholar
  16. Grice, A. C., Westoby, M. & Torpy, C. 1994. Dynamics and population structure of Acacia victoria Benth. Aust. J. Ecol. 19: 10–16.Google Scholar
  17. Grimm, V. 1994. Mathematical models and understanding in ecology. Ecol. Modell. 75/76: 641–651.Google Scholar
  18. Gwynne, M. D. 1969. The nutritive value of Acacia pods in relation to Acacia seed distribution by ungulates. E. Afr.Wildl. J. 7: 176–178.Google Scholar
  19. Halevy, G. 1974. Effects of gazelles and seed beetles (Bruchidae) on germination and establishment of Acacia species. Isr. J. Bot. 23: 120–126.Google Scholar
  20. Hara, T. 1984. A stochastic model and the moment dynamics of the growth and size distribution in plant populations. J. Theor. Biol. 109: 173–190.Google Scholar
  21. Harper, J. L. 1977. Population biology of plants. Academic Press, New York.Google Scholar
  22. Hauser, T. P. 1994. Germination, predation and dispersal of Acacia albida seeds. Oikos 71: 421–426.Google Scholar
  23. Härdle, W. 1991. Smoothing techniques: With implementation in S. Springer-Verlag, New York.Google Scholar
  24. Huston, M. 1986. Size bimodality in plant populations: an alternative hypothesis. Ecology 67: 265–269.Google Scholar
  25. Huston, M. A. & DeAngelis, D. L. 1987 Size bimodality in monospecific populations: A critical review of potential mechanisms. Am. Nat. 129: 678–707.Google Scholar
  26. Jeltsch F., Milton S. J., Dean W. R. J. & Van Rooyen N. 1997. Simulated pattern formation around artificial waterholes in the semiarid Kalahari. J. Veg. Sci. 8: 177–188.Google Scholar
  27. Jeltsch F., Moloney K. A. & Milton S. J. 1999. Detecting process from snap-shot pattern-lessons from tree spacing in the southern Kalahari. Oikos 85: 451–466.Google Scholar
  28. Judson, O. P. 1994. The rise of individual-based models in ecology. Trends Ecol. Evol. 9: 9–14.Google Scholar
  29. Kirkpatrick, M. 1984. Demographic models based on size, not age, for organisms with indeterminate growth. Ecology 65: 1874–1884.Google Scholar
  30. Kiyiapi, J. L. 1994. Structure and characteristics of Acacia tortilis woodland on the Njemps Flats. Adv. Geoecol. 27: 47–69.Google Scholar
  31. Leistner, O. A. 1967. The plant ecology of the southern Kalahari. Memoirs of the Bot. Soc. S. Afr. 38: 11–73.Google Scholar
  32. Levin, S. A. 1992. The problem of pattern and scale in ecology. Ecology 73: 1943–1967.Google Scholar
  33. Martin, D. M. & Moss, J. M. 1997. Age determination of Acacia tortilis (Forsk.) Hayne from northern Kenya. Afr. J. Ecol. 35: 266–277.Google Scholar
  34. Miller, M. F. 1996. Acacia seed predation by bruchids in an African savanna ecosystem. J. Appl. Ecol. 33: 1137–1144.Google Scholar
  35. Milton, S. J. 1988. The effects of pruning on shoot production and basal increment of Acacia tortilis. S. Afr. J. Bot. 54: 109–117.Google Scholar
  36. Milton, S. J. 1995. How useful is the keystone concept and can it be applied to Acacia erioloba in the Kalahari desert?. Z. Ökologie Naturschutz 4: 147–156.Google Scholar
  37. Moloney, K. A., Levin, S. A., Chiariello, N. R. & Buttel, L. 1992. Pattern and scale in a serpentine grassland. Theor. Popul. Biol. 41: 257–276.Google Scholar
  38. Mwalyosi, R. B. 1990. The dynamic ecology of Acacia tortilis woodland in LakeManyara National Park, Tanzania. Afr. J. Ecol. 28: 189–199.Google Scholar
  39. Norton, D. A. & Carpenter, M. A. 1998. Mistletoes as parasites: host specificity and speciation. Trends. Ecol. Evol. 13: 101–105.Google Scholar
  40. Obeid, M. & Seif, E. D. 1970. Ecological studies of the vegetation of the Sudan. I. Acacia Senegal (L) Willd. and its natural regeneration. J. Appl. Ecol. 7: 507–518.Google Scholar
  41. Peled, Y. 1988. Mortality of Acacia trees in the southern Arava. MSc Thesis, Hebrew University, Jerusalem (in Hebrew, with English summary).Google Scholar
  42. Peled, Y. 1995. Death of the Acacias. Eretz, Geogr. Mag. Israel 9: 63–65.Google Scholar
  43. Pellew, R.A. 1983. The impacts of elephant, giraffe and fire upon Acacia tortilis woodlands of the Serengeti. Afr. J. Ecol. 21: 41–74.Google Scholar
  44. Pielou, E. C. 1977. Mathematical Ecology. JohnWiley & Sons, New York.Google Scholar
  45. Prins, H. H. & Van der Jeugd, H. P. 1993. Herbivore population crashes and woodland structure in East Africa. J. Ecol. 81: 305–314.Google Scholar
  46. Ratz, A. 1996. A generic forest fire model: spatial patterns in forest fire ecosystems. PhD thesis, Philipps-Universität Marburg, Germany.Google Scholar
  47. Rhoades, C. 1995. Seasonal pattern of nitrogen mineralisation and soil moisture beneath Faidherbia albida (syn Acacia albida) in central Malawi. Agroforestry Syst. 29: 133–145.Google Scholar
  48. Rohner, C. & Ward D. 1999. Large mammalian herbivores and the conservation of arid Acacia stands in the Middle East. Cons. Biol., 13: 1162–1171.Google Scholar
  49. Ross, J. H. 1979. A conspectus of African Acacia species. Mem. Bot. Soc. S. Afr. 44: 1–155.Google Scholar
  50. Ross, J. H. 1981. An analysis of the African Acacia species: their distribution, possible origins and relationships. Bothalia 13: 389–413.Google Scholar
  51. Ruess, R. W. & Halter, F. L. 1990. The impact of large herbivores on the Seronera woodlands, Serengeti National Park, Tanzania. Afr. J. Ecol. 28: 259–275.Google Scholar
  52. Shackleton, C. M. 1993. Fuelwood harvesting and sustainable utilisation in a communal grazing land and protected area of the eastern Transvaal Lowveld. Biol. Cons. 63: 247–254.Google Scholar
  53. Silverman, B. W. 1986. Density estimation for statistics and data analysis. Monographs on statistics and applied probability. Chapman and Hall, London, New York.Google Scholar
  54. Sinclair, A. R. 1995. Equilibria in plant-herbivore interactions. Pp. 91–113 In: Sinclair, A. R. & Arcese, P. (eds), Serengeti II: Dynamics, management, and conservation of an ecosystem University of Chicago Press, Chicago, London.Google Scholar
  55. Turner, M. D. & Rabinowitz, D. 1983. Factors affecting frequency distributions of plant mass: the absence of dominance and suppression in competing monocultures of Festuca paradoxa. Ecology 64: 469–475.Google Scholar
  56. Van Sickle, J. 1977. Mortality rates and size distributions. Oecologia 27: 311–318.Google Scholar
  57. Walker, B. H., Stone, L., Henderson, L. & Vernede, M. 1986. Size structure analysis of the dominant trees in a South African savanna. S. Afr. J. Bot. 52: 397–402.Google Scholar
  58. Ward, D. & Rohner, C. 1997. Anthropogenic causes of high mortality and low recruitment in three Acacia tree species in the Negev desert, Israel. Biodivers. Cons. 6: 877–893.Google Scholar
  59. Weiner, J. & Solbrig, O. T. 1984. The meaning and measurement of size hierarchies in plant populations. Oecologia (Berlin) 61: 334–336.Google Scholar
  60. Weltzin, J. F. & Coughenour, M. B. 1990. Savanna tree influence on understorey vegetation and soil nutrients in northwestern Kenya. J.Veg. Sci. 1: 325–334.Google Scholar
  61. Wiegand, K. 1999. A model of the spatio-temporal population dynamics of Acacia raddiana. UFZ-Bericht 15/1999, UFZ Centre for Environmental Research Leipzig-Halle GmbH, Germany.Google Scholar
  62. Wiegand K., Jeltsch F. & Ward D. 1999. Analysis of the population dynamics of Acacia trees in the Negev desert, Israel with a spatially-explicit computer simulation model. Ecol. Modell. 117: 203–224.Google Scholar
  63. Wiegand, K., Jeltsch, F., Ward, D. & Rohner, C. 1998. Decline of the Negev's Acacias -a spatially explicit simulation model as an aid for sustainable management. Pp. 63–72. In: J. L. Usó , J. L., Brebbia, C. A. & Power, H. (eds), Ecosystems and sustainable development, Computational Mechanics Publications, Southhampton.Google Scholar
  64. Wiegand T., Milton S. J. & Wissel, C. 1995. A simulation model for a shrub ecosystem in the semiarid Karoo, South Africa. Ecology 76: 2205–2221.Google Scholar
  65. Wiegand, T., Milton, S. J., Esler, K. J. & Midgley, G. 2000. Fast growth and early death: estimating size-age relations and mortality pattern of shrub species in the semiarid Karoo, South Africa. Plant Ecology, 150(1-2) in this issue.Google Scholar
  66. Young, T. P. & Lindsay, W. K. 1988. Role of even-age population structure in the disappearance of Acacia xanthophloea woodlands. Afr. J. Ecol. 26: 69–72.Google Scholar

Copyright information

© Kluwer Academic Publishers 2000

Authors and Affiliations

  • Kerstin Wiegand
    • 1
  • David Ward
    • 2
  • Hans-Herman Thulke
    • 1
  • Florian Jeltsch
    • 1
  1. 1.UFZ Centre for Environmental Research Leipzig-HalleDepartment of Ecological ModellingLeipzigGermany
  2. 2.Ben Gurion University of the NegevSede BoqerIsrael

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