Linking a population model with an ecosystem model: Assessing the impact of land use and climate change on savanna shrub cover dynamics

• Published in: Ecological modelling Vol. 195; no. 3; pp. 219 - 228
• Main Authors: Tews, Jörg, Esther, Alexandra, Milton, Sue J., Jeltsch, Florian
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.06.2006; Elsevier
• Subjects: Acacia erioloba; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Bush encroachment; Fundamental and applied biological sciences. Psychology; General aspects; General aspects. Techniques; Global change; Grewia flava; Methods and techniques (sampling, tagging, trapping, modelling...); Overgrazing; Seed dispersal; Shrub encroachment; Southern Kalahari; Spatial-explicit simulation model; Synecology; Botswana, Kalahari; Africa; Acacia erioloba; Bush encroachment; Southern Kalahari; Grewia flava; Global change; Overgrazing; Shrub encroachment; Seed dispersal; Spatial-explicit simulation model; Seeds; Dicotyledones; Ecosystem; Angiospermae; Planetary scale; Simulation model; Shrubbery; Savannah; Shrub; Grazing; Dispersion; Land use; Leguminosae; Acacia; Spermatophyta; Climate modification
• ISSN: 0304-3800; 1872-7026
• DOI: 10.1016/j.ecolmodel.2005.11.025

In semiarid savannas of Southern Africa current land use practices and climate change may lead to substantial changes of vegetation structure in the near future, however uncertainty remains about the potential consequences and the magnitude of change. In this paper we study the impact of climate change, cattle grazing, and wood cutting on shrub cover dynamics in savannas of the southern Kalahari. We use an established savanna ecosystem model to simulate landscape dynamics in terms of rainfall, fire and distribution of the dominant tree Acacia erioloba. We then incorporate these data into a spatial population model of the common, fleshy-fruited shrub Grewia flava and investigate shrub cover dynamics for a period of 100 years. Depending on the intensity of commercial wood cutting practices tree removal of A. erioloba led to a strong decline of the G. flava population, as shrub recruitment is concentrated in tree sub-canopies due to bird-mediated seed dispersal. Under climate change shrub cover slightly decreased with decreasing precipitation and was unchanged with increase in precipitation variability. Contrarily, grazing by cattle strongly increased shrub cover and facilitated shrub encroachment because of cattle-induced distribution of G. flava seeds into the matrix vegetation. Knowledge of the latter process is particularly important because shrub invasion is a major concern for conservation and savanna rangeland management as a result of its adverse effects on livestock carrying capacity and biodiversity.