Document: LIN-3-87-1

Modeling the effects of livestock densities with the Savanna ecosystem model.

CHRISTENSEN, L.*, M.B.COUGHENOUR and J.E.ELLIS

Natural Resource Ecology Laboratory, Fort Collins, CO 80526 USA ¹

Abstract:
The Savanna ecosystem model was used to examine the effects of different livestock intensities on the Mongolian Steppe to approach the question of sustainability and resilience. Although it is well determined that extreme overgrazing can lead to degradation in this region, there is uncertainty in which livestock intensities and management strategies are appropriate. Savanna is a spatially explicit, dynamic, process-oriented model that simulates ecosystem processes at local and regional scales. We used Savanna to focus on spatial and temporal climate, vegetation, and ungulate grazing dynamics. Savanna was run with 12 different livestock intensities (au/km²) to examine grazing effects on vegetation, including primary production, vegetation composition, and root biomass. Simulations were run for 100 years in length: 50 years to examine sustainability and 50 years to examine resilience of the system. Results show a grazing intensity (1-g/u; g = biomass in grazed area, u = biomass in ungrazed area) of 0.40 is sustainable for this particular system. Grazing intensity above this level resulted in decreased primary production and root biomass. This region was resilient to grazing up to an intensity of 0.40. Higher intensities resulted in a change in vegetation composition: A decrease in herbaceous biomass and an increase in shrub biomass; consequently the system was unable to return its original composition.

Keywords: Savanna, modeling, grasslands

This abstract is being presented at: 4:15 PM in session:
Oral Session #51: Disturbance Ecology: Harvesting, Grazing and Roads.