International Symposium on
Drylands Ecology and Human Security
Evaluation of Future Scenarios of Biomass Dynamics under Pastoral Conditions and Regional Water Balance Aspects for the Drâa Catchment in South-eastern Morocco
Roth, A.1, Coughenour, M.2, Gresens, F.1, Goldbach, H.1, Burkhardt, J.1
Predicting the impact of land management on the hydrology of agricultural and natural ecosystems will become essential as public demand for water increases. More over, grazing may affect transpiration and evaporation of water from the soil by removing significant amounts of vegetation. Furthermore it determines species composition and thus directly the regional water cycle of arid and semiarid environments. We use the process-oriented and spatial explicit ecosystem model SAVANNA (Coughenour 2005) to assess biomass dynamics in rangeland landscapes in south-eastern Morocco. Model scenario results with a prospective to 2020 were implemented in interdisciplinary working groups to develop sustainable strategies relying on transhuman decision making.
The model was first calibrated for a rangeland area of 200 km2 of the northern Drâa River Catchment at Taoujgalt (1900 m a.s.l.), located at the southern slope of the High Atlas mountains.. Measurements of biomass (kg/ha) and plant component parameters (g/m2 DWT, Dry Weight Matter) of many saharan, iranoturanean and oromediterranean species were collected for calibration and validation purposes. These species are the basic feed of trespassing nomadic as well as sedentary herds. Multiple calibration runs with ‘no grazing’ (NG) and ‘grazing’(G) conditions were carried out. For sensitivity analysis (Roth, A. (2005)) with three basic SAVANNA vegetation types: herbaceous (e.g. Stipa ct. parviflora), shrub (e.g. Artemisia herba-alba/-mesatlantica) and woody (e.g. Juniperus ph.) being the pre-dominant perennial species. So far model results indicate a high sensibility towards drought for shrub biomass development. Furthermore animal grazing conditions stimulate growth rates of shrub respectively herbaceous standing biomass. These outcomes were used to determine regional influences of sheep, goat and dromedary herd populations on vegetation cover, species composition and distribution in order to assess their influence on the local/regional water cycle.
Keywords: Ecosystem modeling, biomass dynamics, herd dynamics, transhumance, Morocco