Analysis of GPS trajectories to assess goat grazing pattern and intensity in Southern Morocco

Abstract

The assessment of grazing intensity is important for making adequate management decisions on rangelands. Using GPS collars, tended goat herds from three villages in southern Morocco were studied. The aim was to characterise their spatio-temporal movement patterns, i.e. the seasonal variation in grazing intensities, and daily trajectories of the herds. Furthermore, the effect of recording interval on recorded daily walking distances and the relationship between grazing intensities and distance was assessed. Grazing intensities were calculated within 4-ha grid cells for areas around settlements. The highest grazing intensities were found in the 250 m nearest the settlement. Some directions were totally avoided due to either community boundaries or adverse topography. The daily and maximum walking distances were significantly different between seasons. In the arid ecosystems the longest mean daily walking distance were found to be in the spring whereas in semiarid ecosystems it was in summer. It is argued that this variation in grazing pattern is mainly driven by varying fodder availability and its nutritive value, weather conditions and the length of day. The distances were longer in periods when fodder of high nutritive value was available, while cold temperatures and short days in winter limited the distances walked. The relationship between GPS recording interval and recorded trajectory length was described well by an exponential function, which in turn allows extrapolation from data with longer intervals to the actual distances travelled. Using non-linear regressions, the decay of grazing intensity with increasing distance was described better with power functions. The exponents ranged from –1.69 to –2.18, demonstrating that the goats were clumped around the settlements. The description of the grazing patterns of goats in this study provides valuable data for the parameterisation of grazing models.