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Universität Hamburg (2012)

Pastoral systems and their interaction with spatiotemporal vegetation dynamics in the Atlas Mountains, Southern Morocco

Akasbi, Zakia

Titre : Pastoral systems and their interaction with spatiotemporal vegetation dynamics in the Atlas Mountains, Southern Morocco

Hirtenbewirtschaftungssysteme und ihre Wechselwirkungen mit raumzeitliche Vegetationsdynamik im Atlas Gebirge, Südmarokko

Auteur : Akasbi, Zakia

Université de soutenance : Universität Hamburg

Grade : Doktor 2012

Résumé
Rangeland degradation is an important issue in ecology and rangeland management, especially in the context of global change. Degradation is particularly severe in arid and semi-arid regions and is caused increasingly by livestock overgrazing. In these fragile ecosystems, rangelands are the main fodder resource for livestock. However, rangeland management strategies are still not sufficiently focused on the prevention of rangeland degradation. Therefore, this research has been conducted in semi-arid southern Morocco to study the two grazing systems occurring in this region – the sedentary and the transhumant – and their interaction with the environment and rangeland productivity. In the first paper, a study in browsed and unbrowsed permanent plots in a sagebrush steppe was conducted. The interannual variability in standing biomass of the three most dominant dwarf shrubs (Artemisia herba-alba, Artemisia mesatlantica and Teucrium mideltense) was assessed in order to study the effect of browsing on biomass changes. Length, width and height of ten plant individuals from each species were measured to calculate their volumes in each treatment. Power-law regression functions of dry biomass on volume were used to estimate the interannual standing biomass variation from 2004 to 2009. Browsing affected the architecture of the dwarf shrubs and thus different functions for the browsed and unbrowsed plots were found. Moreover, browsing affected the three species differently. While browsing had a negative effect on biomass change of Artemisia herba-alba, it had no significant effect on Artemisia mesatlantica. Teucrium mideltense reacted inconsistently to browsing between the years. The fact that the later two species were only marginally benefited from browsing exclusion could be due to the increased competition of the most dominant species Artemisia herba-alba. Interestingly, the standing biomass increased whether or not browsing was excluded, but the increase without browsing was almost double that with browsing. This increase might be due to the recovery of the studied species after a preceding long drought. To generalise the findings of this study, I recommend carrying out others studies on the same species at a larger scale. In the second paper, the general framework of transhumant migration movements was studied, in addition to the drivers and constraints affecting migration decisions by transhumant pastoralists. For this purpose, the three neighbouring tribes of Ait Mgoun, Ait Toumert and Ait Zekri were selected to conduct an ARGOS tracking study and an interview study. One goat herd within each tribe was tracked for a year, and structured interviews were used to describe the transhumance trajectories of the herders. Four transhumance types were defined in order to describe migration trajectory length : semisedentary (less than 20 km), short-distance transhumance (20–40 km), medium-distance transhumance (40–100 km), and long-distance transhumance (more than 100 km). In all the tribes, different types of transhumance occur and the type of transhumance practised could vary between years within the same tribe and even by the same herder. Ecological and socio-economic factors were influencing transhumant migration. The most important factors that drive migration direction were firstly fodder availability and secondly the harsh climate, which forces the pastoralists to leave the cold high mountains in winter and the hot lowlands in summer. Other factors were herd-specific risk and cost assessment as well as personal constraints of the herdsmen. To conclude, this study provided important knowledge on transhumance in southern Morocco and therefore contributes to a better planning of development and management strategies. In the third paper, which considers sedentary herds, the seasonal variation of the grazing patterns and intensities of tended goat herds were studied as well as their daily trajectories. For this purpose, one herd from each of the villages Ameskar, Taoujgalt and Bou Skour was selected. A GPS collar was fixed on one goat from each herd to track the movement of its herd for a period of a year. Two different recording intervals, 2 hours and 15 minutes, were used to assess the effect of each on the measured daily walking distance. Grazing intensities were calculated within 4-ha grid cells using ArcGIS. The highest grazing intensities were found in the first 250 m from the stable, while they were very low between 2,000 and 4,000 m from the stable. The seasonal mean daily walking distance varied between 3,480 and 4,460 m. It was longest in summer in Ameskar and Taoujgalt while in Bou Skour it was longest in spring. The shortest distances were in winter and autumn. This variation is mainly driven by fodder availability, climatic conditions, and day length. The relationship between GPS recording interval and the daily distance was explained well by the exponential function. This function allows the extrapolation from longer interval data to the actual walking distances. The decay of grazing intensity with increasing distance was described better with power functions and showed that grazing was concentrated around the stables. According to the results of this study, the area within the first 500 m from the village is the most affected by overgrazing and therefore requires specific management strategies. In conclusion, the three studies provided insights into important issues related to rangeland management and sustainable land use ; i.e. the assessment of rangeland productivity and grazing intensity as well as migration patterns of transhumant herds. Moreover, I estimated a range of carrying capacities in the sagebrush steppe of Taoujgalt : between 0.34 SSU ha-1 in a dry year under continuous browsing and 2.32 SSU ha-1 in wet years within the exclosure. The carrying capacity within the exclosure was two to five times higher than outside the exclosure. The actual grazing intensity was nearly 13 times higher than the carrying capacity in the 250 m around the village, while the areas over 1000 m from the village were understocked by sedentary herds. The carrying capacity was strongly influenced by precipitation and rangeland conditions ; therefore, it should be adjusted depending on precipitation and fodder availability. Consequently, I recommend doing similar studies within other villages and other tribes in order to complement this thesis and to generalize the findings to a larger scale. Additionally, rangeland managers should take into consideration the estimated carrying capacities in their conservation strategies.

Mots clés : allometric function, Atlas Mountains, nonlinear regression, standing biomass , Transhumance, GPS collar, goat grazing , grazing intensity

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Page publiée le 24 novembre 2013, mise à jour le 7 janvier 2019