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Instituto Politécnico de Bragança (2020)

Spatial modelling of grazing pressure by small ruminants in Bragança Region

Mangad, Ghita

Titre : Spatial modelling of grazing pressure by small ruminants in Bragança Region

Auteur : Mangad, Ghita

Université de soutenance : Instituto Politécnico de Bragança

Grade : Master of Science in Forest Resources Management 2020

Extensive grazing systems are characterised by low stocking densities, with positive impacts on the landscape, promoting diversity and heterogeneity. In order to manage this type of systems, we have implemented a robust tool which is the evaluation of the grazing pressure. This latter can establish the relationship between the ruminant and the pasture. This study is made in Bragança region, situated in the northeast part of Portugal. We used available databases such as : land use and cover (LUC) map of Portugal (COS2018), parishes’ administrative boundaries (CAOP2012) and sheep and goats’ locations and headcounts of the study area (OTSA). We define eight LUC classes : permanent crops (PC), annual crops (AC), grasslands (G), shrublands (S), grazed (GF) and ungrazed forests (UF), urban (U) and water bodies (W). The stocking densities and the distribution of the grazing pressure over the LUC classes was done by GIS geoprocessing techniques involving multiple ring buffer zones, data overlapping and spatial interpolation. We used two different methods for spatial interpolation of stocking densities ; the weighted inverse distance (IDW) and the ordinary kriging (OK), with better results for the latter, with average prediction errors of 0.0003. Overlapping the grazing areas of the LUC map and the stocking densities, it allows us to obtain the grazing pressure (GP). The most common GP in Bragança is about 1-1.5 sheep or goats/ha. The LUC class with the highest grazing pressure is annual crops (2.22 sheep or goat/ha), the less grazed class is shrublands (1.42 sheep or goat/ha). Regarding the availability of LUC, shrublands have the highest coverage in Bragança region (26.8%), followed by PC (20.5%), GF (18.5%), AC (15.7%), UF (9.2%), G (5.5%), U (3.1%) and W (0.7%). The herds in the study area are globally composed of 11.42% goats and 88.58% sheep. The grazing pressure is related to the food preferences of each species and has been taken into account in this assessment in order to increase the accuracy of the results obtained.

Mots clés  : Grazing pressure GIS Extensive livestock system Stocking density Land-use cover Grazing management Spatial interpolation


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