Assessment of grazing selectivity in relation to land cover: a comparison between sheep and goats
Artigo de ConferênciaTeses
Visão geral
Pesquisas
Informação adicional documento
Ver Todos
Visão geral
resumo
Each agroforestry system has developed differently to each ecological, economic and social region of
the world. ln Portugal, the traditional agroforestry landscape of Terra Fria is a mosaic of very small patches of
annual and perennial agriculture, shrub and woodlands. This patch diversity- composition and configuration -
plays a vital role in supporting biodiversity. On the other hand, traditionallivestock systems are based on grazing
itineraries searched for different functions- gathering and resting among others- on this landscape mosaic. These
agroforestry systems can be considered as a sustainable landscape management which integrates agriculture,
livestock and forest on the same land management base.
Landscape attributes such as topography, land cover and land use patterns influence the organization of grazing
circuits and patch selection. The comparison between land use territory and land use crossed by flocks can be
seen as a result of grazing selectivity made by animais and shepherds. The analysis of grazing selectivity is carried
out by calculating a selection ratio (SR) for each land cover type :% of land cover of grazing circuit/% of available
land cover type. A SR of 1 means that and cover type is used in a random way; a SR lower than 1 means that land
cover type is rejected and SR higher than1 means that that land cover type is preferred.
We investigated the set of land use patches crossed by sheep and goats flocks during a year and we compare it to
the landscape composition, in a village context. For each month, we calculated a Selectivity Index (SI) for each land
use- annual crops, perennial crops, forests, pasture and natural grasslands and shrubs.
Our results indicate that flock displacement patterns are related with the shepherd and animais perception of
benefits and requirements. They are guided by a complex interpretation of land uses and expectations of profitsforage,
shade o r circulation among patches- in function of environmental constraints and land use types occurring
around villages. The seasonal variation of SR for each land use suggests that the itineraries vary along the year
regarding the different needs of animais and the resources availability. Shepherds recognize this complexity and
use them accordingly to manage the productivity of the system.
Portugal’s Northeast production of sheep and goats are based on the exploitation of landscape by-products such as spontaneous native vegetation and agriculture leftovers. Shepherds tend the flocks throughout grazing itineraries every day, crossing a mosaic of patches of varied land uses. During the journey, the shepherd acts together with the sheep and goats to select each patch in creating an ordered sequence of land uses.
The focus of the research is on the land-use composition of the grazing itineraries; determinate how they depend on the patterns of the landscape mosaic. It is utilized a data set of 26 monthly herd’s itineraries, 13 of sheep and 13 of goats, to investigate the relationship of the land uses crossed by the flocks and the land uses of the landscape, evaluating the land-use preferences and selectivity of the sheep and goats.
It is utilized the divergences in the time spent and distance travelled by the herds and the area of the land uses in the landscape, the chi-square test to relate the preferred land used and the season, and the discriminate analysis to distinguish the preferences and the selectivity of the herd of sheep and the herd of goats.
The herds of the sheep and the goats presented different land-use preferences over the seasons and the discriminant analysis shows that they have different landscape preferences. The herd of sheep has the highest selectivity indexes for the annual irrigated crops, the agricultural complex systems and the agroforestry land uses. The highest selectivity indexes for the herd of goats were found for the deciduous forest, the agriculture with natural and semi-natural spaces and the shrublands land uses. It was concluded that the landscape management for sheep and goats herding has to be different: the agricultural land uses are essential to the flocks of sheep and the forest land uses are decisive to the flocks of goats.
