Assessment of grazing selectivity in relation to land cover: a comparison between sheep and goats
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abstract
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.
