Analysis of the ecological evolution of an area in the Setubal Peninsula (Apostiça) caused by changes in land use patterns

The aim of the study was to analyse the evolution of land use patterns and environmental functions in Apostiça (Setubal Peninsula, Portugal). The study area was chosen for study because it serves as a dynamic model of land use modification, while simultaneously plays an important role in connecting habitats of great ecological value. The year 1966 was considered the starting point (base year) for the modifications, as that year marks the opening of a bridge over the Tagus River and the beginning of a direct traffic connection between Lisbon and the Setubal Peninsula. A structural characterisation and analysis of the main elements belonging to the overall ecological structure was completed for each year identified in the study in order to analyse the modification of the biological structures in the study area. Three indices were tested as measures to describe different proprieties of the landscape, the habitat layers index (Short 1988), the diversity index originated in information theory (Shannon and Weaver 1962) and the landscape contrast index (Romme et al, 1982; Hoover et al. 1991). The result of the application of the habitat layers index (Short 1988) indicates that this index could be useful to analyse de changes in biotope quality. The agricultural land use units abandoned, are well identified by a decrease of the habitat layers index. To study the structural diversity of the landscape was applied a diversity index originated in information theory (Shannon and Weaver 1962). That index gives information about the degree of heterogeneity of the land forms and vegetation cover belonging to a land use unit. The mapping of the Shannon index could be important in order to analyse the natural and semi-natural structures. For artificial structures the results are not so correct, and was difficult to establish a relation between the land use quality and its structure. The mapping of the landscape contrast index could be useful to identify potential corridors for species flows across the landscape.