Fragmentation and Connectivity of Island Forests in Agricultural Mediterranean Environments: A Comparative Study between the Guadalquivir Valley (Spain) and the Apulia Region (Italy)

Abstract

Habitat loss and fragmentation are considered some the main threats to biodiversity. Original forests have suffered an accentuated fragmentation and agricultural homogenization, leaving only some areas of natural vegetation, relegated to strongly anthropized disconnected patches (island forests, IFs) in a hostile matrix. These patches of original vegetation could be the key for the design and management of ecological corridors to promote species migration, an essential strategy for meeting the consequences of Global Change. This study proposes a comparative analysis of the fragmentation and connectivity of IFs of Quercus in two typically Mediterranean areas of predominantly agricultural use: the Guadalquivir valley (Spain) and the Apulia region (Italy). A retrospective comparison is also carried out in the Guadalquivir valley. The aim is to develop an objective new methodology to locate the patches of most interest using quantitative and qualitative data. Reference cartography of current island forests of Quercus species was developed from several digital sources and validated with orthoimages and field observations. Fragmentation analysis was based on graph structures using the software Conefor 2.6, a reliable tool for assessment of the role of patches in the landscape. Area and distance were used as node and connector values. Dispersion distance was established as 500 m, based on the maximum dispersion of acorns. Results indicate that the Guadalquivir valley has suffered an intensive fragmentation in recent decades. Both the Guadalquivir and Apulia regions host some IFs with the relevant potential to contribute as core habitats in the creation of connections to other natural protected sites. Many residual IFs in the landscape could contribute as stepping stones in the design and management of ecological corridors. Our methodology highlights the value of IFs to develop assessment strategies using homogenized available digital cartography and common criteria for the dispersion distances in graph theory analysis. The application of this new methodology could help in the management of protected sites using highly fragmented areas to allow the species movement through inhospitable landscapes in a unique opportunity to connect the different protected areas.