Site and landscape scale drivers of bird and insect diversity in Native and novel forest ecosystems of Central Portugal

Abstract

The natural forests of southern Europe have been altered over the last decades. One of these changes is the proliferation of invasive woody alien species, resulting in highly altered ecosystems, the so-called “novel ecosystems”. These changes affect biodiversity at both local and landscape scales. Using piecewise structural equation models, we evaluate the effects of local and landscape variables on the diversity of birds and insects across three common forest types in Central Portugal, namely: Native Forests (dominated by Quercus sp.) and two novel forest ecosystems, Acacia Forests and Eucalyptus Forests (forests formed by natural regeneration of Acacia dealbata Link and Eucalyptus globulus Labill). Local variables were the most influential on bird and insect diversity, and Native Forests was the forest type that most favored diversity in both groups. The structure of this forest type may explain this difference, as Native Forests have a greater local complexity compared to novel forest ecosystems, providing foraging and breeding resources and increasing the microhabitats. Contrarily to what was expected, no variable, including structural landscape complexity, has significantly influenced biodiversity at the landscape level. Fire seems to promote Eucalyptus Forest, resulting in negative impacts upon biodiversity in fire-prone areas. Our results show the extended impacts of deep ecosystem alterations on diversity patterns, with relevant insight into management and conservation practices.