Hierarchic species–area relationships and the management of forest habitat islands in intensive farmland Angela Lomba a,b,c,⇑ , Ana Sofia Vaz a,d , Francisco Moreira e , João Pradinho Honrado a,d a Centro de Investigação em Biodiversidade e Recursos Genéticos (CIBIO), Edifício FC4, sala 1A, Rua do Campo Alegre, S/N, PT-4169-007 Porto, Portugal b Alterra Wageningen University and Research Centre, NL-6708 Wageningen, The Netherlands c Départment d’Ecologie et d’Evolution (DEE), Université de Lausanne, Bâtiment de Biologie, CH-1015 Lausanne, Switzerland d Faculdade de Ciências da Universidade do Porto, Departamento de Biologia, Edifício FC4, sala 1A, Rua do Campo Alegre, S/N, PT-4169-007 Porto, Portugal e Centro de Ecologia Aplicada ‘‘Prof. Baeta Neves’’ (CEABN), Instituto de Agronomia, Universidade Técnica de Lisboa, Tapada da Ajuda, PT-1349-017 Lisboa, Portugal article info Article history: Received 22 August 2012 Received in revised form 6 November 2012 Accepted 9 November 2012 Keywords: Dairy farmlands Exotic plantations Habitat fragmentation Plant diversity Semi-natural forests Species–area relationship (SARs) abstract Habitat loss and fragmentation due to land use changes are major threats to biodiversity in forest ecosys- tems, and they are expected to have important impacts on many taxa and at various spatial scales. Species richness and area relationships (SARs) have been used to assess species diversity patterns and drivers, and thereby in the establishment of conservation and management strategies. Here we propose a hierarchical approach to achieve deeper insights on SARs in small forest islets in intensive farmland and to address the impacts of decreasing naturalness on such relationships. In the intensive dairy landscapes of Northwest Portugal, where small forest stands (dominated by pines, eucalypts or both) represent semi-natural habitat islands, 50 small forest stands were selected and surveyed for vascular plant diversity. A hierarchical analytical framework was devised to determine species richness and inter- and intra-patch SARs for the whole set of forest patches (general patterns) and for each type of forest (specific patterns). Differences in SARs for distinct groups were also tested by con- sidering subsets of species (native, alien, woody, and herbaceous). Overall, values for species richness were confirmed to be different between forest patches exhibiting different levels of naturalness. Whereas higher values of plant diversity were found in pine stands, higher values for alien species were observed in eucalypt stands. Total area of forest (inter-patch SAR) was found not to have a significant impact on species richness for any of the targeted groups of species. However, significant intra-patch SARs were obtained for all groups of species and forest types. A hierarchical approach was successfully applied to scrutinise SARs along a gradient of forest natural- ness in intensively managed landscapes. Dominant canopy tree and management intensity were found to reflect differently on distinct species groups as well as to compensate for increasing stand area, buffering SARs among patches, but not within patches. Thus, the maintenance of small semi-natural patches dom- inated by pines, under extensive practices of forest management, will promote native plant diversity while at the same time contributing to limit the expansion of problematic alien invasive species. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Forests have been acknowledged worldwide as essential pro- viders of valuable ecosystem services, from habitat for biodiversity to provision of economic goods (Magura et al., 2008; Proença et al., 2010). The provision of such services is known to be dependent of the high diversity of living organisms inhabiting forest ecosystems (Benayas et al., 2008; Proença et al., 2010). Even so, biodiversity is declining at rapid rates, with the loss of habitat through land-use change, the expansion of alien species, direct exploitation e.g. through hunting and trade, climate change, and pollution identi- fied as major causes (Sala et al., 2000; Trisorio et al., 2010). Distinct scales of influence have been related to the drivers of change in forest biodiversity patterns, with climate driving changes over large areas (Laughlin et al., 2011), human activities impacting on diversity patterns in intensively managed regions, and land-use and landscape heterogeneity influencing those pat- terns in local, finer grained contexts (Cayuela et al., 2006). Forest ecosystems have particularly been under the threat of land-use conversion and landscape fragmentation (Bengtsson et al., 2000; Guirado et al., 2007; Trisorio et al., 2010). Effects of habitat frag- mentation have been documented for many taxa and at various spatial scales (e.g. Golden and Crist, 1999; Ewers and Didham, 0378-1127/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.foreco.2012.11.012 ⇑ Corresponding author at: Centro de Investigação em Biodiversidade e Recursos Genéticos (CIBIO), Edifício FC4, sala 1A, Rua do Campo Alegre, S/N, PT-4169-007 Porto, Portugal. Tel.: +351 220402790; fax: +351 2204027098. E-mail address: angelalomba@fc.up.pt (A. Lomba). Forest Ecology and Management 291 (2013) 190–198 Contents lists available at SciVerse ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco