Grassland vegetation height affects bird responses to forest edges in Mediterranean open farmland

Afforestation affects Mediterranean farmland biodiversity due to loss and fragmentation of grassland habitats. While the influence of landscape context and plantation edges on farmland bird responses to afforestation is well-documented, less is known about the influence of grassland vegetation height and how it interacts with afforestation to influence bird communities. Here, we examined how changes in grassland vegetation height affect bird responses to afforestation in a farmland region in southern Portugal, and how these are affected by plantation type and edge. This region has experienced afforestation with eucalyptus, pine and oak stands, agricultural intensification, and frequent dry periods. To capture local and landscape-level changes, we collected data in two periods (2005 and 2014–15). Grassland vegetation height varied between sampling periods, emerging as a key factor affecting changes observed. Ground-nesting and cereal-associated species increased in abundance with taller vegetation in 2014–15, while in 2005, with drier weather and shorter vegetation, the species associated with ploughed fields were more abundant. Vegetation height effects on bird assemblages depended on plantation type and distance to plantation edges. Farmland bird abundance, including ground-nesting and cereal crops-associated species, increased with taller vegetation, particularly near oak and pine plantations. Conversely, species associated with ploughed fields declined with taller vegetation, especially near eucalyptus plantations. Results highlight complex interactions between vegetation height, plantation type, and edge proximity shaping avian assemblages. This study supports the importance of field and landscape-level management with special focus on grassland vegetation height and landscape heterogeneity for preserving open-farmland birds in fast-changing Mediterranean farmland landscapes.

This work was supported by the Portuguese Ministry of Education and Science and the European Social Fund, through the Portuguese Foundation of Science and Technology (FCT), in the scope of the project UIDP/50027/2020 and with grants to JF (SFRH/BD/ 131809/2017), FM (IF/01053/2015); contracts to IC (CEECIND/03224/2021), LR (CEECIND/00445/2017) under the programme of “Stimulus of Scientific Employment—Individual Support”; and the project PTDC/BIA-BIC/2203/2012-FCOMP-01–0124-FEDER- 028289 by FEDER Funds through the Operational Programme for Competitiveness Factors–COMPETE. JS has received funding from the FEDER Funds through the Operational Competitiveness Factors Program-COMPETE and by National Funds through FCT- Foundation for Science and Technology within the scope of the project “PTDC/ BIA-EVL/30931/2017-POCI-01–0145-FEDER- 030931″ and from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No 101003553 - EuropaBON - H2020-SC5–2018-2019–2020 / H2020-SC5–2020-1.