Habitat changes explain shifts in bird community composition in abandoned military training areas: Lessons for conservation

Abstract

Military training areas are important biodiversity refuges and may serve as viable components of regional conservation networks, mainly due to the blocking of ecological succession by the disturbance regime creating a heterogeneous open habitat mosaic hosting many threatened species. However, European armies have undergone downsizing over the past decades and numerous military training areas have been abandoned. The assessment of the consequences of this abandonment for biodiversity would show us whether these abandoned areas still provide conservation benefits. For this purpose, we carried out bird surveys in 30 abandoned military training areas in Czechia. The surveys were performed in two periods (2009 and 2020–2021) to track small-scale changes in land cover and bird abundance after the areas were abandoned in the 1990s. We tested (i) whether changes in bird abundance were related to land cover changes and (ii) whether the observed bird species’ responses to the land cover changes can be explained by species-specific characteristics. Multivariate spatial analyses uncovered significant shifts in land cover composition towards a higher representation of dense shrub, forest and built-up areas at the expense of open areas represented by grassland and sparse shrub. These land cover changes explained a small but significant part of bird abundance variation across the areas. Correspondingly, species benefiting from these land cover changes were associated with dense scrub or forest, such as the Common Chiffchaff, Willow Warbler, or Eurasian Blackcap, whereas species suffering from these changes were associated with grassland, such as the European Stonechat and Eurasian Skylark. Phylogenetically informed interspecific analysis aiming to explain changes in bird abundance between periods confirmed that population declines were linked to open habitat preference, while population increases were linked to the preference for dense shrub and forest. In addition, we found that protected species increased their abundance, most likely due to the existence of conservation management that kept their habitats available. These patterns indicate that military training areas transform toward later successional stages after their abandonment with corresponding changes in bird community composition. However, these changes may not necessarily be negative provided that species of conservation concern enjoy the support of conservation management.