| Summary: | Vegetation has been increasing in northern latitudes in recent decades and can be attributed to higher temperatures from global warming as well as changes in agricultural practices and grazing by livestock. This increase has lead to encroachment of shrub species into lower vegetation ecosystems. These changes in habitat can influence abundance and communities of species. Iceland has internationally important breeding populations of several terrestrial bird species where most have their stronghold in lowland areas. The aim of this study was to estimate the effects of shrub encroachment on avian communities in lowland Iceland. The study was conducted in lowland Iceland in 2017 and 2018. Birds were counted on plots with shrubs and on adjacent control plots. On shrub plots an estimation on shrub size and density was carried out. Landowners were visited and asked questions to ascertain which types of grazing were prevalent on plot sites the last decade. To estimate temporal changes in shrub encroachment a survey from 2001 was repeated in the summer of 2018. The results showed that the frequency of plots where shrubs were visible had increased 95.7% between 2001 and 2018 for birch (Betula pubescens and B. nana) and 51.5% for willow (Salix spp.). The questionnaire survey showed that shrub encroachment was evident on plots which had been entirely protected from grazing for several years or were protected from sheep grazing. Grazing by horses did not prevent shrub encroachment. Bird species which were in significantly lower density on shrub plots were Oystercatcher (Heamatopus ostralegus), Golden Plover (Pluvialis apricaria), Whimbrel (Numenius phaeopus) and Common Redshank (Tringa totanus). Species which were significantly more abundant on shrub plots were Common Snipe (Gallinago gallinago), Redwing (Turdus iliacus) and Meadow Pipit (Anthus pratensis). Black-tailed Godwit (Limosa limosa), Dunlin (Calidris alpina) and Golden Plover were significantly reduced in density with larger shrubs within shrub plots. The results ...
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