Agricultural systems and biodiversity: evidence from European borders and bird populations
利用瑞士、德国和法国交界处的自然实验，研究不同农业系统对鸟类多样性的影响，发现瑞士的农业政策导致鸟类种群更小、多样性更低，但差距在1990年代比2010年代更明显。
Countries' agricultural systems have an important impact on biodiversity, for example bird populations. Here, we estimate such impacts by exploiting a natural experiment in the middle of Europe, where there is a naturally homogenous area that is divided into three countries: Switzerland, Germany, and France. These countries have markedly different agricultural systems and policies. Using a methodologically unified and unusually rich bird dataset available across these borders, both for the 2010s and 1990s, we analyze (a) whether there is a clear pattern that bird diversity systematically changes when crossing these borders and (b) whether this has changed over time. To assess bird populations, we focus on Shannon diversity, species richness and number of territories, as well as the individual effect on 29 common bird species. We find that Switzerland has systematically smaller and less diverse bird populations compared to Germany and France, driven entirely by agricultural differences. At the same time, we find that the difference between the countries was considerably more pronounced in the 1990s than in the 2010s. Yet, to reach the bird friendliness of Switzerland's neighboring countries, additional policy effort seems required, for example in the form of targeted agri-environmental payments.