The wild boar Sus scrofa in northern Eurasia: a review of range expansion history, current distribution, factors affecting the northern distributional limit, and management strategies

1. The wild boar Sus scrofa is one of the most widely distributed large mammal species in the world, existing on all continents except Antarctica. In the late 20th Century, its geographical range expanded naturally and through intentional releases. Despite the environmental, social, and economic importance of the wild boar, its current distribution in northern Eurasia remains uncertain, and the factors that limit and promote expansion in northern ecosystems are unknown.
2. We aimed to summarise the history of wild boar range expansion and current distribution in the countries of northern Eurasia. We also assess the relative importance of climate (both harshness and warming), habitat (both current diversity and possible change), predators, releases, supplementary feeding, and hunting in limiting or promoting the distribution and range expansion of the species. We review hunting management and other regulations that may affect further northward expansion.
3. Information on wild boar expansion and distribution was collated from available scientific publications, official statistics, volunteer reports, and expert knowledge. The effects of natural factors (climate harshness, habitat variation, predators) and anthropogenic factors (climate warming, habitat change, releases, supplementary feeding, hunting) on wild boar distribution were assessed using estimates (scores) provided by experts from the target regions.
4. The wild boar in Europe is distributed up to 64°N. In Asia, the northern distributional limit is up to 61°N. The species' northern distributional limit is further north in the west than in the east of the geographic range.
5. Experts regarded climate harshness, habitat, and hunting as the most important factors limiting wild boar distribution. Important factors that promote the expansion of the wild boar's range include climate warming and supplementary feeding.
6. Our analysis of the official approaches to wild boar management suggests that the northern Eurasian countries do not have a united approach to the challenge of wild boar expansion. Collaboration between managers, policymakers, and researchers is needed for monitoring the wild boar distribution and range expansion throughout northern Eurasia. This data collection is especially important now, as parts of Europe and Asia are facing the challenge of African swine fever as well as other human–wildlife conflicts related to increasing wild boar populations.