Protected areas enhance expanding populations and mitigate declines on range edges under climate change

Warming climate is changing geographical distributions of species. However, keeping pace with the climate may be complicated. The climate is indeed changing faster than species are capable of following it. Other environmental changes can hamper the ability of species to move if they face difficulties following climatic preferences in a fragmented landscape. This may lead to increased extinction risk especially for species inhabiting high latitudes and altitudes. These species are expected to be particularly exposed to the consequences of climate change due to the lack of space into which they can retreat. Evidence is mounting that this may indeed be the case, since boreal and montane species in northern Europe have shifted their abundances faster than southern species, and exhibit decreasing populations. Protected areas are the cornerstones of our conservation strategies. Yet their role in mitigating climate change impacts has been debated since species distributions are dynamic while a network of protected areas remains static. There is however evidence that protected areas are important for conserving rare species and for the overall maintenance of biodiversity under climate change. Most findings concerning species distribution changes under climate change are based on occurrence data, despite recent evidence showing the increased reliability in generating outcomes for conservation prioritization when abundance data are used. Many studies have concentrated on modelling and predicting the future and therefore more attention is required on studying changes which have already happened for increasing empirical knowledge on climate change impacts on species, and for validating and improving projections of future impacts. To assess the effects of protected areas against climate change driven distribution shifts we compared changes in abundances inside and outside protected areas on the range edges of 100 Finnish land bird species on a time span of five decades. On the trailing range edge of northern species abundances declined less inside than outside protected areas and abundances were in general higher inside protected areas. In turn the abundances of southern species on their leading range edge increased more inside than outside protected areas for species with high reliance on protected areas. The results show that protected areas mitigate the retraction of northern species, although are not fully able to prevent it. Results also indicate that protected areas help southern species of conservation concern to expand their distribution farther North. Our results represent an encouraging message for biodiversity conservation. We show that PAs play an important role in mitigating impacts of climate change on biodiversity, providing strongholds for species persistence in the short term. Thereby PAs allow some time for wider protection efforts to start yielding positive effects but also time for counteracting the constitutive reasons of climate change.peerReviewe