The role of protected areas for boreal bird populations and communities in the face of climate change

The coverage of protected areas on Earth should reach 30 per cent by 2030, according to the Kunming-Montreal Global Biodiversity Framework. This joint target, shared by 180 United Nations countries, aims to mitigate nature loss, and restore ecosystems. Protected areas have proved to be an efficient method to preserve habitats and species. Species richness and abundances tend to be higher inside protected areas compared to the surrounding matrix. However, simultaneously anthropogenic climate change and land use intensification increase the pressure of static protected areas' ability to preserve biodiversity.

Despite the positive effects of protected areas, the current understanding on which protected areas succeed or fail and why to fulfil conservation purposes set for them remains limited. In addition, it is unclear how well current protected areas mitigate the negative effects of climate change. The results of previous studies are not consistent, as population trends can be positive or negative inside protected areas. Some species or taxonomic groups benefit from the protection status of an area, but species richness may also decline just as rapidly under global change whether a site is protected or not.

The aim of this thesis is to provide further insight to the importance of protected areas in mitigating the negative effects of climate change on species and ecological communities. Thesis addresses the thermal niches of species that vary with species’ distribution ranges. That is, species with northern distributions are cold-dwelling and species with southern distributions are warm-dwelling. I focus on the thermal niches of species in protected areas at landscape level. In addition, I take a more detailed interest in the characteristics of the protected areas that determine protected areas’ ability to mitigate global change effects on species and ecological communities. For these topics, I utilise long-term data of breeding birds from the boreal zone in all chapters.

In the first chapter, I consider a large protected area network as a whole, and study how bird communities have changed inside and outside of them, measured as changes in the balance between cold- and warm-dwelling species. The study shows that under climate change, bird communities are increasingly dominated by warm-dwelling species, and this change is more rapid inside than outside protected areas. I also show that warm-dwelling species are the drivers of the community-level change. My results suggest that the current protected area network is not sufficient to mitigate the declines of cold-dwelling species or even extinctions at the high northern latitudes. On the other hand, protected areas can act as stepping-stones for warm-dwelling species when colonising new areas.

In the second chapter, I focus in more detail on the edge areas of protected areas and their effect on bird communities. The results reveal that bird communities are dominated by warm-dwelling species in the immediate vicinity of the protected area edge, while communities further from the protected area edge have higher abundances of cold-dwelling species. However, the designated protected area alone does not explain community-level changes, so I also study the effects of habitat type on bird communities. At the opposite ends of the habitat spectrum are needleleaf forests maintaining higher abundances of cold-dwelling species and croplands maintaining higher abundances of warm-dwelling species. These results suggest that the protected area edges and the habitat surrounding the protected areas should be integrated into the management and planning of protected areas.

The two first chapters focus on the changes at ecological communities, but the third chapter concentrates on species-specific population trends at different sizes of protected areas. I study how the abundances and population trends of species vary between small and large protected areas. The results show that population trends of cold- and warm-dwelling species as well as abundances of species associated with large and small protected areas differ. To be more precise, the population trends of cold-dwelling species were less negative in large protected areas compared to small protected areas. Moreover, small protected areas have higher abundances of warm-dwelling species. These results underline the importance of large protected areas for conserving cold-dwelling species in a warming climate.

My thesis reinforces the relevance of global protected area coverage targets by providing evidence of the inadequacy of the current protected area network in the northern hemisphere. However, this thesis stresses that not all protected areas are necessarily effective in conserving species or communities that they are designated to protect. Small protected areas are less effective at mitigating the negative effects of climate change, because they have a lot of edge areas. In addition, small protected areas are not sufficient to protect cold-dwelling species. In contrast, the results of this thesis suggest that large protected areas play a significant role in conserving cold-dwelling species. Thus, when designing protected areas, the aim should be to develop large protected areas that are more effective in protecting the fragile northern nature.