Observed bioclimatic changes across the protected area network of Finland

In boreal regions, trends in biologically relevant climate variables (i.e., bioclimate) over protected areas (PAs), important for biodiversity, have largely remained unquantified. Here, we investigated the changes and variability of 11 bioclimatic variables of both seasonally-integrated variables and extreme-events across Finland during the period 1961–2020 using a gridded climatology. Our results highlight significant changes in growing season temperature over the entire study area, whereas, e.g., annual precipitation sum and April–September water balance have increased especially in the central and northern parts of Finland. Moreover, we found substantial spatial variation in bioclimatic variables over the 631 studied PAs describing e.g. snow conditions and number of frost days in spring with absent snow cover, reflecting the changing exposure of biota to frost. The observed increases in accumulation of heat in the southern boreal zone and more frequent rain-on-snow events in the northern boreal zone can be important for the drought tolerance and winter survival of species, respectively. A multivariate ordination analysis suggested that the main dimensions of bioclimate change in PAs vary by vegetation zones. For example, in the southern boreal zone the changes are mostly related to annual and growing season temperatures, whereas in the middle boreal zone the changes are related to altered moisture and snow conditions. Our findings underpin the marked spatial variation in bioclimatic trends and climate vulnerability in northern Europe. The large suite of bioclimatic indicators provides new understanding of how climate change is manifesting over the northernmost Europe with sensitive ecosystems, and helps to develop biodiversity conservation and ecosystem management.