Climate change refugia for the flora and fauna of England.
Abstract
A variety of evidence suggests that species may be able to withstand the effects of climate change in localised environments known as refugia, where specific environmental conditions act as a buffer against broader scale climatic changes. This report assesses the published evidence for such refugia, while also establishing novel empirical evidence for their existence in England, based on recent changes to the distributions of a wide range of taxa. Properties of the landscape identified in the published literature as contributing to 'refugium potential' were modelled at 100 m resolution for England, and summarised at the scale of 10 x 10 km grid squares. Maps are presented showing variation in these properties, as well as variation in rates of change in temperature, precipitation and snow cover. Using data from the Centre for Ecology and Hydrology's Biological Records Centre, the persistence (or extinction) of 1,082 species that retracted their range over the past four decades was modelled against these environmental properties. After controlling for the effects of recorder effort and agricultural intensity, there were strong indications that rates of population persistence were influenced both by rates of climate change, and by microclimatic variability. There were consistent differences in the responses of different taxonomic groups to different properties of landscape and climate change. Hence a refugium for one particular group may not be suitable for another group. Plant persistence tended to be reduced in regions of greater summer warming; however, this negative effect of warming was buffered by topographic variability in slope, aspect and elevation. Beetles showed stronger responses than the other taxa to changes in rainfall, and to modelled topographic variability in moisture levels. Persistence in the other invertebrate groups (e.g. butterflies and moths) showed stronger relationships with changes in summer temperature, which were modified by regional topographic variability. The models of species persistence were used to provide maps of refugium potential in England. Maps were created to represent: (i) all modelled variables, including geology and agricultural intensity; (ii) climate change and microclimate effects; (iii) microclimate variables only. There was a positive correlation between modelled refugium potential and designation as Sites of Special Scientific Interest (SSSIs). Thus, the English protected area network is generally well placed to take advantage of environmental characteristics that increase the potential of landscapes to act as refugia. The patterns of persistence/extinction in animal groups were related to the distribution of SSSIs, especially in the butterflies and moths, where probability of persistence had a strong positive relationship with SSSI cover in 10 km grid squares. In contrast, higher plant persistence had a weakly negative relationship with SSSI cover. Six 20 km x 20 km landscapes in three regions were selected for more detailed study at higher resolution. These landscapes were located in West Cumbria, Upper Teesdale, Dartmoor, Exmoor, South Brecks and the Norfolk Broads. Responses to microclimate differed in each of these landscapes, and it was difficult to identify general patterns. Given the limited number of high resolution records available, it is unsurprising that the statistical models have identified different microclimatic drivers of trends in persistence. The reliability of the microclimate proxies used in this study was also assessed using field surveys of plants and butterflies in the Dartmoor landscape. We examined whether species with high moisture requirements were located in areas with high topographic wetness index values and whether those with high thermal requirements were located in areas with high solar index values. In the field, species with high moisture requirements were significantly more likely to be recorded in areas with a high topographic wetness. The majority of plant species with low temperature requirements occurred more frequently in areas with a low solar index, but this association with topographic features promoting cool temperatures was weaker at field locations with long vegetation. This suggests that reductions in grazing pressure could be used as a tool to offset the effects of climate change. The literature review revealed few studies examining the influence of fine-scale climate on endothermic organisms. We therefore tested whether fine-scale microclimate heterogeneity affected the UK distribution of an exemplar endotherm: the meadow pipit (Anthus pratensis). Meadow pipits were more likely to occur in areas with high variation in the topographic wetness index and low variation in the solar index. Response to wetness was stronger in regions where the macroclimate was less suitable. Therefore, the importance of microclimate to the English distribution of this species is likely to increase as the climate warms. Overall, our results provide support for the hypothesis that refugia can be identified where the impacts of climate change on organisms have been less detrimental than elsewhere. This effect arises because of heterogeneity in both: (a) the microclimate; and (b) the rate of recent climate change across the landscape.