Climate change vulnerability assessment limitations

In addition to some of the inherent uncertainty with any approach to

assessing future risk from climate change to species, there are some other limitations more specific to my assessments of risk in Chapters 3 and 4. A limitation of my climate change vulnerability assessment in Chapter 3, for the birds particularly, is of the focus on climate change impacts on only the breeding distributions of species, without explicitly including information on the wintering distributions of migratory species (Small-Lorenz et al. 2013). The climate change vulnerability assessment framework used to assign climate change risk categories does include migratory status as one of the exacerbating factors, so species spending some part of their lifecycle outside of Europe have their climate risk score weighted more highly than resident

126 species, but an important component of risk may still not be accurately

captured.

With some bird species dependent on relatively geographically constrained wintering areas (Newton 2004) or with limited areas at which they can stop while following their migratory flyways (Huntley et al. 2006), changing climate in these locations could have serious negative effects on European breeding populations if they become unsuitable for the transient bird populations dependent on them. It is also possible that total migratory distances will increase as a result of changes in stopover sites, increasing the total time spent on migration with potential reductions in fitness of individuals as a consequence (Howard et al. 2018).With growing evidence that climate change is already having a strong negative impact on populations of migratory European birds (Gregory et al. 2009), particularly through

phenological shifts in the timings of departures leading to mismatches in food availability (Moller et al. 2008; Beresford et al. 2018), any additional impacts of climate change on key wintering locations are likely to further exacerbate these declines. Incorporating these additional climate change threats within the climate change vulnerability assessment process would improve the overall species level prioritisation and allow for more informed conservation decisions to be made.

The climate change vulnerability assessment carried out in Chapter 3 is also limited in how well it incorporates the arrival of colonising species into

Europe from the Western Palearctic, as their distributions shift into newly climatically suitable areas. A total of 335 species of birds and butterflies are recorded with breeding distributions within the Western Palearctic, it is plausible that a proportion of these species will be able to persist in regions of novel climate space projected to occur within Europe and will have the required dispersal ability to reach these areas. These potential colonisers are not recorded in the opportunity categories in the climate change vulnerability assessment, but their inclusions could change the overall pattern of risks reported.

127 The 50 x 50km scale distribution data used for modelling both taxonomic groups are also inherently limited in how accurately it can predict species distributions which may only occupy small percentages of the total area of each cell. With all of the assessments based on this macro scale species distribution modelling I am only able to make predictions of potential future risk based on broad patterns of distribution shifts, which may be missing some important fine scale detail. With microclimates within a landscape offering upwards of 1°C of variation in temperature over relatively short distances (Maclean et al. 2017), this fine‐grain heterogeneity in climate may allow species to persist in localities my macro models project will become unsuitable (Rull 2009; Hannah et al. 2014), with suggestions that

microclimate buffering might reduce extinction risk at some localities by up to 22% (Suggitt et al. 2018). With the spatial prioritisations for Europe

highlighting the continuing importance of montane regions in particular, the large microclimate gradients in these areas are unlikely to be fully captured at the scale I am modelling at and some species projected to be at high risk due to climate space in these areas becoming unsuitable may actually be able to persist in reality due to the presence of these microrefugia. The 50 x 50 km resolution models were also used for the spatial prioritisation analysis, which is too broad a spatial scale to make practical, on the ground

conservation management decisions. The broad patterns of change in priority areas, as well as the drivers behind those changes, should still be of value to conservation decision makers as they highlight currently

underrepresented regions and can be used to start early discussions of future conservation planning under climate change.

My assessments of both species level risk as well as broader geographic patterns of risk are based on just two taxonomic groups, representing only a very small fraction of the terrestrial biodiversity present across Europe. As responses to and risk from climate change can vary widely between different taxonomic groups (Foden et al. 2008), a more diverse range of species will need to be assessed using a climate change vulnerability assessment to give a more accurate prognosis of the potential impacts of climate change on European biodiversity. However, birds in particular have been shown to be

128 useful surrogates for a wide range of biodiversity when planning

conservation action and focussing on protecting them can lead to benefits for other taxonomic groups as well (Roberge & Angelstam 2004; Gregory et al. 2005; Larsen et al. 2012; Kukkala et al. 2016). Both birds and butterflies also demonstrated broadly similar priority areas in the spatial prioritisations, as well as the same shift in priority areas under climate change which would suggest other taxonomic groups may be expected to also respond similarly. Protected areas have also been shown to provide a range of benefits and are often key sites for species they were not originally designated to protect (Butchart et al. 2012, 2015; Di Marco et al. 2015), again suggesting that the focus on just two taxonomic groups in this thesis should not be too limiting on the overall implications for conservation in Europe under climate change.