What’s All This About Refugia and Climate Change?

So, we’ve established that refugia could potentially play a role in future conservation efforts, but to what extent? And what are the consequences of this? Ashcroft (2010) provides an overview of the different interpretations of climate change refugia and points out a few potential problems and methodological discrepancies that can result from these (some of which are listed in the table in Figure 1). I apologise in advance for the length of this post but I think it is important to point out some of these potential problems and discrepancies rather than simply championing the role that the concept of refugia can play in predicting and managing species’ responses to climate change.

Source: Ashcroft (2010)

Refugia From Climate Change

As we’ve discovered already, both temperate and cold-adapted species have been known to persist in refugia. Ashcroft (2010) points out that whilst both types of refugia should be conserved to ensure long-term conservation of biodiversity, it is the cold-adapted species that are of ‘most immediate concern’ because they are presently restricted to refugial areas which are under increasing threat as global temperatures rise. The author then emphasises the difference between in situ and ex situ refugia, with in situ refugia referring to ‘locations that remain suitable for a species’, and ex situ refugia referring to locations where species are able to survive but did not previously occupy (maybe my post on assisted migration could be relevant here?). He states that identifying and conserving in situ refugia from climate change might be appropriate for species who aren’t able to disperse quickly or easily or where humans have created man-made landscapes that act as migration barriers. Humans can potentially assist in the colonisation of ex situ refugial areas or create habitat corridors to allow species to reach new suitable climate change refugia. As you can see, the 2 types of refugia have quite different meanings when it comes to applying them to issues of conservation in the face of climate change, so scientists should always be careful to specify which type they are discussing based on species’ dispersal characteristics (rather than just using the word ‘refugia’). Likewise, Ashcroft (2010) urges scientists to clarify both the spatial and temporal context of their use of the word refugia.

Microrefugia and Macrorefugia

In general, macrorefugia refer to the larger ‘classical’ refugia like the Southern refugia that temperate species migrated to during glacial periods, and microrefugia refers to the smaller refugia such as the cryptic Northern refugia. Climate grids are often used to identify potential refugia but Ashcroft (2010) points out that different ones are needed to identify macro and microrefugia yet, when discussing these climate grids, some scientists just use the term ‘refugia’ without distinguishing between micro and macro. This makes evaluating appropriateness of the climate grids difficult. As we saw with the tree example in my post discussing McLachlan et al (2005) and Pearson (2006)’s work, the risk of extinction for species may be overestimated or exaggerated because the climate grids are ‘too course’ to predict accurately. The distinction between micro and macro refugia is also important when it comes to conservation. Macrorefugia can act as a more protected buffer against the changing climate, but as microrefugia can house endemic endangered species and can exist on a regional scale even after climate change has affected the surrounding environment and eliminated marcorefugia, they can tolerate a greater amount of warming – they should both be seen as targets for conservation, however.

Climate or Habitat?

Ashcroft (2010) points out that ‘there is some confusion over whether species should be defined with respect to stability in climate or habitat’. Some scientists refer to refugial (or I better say microrefugial to be more specific!) areas that haven’t been affected as much by climate warming (i.e. stability in climate), but species distribution models are usually used to predict habitat stability. Although these often correlate, not distinguishing between the two can lead to some discrepancies. The author points out that one problem with identifying refugia in terms of climate stability is that plants and animals often become specifically adapted to stable climates and so even if the degree of warming is less in these refugial areas, the effect it has on the species may be just as much because of their unique adaptions. Also, climate stability can be defined in terms of a number of different parameters, such as humidity or maximum summer temperature, and the areas and species targeted by conservation efforts would vary according to which parameters were chosen. Climate stability may be useful in identifying in situ refugia but species distribution models based on habitat stability are still needed to identify potential ex situ refugial areas. Scientists, therefore, need to include both climate stability and habitat stability in studies of refugia.

Concluding Remarks from Ashcroft (2010)

The potential problems and methodological discrepancies discussed (and summarised in the table in Figure 1) highlight the need for more clarification and context when using the term ‘refugia’. Personally, I think this clarification is especially when we are talking about the role that these studies could have in future wildlife conservation efforts – if scientists present transparent, precise findings from the start then we might be able to avoid some of the issues like those associated with public trust and global warming science and their studies may be more likely to be used in policy decision making. Ashcroft (2010) adds that this clarification will make it easier for other scientists to assess the appropriateness of the methodologies used and to place their findings in the appropriate ecological context.