It’s looking up, and then down… and then up again for trees!

In 2005 McLachlan et al published evidence that migration rates of 2 tree species at the end of the last glacial were much slower than was once thought. They concluded that the 2 tree species may only be able to migrate at a rate of 100m per year, rather than 1000m per year (which was often seen as a reason for optimism that tree species may be able to keep up with anthropogenic climate change). Their research findings prompted Pearson (2006) to consider the role that cryptic refugia might possibly play in reducing the threat of extinction posed by future climatic change.

One element of McLachlan et al (2005)’s research that Pearson (2006) focused on was the genetic evidence pointing towards the idea that re-colonisation of the 2 tree species after the last glacial was driven by ‘local dispersal from disjunct glacial refugia’ – so, more along the lines of the dispersal mechanism shown in diagram (b) in Figure 1, rather then that shown in (a).

Source: Pearson (2006)

So, even though McLachlan et al (2005)’s data predicted that the 2 tree species would only potentially be able to migrate at an order of magnitude lower than previously thought, it doesn’t mean that all hope is lost for species being able to cope with anthropogenic climate warming. If the tree species in question did in fact re-colonise from isolated refugial populations after the last glacial period then their ability to persist in low-density isolated populations for long periods of time becomes ‘of paramount importance’. It challenges the underlying assumptions of the ‘bioclimate envelope’ models that are often referred to when predicting future impacts on biodiversity as these can sometimes be too course to include microrefugial areas.

 

Although they're a few years old now, these 2 articles show us how predictions of how species may respond to climate change in the future are riddled with uncertainties. They also highlight the need for new modelling techniques that work on smaller scales, identifying finer-scale impacts than the bioclimate envelope models so as not to overlook potential refugial areas. Finally, as discoveries are made (like the cryptic northern refugium concept) about how species responded to climate in the past, they may provide us with reason to think that some of our most catastrophic projections of climate change impacts are overstated (although, this shouldn’t be taken as a optimism or a reason not to act to mitigate climate change).