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The picture has no real significance, just a nice photo of Bodmin Moor to brighten up this post!

As with many scientific publications, Kelly et al (2009)’s article prompted some comments from another scientist. Scourse (2010) points out that whilst Kelly et al (2009)’s data do not contradict the cryptic Northern refugia hypothesis in any way, they can be explained by an alternative hypothesis. The bottom line of their argument is that without plant macrofossil data, their pollen data alone does not provide strong enough evidence for the persistence of temperate tree taxa in refugia at Bodmin Moor during the LGM. Scourse (2010) acknowledges the fact that, together, studies based on pollen analysis do tend to support the cryptic Northern refugia hypothesis, but then goes on to state that, alone, their support of this hypothesis is ‘merely circumstantial’, with the authors jumping to ‘premature’ conclusions. Scourse (2010) highlights the role that long-distance dispersal of pollen may have had on the data and questions the inclusion of extremely low pollen counts for certain taxa, stating ‘pollen can be found in any sediment if one really looks hard enough’. It would have been better if Kelly et al (2009) had presented a pollen concentration diagram instead of a pollen percentage diagram. Scourse’s (2010) second point is to do with the origin of the sediment in the Bodmin Moor core, which he suggests is the result of ‘soliflual and aeolian sedimentation’. If the sediments containing the pollen did not originate in the area then this has implication for the origin of the pollen itself. Scourse (2010), therefore, notes that more information about the origin of the sediments is needed before conclusions can be made.

All of these points are continuous with the ambiguity of studies focusing solely on the analysis of pollen data. Scourse (2010) suggests that long-distance travel and the possible reworking of earlier sediments containing tree pollen is a more likely explanation for the data than the cryptic Northern refugial hypothesis. If accurately-dated plant macrofossil evidence was found in the area then the case for the existence of glacial refugia in Bodmin Moor would be much stronger.

Kelly et al (2010) respond by highlighting the use of ‘possible’ in their title to describe the proposed cryptic Northern refugial site, acknowledging the uncertainty of their data. They defended their decision to include such low pollen concentrations as they were ‘sufficient in volume to allow counts of <300 total land pollen (TLP) per sample in most cases’. Furthermore, based on the pollen rain percentage data from high-latitude regions, they do not see how it is possible to show conclusively that long-distance transport of pollen is the only explanation for their data. They also present evidence for reworking of sediments not being the case. Kelley et al (2010) then go on to defend their choice of pollen analysis as the tool on which to base their study, urging the reader to look back at the range of other palaecological evidence and the results of climate modelling that also point to the existence of cryptic Northern refugia. They emphasise that the cryptic Northern refugia hypothesis is just one of several that can be used to explain their data and that it shouldn’t be rejected just because other explanations seem plausible as well.

I don’t think we should discount pollen analysis all together as a technique for producing evidence in favour of the cryptic Northern refugia hypothesis, especially if numerous studies reach corresponding conclusions, but the weaknesses and limitations of using pollen data alone must be taken into consideration.