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expert reaction to study looking at climate change and local plant diversity

Research, published in Current Biology, reports that faster rates of climate change could be increasing the diversity of plant species in many places.

 

Prof Peter Convey, biodiversity specialist focusing on the polar regions, British Antarctic Survey, said:

“In the southern hemisphere, the paper explicitly doesn’t include Antarctica or the remote southern ocean islands, with its limit being what is classified in the paper’s terms by the ‘polar’ part of Tierra del Fuego, but it does include the Arctic land area.  Interestingly nevertheless, the Southern Ocean or sub-Antarctic islands do provide what looks like a good example of what the study is proposing, i.e. in most cases a strong increase in species head count (alpha diversity) over the last several decades, consistent with regional warming and changing precipitation (i.e. perturbations).  In this case these changes are entirely due to human assisted introductions, which is also to a large extent the case in many of the temperate areas referred to I think in the study – for instance in the UK as I understand a large part of the ‘increased’ diversity, and diversity that is occupying new areas, derives from human introductions (and this does not deny that some native species are moving too, as predicted under climate change).

“In essence this is a paper that needs to be read very carefully, and that would be all too easy to misquote or oversimplify.  It documents nicely what it says in its abstract, that climatic/environmental perturbation can be linked with local-scale increases in diversity, at least on a temporary (and undefined) timescale, and particularly in the most rapidly changing areas and in association with increased precipitation.  It also recognises that in ‘cold’ areas that are becoming warmer and wetter, increased diversity is also expected and seen, and that this and the previous effect are not mutually exclusive.  Perhaps also importantly, it is implicitly recognised that new species arrival rates do not equate to the extinction or loss rates of previously occurring species, either immediately or on longer timescales.

“All of this is entirely reasonable, as long as the fact it is referring to in some sense ‘local’ scale is recognised.  If so, as the authors also recognise, then these observations do not contradict the more general predictions of overall loss of global biodiversity in the ‘Anthropocene’.  What the study does is add important detail and understanding as to what can happen ‘temporarily’ to biodiversity at scales smaller or much smaller than global scale.

“It is perhaps also pertinent to recognise that there are already many clear demonstrations that not all recent ‘increases’ in diversity are a good thing for biodiversity in the long term, particularly recognising that most new species arrivals are in some way human-assisted (i.e. often called aliens, introductions, etc.), and that while it is recognised that most new introductions/arrivals have fairly neutral effects (often described as persistent), a small proportion typically are capable of having much more aggressive and harmful effects and spread rapidly becoming invasive, and strongly damaging native biodiversity (which can be to the point of extinction) – many clear examples exist, but a few from UK include: American crayfish in freshwaters, Japanese knotweed on land, Dutch elm disease, ash dieback, new leaf miner moth transmitting fungal disease in horse chestnuts, certain rhododendrons species or cultivars, and so on.  One example from the sub-Antarctic islands, where for every proposed natural colonisation event in the last more than 200 years there are thought to have been over 100 human assisted events, is given by predatory carabid beetles (ground beetles), for which there is no native equivalent, and no resistance in the native invertebrate communities, so a real danger of drastic extinction in the mid to long term.”

 

Dr Ruth Mitchell, plant-soil ecologist, Ecological Sciences group, James Hutton Institute, said:

“The study shows similar results to our own work looking at long-term changes in vegetation communities in a variety of habitats across Scotland where we have also found an increase in species richness.  The key question arising from this study is which species are increasing?  An increase in species richness per se might not necessarily be a good thing.  It is often the common and generalist species that are increasing, while rarer and more specialist species, such as northern and alpine specialists are declining.  This has been called homogenization – plant communities becoming more similar to each other.  If it is the common and generalist species that are increasing there could also be an extinction debt occurring.  An extinction debt is where species go extinct from an area years after the event which caused the change.  If common and generalist species establish this might initially increase the species diversity, but over time, if these common species are more competitive due to a change in climate, the more specialist species might eventually decline.”

 

Prof Simon Lewis, Chair of Global Change Science, UCL, said:

“This study is easy to misinterpret.  Globally plant diversity is decreasing.  What is shown here is that as the climate changes some species move with the changing climatic condition.  At the local scale, if more species arrive than are lost locally, plant diversity goes up.  This is good news in the sense that some species are adapting to climate change by moving, but beneath that news lurks something much more alarming.  The species that are appearing are those that are adapted to more disturbed environments.  These are the species that were already thriving due to other direct human impacts like farming.  These relatively common species are on the march, which is not good news for rarer species because they face increased competition from the new arrivals.  If species that are unique to a region are replaced by those already living elsewhere, the seemingly paradoxical result of increasing local diversity and decreasing global diversity can be explained.”

 

Prof Katie Field, Professor of Plant-Soil Interactions, University of Leeds, said:

“By using data on plant species diversity and climate collected from more than 200 sites around the world, this research provides new insights into how climate change is affecting the diversity of plant communities at local scales.  The new research adds some much-needed local detail to a broader, global story of declining biodiversity.

“The researchers show that plant communities in the cooler regions of the world that are set to experience the most extreme and rapid changes in climate, such as the Arctic, will be the most affected, with the number of plant species within those communities increasing over time.  This effect is likely a result of previously un-inhabitable areas becoming warmer and wetter, and therefore more suitable for a broader range of plant species than they were previously.  This leads to the encroachment of “new” plant species into those habitats, thereby increasing plant species diversity at a local scale.

“On the face of it, the finding that rapid climate change is having a positive effect on plant diversity in certain areas seems like good news, but it’s really important that we don’t take this to mean that climate change isn’t having a detrimental impact on plant diversity overall.  The local increases in plant species diversity reported here are not supported at a global scale; the losses of species from some areas are not mitigated by gains elsewhere.  We also don’t know how long the reported effect of increased species diversity in areas of rapid change will last – this may well reflect a transition period for these particular habitats and so, the emerging picture over time could be actually end up being of species losses from these areas.

“It is now critical that scientists work to plug the gaps in the plant diversity data across more habitats and over longer periods of time to improve our understanding of how climate change will affect plant communities in the short- and longer term, at both local and global scales.”

 

Dr Helen Metcalfe, Ecosystems Modeller, Rothamsted Research, said:

“This study indicates that the greatest changes in alpha diversity (local species richness) are being observed in cooler regions with large changes in precipitation over recent years.  They observed significant increases in local species richness in regions that had the greatest changes in precipitation.  Nevertheless, the size of this effect due to the climate was small compared to other documented drivers of changes in biodiversity such as land use change.  The data set they used to draw these conclusions largely comprises records from Europe and the United States, where these other factors (such as land use) may be more stable than elsewhere in the world and so the conclusions drawn here should be limited to sites represented by these data.

“The authors indicate that these changes in local richness are likely due to a disparity in species range shifts: “colonists are tending to arrive faster than incumbents disappear”.  I tend to agree as species poor areas such as the polar regions, identified here as those where the largest increases in diversity are observed, will have a high capacity to increase species richness through displacement of species into these regions.  However, in the longer term the arrival of these new species may lead to ecosystem imbalance and therefore to the loss of native species.”

 

Prof Tom Oliver, Professor of Applied Ecology, University of Reading, said:

“The study found precipitation rather than temperature was more important in predicting changes in the number of plant species.  Global climate models predict regional changes in temperature well but precipitation less so, meaning for some regions there is now substantial uncertainty about how local plant species richness will change in the future.

“The paper re-analyses an existing global dataset of plant species richness in the context of the climate change experienced at each local site.  Its strength is the large number of sites covered across the globe even though, as the authors acknowledge, there is a scarcity of data from large swathes of Asia, Africa and the tropics.  The extent to which increases in plant species numbers are temporary as conditions change (i.e. new species being recruited and old species temporarily persisting) is still up for debate.  Nevertheless, the results represent an intriguing link between the rapidly change climatic conditions on our planet and the response of plant communities.”

 

Dr Rob Brooker, plant ecologist, Ecological Sciences group, James Hutton Institute, said:

“The study highlights once again the fact that we are seeing substantial and often complex responses of different aspects of biodiversity to climate change.  Although the research shows in some cases increases in biodiversity in response to climate change, it’s important to remember that some habitats of high conservation importance (for example upland and alpine habitats) are inherently low in biodiversity for some species groups, so increases in biodiversity are not necessarily good news.  The study also demonstrates the importance of understanding the responses of biodiversity to climate drivers, and we all need to recognise the need to address both the climate and biodiversity crises simultaneously.”

 

Dr Mark Lee, Researcher in the Natural Capital & Plant Health team, Royal Botanic Gardens, Kew, said:

“This study looked at the number of different plant species recorded at sites around the world and compared them with records from at least 10 years ago (average of 26 years).  The researchers found that the number of plant species increased in cold and polar regions.  Regions where the climate is changing the most rapidly.  This pattern is contrary to the declines in biodiversity which have been commonly observed around the world.

“Great care must be taken in interpreting these findings, because some might incorrectly conclude that climate change is a good thing for conservation.  However, it is likely that this pattern represents the beginnings of a transition with the warmer and wetter conditions favouring common plant species at the expense of rarer polar or tundra species.”

 

Dr Nichola Hawkins, Plant Biologist, Rothamsted Research, said:

“This study deals specifically with ‘alpha’ diversity: that is, the most localised measure, which doesn’t necessarily scale up to greater diversity overall.

“For example, there could be certain species that greatly increase their range, adding to the total number of species in any given location, but if that’s at the expense of rare, specialised or endemic species, being replaced by the same few species everywhere, then global diversity will suffer.

“In this study, the greatest increases were found in polar regions, which naturally support a lower density of species than temperate regions, so as temperatures go up, local diversity will go up but specialist cold-adapted plants may be lost.  As the authors themselves state, “It is important not to confuse this positive effect of climate change on local-scale species richness with its heightening of global extinction risk for a substantial portion of the species on our planet”.

“They report that at one third of sites, diversity actually decreased, and that more data are needed for tropical regions in order to get a more complete global picture.  They also show that climate effects need to be studied in combination with other drivers of environmental change and ecosystem disturbance.  This shows that the impacts of climate change are likely to be complex and ecosystem-specific, and highlights the importance of long-term studies over a range of spatial scales and global locations.”

 

‘Widespread effects of climate change on local plant diversity’ by Andrew J. Suggitt et al. was published in Current Biology at 16:00 UK time on Thursday 15 August 2019. 

 

Declared interests

Prof Peter Convey: “I don’t have any conflicts of interest to declare.”

Dr Ruth Mitchell: “No interests to declare.”

Prof Simon Lewis: “No conflicts of interest to declare.  But my book, The Human Planet covers this increasing local/decreasing global diversity issues, pages 166-7.”

Dr Rob Brooker: “No interests to declare.”

Dr Helen Metcalfe: “No conflicts.”

Dr Mark Lee: “No interests.”

Dr Nichola Hawkins: “No conflicts.”

None others received.

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