Species invasions and climate change: can grasslands cope?

Lizzie Jones and I contributed a chapter about grassland invasions to Grasslands and Climate Change, the latest volume of the British Ecological Society’s Ecological Reviews series. This is a blog post that Lizzie – a former MSc student of mine at Southampton – and I wrote for the Journal of Ecology blog.

Imagine a typical grassland ecosystem. You might see American prairies, rangelands of Australia, or African savannah. Either way, you’re probably thinking of wide-open spaces, dominated by resilient grass-like species. Yet, despite covering over 35% of the ice-free land surface, grasslands are an increasingly fragile ecosystem, experiencing some of the highest levels of exotic plant species invasion of all ecosystems. While there are strong links between levels of grassland invasion and human activity (as work by the Nutrient Network shows), climate change is also thought to be a key driver of such invasions.

© Getty Images

It is well established that there will be both winners and losers with climate change, where some species experience increases in range and population sizes, while other experience reductions. A key prediction nevertheless remains that exotic species invasion will increase with climate change, especially with rises in temperature and increases in extreme climatic events. Given that – like native species – individual exotic species can be helped or hindered by climate change, why does this remain a general prediction? It makes sense that some species will benefit from changes in climate regimes, and others will not, but why should some species experience an advantage simply because they are non-native?

In our chapter of Grasslands and Climate Change, we address these questions by concentrating on the effects of climate change on exotic plant invasion in global grasslands. We specifically ask whether climate change will favour exotic species, why that might be the case, and what sort of species (including their functional traits) will be favoured. In the chapter we used a systematic approach to review three key environmental changes that may give advantage to invasive species: changes in background climate conditions including temperature and rainfall; increased disturbance from extreme events such as storms and droughts; and human responses to climate change, either to mitigate its effects or to adapt to them.

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A warming and biodiversity grassland experiment at Cedar Creek Ecosystem Science Reserve: experiments like these provide insights into the impact of climate change, including species invasions. Photo by Jacob Miller.

Exotic species are well-adapted to capitalise upon change – their very invasion shows that that they are able to expand their distributions and deal with what might be unfamiliar ecological conditions. Increases in the frequency and magnitude of storm events, floods, fires and other disturbances will increase opportunities for invasion, and species that can reproduce and spread quickly will be particularly well placed. For example, some Bromus grasses can recover very rapidly when drought eases, which has allowed them to invade and convert woody scrubland areas in North America. The ability to seize opportunities and cope with a broad range of environmental conditions means that climate change will favour many exotic species – especially compared with native species, which may be less able to keep pace with changing conditions.

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Finally, humans have a huge impact on grassland invasion. In our efforts to mitigate, offset and adapt to our changing climate, we are unwittingly exacerbating the invasion of exotic species globally. A key culprit is the production of biofuel, such as Miscanthus species, now widely used in North America and Asia and predicted to spread with climate change.

So, to respond to the question “can grasslands cope with species invasions and climate change?” – native grassland species are certainly under threat not only by exotic species but by a multitude of human and climate-related issues. But, as this book shows, work towards adapting current conservation and management strategies is already underway to keep pace with our changing climate, not only in grasslands but in all other ecosystem types.

Lizzie P. Jones (Royal Holloway, University of London and Institute of Zoology, London, UK) and Jane A. Catford (King’s College, London, UK)


Grasslands and Climate Change is part of the Ecological Reviews series. BES members get 25% off all titles in the series when buying directly from Cambridge University Press. See also, David Gibson’s blog post: Grasslands and Climate Change.

Sunshine and visitors

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Esti, Luis and Alan make the most of the sunshine at New Forest NP

Long days, warm weather, dry roads and visitors. I love summer!

Esti Palma from the University of Melbourne and Dr Luis Mata from RMIT University (and, the all-important, Alan Mata) came to visit for a couple of weeks recently. They both gave excellent talks to our ecology group in Biological Sciences.

Luis spoke about “The Little Things That Run the City”, drawing on the pioneering work in Melbourne where Luis and other folk from RMIT are joining forces with Melbourne City Council to bring biodiversity into the city – and to make people aware of, and value, it. They’ve produced a beautiful children’s book as part of this work. I’m looking forward to seeing the other things that this innovative and productive group produce.

Esti focused on her invasive species traits work where she is using 80 plant species to test whether it is more informative to separate invasive species into different “types” based on their dimension of invasiveness, or whether it doesn’t matter if all species are lumped into one category. Early results seem to point to the former – but watch this space!

Esti also spoke briefly about her work that shows trait-based trends in the types of species that are being both lost from and gained in cities. As a bit of extra excitement, Esti’s paper featured on the cover of Ecography.  

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John and fellow Southamptonite, Bjorn Robroek, enjoying a cleansing ale after a walk along the River Itchen (we did talk ecology, promise!).

While talking about sunny visitors, it would be remiss of me not to mention Dr John Dwyer from the University of Queensland who stopped to say hello in June.

John also educated us with a talk, this time on how trait covariance can help us understand biodiversity trends along environmental gradients. Some really lovely work by John and Daniel Laughlin.

 

How plant traits determine where native and alien species occur along rivers

Ever wondered why there are so many plant species – and so much weed invasion – along rivers?

At first glance, one might attribute this to the lush conditions of riparian ecosystems: lots of nutrients + loads of water = ideal conditions for plants. This coupled with the fact that riparian systems are on the interface of aquatic and terrestrial ecosystems, so are home to a rich mix of wet- and dry-loving species? Makes sense.

 I have much respect for this tree!
Balancing on a rock can’t be easy. I have much respect for this Mekong River tree!
(Source: JAC)

However, when you really think about the conditions of riparian ecosystems – physical disturbance from floods, inundation and desiccation, ice scour in cold places – then they perhaps don’t seem quite so hospitable. Like rocky intertidal platforms, presumably the species that live in riparian zones need to have some pretty specialised adaptations to be able to cope.

In a recently published Tansley Review in New Phytologist, Roland Jansson and I focus on the key structuring forces of riparian zones, plant ecophysiological traits and mechanisms of species coexistence to resolve the apparent conundrum between the high floristic diversity of riparian ecosystems and their challenging environmental conditions.

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Would you drop your offspring in there?
(Source: JAC)

We describe 35 traits that enable plants to cope with riparian conditions. These include traits for tolerating or avoiding anoxia and enabling underwater photosynthesis, traits that confer resistance and resilience to hydraulic disturbance, and attributes that facilitate dispersal, such as floating propagules. This diversity of life-history strategies illustrates that there are many ways of sustaining life in riparian zones, which helps to explain high riparian biodiversity.

Using community assembly theory, we examine how adaptations to inundation, disturbance and dispersal shape plant community composition along key environmental gradients, and how human actions have modified communities. Dispersal-related processes seem to explain many patterns, highlighting the influence of regional processes on local species assemblages.

Treating alien plant invasions like an (uncontrolled) experiment in community assembly, we use an Australian and a global dataset to examine possible causes of high degrees of riparian invasion. We found that high proportions of alien species in the regional species pools have invaded riparian zones, despite not being riparian specialists, and that riparian invaders disperse in more ways, including by water and humans, than species invading other ecosystems.

You can find the paper details here and a free pdf copy here.

Please get in touch if you have any comments or questions – I’d love to hear them.

How do riparian plants even begin to survive a nordic winter?  Read our paper to find out!
How do riparian plants even begin to survive a nordic winter?!
Read our paper to find out!
(Source: Johanna Engström)

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