Flow regulation and drought drive riparian plant invasion

Ecologists, like epidemiologists, are often confronted with the challenge of trying to determine causality by piecing together bits of information observed in nature. When the presence or absence of a species at a site is affected by the characteristics of the environment and community, the availability and dispersal success of propagules, stochastic events and the peculiarities of the species itself, it can be very difficult to isolate the likely mechanisms that lead to the occurrence – or lack thereof – of a particular species, especially when the influential factors are highly correlated.

The joys of being in control.  (Source: thecampaignworkshop.com)

The joys of being in control.
(Source: thecampaignworkshop.com)

Experiments are obviously made for getting around such problems; by controlling and isolating one factor at a time, the relative importance of different factors can be quantified. However, experiments are not always possible, desirable or ethical. Take plant invasions along rivers, for example: they occur at large spatial and temporal scales; many factors may drive the invasion process; introducing and augmenting the supply of invasive species is unpalatable and likely prohibited; plus, river environments are very hard to control and manipulate, as any manager will tell you. So, if we are limited to potentially confounded survey data, how can we more effectively identify the drivers of plant invasion so that we know which factors to target in weed management?

In a paper recently published in Diversity and Distributions, my colleagues and I contend that incorporating data about species characteristics into survey-based approaches provides an additional line of evidence that can be used to improve inferences drawn from patterns. We illustrate how using information about environmental gradients, species distributions and species characteristics can increase understanding of ecological phenomena – here, riparian plant invasion, which can help inform management responses.

Using this approach, we find that, of four hypotheses examined, hydrological modification (indicated by flood magnitude) most likely drives invasion in River Murray wetlands. Flow regulation may inhibit native species adapted to the historical hydrological regime, facilitating exotic species with different environmental ranges. A symptom of environmental change, invasion may have been exacerbated by drought, although it is unclear why.

By hitching a ride on walkers' shoes and boots, exotic plants may even invade places like this.  Columbia River Valley, Oregon. (Source: JAC).

By hitching a ride on walkers’ boots, exotic plants may even invade places like this.
Columbia River Valley, Oregon. (Source: JAC).

There was no indication that human-increased propagule pressure or colonisation ability facilitated invasion. Exotic cover was unrelated to proximity to towns, recent flood frequency and cattle grazing intensity. Additionally, similar proportions of exotic and native species were used in cultivation and, despite a higher proportion of exotics being known weeds, weed status was unrelated to exotic species occupancy. Overall, colonisation ability was unrelated to species’ origin or response to water depth and hydrological change. Although exotics had higher specific leaf area and shorter longevity (indicative of higher colonisation ability), they had heavier (not lighter) seeds and did not differ in height from natives.

Based on our findings, we conclude that (i) using environmental flows to reinstate mid-range floods and (ii) augmenting the propagule supply of native species with characteristics suitable for modified conditions may help limit invasion in these wetlands.

For more, have a look here or drop me a line and I’ll send you a copy. I’d be delighted to hear any thoughts, comments or queries that you may have.

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A fabulous surprise! Australian Society for Limnology award

While perusing my emails recently, I had a delightful surprise: an email notifying me that I have been awarded the 2015 Australian Society for Limnology Early Career Excellence Award.

The award is given to limnologists based on the contributions they have made in the first ten years of their professional life. I am thrilled, humbled and very honoured to receive such an acknowledgment from my freshwater colleagues.

As part of the award, I will give the Christy Fellows Lecture at the joint ASL and New Zealand Freshwater Sciences Society conference in New Zealand next year. Very exciting!

Fittingly, I am currently in Minnesota - where freshwater abounds! This is one of the many beautiful wetlands at Cedar Creek Ecosystem Science Reserve.

Fittingly, I am currently in Minnesota – where freshwater abounds! This is one of the many beautiful wetlands at Cedar Creek Ecosystem Science Reserve.

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Bringing resilience back to its ecological roots

Resilience, along with its sister term, resistance, is among the first ecological concepts taught to ecology undergraduates and remains central to conceiving how ecosystems cope – or do not – with environmental change. Despite its potential importance to conservation decisions and environmental management, confusion about how to define and measure resilience has impeded its application.

In an effort to reclaim the utility of resilience, Rachel Standish (UWA), Nancy Shackelford (Victoria Uni., Canada) and I brought 20 community ecologists together with the aim of quantifying ecosystem resilience and identifying the characteristics associated with it. Using experimental data gathered from around the world, we will compare the extent and speed of recovery of different ecosystems from different types of disturbance.  In doing so, we intend to learn more about resilience and make its application to ecosystem management more feasible. More information. 

Working hard at Rottnest Island, December 2013

Working hard at Rottnest Island, CEED Workshop, December 2013

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Congratulations, Sam!

Samantha Dawson, a PhD student I’m co-supervising at UNSW, was recently awarded the fifth Peter Cullen Postgraduate Scholarship by the NSW Government.

Katrina Hodgkinson MP and Vicky Cullen present Sam with her award

Katrina Hodgkinson MP and Vicky Cullen present Sam with her award

Funded by NSW Government water agencies, the scholarship is in honour of the late Professor Peter Cullen AO FTSE, who contributed significantly to water policy and water management in Australia and NSW. Only one scholarship is awarded each year. It is worth $48,000 over three years, so will make a pretty significant contribution to Sam’s research.

The NSW Minister for Primary Industries, Katrina Hodgkinson, and Vicky Cullen presented Sam with the award last week at a ceremony at NSW Parliament House in Sydney.

Well done, Sam. A fabulous achievement that is very well deserved.

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Gauging the extent of ecosystem novelty: measuring levels of biological invasion

The Quantitative & Applied Ecology Group

By Jane Catford (This article was first published in the July 2013 issue of Decision Point, The Monthly Magazine of the Environmental Decisions Group)

It is all very well having an academic definition of novel ecosystems, but how do we identify them in practice?

In reality, ecosystems and communities are always in a state of flux—they are never stable—so there will be constant, continuous changes in species assemblages. Species will flicker in and out, and their relative abundance can be as dynamic as environmental conditions are. In Australia, with its great environmental variability, ecosystems can be very dynamic. Consequently, quantifying ecosystem novelty and determining whether a change in community composition is meaningful or not can be a little tricky.

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Where are the goal posts now? Setting environmental objectives in novel ecosystems 

The Quantitative & Applied Ecology Group

By Jane Catford (This article was first published in the July 2013 issue of Decision Point, The Monthly Magazine of the Environmental Decisions Group)

In a rapidly changing world full of strange new assemblages of species, the goal posts for conservation aren’t as clear as they once were. What is it we’re trying to conserve, and against what threat? And where do we look for guidance on how to do it when the rules appear to be changing faster than ever? Dealing with novel ecosystems in a time of accelerating change is an enormous challenge. However, two recent collaborations I’ve been involved in have come up with some helpful guidelines on how to proceed. One examines how to predict characteristics of novel ecosystems (Catford et al. 2013, discussed in this story). The other focusses on measuring levels of biological invasion as one way of gauging the extent of…

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The divine glory of our nation’s capital

It may come as a shock to some people, but I am delighted to say that Canberra is now my home.

For those who aren’t so familiar with Australian snobbery, Canberra (along with our South Australian sister, (R)Adelaide) tends to get a pretty bad rap. Boring; nothing to do; weird; where are the milk bars?!

While I nod my head appreciably at the last comment (and, dare I say, groovy wine bars?!), the first few seem to come from people who a) have never been to Canberra, b) came once during primary school to visit Parliament House or c) have very poor taste.

My response to this:

  • fast, flowing mountain bike trails winding through beautiful grassy woodland all of ten minutes from Canberra’s CBD;
  • Two hours to the coast, two hours to the mountains;
  • And then there are the after work strolls with kangaroos, kookaburras, cockatoos, wallabies, rosellas…

    What I did at the weekend: Canberra to Kosciuszko by bike. Photo by Milly Brent

Clearly, I am a “nature lover” (surprising, I know) and Canberra offers “nature” in droves. As well as being great for one’s physical and mental wellbeing, this also presents some great work opportunities as the field really isn’t that far away. To illustrate, I’ll briefly introduce a couple of the field sites where some of my colleagues in the Fenner School of Environment and Society work.

Mulligans Flat–Goorooyarroo Woodland Experiment

MulligansExperiment fig

Response variables being studied in the woodland experiment: 1 Dead wood; 2 Birds; 3 Invertebrates; 4 Vegetation; 5 Reptiles; 6 Fungi; 7 Bettong reintroduction; 8 Brown Treecreeper reintroduction; 9 Kangaroos; 10 Small mammals; 11 Litter, soil and soil microbes; 12 Exclusion of feral pests. See link to the left for source info.

Located in a couple of nature reserves 15 km north of central Canberra, the Mulligans Flat–Goorooyarroo Woodland Experiment is a partnership between the Australian National University, the ACT Government and CSIRO. The aim of the project is to find ways of improving box-gum grassy woodland for biodiversity and the experiment manipulates and monitors a whole raft of factors (see figure above).

One of the many exciting aspects of this experiment is the reintroduction of the Tasmanian Bettong (Bettongia gaimardi) – it has been extinct from the mainland of Australia for 80 years.  Regarded as an ecosystem engineer, it will be interesting to learn what effects the Bettong has on the ecosystem.

Tumut Fragmentation Study

Based in the Buccleuch State Forest 100 km west of Canberra, the idea for the Tumut Fragmentation Experiment was sparked when David Lindenmayer was flying from Canberra to Melbourne. Peering out of the plane window, David saw an area of native forest that had been cleared for a radiata pine (Pinus radiata) plantation. Rather than just bulldozing the whole lot of it though, patches of native forest had been left. Representative of the original forest, these patches varied in size from half a hectare to 200 hectares thus providing a great way to study effects of forest fragmentation on biodiversity.

The Tasmanian Bettong (Bettongia gaimardi). Photo by JJ Harrison (jjharrison@facebook.com)

The Tasmanian Bettong (Bettongia gaimardi). Photo by JJ Harrison (jjharrison@facebook.com)

In all, the Conservation and Landscape Ecology group at Fenner run seven large-scale longitudinal field studies, all located in south eastern Australia. Long-term, large-scale ecological studies are pretty rare in Australia, yet provide incredibly valuable insights because many ecological processes occur at the landscape-scale, it can take a long time for ecosystems to respond to certain actions and it can also be very hard to detect ecological responses when background levels of variability are so high (just think of weather patterns versus climate change). A major impediment to establishing long-term studies is the fact that most grants last for only a few years. While there is increasing support and appreciation of long-term studies (the merits of which are nicely illustrated by the Long Term Ecological Research Network in the US), many researchers rely on passion, strong working relationships and cheap labour (i.e. their own) to maintain such research.

I have been in the Fenner School at the Australian National University for a few months now and I am just loving it. Although I am still employed by the University of Melbourne and retain strong links with the Quantitative and Applied Ecology research group, I will be based here for the duration of my grant and hopefully, fingers crossed, beyond that.

If you are ever in town, or are keen to visit, please drop me a line. We could even go to Parliament House.

Parliament House. Source: Milly Brent

Parliament House. Source: Milly Brent

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Managing the Murray’s water to combat invasive species

An invasive exotic species, Sagittaria platyphylla, dominating a wetland in Cobrawonga, Victoria (2008)

About this time last year, I wrote an article for H2O Thinking, a water management magazine published by eWater (until recently the eWater CRC). While the turnaround time is nothing to envy, the piece found its place on the web earlier this week.

In the article, I focus on two questions that anyone* who has spent any time along a river will surely have asked:

Why are river banks, floodplains and floodplain wetlands so susceptible to alien species invasion?

And what can we do about it?

Well, I’m not going to give the game away, but lets just say that the words “flow” and “regulation” do make an appearance. Click here for more scintillating reading (?!).

A very nice wetland near Cobram, Victoria (2007)

*OK, anyone like me would surely have asked…

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Land of 10,000 Lakes

Located on the Canadian border, smack bang in the middle of the US, Minnesota is indeed a land of many lakes. While this  postcard does sell them a bit short (there are in fact about 15,000 lakes and that doesn’t include those with more pond-like dimensions), it communicates the basic facts: there are a LOT of water bodies in this part of the world. And for someone who is partial to water, that is a pretty cool thing.

As part of my DECRA research, I am spending a couple of months in Minnesota this year.  I am planning to conduct an invasion-style experiment at Cedar Creek Ecosystem Science Reserve in 2013 and 2014, so this is the essential reconnaissance trip.

So, what have I discovered so far?

1). My University of Minnesota mentor (Dave Tilman), his lab and the Dept of Ecology, Evolution and Behavior (EEB) are all tops. Widely recognized as a place of (i.e. people that do) cutting edge ecological research, it is also proving to be a really fun and dynamic place to work.

Me obscuring a beautiful Bur Oak (Quercus macrocarpa) in sand savanna. Sand savanna now only makes up 0.00005 of its former range, so this patch of habitat is pretty precious.

To illustrate: within 10 days of arriving, I have had dinner at Dave’s house with his lab group and Simon Levin (another super high-echelon ecologist visiting from Princeton), gone to an EEB summer barbeque, spent a day out at Cedar Creek and to top it off, I’ve just returned from a “lab get-away” at the Tilman family cabin that is situated on a lake (of course!) ~3 hours north of Minneapolis. A pretty good start, I would say. 

2). A staggering amount of high quality research has taken place at Cedar Creek. Owned and operated by the University of Minnesota in cooperation with the Minnesota Academy of Science, Creek Creek is a large ecological research station that is part of the Long-Term Ecological Research Network that exists in the US. Established in 1940, Cedar Creek is located in central Minnesota and contains natural habitats that represent the entire state. To cite Nee and Lawton’s (1996) Nature paper, Cedar Creek “is rapidly becoming one of ecology’s classic localities” (p. 672). Well, not wanting to assume that I am qualified to make the call, but I would say that Cedar Creek is one of ecology’s classic localities. If you’re in any doubt, then check out the publications that have been generated from work at Cedar Creek (be prepared to scroll!).

Dave Tilman chatting to some interns who are weeding a plot of the big Biodiversity Experiment at Cedar Creek

Like all things that work well, the strength of Cedar Creek comes down to its workforce. 24 Faculty members work at Cedar Creek, as well as 15 support staff, 10s of postdocs and postgrads and even more summer interns. This summer there are about 60 people working at Cedar Creek and – in two days time – I’ll be one of them. Yippee!

 

3). As an upshot of (1) and (2), some incredibly exciting opportunities are available for my research. I can take a fresh look at past experiments and surveys, tweak experiments that are already up and running and then there is the option of setting up an experiment myself. The world is most definitely my oyster – I can hardly believe my luck!

While being completely spoilt for choice is a wonderful situation to find oneself in, it does present the inevitable challenge of narrowing things down. So, in the next little while I plan to do some general reading, some Cedar Creek-themed reading, some Cedar Creek fieldwork and then a generous dose of coffee-fuelled and bike-inspired thinking. At the end of that, and the end of my two months here, I hope that some sparks will have flown, some light bulbs lit and some cool ideas arisen. Exciting times!

And now, off for a bike ride and a swim… You probably have an inkling where those activities will take place!

My ride home from work: Lake Calhourn with downtown Minneapolis in the background

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New paper: Predicting novel riparian ecosystems in a changing climate

Image

A bit of a stretch, but I couldn’t resist including this image!

I was fortunate to attend a workshop hosted by the National Climate Change Adaptation Research Facility last year that focused on riparian ecosystems under climate change. Among the various discussions at the workshop, some colleagues and I started discussing how riparian ecosystems might be affected by climate change and ways in which their abiotic and biotic characteristics are likely to change. It soon became clear that envisioning future ecosystems is no easy task, so we set about trying to come up with an approach by which to do so. 

We present our approach in a paper that has recently been published in the journal Ecosystems. Based around four recommendations, we present the approach in the first part of the paper.  We then use four case studies from contrasting environments to illustrate the approach and to determine:

–        Whether certain characteristics make some ecosystems more susceptible to climate-induced shifts in community structure than others; and

–        Which aspect of climate change seems to have the greatest effect on community structure and therefore should be a research priority.

Focusing on changes in community structure, we use qualitative process models to predict likely abiotic and biotic changes in four case study systems: tropical coastal floodplains, temperate streams, high mountain streams and urban riparian zones. We concentrate on functional groups rather than individual species and consider dispersal constraints and the capacity for genetic adaptation.  Our scenarios suggest that climatic changes will reduce indigenous diversity, facilitate non-indigenous invasion (especially C4 graminoids), increase fragmentation and result in simplified and less distinctive riparian ecosystems.

Compared to models based on biota-environment correlations, process models built on mechanistic understanding (like Bayesian belief networks) are more likely to remain valid under novel climatic conditions. We posit that predictions based on species’ functional traits will facilitate regional comparisons and can highlight effects of climate change on ecosystem structure and function. Ecosystems that have experienced similar modification to that expected under climate change (e.g. altered flow regimes of regulated rivers) can be used to help inform and evaluate predictions.

While the paper centres on Australian riparian zones experiencing climate change, the approach can be applied to ecosystems in other biomes that are subject to environmental change.

The paper is now online early; you can find the abstract and link here.

Please drop me a line if you’d like a copy.

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