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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