Weed or feed? New pasture plants intensify invasive species risk

Pasture plants gone rogue: Phalaris is highly invasive but new varieties are still being developed

Pasture plants gone rogue: Phalaris is highly invasive but new varieties are still being developed

To meet increasing demands for livestock production, agribusinesses around the world are breeding new varieties of pasture plants. Unfortunately, many of the plant characteristics promoted for use in pasture – higher growth rates, greater resistance to disease, higher tolerance of environmental extremes and higher reproduction – are shared by invasive species. Coupled with the fact that many pasture species are already highly invasive, this effectively means that agribusiness may be inadvertently breeding “super weeds”, which farmers then spread across the landscape.

And, just to make matters worse, this increased weed threat is going largely unchecked: even countries with leading biosecurity do not consider the weed risk posed by plant varieties that are developed within-country.

But all is not lost!

As described in a new PNAS paper led by Don Driscoll, there are various ways in which this problem can be fixed.

Read more about this issue in Nature, The Conversation and ESA’s Hot Topics or see more about it in Don’s video.

Invasive Gamba grass, planted for pasture, can increase bush fire intensity five fold

Invasive Gamba grass, planted for pasture, can increase bush fire intensity five fold

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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.

OLYMPUS DIGITAL CAMERA

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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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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