Our research focuses on the population dynamics of plants and how they are influenced by impacts of natural disturbances and global environmental change. We are particularly interested in the interactive effects of fire, grazing and drought in grasslands and woodlands in southern Australia, and how climate change, fragmentation and shrub encroachment affect ecosystems.

Wednesday, 20 November 2013

What constitutes a 'substantial' contribution to ecological science?

Good dress sense only gets
 you so far in science!
I've been musing about how one decides whether they've made  a contribution to ecological science. This thought process arose because I was asked the other day, for an educational video being developed for high school students: "what is your most important contribution to plant ecology?" Wow! Condense 20 years of work down to one key finding or breakthrough. No pressure!

I'm not bold enough to nominate what that contribution might be (others can do that), although I do suspect that rather than one key contribution, my work probably needs to be seen as a series of inter-related studies that have enhanced ecological understanding of herbaceous ecosystems at a range of spatial and temporal scales. I've been interested in population processes, competitive interactions, species coexistence concepts, outcomes of disturbance regimes such as fire and, more recently, controls on species distributions and how plant traits help us both understand and predict vegetation responses. But how does this contribute to ecological science.

There are many ways one could assess this.

Are my scientific papers being read and cited. The short answer is "yes". This is good for ones ego. But it also says the work you do - be that the hypotheses you're testing, the experiments you're conducting, or the conclusions you are drawing - are legitimate in the eyes of your peers. This is a pretty crucial starting point for making a contribution to the discipline.

Am I getting asked to collaborate with others. Thankfully, "yes". Some of the most interesting work that I've contributed to recently has been as part of Working Groups that come together to develop new ideas on a current topic, or to analyse big datasets in meta-analyses such as the one I was recently involved in with Margie Mayfield (UQ) and others. I'm also a network contributor to projects such as the global NutNet project. This, I'm really pleased to say, has been a real eye opener about collaboration and excellent science. I think we will leave some really important legacies from such work.

Is my work (which is primarily of an applied nature, but based on sound ecological theory) being adopted by managers. The short answer is "yes". Recently it has been very satisfying to find that grassland managers around Melbourne have been trying to implement many of the recommendations my research has made over the years. This includes implementing fire regimes to advantage preservation of grassland vigour and diversity, a challenging task in urban environments.

But I think the real acid test of how your work is perceived really plays out in a wider forum. Much of my work probably hasn't had such an impact at this level (although I've got time to remedy this). But real, long-lasting contributions play out when you speak to the core of the discipline. This is hard (impossible) for most of us, but that should not stop us from thinking about making these types of contributions. 

The debates that have persisted over 20-30 years now about how plant communities are structured in calcareous pasture (Phil Grime's study system in England) versus the Minnesota sand plain (where Dave Tilman has worked most of his life) have had a profound impact on me as a plant ecologist. And probably shaped the type of ecology I do. No. They have shaped my ecology. Why? Because at their heart, both ecologists (with very different views of the world) have made me think. How do these divergent ideas apply to grasslands in Australia? Do I understand their core concepts? Why do I find such work fascinating? How is this relevant to management? How do I make managers / Post-Grads/ under-grads appreciate such theory?

In many respects, these ecologists from half way around the world epitomize what it means to have a career that matters ‐ both have forced others to have an opinion about their work, to take a side, to test claims with their own experiments and decide for themselves whether the world is structured according to resource ratios and local niches (Tilman) or CSR theory and infrequent disturbance (Grime).

The lesson to young ecologists is both inspiring and clear: at the end of the day, have you stuck your neck out enough? Both careers have involved a series of (sometimes heated) debates. At their core,  however, both ecologists - whose work is steeped in theory - have made important observations about, and given importance guidance to,  the field of environmental sustainability. Indeed, as others better versed in such matters have stated, "Dave Tilman has brought what were once academic disagreements into the forefront of the modern environmental movement. I can think of no higher achievement for an ecologist in our era."

Monday, 18 November 2013

Kangaroo Grass; Rooigrass; Red Grass

Kangaroo Grass, Wonangatta Valley, Victoria

One of my favourite plants of grasslands in southern Australia is the dominant grass Themeda triandra. So much of grassland ecology revolves around the species: competition, gaps, nutrient cycling, fire, litter, habitat. And I'm intrigued by its capacity to be so adaptable. In Victoria alone you can find it growing in dune swales at Wilsons Promontory, in subalpine plains near Mt Hotham at about 1350 m and in vegetation verging on mallee at 400 mm near Quambatook.

Two new reviews on Themeda triandra have been published in the last year and I thought I'd bring them to your attention. They focus primarily on distribution, cytology, germination biology, forage quality, fire response and ecosystem processes. I've include the Abstracts below in case you want to chase them up.

Some things you may not know about Themeda triandra:
  • The species is found in all states of Australia, South Africa, Indonesia, New Guinea, Japan, India, Saudi Arabia, southern Turkey and Mongolia! It's also become naturalised in New Zealand.
  • In Australia, there are two main genetic races - the diploids that occur south and east of the Great Divide (i.e. coastal populations), and tetraploids that occur in drier, inland areas.
  • The species probably evolved in tropical Asia and migrated down the east coast of Australia (although there is a crazy hypothesis that suggests that Themeda colonised Australia via the importation of camels from Asia and Africa in the 19th century!!)
  • there have been no crossing trials between South African and Australian populations to see if they can breed.
  • it is an important forage species in Africa for impala, antelope, wildebeest, zebra and buffalo.
  • Themeda can decline in the absence of disturbance because tillers are shade-intolerant, and flowering culms are rarely produced on plants that are moribund.
  • up to 94% of seed falls within 50 cm of maternal plants.
  • Almost without exception, sheep have been shown to negatively impact Themeda.

Dell'Acqua et al. (2012) A tropical grass resource for pasture improvement and landscape management: Themeda triandra Forssk. Grass and Forage Science 68, 205-215.

Themeda triandra Forssk. is one of the most widespread grasses in the dry to mesic prairie ecosystems of Africa, Asia and Australia. It is of particular interest due to its high value as a forage species for wildlife and livestock, and its potential use in landscaping practices. In this review we have collated information from the many studies that have been devoted to this species since the 1960s to provide information about the species’ distribution, taxonomy, morphology, ploidy and reproduction, and to describe its vegetation and germination and their relationship with the most important ecological aspects of its preferred habitats. Agronomic aspects are considered in detail, with particular focus on the role of T. triandra as a forage species and the relative importance of grazing, fire and rainfall regimes for its management. We also explore how this species can help with the rehabilitation of degraded areas, soil and water conservation, countering exotic species invasion and landscaping in general. We conclude with a brief discussion of the as yet unresolved taxonomic relationship between the African species T. triandra and the Australian species Themeda australis.

Snyman et al. (2013) Themeda triandra: a keystone grass species. African Journal of Range and Forage Science 1-27.

Themeda triandra is a perennial tussock grass endemic to Africa, Australia and Asia. Within these regions it is found across a broad range of climates, geological substrates and ecosystems. Because it is widespread across these areas it has great economic and ecological value, as it is a relatively palatable species across most of its range. It is of critical importance in supporting local populations of both native and introduced herbivores, and is thus central to wildlife and livestock production, and consequently rural livelihoods. It is an important climax or subclimax species that is well adapted to fire, a common element in many areas where it is found. Inappropriate grazing management, however, can result in a decline of Themeda, as it is not well adapted to an uninterrupted, selective grazing regime. A decline in abundance of Themeda in a grassland is usually coupled to a decline in grazing value, species richness, cover and ecosystem function. In spite of its significant ecological and economic importance, there has been no attempt to review and synthesise the considerable body of research undertaken on this grass. Our aim is to summarise and synthesis work previously undertaken and identify areas where further research is required.



Friday, 8 November 2013

Signs of Life: Part 2

The seeds I found hidden away
after 25 years of storage.
A few months ago, I posted a Blog on Signs of Life. This was about some seed I'd discovered, hidden away in a cold room, that had been stored at about 2 degree Celsius in the dark. Seeds that were in sealed containers that dated back to the mid-1980s.

And these weren't just any seeds. These were seeds of native grassland plants that we know have now been lost from some of the sites where they had been collected from. A good example was some glass jars that had somewhere between 5000 and 10000 seeds of the Button Wrinklewort from a population on a railway line near Melbourne (called 'Manor'). We know that this population has now disappeared despite the fact that the population numbered more than 300 plants just two decades ago. There were other rare plants such as the Large-fruited Groundsel (Senecio macrocarpus) and orchids such as the White Diuris (Diuris fragrantissima) that have been lost from the wild populations from where they were collected.

So this was rather exciting. Here were seeds of populations of plants now extinct at those locations and hence, potentially an opportunity to restore those plants (and maintain the genetic diversity as well).

Of course, we don't know much about seed longevity, so I was unsure whether these seeds had remained viable.

So we took the seeds, and my trusty research assistant Karina Salmon and I tried to germinate them under controlled conditions in the growth cabinet. We placed them on wetted filter paper in petri dishes, at 20 degrees Celsius, a condition known to germinate many of these species without any pre-treatment. There were lots of species, and lots of populations. We focused on all the non-orchid populations. After a month, we scored the seeds for germination. Previous work of mine says that many grassland species should have germinated by then.

Unfortunately, almost all of the species and all of the populations failed to germinate.

Of the 21 species we sowed (encompassing over 35 populations), only three species germinated (see the list below for those species that did germinate, and those that did not). Of those that didn't germinate, a squeeze test at the end of the experiment confirmed there was no live embryo.

Frankly, this was a huge disappointment.

An example of a grassland "tuber bank" - this is the
enormous root storage structure of Featherheads
(Ptilotus macrocephaalus)
All the daisies did not germinate, and these made up the majority of the collection. This was perhaps not surprising. In the grassland flora near Melbourne, much of the annual regeneration comes from a 'bud and tuber' bank, not a soil seed bank. Ecological work by Ian Lunt (who did some neat seed burial experiments), Andrew Scott and others tells us that many seeds are short-lived in the soil - this is termed a "transient soil seed bank".

Under storage conditions, we might expect persistence to be longer. There are no soil organisms devouring seeds, seeds are not germinating, nor is rotting an issue.  But inherent survival clearly did not extend to two and a half decades of storage.

So where does this leave us?

To me, it suggests a few things. If you are going to collect seed from wild populations, you should use it! Storing it in a paper bag in the back of a cupboard, to be forgotten about, is wasteful. You may as well be collecting the seed and putting it in the bin. This type of data tells us  that many seeds are not viable for the long-term under the conditions many of us would store such seeds. Hence, we lose the opportunity to maintain genetic diversity from small, compromised populations. Projects such as the Millenium Seedbank have much more advanced seed storage techniques that may keep seeds alive for decades - and will be crucial for protecting many threatened species - but most of us work at very local scales and on short-time frames with far less sophisticated storage facilities.

This study provides us with a bit of a reality check. Averting extinction is not just about saving seeds in seed banks. It's also about saving the plants in the wild. My discovery of seeds in jars, while the source populations went extinct, highlights just this point. No matter how well meaning seed collection and storage is, if there is never any intention of using that seed and returning plants to the wild, we are (perhaps) exacerbating small population decline. Populations size is one of the best ways to estimate extinction risk - so any intervention (such as seed collection) that affects long-term population size, must have a sound rationale for its practice.

Below is a list of species that did  and did not germinate in our study. Remember, most seed here was collected between 1984 and 1987. It remains unclear just how long seed of herbaceous grassland species can be stored, but my guess would be that its is years rather than decades.

Species that did germinate after >25 years storage: Ptilotus spathulatus; Glycine tabicina; Rytidosperma laevis

Species that did not germinate after >25 yrs storage: Arthropodium strictum, Caesia calliantha, Chrysocephalum apiculatum, Chrysocephalum semipapposum, Cynoglossum suaveolons, Elymus scaber, Lepidium aschesonii, Lepidium hyssopifolium, Leucochrysum albicans var. tricolor, Microseris lanceoloata, Minuria leptophylla, Plantago gaudichaudii, Podolepis jaceoides, Rutidosis leptorrhychoides, Senecio macrocarpus, Senecio quadridentatus, Velleia paradoxa, Vittadinia cuneata