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.

Monday, 25 July 2011

Monodominance in C4 grasslands

A typical view in southern Australia. Here,
Kangaroo Grass dominates the structure
and cover of a native grassland.
(Photo: John Morgan)
One of the things that strikes you about the C4 grasslands in southern Australia is the complete dominance by Kangaroo Grass (Themeda triandra). The concept of monodominance is actully rather rare in grasslands. Only a minority of the world's grasses (around 600 out of 11,00 speces) are documented as being ecologically dominant. These dominant species, however, seem to share a common(ish) evolutionary history.

In an interesting paper on the origins of C4 grasslands by Erika Edwards and collegues, dominant grasses appear to be phylogenetically clustered, suggesting that certain clades of grasses are more prone than others to evolve traits that promote ecological dominance. But what might these traits be?

The answer to this question is not as straightforward as we might presume. While we accept the fact that Kangaroo Grass dominates the grasslands of southern Australia, there is still some uncertainty about why it does so. There's likely to be a few reasons. Some of them are evolutionary, while others are more ecological. Here, I outline a couple that I think are likely to be important.

Kangaroo Grass is a C4 species. "C4 photosynthesis" refers to a suite of biochemical and anatomical traits that increase photosynthetic efficiency in high light and high temperature environments. While C4 enhances the efficiency of photosynthesis, C4 plants only have an advantage over C3 plants in certain conditions - namely, high temperatures and low rainfall. Hence, C4 grasses are conspicuously absent from the world's cooler regions. This may, in part, explain the dominance of C4 grasses such as Kangaroo Grass in southern Australia.

Kangaroo Grass, in Grime's CSR plant strategy scheme, would comfortably be considered a competitive species. Such species are able to outcompete other plants by most efficiently tapping into available resources. Competitors do this through a combination of favorable characteristics, including rapid growth rate, high productivity (growth in height, lateral spread, and root mass), and high capacity for phenotypic plasticity. This last feature allows competitors to be highly flexible in morphology and adjust the allocation of resources throughout the various parts of the plant as needed over the course of the growing season.

Kangaroo Grass might be thought of as a pyrogladiator. It is fire-adapted, resprouting strongly from basal meristems with very little fire-induced mortality. By contrast, our Lab has shown that C3 grasses, such as Wallaby Grass and Spear Grass, can experience substantial levels of tussock mortality after fire (perhaps because of the fire event itself), further weakening their position in C4-dominated grasslands. Kangaroo Grass, by contrast, quickly accummulates biomass between fires, probably because the C4 pathway supports high photosynthetic rates and nitrogen use efficiencies, especially in the high-light environments after fire. The high water-use efficiency afforded by C4 metabolism probably also provides a competitive edge.
Beth Forrestel, from Yale University, admires
a C4-dominated grassland at Vite Vite on the
western plains of Victoria.  (Photo: John Morgan)

The concept of monodominance is not just of academic interest.

Dominant species shape communities and drive ecosystem processes. Our research has shown that healthy swards resist weed invasion. Hence, they should also be of key interest to restoration ecologists wanting to restore resilient ecosystems (see my last Blog as an example of this). Finding ways of returning dominant species (across large scales) might therefore be just as important as returning rare species to ecosystems.

And understanding how dominant species respond to climate change is a challenge we are only just starting to tackle.

Thursday, 7 July 2011

Grassy White Box Woodland Restoration

Native grasslands and woodlands in Australia have been transformed since European settlement. Because they occur on the fertile soils (by Australian standards), and are dominated by palatable grasses, they were amongst the first ecosystems settled, and amongst the most intensively utilised. As a result, much of the original ecosystem has been lost - to cropping, to grazing, and to pasture improvement. Probably less than 15% of woodlands remain in eastern Australia, and grasslands occupy much less than 5% of their original range.

White Box woodland in a bush cemetery
(Photo: S. Prober)
But some remnants do survive - in areas that have escaped heavy utilisation such as bush cemeteries, travelling stock routes, town commons and railway lines. And they survive in relatively weed-free states with high native plant diversity. They provide a key insight into how degraded remnants might be restored.

Ian Lunt from Charles Sturt University and Suzanne Prober from CSIRO have been working for a long time now on the conservation and restoration of white box woodlands in southern Australia. Given the perilous state of these systems, their scientific studies are at the cutting edge of practical conservation biology.

They have looked at why small remnants have maintained their diversity - and come to the conclusion that soil nutrients plays a key role. Where nutrients are high, exotic plants are favoured and these tend to outcompete the small native species that have evolved to survive on scant resources. Where nutrients are low, native species thrive because the exotic species basically have too few resources to survive.

Soil nutrients increase for a couple of reasons - the most obvious one is that they are applied by farmers to increase productivity. Less well known, however, is that when deep-rooted, long-lived perennial native grasses such as Kangaroo Grass are lost from ecosystems, lots of nutrients (including nitrate) are released into the soil and the elevated levels favour annual grasses. Annual grasses, of course, are short-lived - so they use soil nitrate to grow and flower, but because they die each year, that nitrate gets released back into the soil to be used again in the following year by even more annuals. And so the cycle continues.

Therefore, the groundlayer of grazed and degraded remnants rarely recovers well after fencing and livestock exclusion because these sites often have high soil nitrate levels that favour the exotics. So, how to overcome this problem.

Ian and Suzanne have found that it is absolutely imperative that soil nutrients be reduced if native species are to be re-established, but this is easier said than done. Indeed, until their work begun, few conservation biologists had really thought about this problem in Australia. They have trialled a number of techniques in small experimental plots - well replicated of course! Their treatments included i) re-establishing deep-rooted perennial native grasses (to lock up nutrients), ii) burning (this leads to some loss of nitrogen in smoke), and iii) adding sugar (to reduce nitrogen availablility due to microbial activity).

The results have been nothing short of stunning, and give hope that grassy woodlands and grasslands can be restored. It's an example of how really good science can inform practical conservation outcomes. Their work has just featured on the ABC's science program Catalyst - which I've included here so you can see what this long-term study has been able to achieve.

                     video

Tuesday, 5 July 2011

2010 ISI Impact Factors are now out

You can't ignore the fact that Impact Factors have had a huge effect on publishing trends and the choices authors make about where to publish. This is somewaht unfortunate - I now hear scientists talking in the corridors of universities, or worse, at conferences, about where they published their most recent paper, not what they are publishing on!

Regardless of how much weight you put on Impact Factors (see this damning review as evidence that some don't rate IFs at all), all new PhD students and Post-Docs have to play a game of publishing in (perceived) high impact journals if they are to get that next job.

So what are Impact Factors and how are they calculated?

In a given year, the impact factor of a journal is the average number of citations received per paper published in that journal during the two preceding years. For example, if a journal has an impact factor of 3 in 2009, then its papers published in 2007 and 2008 received 3 citations each on average. The 2009 impact factor of a journal would be calculated as follows:
A = the number of times articles published in 2007 and 2008 were cited by indexed journals during 2009
B = the total number of "citable items" published by that journal in 2007 and 2008. ("Citable items" are research papers; not editorials, book reviews or Letters-to-the-Editor)
2009 impact factor = A/B.
I've included the 2010 Impact Factors for journals in conservation and plant ecology (and compared their "performance" to their 2009 rating). The big winners were Ecology Letters, Trends in Ecology and Evolution and Frontiers in Ecology and the Environment. Interestingly, the IFs of most journals rose over the last year.

Applied Vegetation Science: 1.802 (2010) versus 1.349 (2009)
Austral Ecology: 1.820 versus 1.578
Australian Journal of Botany: 1.681 versus 1.868
Biodiversity and Conservation: 2.146 versus 2.066
Biological Conservation: 3.498 versus 3.167
Conservation Biology: 4.894 versus 4.666
Diversity and Distributions: 4.248 versus 4.224
Ecography: 4.417 versus 4.385
Ecological Applications: 4.276 versus 3.672
Ecology: 5.073 versus 4.411
Ecology Letters: 15.253 versus 10.318
Frontiers in Ecology and Environment: 8.820 versus 6.922
Functional Ecology: 4.645 versus 4.546
Global Change Biology: 6.346 versus 5.561
Global Ecology and Biogeography: 5.273 versus 5.913
Journal of Applied Ecology: 4.970 versus 4.197
Journal of Biogeography: 4.273 versus 4.087
Journal of Vegetation Science: 2.457 versus 2.376
Molecular Ecology: 6.457 versus 5.96
Nature: 36.101 versus 34.480
Oecologia: 3.517 versus 3.192
PNAS: 9.771 versus 9.432
Polar Biology: 1.445 versus 0.582
Science: 31.364 versus 29.747
Trends in Ecology and Evolution: 14.448 versus 11.564