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.

Thursday, 30 May 2013

Signs of life???????

I'm not one for holding on to old 'stuff'. Spring cleaning is my thing.

But in science, it pays to never throw things out.

Old data might be useful at some stage in the future. I have learnt this the hard way.

I'm still doing point quadrats. And yes, this data is being used!
I once collected four years of point quadrat data (at 3 month intervals) to assess growth cycles of grasses and forbs in grasslands. I never used the data, let alone even crunched it into a nice graph. I decided to toss out the original data sheets not more than a year ago. What was I going to do with all this hard copy?

Turns out that I REALLY need this sort of data now - there is very little data in grasslands about timing of growth of C3 grasses, forbs and C4 grasses. Indeed, for grasslands near Melbourne, the only data I can find comes from Richard Groves who assessed biomass changes across a couple of seasons in 1965!!

Just the other day I was ferreting around in my cold room at Uni. In the back corner is a cupboard. Hmm, I wonder what's in there. I don't think I've ever looked. My cold room is set at 2 deg C, and is dark. Why would I go into the back corner and see what is shoved into a small, innocuous cupboard?

To my amazement, and surprise, were two cardboard boxes. And they were full of little glass jars. Full of seeds. Written neatly on labels placed in the jars were little jems.
'Rutidosis leptorrhynchoides, Manor Railway Reserve, 6th January 1986, DaT'
'Senecio macrocarpus, Bannockburn Railway Reserve, 5th October 1985, NHS'
'Diuris punctata var. albo-violacea, Tottenham, 4th November, 1986, DaT'
This won't mean much to many of you. But to me, this was like finding $100 in the pocket of a jacket you haven't worn for ages.
Airtight jar full of seeds of an endangered grassland plant.
Here, seeds of Senecio squarrosus, collected from
Rokewood Cemetery in 1987 by Neville Scarlett. This
population no longer exists in the wild.
Seeds of Senecio macrocarpus after 25 yrs of storage - they look OK.
These are seeds of highly endangered grassland plants that have been stored away, un-noticed, for 25 years. That alone is remarkable. But perhaps more telling is what has happened in the intervening 25 years.
The Rutidosis population at the Manor Railway Reserve, from direct counts, was about 330 plants in 1984. Today, no plants exist. A lack of frequent fire for the last 20 yrs saw the population decline rapidly in the 2000s. Like many small populations, conservation action began too late to arrest the decline.
But I have several glass jars full of seeds from this population. These may be the remaining genetic material of the species from that area.
In many respects, these airtight containers, stored in the dark at low temperatures, might be seen as a precursor to the modern seed storage facilities (or 'seed banking' as Kew Gardens in the UK calls it). But, of course, the seeds were collected and stored long before protocols for such activities were developed.
I'm sure there are many people, however, who have collected seeds from their local remnant and placed them in a paper bag and stored them in a dry spot. Is this a valuable thing to do? Or should we really collect seed and then ensure it is propagated/sown so that we don't lose that propagule forever?
Despite my delight at finding these seeds, I'm not hopeful many will germinate. The basic seed biology of Rutidosis hints that long-term storage of seed may not be a particularly viable option. In the wild, Rutidosis has a transient soil seed bank, and seed germinates rapidly upon wetting. From seed burial experiments I did in my Honours year, I know that seeds are lucky to persist in the soil for more than 5-6 months. They are not 'wired' like Cyperaceae, Acacia and Juncaceae for long-term soil persistence. Nor are Senecio.
But I will try and germinate them nonetheless. To learn about long-term seed viability. And to try and recover a locally extinct population of a species now on the brink of extinction in the Melbourne area. I'll give you an update in a few months about the species whose little seeds have persisted through time and, just as importantly, those that haven't.

Saturday, 25 May 2013

Obvious effects of drought in Australian alpine vegetation

When thinking about climate change impacts in alpine ecosystems, rising temperatures are thought to be one of the most important threats to their long-term persistence, particularly in places like Australia where there is very little elevation above treeline. It is generally accepted, and has even been demonstrated, that alpine species will need to migrate upslope to persist with climate warming. This hints that temperature is the most important determinant of alpine species distribution.
The Australian Alps - vulnerable to climate change because there is very
little capacity for upslope migration

But climate change is also likely to affect the frequency, intensity and amount of rainfall that occurs. And in Australian mountains that experience summer drought, the impacts of increasing drought severity and frequency are likely to also be very important to the persistence of alpine plants.

To illustrate this, I have shot a 11 min video about the drought impacts I observed recently in some Australian mountains. Interestingly, Mt Feathertop (which I point out in the video) was burning in a bushfire only 10 days after I shot this footage, hinting that drought also interacts strongly with fire in Australian mountains.

You can find my video on You Tube at

I focus on why I think drought is important in the Australian alps:
  • because our mountains are covered in soil, vegetation grows across the entire mountain and therefore, is subject to water stress on shallow soils when there are dry spells
  • how aspect affects moisture stress (remember, in the southern hemisphere, northerly aspects are the hot, dry slopes)
  • show examples of some species showing signs of drought stress (note the effects on the dominant grass Poa hothamensis)
  • think about the traits that may pre-dispose species to drought stress, and;
  • conclude with the assertion that drought likely will be an important determinant of vegetation distribution in the coming century in mountains. This will likely be exaccerbated by rising temperatures.

Hope you enjoy my foray into 'film' making.

Further reading on drought impacts in Australian alpine vegetation:
  • Griffin & Hoffmann (2012) Mortality of Australian alpine grasses (Poa spp.) after drought: species differences and ecological paterns. Journal of Plant Ecology 5: 121-133.   
  • Morgan (2004) Drought-related dieback in four subalpine shrub species, Bogong High Plains, Victoria. Cunninghamia 8: 326-330.

Monday, 20 May 2013

Below-ground ecology often gets ignored

One way a plant species will deal with the challenge of a changing climate is to track shifts in their climate envelope by dispersal and establishment in new locations that are climatically suitable for that species. Whilst this seems an obvious mechanism to deal with climate change, it fails to account for the fact that plants might be 'migrating' to very different soil types, and these soil types might be unsuitable for their establishment.
Differences in soil texture (which helps inform us about water holding capacity) and soil pH (which tells us something about nutrient availability) are two key ways in which soils might differ from Point A to Point B. So, plants that require free-drainage (like many Banksia in southern Australia that are found primarily on deep, acidic sands) probably won't do very well when they try to establish on poorly-draining clays.

But soils don't just provide nutrients and water. They are also the reservoir of soil biota that includes important groups such as mycorrhizal fungi.

Mycorrhizas are associations between fungi and plant roots that can be beneficial to both the plant and the fungi. The fungi link the plant with soil by acting as agents of nutrient exchange. The fungi receive carbohydrates as energy from the host plant root whilst nutrients such as phosphorus and zinc are passed back into the plant roots from the soil. Mycorrhizal associations may also reduce attack from root pathogens and increase the tolerance of the plant to adverse conditions such as heavy metals, drought, and salinity. In general, mycorrhizas play an important role in plant productivity.

It got me to thinking. How important are mycorrhizal associations when plant disperse to new soils? Could their absence (from the new soil types) inhibit colonisation potential of species trying to track their climate envelope shift?

While we know that mycorrhizal associations are important in plant communities (work in ecological restoration, for instance, has shown that some species are incredibly hard to re-establish if mycorrhizae are missing from the rehab site), it is hard to find much evidence for their existence in the plants I work with in southern Australia. In particular, what about the importance of mycorrhizal fungi for short-lived plants like annuals.

Hyalosperma praecox - one of the annual species
 I work with in grassy woodlands.
A feature of annual plants is their ability to grow rapidly after germination, establish one or more shoots that bear inflorescences, and then to flower and produce seed rapidly. The uptake of water, photosynthates and minerals into the developing flower heads and seeds occurs with some urgency because of the relatively short growing season. I got to wondering if mycorrhizae play a role here - after all, annual plants have very little time to grow roots to explore their soils for mineral nutrition and water.

The starting place to even begin to answer this question has to be: do annual plants form mycorrhizal associations in soils in the short-time that they are active? Using some old fashioned techniques (germinating annuals in their 'native' soil, then extracting them 4 weeks later, preparing roots by staining and using a microscope), we've recently found that many annual plants do indeed form mycorrhizal associations. This is the first study of its kind on grassland annuals in Australia, so rather exciting news.

Vesicles and hyphae, shown here by the staining, in a root

of the annual daisy Triptilodiscus pygmaeus

(Photo: Rohan Ball)
My Research Student Rohan Ball focused on observing what are called vesicular-arbuscular mycorrhizas (or VAM). The fungal hyphae here penetrate root cells and form intricately branched, shrub-like arbuscles within the cells and, at times, bladder-like vesicles as well. They are relatively easy to see, so we thought this was a good place to start.

Of the eight species we surveyed (all in the Asteraceae), we can confidently say that the roots of six species were colonised by VAM within 4 weeks of germination. You can see VAM in the photos as dark, stained areas - both vesicles and hyphae stain here quite clearly.  We are not yet sure what growth advantage this gives these developing plants, but we think it points to an interesting set of experiments. For instance, would VAM form in plant roots grown on 'non-native' soils (i.e. soils that are very different to those the species currently occur on)? If we remove VAM from the 'native' soil, does this affect growth and reproduction? Such questions are important because they have an applied outcome: are VAM necessary for annuals to recolonise agricultural lands? Will the lack of VAM affect colonisation potential of native species that disperse to new areas?

Tuesday, 7 May 2013

Borrowing from others

I've been a little snowed under these last few weeks, so haven't been able to Blog as much as I'd like. But I have some interesting posts in the pipeline.......

For this post, I'd like to point you to a couple of fascinating bits of ecology that I've come across recently. I think they are worth sharing here. Both are challenging, but for different reasons.

Angela Moles, in a TedTalk, talks about invasive plant species in Australia. But not in the way many of you might expect. Ang takes a different approach to invasives. She talks about how, once introduced to Australia, exotic species should be expected to evolve into unique 'new' Australian species. Once species have been transported to Australia, they are isolated - so gene flow potentially stops. Or at the least, is mixed by the introduction of different genotypes from the source. Then, local adaptation kicks in. Exotic species in Australia often exist in a very different context to their point of origin. Soils will be poorer (mostly in N and P), climate is more variable (and extreme) in many cases, and interactions with herbivores and pollinators will likely be altered. Under such circumstances, plants are likely to 'evolve' to suit their new habitats. Given enough time, they should also evolve to be reproductively isolated from plants derived from their source of origin (i.e. new species). Just like Darwin's finches!

You may not agree with Ang here - particularly because of the impacts that exotic plants can have on native plant communities (although it should be noted that in many bits of bush, some exotic species do seem to coexist happily with native species, e.g. Aira spp in grasslands). You can see her talk at: http://www.youtube.com/watch?v=5EV3ZTzSzZE

The second piece of interesting ecology comes from Jeremy Fox. He has a terrific Blog called Dynamic Ecology. I highly recommend it. He covers a range of topics in ecology (almost daily) - from theoretical ecology, to doing experiments, to cool T-shirts for science nerds.

In a old Blog (October 2012), Fox outlines what he thinks is one of the most important contributions to ecology in recent years. He summarises (beautifully) an emerging topic in the field of community assembly: phylogenetic community ecology. If you don't know what this is, then you should read his Blog.

Put simply, co-occurrence of phenotypically-similar species indicates “habitat filtering”, meaning roughly that community membership reflects species’ abilities to tolerate the local abiotic environment. Conversely, co-occurrence of phenotypically-different species means that similar species are being competitively excluded (= limiting similarity). If, as is often the case, phenotypic traits are phylogenetically conserved, so that closely-related species tend to be phenotypically similar, co-occurrence of closely-related species (“phylogenetic clustering” or “attraction”) implies habitat filtering, while co-occurrence of distantly-related species (“phylogenetic repulsion” or “overdispersion”) implies competitive exclusion. This is a simple, novel, creative, and relatively easy-to-implement idea, and so it’s no surprise that it took off.

The problem is, this “simple logical framework” is wrong! That is why you need to read Fox's Blog: http://dynamicecology.wordpress.com/2012/10/09/can-the-phylogenetic-community-ecology-bandwagon-be-stopped-or-steered-a-case-study-of-contrarian-ecology/