Recent papers in the Lab - 2011

Our Lab primarily studies aspects of plant conservation ecology. Most of our work occurs in south-eastern Australia where there are many challenges to the conservation of biota: habitat fragmentation, changing climate, invasion by non-native species and altered disturbance regimes. Currently, I have students working on a variety of themes including multi-decadal vegetation dynamics, the role of endogenous and exogenous disturbance on species diversity, theories that underpin species coexistence and community assembly and plant invasions.

We've had a moderately productive 2011, as evidenced by the publications that have come out of the Lab. I thought I'd put links to them here to make them more accessible. Click on the link and that should take you to the journal website where you'll hopefully be able to download the PDF.

1. Adler et al.. 2011. Productivity is a poor predictor of plant species richness. Science 333: 1750-1753.
2. Briggs, A.L. & Morgan, J.W. 2011. Seed characteristics and soil surface patch type interact to affect germination of semi-arid woodland species. Plant Ecology 212: 91-103.
3. Firn et al. 2011. Abundance of introduced species at home predicts abundance away in herbaceous communities. Ecology Letters 14: 274-281.
4. Geddes, L.S., Lunt, I.D., Smallbone, L.T. & Morgan, J.W. 2011. Old-field colonization by trees and shrubs following land-use change: could this be Victoria’s largest example of landscape recovery? Ecological Management and Restoration 12: 31-36.
5. Morgan, J.W., Cutler, S.C. & Wong, N.K. 2011. Life-form species-area curves in temperate eucalypt woodlands. Plant Ecology 212: 1047-1055.
6. Schultz, N.L., Morgan, J.W. & Lunt, I.D. 2011. Effects of grazing exclusion on plant species richness and phytomass accumulation vary across a regional productivity gradient. Journal of Vegetation Science 22: 130-142.
7. Venn, S.E., Green, K., Pickering, C.M. & Morgan, J.W. 2011. Using plant functional traits to explain community composition across a strong environmental filter in Australian alpine snowpatches. Plant Ecology 212: 1491-1499.

Fighting fire with fire

In 2009, on the hottest day on record in Victoria, and at the end of a decade-long drought, the state experienced one of the worst bushfires since european settlement. Known as the Black Saturday fires, over 170 people died - the worst natural disaster in Australia's history. For many biologists familar with the ecology of southern Australia - one of the most fire-prone parts of the world - it was perhaps not unexpected that such a fire erupted on a day when the Fire Danger Index was literally off-the-scale.

Fighting (bush)fire with (prescribed)fire in the Top End
Photo: John Morgan

What could be learnt from such a day?

After the fires, the Black Saturday Royal Commission was established and it was to be the most comprehensive inquiry into bushfire in Australian history. Lots was discussed about fire ecology, house design, emergency warnings, fire preparedness, etc. Amongst the many recommendations, one of the most important was the recommendation pertaining to forest fuel management by prescibed burning.

The Royal Commission recommended a tripling of the annual prescribed burning in Victoria to reduce the risk of another Black Saturday. This equates to 5%, or 390,000 ha, of the state being burnt each year. This is now government policy, but there’s a fierce scientific debate over whether it will work, and the practical and ecological consequences of burning so much more of the state’s public land.

An excellent report on the ABC's Background Briefing went to air a few days ago where prominent fire ecologists - including Mike Clarke, Andrew Bennett, Ian Lunt, Kevin Tolhurst - talk about the ecological implications of setting targets for burning. It seems to me this is an arguement about "quantity versus quality" of prescribed burning and how asset protection needs to be weighed up with ecological impacts. It is well worth listening to. Follow this link  - http://www.abc.net.au/radionational/programs/backgroundbriefing/2012-02-19/3829372 -  to download the audio file. Questions we might ask ourselves include: does fuel reduction burning work to reduce the size, frequency and intensity of bushfires? What evidence is there that fuel reduction burning impacts (positively, negatively, neutrally) on native ecosystems? Which are the most resilient ecosystems to fuel reduction burning and why?

Contingencies ....in time

Everything happens somewhere. And in nature, the somewhere matters.

One of the most obvious things about the discipline I work in is that the results of one experiment or observation are not always replicated elsewhere across the globe, the nation, or even the state that I live in. Ecologists often talk about the fact that their findings are "contingent" on the organisms being studied (for example, short-lived perennial herbs versus long-lived trees will probably have very different demographies), the setting of the study (e.g. alpine versus lowland grasslands probably cycle nutrients in different ways) and the history of the system under investigation (e.g. evolutionary history and recent landuse legacies will affect successional pathways after disturbance).

This can make it all very confusing to come up with simple, widely applicable and generalisable predictions about the way in which natural ecosystems respond to climate perturbations and the impacts of utilisation. I guess that is why there has been a rapid growth in the use of meta-analyses to tease out ecological principles from spatial contingency, as well as the growth in global collaborative networks. I, myself, am loosely affliated with three such networks - NutNet, ITEX and Shrub Hub - whose chief aim is to study questions pertinent to ecologists working in similar systems across the world, using standardised protocols, to see if ecological patterns emerge beyond the local-scale.

One of the things that is also true about nature is that different things happen in different years. As someone who studies seedling regeneration processes, I know this only too well. But I think we tend to under-estimate the importance of temporal contingencies in our ecological thinking.

Just how much does the timing of an experiment or observation cloud our view of key ecological processes? If we study seedling recruitment in a decade of drought, for example, are the outcomes of such a study sufficiently robust to propagate models that forecast extinction risk? The answer is probably no. But collecting data is a hard excercise. Ask any student at the completion of their doctoral thesis about whether they want to do it all again and you'll get a stern look no doubt.

The Button Wrinklewort in remnant native grassland, Victoria
(Photo: Donna Burns)

Returning to seedlings as a case in point. I've been following the seedling recruitment of the endangered grassland daisy Button Wrinklework for almost 20 yrs now. In 1991/2 (crikey, that makes me feel old), I observed a large seedling cohort in the two populations I have followed ever since. I even wrote up a paper on this (see here) and concluded that "....... seedling recruitment is not restricted to climatically favourable years (i.e. is not episodic) but rather, is potentially on-going provided suitable microsites are available for seedling survival."

How wrong was I! My long-term observations of recruitment in the Button Wrinklewort has revealed that there has NEVER been another recruitment year like 1991/2. This probably has a lot to do with the fact that south-eastern Australia experienced a 13-yr drought from 1996-2009 where rainfall was below-average in just about every year. Rather than observe on-going recruitment, seedlings have been entirely episodic. The number of adult plants have declined in some populations and not been replaced by seedlings (whereas I had suggested declines might occur where microsite limitation limits survival; while this is certainly true, you've got to have seedlings before you have this problem). Interestingly, the recruitment event I observed in 1991/2 was very successful. Many of the seedlings that emerged in that year went on to become reproductive. A couple are even still alive today! This is what Peter Chesson calls the "storage effect" - infrequent recruits are stored in the population and these buffer the population in the intervening years / decades when recruitment is far less successful.

This simple example highlights that temporal studies are crucial if we are to adequately understand the dynamic nature of species populations and their interactions with climate and other species. Of course, this is incredibly difficult to do. Permanent plots, data archiving, and good old fashioned persistence are the keys here. These three things are also terribly unfashionable in ecology today. We need answers now to the pressing conservation questions that face our society. But we also need to acknowledge that what data we do have will be imperfect and model outputs are not final nor definitive. And we need scientists (like me) to champion the need to conduct long-term, old fashioned studies. Otherwise we potentially face a future where decisions are made on data that is temporally contingent and this could have serious implications for the future of the species we are interested in preserving. Particularly in a world undergoing a changing climate. Something to ponder!

More on alpine summits.......

Hi there,

just a couple of short movies from the tops of alpine summits in Victoria featuring myself and Dr Susanna Venn. Note the distance to treeline is really short in movie 1 - alpine plants really have nowhere to migrate to in such marginal habitats. Also note the evidence of fire in the landscape. The ecology of alpine vegetation in Australia is clearly about cold processes, disturbance, as well as biotic interactions. Untangling these effects is a major challenge. There is lots to study......

Enjoy,
JOHN

Mountain summits, species losses and shrubs

The Bluff - a typical alpine summit in
the southern Australian alps
(Photo: John Morgan)

Alpine summits in Australia are thought to be one of the places most vulnerable to climate change. Afterall, the distance between treeline and summits is very small - from a few metres to perhaps only 100-150 m at the higher peaks. Hence, alpine species have nowhere to migrate when air temperatures rise, potentially lengthening the growing season and allowing subalpine species to grow at higher altitudes.

The scenario that is usually described is that trees will migrate up mountain slopes in response to climate warming, and alpine species are lost (presumably) because trees shade out the small herbs and grasses that dominate alpine peaks. The bioclimatic envelope of the alpine species will also shift, undoubtedly affecting the ability of some species to persist in their current location. While most ecologist probably might visualise the process, the mechanism of species loss is actually poorly understood. Indeed, it's perhaps not the trees that will drive local extinctions (nor shifts in climate envelopes in the short-term) but rather, changes in other woody plants (such as shrubs) that will strongly compete with low-statured plants.

Resurveying transects on Mt Sterling; note the
burnt snow gums in the background, a legacy of fire in 2006
(Photo: John Morgan)

Susanna Venn and I have just returned from several days in the field re-monitoring some long-term transects on alpine summits. These were last done about 8 yrs ago and it's clear that few trees have moved above the treeline in that time despite regional warming. Hence, there is a degree of resistance to change in treelines that has long fascinated Australian alpine ecologists.

What is more apparent is that there seems to be a (potentially strong) negative relationship between shrub cover and species diversity. This is really apparent on the different aspects of summits - southerly, colder aspects have far fewer shrubs and much more diversity. Shrubs, like Podolobium and Hovea, grow taller than the herbfield species, deposit lots of litter that accummulates because of slow decomposition, and can grow quickly after disturbance such as fire - in Phil Grime's CSR scheme, they might be considered "competitors". Perhaps the real driver of vegetation change at summits will be shrubs as they affect competitive interactions. Many of these species vegetatively spread so they have a clear "method of encroachment" into alpine areas from surrounding slopes that is not reliant on seed regeneration. And, because they resprout after fire, they are not so senstive to fire return intervals as are obligate-seeders such as Grevillea.

Susanna has just published a paper on shrub encroachment in tundra ecosystems with Shrub Hub Research Network collaborators - a popular press piece can be found here, while the scientific paper in Environmental Research Letters can be found here. It's worth checking out - shrub encroachment is a global phenomenon, from the prairies, to the semi-arid, to the temperate. Clearly, understanding the controls on shrub dynamics on alpine summits, and their potential (negative) feedbacks with plant diversity, is an exciting area of research that we will persue over the coming years. I'll update you when we've crunched our data.