Tuesday, 23 August 2016

Introducing Susanna Bryceson


Susanna Bryceson has joined the Morgan Lab as a PhD candidate. She is studying the spread of Australia’s C4 grasslands from the mid-Miocene (about 12 mya) to the present.


In the Americas, Europe, Russia and Africa, the development of grassland biomes (ie, prairies and savannas) is thought to have gained traction during the low atmospheric CO2 conditions of the Miocene, enabling the dominance and co-evolution of C4 grass types alongside large herds of grazing ungulates, like deer and buffalo.


Little is understood about how C4 grasses arrived and spread in Australia, and how they affected Australia’s Gondwanan vegetation and fauna. This invasion was unique because of Australia’s long isolation and the absence of large co-evolved herbivores that controlled the fuel loads of grasslands elsewhere. Australia’s increasing aridification during the Pliocene created new niches which were inhospitable for much of the Gondwanan-evolved flora and fauna but well suited to C4 grasses, and the Pleistocene saw C4 grasses establish fire as a key driver of our ecology.  Sue’s research is investigating what factors enabled C4 grasslands to spread and drive extinctions of fire-sensitive biota, what factors may be limiting them, and what the implications might be for future grassland management.

Monday, 22 August 2016

New Honours Projects in 2017


Join the Plant Ecology Lab - Honours Projects in 2017

For further info: J.Morgan@latrobe.edu.au

Re-introducing fire into long unburnt grassy ecosystems– accelerated recovery of the ecosystem, or stasis?

Many grasslands and grassy woodlands are now rarely burnt, although it is likely that patch burning once played an important role in the structure and function of these ecosystems. Fire exclusion has led to tree recruitment and loss of diversity (in some cases because biomass accumulates to outcompete poor competitors). Land managers are increasingly re-introducing fire to long unburned landscapes, but what changes occur when fire is re-introduced when it has been absent?  Are trees resilient to fire (or does it depend on their size)? Do species appear that haven’t been seen for a while, presumably re-appearing from dormant soil stored seed? Do some species disappear, having initially profited from the absence of fire?
In this project, we will test ideas about re-introduction of fire to landscapes where much benefit might be derived from such activities. Grassy ecosystems in western Victoria are much restricted (due to agriculture and, increasingly, timber plantations) and need sympathetic management to maintain their natural values. Re–introducing frequent fire to long unburnt grasslands is seen as a desirable management activity – it should serve to open up opportunities for seed regeneration and species coexistence. However, there are almost no examples where this has been tested, at least in good quality vegetation.

In this study, we will burnt long unburnt grasslands and ask whether often reported reductions in species richness due to the cessation of frequent fire can be spontaneously reversed by the return of fire. Additionally, will the abundance of currently sparse species be improved? How will exotic species respond to a change in disturbance regime? What about trees that have established in the inter-fire period? The student will work closely with the CFA, who will be responsible for conducting the trial burns, to design and implement the burning experiment.

‘Extinction debt’ in grassy woodlands


In 1975, Cliff Beauglehole (an excellent amateur botanist) surveyed fragmented grassy woodlands on the Brim Brim Plateau in western Victoria, identifying all native species and their abundance. Across a range of sites (many small, linear and isolated), the surveys provides a time stamp on floristic composition of these woodlands from which to assess changes in composition. In particular, they provide a capacity to identify which plant species can persist in highly modified agricultural landscapes, and which can’t.

Many species occur at very small population sizes and face threat (such as invasion by exotic species), meaning their local extinction is likely. The timescales over which this process are unknown. In 2006, my Honours student Fiona Sutton revisited these sites and identified substantial change that likely result from habitat fragmentation and small population size (Journal of Ecology 97, 718–727). This project would build on prior work by revisiting the sites to determine just how the extinction debt is playing out a decade later. One important new aspect of the work will involve assessing seed production and dispersal capacity of species in grassy woodlands. In my Lab, we’ve been interested in trying to understand which species can persist in fragmented woodlands and grasslands, and which ones can’t. Maybe the native species that go extinct are those that have low seed production, while those that expand in the landscape are those that have lots of seed production and whose seeds are easily dispersed. After all, regeneration is a key plant trait but rarely has it been directly tested in terms of its importance for predicting persistence. We’d need to do two things. We would need to quantify seed production (per plant) across a large range of species (increasers, decreasers) to see if seed production is a trait that differs dramatically across these groups. We would also need to quantify something about how seed production varies with plant size (what is called ‘reproductive economy’). Are plants that are successful the ones that produce lots of seeds regardless of size, while decliners are the ones that have size-related thresholds for production. You can read more about the genesis of these ideas in a paper by Poschlod et al. (2013) Seed ecology and assembly rules in plant communities. pp 164-202. In: Vegetation Ecology (eds. E. van der Maarel and J. Franklin), John Wiley & Sons). This project would suit a student who wants to learn lots of plants!

Endemic plant species on restricted soils: 'early victims' or 'hardy survivors' of climate change?

One of the greatest challenges that land managers face today is anticipating how climate change will affect the diversity and composition of ecological communities to develop effective strategies for adaptation and mitigation. The direct effects of climate change on species via changes in temperature and precipitation have been the focus of many studies. Many conclude that altitudinal and latitudinal shifts in distribution will be necessary to survive the impacts of predicted climate change.  Little attention, however, has been given to how plant species on 'restricted' soil (i.e. very infertile) will respond to climate change. Here, suitable habitats for such species are patchily distributed, and the dispersal distances required to move to newly suitable habitat are large, making successful migration unlikely. Are species confined to low-nutrient soils, which may reflect their tolerance of such conditions and intolerance of other biotic factors such as competition, make them particularly vulnerable to climate change?  Some studies suggest that soil specialists may be at less risk than species on 'normal' soils due to their stress-tolerant functional traits, but there is also contrary evidence.

Plant communities on low-nutrient soils have two distinctive attributes that may cause them to respond uniquely to climate change. First, they are often found in discrete areas making them more spatially isolated from one another than species on ‘normal’ soils that tend to be more contiguous. This spatial isolation may make it much more difficult for species to successfully migrate under climate change. Second, because these species are on unproductive substrates, they may differ from communities on ‘normal soils’ in terms of limiting resources, functional traits, and the relative importance of disturbance, competition and other ecological processes. Plants in these special soil habitats often have traits associated with tolerance of drought and nutrient-limitation [e.g. small stature, low-specific leaf area (SLA), high allocation to roots relative to shoots] because nutrient availability is limited, water can be scarce, and soils may have additional unusual chemistries (e.g. particularly acidic pH). Special soil communities are more strongly water-limited than others; therefore, they may be especially responsive to changes in available precipitation. On the other hand, because plants on special soils already have adaptations for stress tolerance, they may be particularly well-suited to withstand climatic changes.
In this study, we ask: what are the potential responses to climate change of endemic plant species when soil factors appear to limit their current distribution? We focus on the Wellington Mint-bush (Prostanthera galbraithiae), a vulnerable species, as a model species. The species is endemic to the Gippsland region of Victoria, restricted to sandy podzol soils typically low in macronutrients (especially N, P and K) and subject to long periods of soil moisture stress. To address the role of non-spatial factors, we will compare the plasticity to water and temperature stress of the endemic Mint-bush to that of two more widespread species (Prostanthera lasianthos, P. rotundifolia) to test the hypothesis that soil specialists are already well-adapted to environmental stress and they may be particularly well-adapted to withstand climatic changes.

Quantifying the wind dispersal capacity of seeds at mountain summits

The dispersal of plants and animals is of fundamental importance as it underlies landscape-scale ecological processes such as species invasion, immigration and meta-community dynamics. Dispersal is particularly critical if plants are to keep pace with climate change, migrating into new locations within the climate niche envelope. This is particularly true in mountain ecosystems where upslope migration will be crucial for cold-adapted species to maintain their advantage over warm-adapted species.
Understanding the aerial movement of seed, however, has proven difficult to measure and I am not aware of community-wide quantification of seed dispersal in alpine areas (although models of seed dispersal have been developed by Morgan & Venn). We will use a quantitative approach to measuring the aerial movement of seed in field situations, using a newly developed seed trap design, to assess the capacity of wind-dispersed seeds for long-distance migration. Using a series of alpine peaks distributed across the Victorian Alps where long-term observations of vegetation change are being conducted, we will quantify the composition of the seed rain and contrast it to local community assemblages. Quantifying dispersal remains a critical part of determining the contribution of these processes to shaping patterns of biodiversity at a landscape-scale. Determining rates of propagule supply to different parts of the landscape will provide guidance on which areas might respond to climate warming by natural regeneration processes, and which (poorly dispersed) species could be priorities for climate mitigation strategies.
 The student will work closely with DECRA fellow Dr Susanna Venn (Australian National University)
 
Grassland litter decomposition across climate gradients
In south-eastern Australia, fire and grazing regimes have long been recognised as influential drivers of species diversity in native grasslands. Over time, in the absence of such disturbances, senescent Kangaroo Grass (Themeda triandra) tussocks create a thatch of dead leaves over the soil surface. This layer of leaf litter decomposes very slowly in temperate climates, shading out inter-tussock species, smothering seedlings and contributing to the decline of plant diversity. As such, a common assumption is that native grasslands require frequent disturbance to remove accumulated biomass in order to optimise species diversity. However, not all grasslands accumulate litter. In sub-tropical and semi-arid ecosystems, low biomass accumulation might reflect high decomposition rates. Here, litter is unlikely to smother intertussock species, as is the case in temperate climates. Different climates may influence the rate of decomposition and accumulated biomass within tussock grasslands and hence, the disturbance requirements of grasslands to maintain species diversity. However, this contention remains untested.

To quantify how litter decomposition varies across native grasslands, and how this may be related to litter type (C4 vs C3 grasses, native perennials vs exotic annuals), climate and rates of photodegradation, we will conduct a litter decomposition experiment in the field across northern, central and southern Victoria using litterbags. The effect of UV radiation on decomposition rates will be investigated using structures to manipulate UV radiation (see Brandt et al. (2010) Ecosystems 13, 765-781). The field experiment will be complemented with a glasshouse experiment to test germination success of grassland species according to high or low biomass accumulation. A range of species typical of grasslands (e.g. daisies, lilies) will be sown under grass litter (at depths that correspond to field observations) to determine whether litter suppresses germination. This is a critical experiment as it has been assumed that litter smothers herbaceous germination, but quantitative data are lacking.

The student will have the opportunity to work with a range of grassland managers (e.g. Trust for Nature, Brimbank City Council, Parks Victoria) and scientists.


Exotic grasses as drivers of species decline in threatened native grasslands
Weedy grasses pose a significant threat to the diversity of native temperate grasslands. This is particularly true in the Victorian Volcanic Plains where soils are fertile and rainfall is moderate. Although we know weedy grasses can outcompete native species at local scales if appropriate disturbance regimes are not maintained (e.g. frequent burning), we do not know at what point weedy grasses will cause a significant, and often irreversible decline in native grassland diversity at larger spatial scales. It seems intuitive that there would be a negative relationship between the cover of weedy grasses and the number of native species (as weed cover goes up, native species diversity goes down). However, the strength and shape of this relationship remains unclear. This applied project aims to provide grassland managers with clear and unambiguous recommendations that will enable the identification of problem areas that can be treated prior to the deleterious effects of weed invasion.



This study will utilise a series of sites across the VVP to assess the broad scale effects of a high threat perennial weedy grass, Phalaris aquatica, on temperate native grasslands. In particular, this study aims to: i) establish what the relationship between Phalaris cover and native species diversity looks like (i.e. is it linear or non-linear); ii) establish whether an impact threshold is evident (i.e. is there a point at which Phalaris cover leads to dramatic declines in native species diversity?) And, iii) identify whether species losses were associated with particular life forms or whether impacts were across many life forms. The student will work in collaboration with ecologists at the Arthur Rylah Institute for Environmental Research (the Victorian Government Dept. of Environment, Land, Water and Planning biodiversity research base).





Welcome - Daniel Flaim

Daniel Flaim has joined the Plant Ecology Lab and will be working on a project titled "Managing the Natural Grasslands of the Murray Valley Plains for conservation of native biodiversity".


Daniel is investigating processes which drive a) biomass, and b) vegetation community development, and thus habitat provision for native animals, in the Natural Grasslands of the Murray Valley Plains of Victoria. This nationally Critically Endangered vegetation community is vital to the survival of many rare and endangered plant and animal species, but has almost been extirpated in Australia through agricultural practice. Remaining high quality examples are fragmented and limited in extent. He will seek to understand how and when management inputs such as grazing or burning might drive the system towards configurations which best secure threatened biota. Daniel will be supervised by Dr John Morgan, Dr Nick Schultz (Federation University) and Dr Nathan Wong (Trust for Nature).

Saturday, 4 June 2016

Paul Foreman joins the Plant Ecology Lab


Paul Foreman is a PhD candidate at La Trobe University, Bundoora. His research focuses on using the historic record to map and describe ‘overlooked’, higher-rainfall, kangaroo-grass-dominated grasslands in central and northern Victoria; searching for evidence of Aboriginal burning; and looking at the role of fire in protecting and restoring these critically endangered grasslands.

Paul is botanist and ecologist with over 25 years of experience in land management and nature conservation across a range of sectors and in a range of technical, strategic and management roles throughout Victoria and many other parts of Australia. Paul has an undergraduate degree in Forestry from the University of Melbourne and completed a Botany Masters of Science in Northern Plains Grassland ecology at La Trobe University in 1996.

Paul has worked professionally with: State Government; Trust for Nature; Local Government; and most recently, Bush Heritage Australia. He is also a Senior Ecologist and Botanist with Blue Devil Consulting, a Castlemaine-based business specialising in grassy ecosystem conservation and threatened species recovery.

Tuesday, 3 November 2015

New Honours Project for 2016

I have several positions available in my Lab for Honours students in 2016 working on the following project ideas:



Does rainfall trigger landscape-scale recruitment in Acacia?

The broad goal of this Honours project is to quantify variation in the demographic processes and ecological conditions that permit native plant establishment along major environmental gradients (e.g. rainfall variability). Temporal variability in climate probably underlies a lot of things in ecological systems (e.g. births, deaths), but Australian plant ecology has little conceptual framework about the importance of climatic extremes (e.g. ENSO wet and dry periods) on natural ecosystems. There are some scientific papers describing local drought effects, but many give the impression that this is a bit of an aberrant phenomenon rather than a key driver. The chapter on El Nino in Attiwill & Wilson’s Ecology: An Australian Perspective text book is quite illuminating in this regard - the section on El Nino provides virtually no references to terrestrial vegetation responses to climate extremes. How can we deal with climate change if we don’t have a handle on responses to climate variability? This project provides an exciting opportunity to ask important questions about native plant recruitment and population dynamics in relation to environmental variation and environmental change.


Controls on litter decomposition in native grasslands

Most grass leaves have short life spans, so accumulated biomass in grasslands is mostly comprised of dead leaf material produced in earlier years. Undisturbed native grasslands in mesic regions accumulate large quantities of dead grass, which decomposes very slowly. Approximately 90% of phytomass in long unburnt grasslands is litter. This can smother intertussock species, leading to declines in plant diversity. By contrast, dead grass does not appear to accumulate over long periods in drier grasslands, but instead appears to decay relatively quickly. Low levels of accumulated biomass in semi-arid grasslands reflect high decomposition rates. Hence, litter is unlikely to smother intertussock species in such places. This remarkably simple hypothesis remains to be tested. By comparing grasslands across a productivity gradient (from the Darling Downs in SE Queensland, the Liverpool Plains in Sydney, the Monaro in the Southern Tablelands, the Victorian Volcanic Plains, the Riverina and the Midlands of Tasmania), we can quantify how litter decomposition varies (via litter bag experiments), and how this may be related to litter type, climate and rates of photodegradation.

 

Why does this matter? A quick review of the literature suggests that the paradigm that grasslands require disturbance to maintain species diversity does not have universal application.  Although quantitative data is lacking, we can postulate that a lack of litter accumulation determines whether disturbance is necessary to maintain diversity. The cool winters and dry summers of the temperate environments supporting native grasslands may retard decomposition (hence, biomass accumulates through time and species richness declines) relative to the warmer, wetter sub-tropical climate that supports C4 grasslands that accumulate less biomass. We hypothesise that the accumulation of litter may be the critical mechanism that suppresses some plants in the intertussock space of grasslands and results in suppressed species diversity in undisturbed grassland. This study would help gain insight into this important proposition.

Novel Competitors Shape Species' Responses to Climate Change

In alpine areas, species distributions will change as global climate change accelerates. Typically, species will need to disperse to track their climate envelopes. However, biotic interactions clearly play a role here in terms of the ability of a species to establish at a new site, outside of the species' range.

At the leading edge, species will be dispersing into new vegetation, likely low statured alpine vegetation dominated by herbs and grasses. At the trailing edge, invaders from lower down the mountain may establish and it may be this biotic interaction that causes distribution shifts at this end of the range (i.e. strong competition from functionally different species like shrubs). There are almost no studies that have separated out the potential for alpine species to establish into new areas, nor their ability to establish in areas where functionally different species dominate. We have an opportunity to test the idea that biotic interactions are likely to be really important at the trailing edge of the distribution of alpine species but not so much at the leading edge.

In this study, conducted at Mt Hotham where there are very steep environmental gradients (typically temperature and snow lie), we will:
1) Identify candidate species for study - looking for species not yet at the top of mountains so that upward migration is possible, while trailing edge declines should occur with increasing competition
2)  Plant at a low (1600m), middle (1750m) and high (1900m) elevations; these represent home site (middle), trailing edge (low) and leading edge (high) conditions
3) Remove vegetation to compare in the presence or absence of competitors
4)  Follow survival and then harvest at end for biomass as a measure of fitness
5) To separate out climate effects versus soil differences, we would take soils from low, medium and high sites, bring to the La Trobe Glasshouses and grow our target species under uniform conditions. If growth is better on a soil type over another, this hints that soils may contribute to fitness and hence, distributions
6) To test if pathogens in the soils at different elevations limit distributions, we would take soils from low, mid and high elevations and remove fungi in half of them to see if there is a below-ground microbial interaction that limits establishment (i.e. lower soils have higher pathogen loads and it is this factor, not competition that limits trailing edge).
 8. Collect trait data of species in the low and high sites to see if trait differentiation might be a reason species don't cope in the low sites relative to high sites.

 At the end of this study, we would be able to impart a better understanding on the role of other plants on species distributions in high mountains. This study requires a mid-year start, and working at Mt Hotham for extended periods over the growing season.

Further information: J.Morgan@latrobe.edu.au

Sunday, 25 May 2014

New Honours Projects for 2015

I am a plant ecologist interested in the long-term dynamics of native plant communities. I focus on plant communities in south-east Australia. In general, I am interested in the factors that govern local species richness and coexistence in plant communities, how recruitment shapes plant communities, how native ecosystems re-assemble following disturbance, using plant functional traits to assess vegetation responses to environmental change, using historical datasets and revisitation studies to assess long-term vegetation dynamics, and understanding the processes that underpin local extinction and persistence in communities, and the implications this has for ecosystem function and stability.

The process of applying for an Honours project in my Lab is easy. Firstly, let me know that you are keen to discuss undertaking research under my supervision and we can talk about potential projects. If you wish to apply for a project, I expect a grade average in Botany subjects >75%. I will generally supervise one to two students per year and I select these on the basis that I think that will conduct a good thesis, are inquisitive about the natural world, are likely to become plant ecologists, are motivated and independent workers, and have something to contribute to the Plant Ecology Lab more broadly. Students with good recommendations will be looked upon favourably.

Below, I list some ideas I have been thinking about as potential projects. All are necessarily vague at this stage but give an indication of the studies that currently occupy my thinking. If you have some ideas, I’m also happy to discuss those.


Project 1: How local-scale environmental factors drive novel community assembly in Victoria’s herb-rich woodlands  

The development of ecosystems that differ in composition and/or function from past systems is an inevitable consequence of global change. These new systems, termed “novel” or “no-analogue” communities, are composed of mixes of native and exotic species and result from species invasions and environmental changes and are increasingly recognised for their global prevalence and importance to conservation. Similar invasions and disturbances can also lead to “degraded” communities that are composed entirely of exotic species. These communities are of great concern to conservation biologists as they support little if any native diversity and can differ dramatically in ecosystem function from the communities they replace. Given that humans will continue to drive major changes in the planet’s natural ecosystems for the foreseeable future, an understanding of novel communities must be central in our planning for sustained biodiversity.

In this study, I’d like to tackle two important questions:

  1. What environmental factors give original communities resilience against full degradation?
  2. What environmental factors facilitate community degradation and drive the transition of novel communities to degraded communities?
 
 
Project 2: Does environmental history drive ‘habitat segregation’ in the Box-Ironbark forests of central Victoria?
 
Box-Ironbark forest remnants that now exist as large blocks (100s of hectares) have a history of timber cutting, mineral extraction and grazing. Small forest blocks (few hectares), however, also exist in the same landscape and generally are found on roadsides – these have a history no grazing and timber cutting, but probably have a substantial spillover of flora from the adjoining (non-native) paddocks. So, there are two 'histories' here relating to different disturbance regimes experienced for perhaps more than a century. Ian Lunt coined the term 'habitat segregation' to describe the effects of different disturbance history on resulting floristic composition, hinting that multiple contemporary floras can have ‘evolved’ from the same source flora. He did his work on the Gippsland Plains in grassy woodlands and I'm not sure the theory has been tested elsewhere in forest systems in SE Oz. Another important explanation for the outcomes of forest fragmentation, however, can be addressed by considering ‘Island Biogeography Theory’. Here, small ‘islands’ of habitat will contain a subset of the species seen on bigger islands because of reduced area effects. Hence, it might be expected that linear/small remnants support fewer of the native species seen in large islands simply based on species-area relationships.

This raises an interesting question. Does the habitat segregation model better explain current floristic differences in the box-ironbark region, or are more traditional theories like IBT more appropriate? My money is on the first hypothesis - that different environmental histories over the last century have driven the flora in divergent ways - so small remnants may support a whole range of species now not supported in big blocks because of overgrazing/timber cutting, etc. Big blocks may have species that are more abundant than linear strips because they like the disturbance. Small linear strips may be more invaded than large blocks because of edge to area effects.

So, we could look for evidence of habitat segregation - and take it further by examining the traits of plants that prefer less 'disturbed' habitats - I suspect these will be grazing-sensitive grasses and herbs while shrubs might be more common in large blocks based on palatability and soil disturbance/colonisation potential. The implication of this work is that it may identify that both remnant types are crucial for maintaining the regional pool of species.

 
Project 3: Endemic plant species on restricted soils: 'early victims' or 'hardy survivors' of climate change?
 
One of the greatest challenges that land managers face today is anticipating how climate change will affect the diversity and composition of ecological communities to develop effective strategies for adaptation and mitigation. The direct effects of climate change on species via changes in temperature and precipitation have been the focus of many studies. Many conclude that altitudinal and latitudinal shifts in distribution will be necessary to survive the impacts of predicted climate change.  Little attention, however, has been given to how plant species on 'restricted' soil (i.e. very infertile) will respond to climate change. Here, suitable habitats for such species are patchily distributed, and the dispersal distances required to move to newly suitable habitat are large, making successful migration unlikely. Are species confined to low-nutrient soils, which may reflect their tolerance of such conditions and intolerance of other biotic factors such as competition, make them particularly vulnerable to climate change?  Some studies suggest that soil specialists may be at less risk than species on 'normal' soils due to their stress-tolerant functional traits, but there is also contrary evidence.
Plant communities on low-nutrient soils have two distinctive attributes that may cause them to respond uniquely to climate change. First, they are often found in discrete areas making them more spatially isolated from one another than species on ‘normal’ soils that tend to be more contiguous. This spatial isolation may make it much more difficult for species to successfully migrate under climate change. Second, because these species are on unproductive substrates, they may differ from communities on ‘normal soils’ in terms of limiting resources, functional traits, and the relative importance of disturbance, competition and other ecological processes. Plants in these special soil habitats often have traits associated with tolerance of drought and nutrient-limitation [e.g. small stature, low-specific leaf area (SLA), high allocation to roots relative to shoots] because nutrient availability is limited, water can be scarce, and soils may have additional unusual chemistries (e.g. particularly acidic pH). Special soil communities are more strongly water-limited than others; therefore, they may be especially responsive to changes in available precipitation. On the other hand, because plants on special soils already have adaptations for stress tolerance, they may be particularly well-suited to withstand climatic changes.
In this study, we ask: what are the potential responses to climate change of endemic plant species when soil factors appear to limit their current distribution? We will focus on the Wellington Mint-bush (Prostanthera galbraithiae), a vulnerable species under the EPBC Act, as a model species. The species is endemic to the Gippsland region of Victoria, restricted to sandy podzol soils typically low in macronutrients (especially N, P and K) and subject to long periods of soil moisture stress. To address the role of nonspatial factors, we will compare the plasticity to water and temperature stress of the endemic Mint-bush to that of two more widepread species (Prostanthera lasianthos, P. rotundifolia) to test the hypothesis that soil specialists are already well-adapted to environmental stress and they may be particularly well-adapted to withstand climatic changes. You can read more about the genesis of these ideas in the paper by Damschen et al. (2012) Journal of Ecology 100: 1122-1130

Project 4: How exotic grasses transform the fire ecology of native grasslands
 
Fire is a key disturbance agent in native grasslands of temperate Australia. It affects patterns of native plant species diversity and sward vigour, as well as habitat structure for animals. Recently, we’ve started to quantify fire behaviour in grasslands to better understand how the timing of fire and grassland type affects things such as fire intensity and regrowth capacity.

One of the biggest threats to native grasslands is the invasion of exotic perennial grasses such as Chilean Needle Grass, Phalaris and Sweet Vernal Grass. These directly threaten native diversity because their tall stature, litter accumulation and rate growth rates smother inter-tussock species. This is mostly inferred rather than having been documented. We could start this project by assessing species persistence with/without exotic perennial grasses.

However, I’m more interested in assessing the impact of exotic invasions on ecosystem properties such as fuel loads. It’s obvious that many perennial exotic grasses produce much more biomass than native grasses and so I’m guessing that when burnt, exotic grasses will change the nature of the fire – maximum temperatures, residence time, fire intensity. Crucially, we need to then know how this translates to ecosystem recovery. Do exotic grasses burn “hotter” and hence, do they elevate mortality in native trees, grasses and forbs. We could test this idea by artificially introducing some plants (or seeds) into areas with exotic grasses and native grasses prior to fire, and seeing just how successful they are at surviving the (presumably) different fires that occur in invaded/uninvaded areas. We know from work in the Top End, where the exotic Gamba Grass has invaded into savannah, that exotics can completely change fire behaviour and weaken the resilience of the native ecosystem by elevating mortality of natives. Is that also occurring in grasslands? Do exotic grass invasions create positive fire feedbacks that promote their future invasion? Some of the thinking that has gone into this project originates from Setterfield et al. (2010) Turning up the heat: the impacts of Andropogon gayanus (gamba grass) invasion on fire behaviour in northern Australian savannas. Diversity and Distributions 16, 854-861.


Project 5: How do seed ecological traits predict persistence / extinction in grassy woodlands?
We’ve been interested in trying to understand which species can persist in fragmented woodlands and grasslands, and which ones can’t. We now have a good idea about extinction/colonisation rates (using revisitation studies) but are still struggling to find plant traits that help explain this. We’ve looked at things like growth form, dispersal strategy, seed mass and even SLA, but so far it’s not clear if extinctions (and persistence) can be readily predicted using a plant functional trait approach.
 
In this project, I want to test another idea. Maybe the native species that go extinct are those that have low seed production, while those that expand in the landscape are those that have lots of seed production. After all, regeneration is a key plant trait but rarely has it been directly tested in terms of its importance for predicting persistence. We’d need to do two things. We would need to quantify seed production (per plant) across a large range of species (increasers, decreasers) to see if seed production is a trait that differs dramatically across these groups. However, we would also need to quantify something about how seed production varies with plant size (what is called ‘reproductive economy’). Are plants that are successful the ones that produce lots of seeds regardless of size, while decliners are the ones that have size-related thresholds for production. I think it would also be excellent to quantify whether soil seed banks can be predicted from seed production/seed size and hence, are our decliner species the ones that produce fewer seeds that don’t form soil seed banks. You can read more about the genesis of these ideas in a paper by Poschlod et al. (2013) Seed ecology and assembly rules in plant communities. Pp 164-202. In: Vegetation Ecology (eds. E. van der Maarel and J. Franklin), John Wiley & Sons)

Sunday, 18 May 2014

Congratulations to Dr Nathan Wong

Another of my PhD students graduated this week. Congrats to Nathan Wong for getting to the end of his thesis on the role of disturbance in long-grazed Riverine Plains native grasslands. It's taken a while, but good things happen to those who wait! Nathan is currently working with the Trust for Nature, busily helping to protect the endangered grassy ecosystems of Victoria.