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)

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