Tuesday, 8 May 2012

thinking of Honours in plant ecology in 2013????

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: Common species declines and niche limitation
Common plant declines don't get much more dramatic than that of Microseris (Yam Daisy) - a once common and extensive forb in Themeda grasslands of the Victorian Volcanic Plains, they are now incredibly hard to find. While such declines have been noted for some time, they probably continue unabated and it’s still unclear what factors favour the maintenance of such species. Taking historical data (sites where it was recorded, regardless of abundance measures) we could first ask: what evidence is there for continuing decline of the species in plains grasslands over the last few decades (using species detection theory to enhance our estimates). Then, in an experimental study, we might ask: how does seed limitation versus microsite limitation affect Microseris patterns - have grasslands changed so much that Microseris re-entry is prohibited by lack of germination and adult niches. This might entail a study sowing seed into different microsites (control native grassland, canopy removed but no soil disturbance, soil disturbance but no canopy removal, canopy removal and soil disturbance). It's thought Yam Daisies proffered from soil disturbance by aboriginal digging/bandicoot digging, but such processes have long been lost from plains grasslands. Might this be a key factor in the decline of the species?
Where: grasslands on the western volcanic plains

Project 2: Heterogeneity, species diversity and conservation management
In Australia, native grasslands are highly endangered because they have been transformed by agriculture over most of their historic range. Hence, they are being acquired and managed for conservation of their important biodiversity.  On the northern riverine plains, for example, many sheep grazing properties are being acquired for conservation by Parks Victoria and the Trust for Nature. Because many / most of these have been grazed by sheep, they are somewhat degraded (but stable). Grazing is used as management tool because it can maintain species richness (at high numbers in small quadrats) - based on the idea that competitive exclusion reduces small scale diversity. But, and this is the point of the project, is it the 'best' way to manage grasslands for their structural, functional and floristic diversity? Maybe grazing maintains a subset of native species (i.e. the grazing-tolerant ones) but reduces heterogenity across sites. While alpha diversity is high, beta diversity across the landscape may be low when grazed - i.e. grazing promotes species similarity from one point to the next, whereas destocking enhances variation in composition. Conservation managers are loathe to remove stock from native grasslands because they are acutely aware that destocking might lead to declines in alpha diversity. This fails to recognise that destocking might lead to increases in beta diversity because it promotes heterogeneity via microsite differentiation. We could survey a range of grasslands (with different management regimes - grazed, recently destocked, long destocked) and ask: does grazing promote alpha and beta diversity. Does destocking lead to loss of species, or shifts in species composition? Should we manage for habitat variability more explicitly across grasslands.
The game changer here would be to accept that changing long-term grazing might actually lead to instability in the system, but improved conservation outcomes because it favours more species ultimately (at landscape scales). Alternatively, we could ask: does grazing nullify the ability of certain species to establish because it reduces their germination niche availability - this might be the mechanism that underpins why grazing favours some species over others.
Where: this is a field-based project located across the grassland ecosystems of northern Victoria

Project 3: Establishment of native shrubs in temperate woodlands
Many native temperate woodlands have being undergoing a process of woody plant encroachment over the last few decades in response to land use change. Good examples include Kunzea increases in the foothills forests of the Yarra Valley, Coast Tea Tree encroachment in grassy swale woodlands at Yanakie Isthmus, and Leptospermum domination of herb-rich woodlands in the Grampians. Students in my Lab have also shown that Hedge Wattle (Acacia paradoxa) has increased in cover in temperate woodlands over the last five decades, but the processes that underpin this spread remain unclear.  High levels of herbivory by kangaroos (which reduce competition from ground layer plants) and soil disturbance (which create microsites for germination) are thought to be important precursors to shrub establishment in many woodlands, while the absence of fire also enables fire-sensitive species to become abundant. Using herbivore exclosures in grassy woodlands where groundcover biomass is now much higher than in surrounding (over)grazed woodland, this project aims to examine how competition and disturbance contributes to initial seedling establishment of species such as A.paradoxa to better understand this widespread process.

Where: this is a field-based project located in grassy woodland near Geelong

Project 4: Building a framework for temperate ecosystem dynamics that includes rainfall variability

Climate fluctuation is the ‘norm’ in southern Australia, with climate variation driven by El Nino/La Nina oscillations.  Most ecological focus of climate variability has been on the effects that drought has on tree mortality in woodlands and forests. But what about the effects of La Nina, above-average rainfall years? In non-fire prone ecosystems such as Box-Ironbark forest and herb-rich semi-arid woodlands, where fire is not the cue for germination, might recruitment of key species such as Acacia be linked to rainfall variability. Hence, might La Nina recruitment vs. El Nino mortality be the chief driver of population processes in many ecosystems (as opposed to fire-driven systems where time since fire is of primary importance). If population processes are clearly linked to rainfall variability, this should be observable in the stand structure of species i.e pulsed recruitment that coincides with wet years. Additionally, what traits of species that are responsive to rainfall variability – we know this for fire but not climate-driven recruitment.
Where: this is a field-based project located in ecosystems such as Yellow Gum woodlands of far western Victoria

Project 5: Woodland tree recruitment and patch-dynamic theory
Tree–grass coexistence in savanna ecosystems – or the ability of grassy and woody vegetation to co-occur without either life-form becoming dominant – is not well understood, although rainfall and disturbance regimes are generally implicated.  According to patch-dynamics theory, woody vegetation does not become dominant because dense episodic recruitment is mirrored (over time) by episodic mortality (caused by drought). Alternatively, following dense episodic recruitment, trees self-thin over time as slightly larger trees out-compete smaller trees in an even-aged stand. Tree spacing and size inequality may be related to self-thinning because patterns of tree distribution can be the result of competitive interactions among individuals. For example, regular spacing could indicate competitive interactions and self-thinning among individuals in a population, such that larger trees are further from neighbours than small trees. Both concepts generally apply to trees that recruit en masse (e.g. Red Gums) but I think they could be applied to understand recruitment dynamics in the iconic eucalypt woodlands of eastern Australia. Hence, this project will investigate the applicability of the patch-dynamics model of tree–grass coexistence as a means of explaining the recruitment of temperate woodland trees and the capacity of woodlands to resist thickening into forests.
Where: this is a field-based project located in woodland ecosystems

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