Monday, 4 September 2017

Come work in the Plant Ecology Lab in 2018

In 2018, the focus of Honours projects in the Plant Ecology Lab will firmly be on factors that affect species distributions & abundance (change in climate, fire regimes, competitors) and the plant population dynamics that underpin these processes. One of the key research questions in my Lab is: how do C4 grasses shape ecosystems via their effects on fire regimes & competitive interactions, and how do plants species in ecosystems respond to ecosystem drivers over decadal timescales. These questions have important implications for how we view ecosystem change, and management to maintain biodiversity. Below are some ideas for projects. I am happy to discuss other projects with students whose broad interests align with the types of research I undertake. Please contact me on


Project 1: How fire regimes can shift a biome. In the tropical savanna of northern Australia, fire regimes shape the structure and function of ecosystems. But what exactly is the mechanism and are feedback loops involved? One clear pathway is that fire affects savanna “receptivity” to establishment by Sorghum intrans (an annual native C4 grass that establishes & persists under high light environments; it seems not to like growing much under eucalypt canopies). This alone, however, is probably only half the story. With an increase in Sorghum (dominance and extent), this species likely changes the fire regime by increasing the intensity of fire, further promoting this species over woody plants (by negatively affecting mid-storey and overstorey woody plant cover and light interception). It may also affect the distribution of other grass species because of a) competitive effects and b) fire intensity effects. This simple (and oft-quoted) feedback is poorly documented in the literature but can be directly tested in one of Australia’s few long-term fire regimes experiments. At the Territory Wildlife Park (Darwin), CSIRO and Charles Darwin University have been investigating how fire regime (1, 2, 3, 5 yr burn frequency vs. unburnt controls) affects biota, starting from a little burnt tropical ecosystem. The experiment has been going for 15 yrs. Early studies (after just 4 yrs of the experimental implementation) hint that Sorghum was increasing and woody plants were in decline, but it was too early to determine whether fire could switch the system from woody to grassy. In this study, we will build on previous work and ask: what is the current extent of Sorghum and how does fire regime affect this relationship? How is Sorghum cover related to woody plant cover (i.e. competition by canopy and mid-storey species for light)? How is grass diversity distributed in relation to fire regime, and Sorghum dominance? How does Sorghum affect properties of fire such as intensity? We will re-survey the plots to model changes in dominance over time (ecological tipping points versus linear trend change) and how Sorghum affects fuel dynamics and fire behaviour. Spatial patterns of Sorghum versus woody (and other grass) plant cover will be investigated, possibly using transplant experiments. The project involves a month of field work in Darwin. Co-supervised with Dr Warren Paul (LTU – AW), Dr Anna Richards (CSIRO) and Dr Dick Williams (CDU).


Note: Project 1a. I may also have a project on faunal responses to fire in the Territory Wildlife Park. Arthropods found in fire-adapted habitats have specific traits and dispersal strategies to deal with frequent fires. For example, they seek refugia during fires where temperatures may be lower. Refugia are areas adjacent to or within a burn area that enhance arthropod survival during a fire, facilitate persistence of individuals, or allow for post-fire recovery. These may include insulated underground burrows, fire-resistant termite mounds, or patches of unburned vegetation. Dispersal is another obvious response to fire for arthropods, and as a result, winged orders have higher survivorship than less-mobile taxa. A couple of years ago I observed, ahead of an experimental fire, insects, lizards and even frogs moving up the trunk of a tree. They were clearly trying to get away from the flame zone. What warning signals are they cueing into? This project will quantify movement patterns up and down tree trunks, before and after fire in frequently burned tropical savanna. Depending on what we find, we will try and unravel the sensory cues that lead to this fire-scape behaviour. Co-supervised with Dr Alan Andersen (CDU).


Project 2: 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, woody plant encroachment and loss of diversity. Land managers are increasingly re-introducing fire to long unburned landscapes to promote diversity, but what changes occur when fire is re-introduced to ecosystems when it has been long 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 burn 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.


Project 3: Banksia decline in coastal grassy woodlands: encroaching shrubs and the water balance. Coastal grassy woodlands have declined across much of their range. One main reason for decline has been an increase in woody plants (like Coast Tea-tree, CTT) in the decades where fire has been excluded from the ecosystem. Here, CTT shrubs have established and infilled between trees, largely causing the elimination of the ground flora. This process is now well-documented. What still mystifies ecologists is the long-term decline of overstorey trees like Coast Banksia (Banksia integrifolia, Proteaceae), a foundation species of grassy woodlands that can achieve i) enormous size, ii) store vast amounts of carbon, iii) provide abundant floral resources for nectivores and iv) important nesting sites via hollows. The decline of Coast Banksia in places like Yanakie Isthmus and Oberon Bay at Wilsons Promontory National Park has been a slow, drawn out process, with canopy loss and health the most obvious sign of ill-health. Some studies have tried to understand why trees are in decline – and to date, the answer has largely eluded researchers. We know that it’s not a) mineral nutrition imbalances, b) root pathogens or c) disease. In this study, we will explore the hypothesis that encroaching CTT shrubs have reduced water availability to Coast Banksia, and that Coast Banksia surrounded by dense CTT are under more water stress than trees in the absence of encroaching CTT. This study will be the first to determine if water stress could account for loss of canopy and necrotic foliage and, ultimately, to tree mortality in what is a water-limited ecosystem (due to deep, well-drained calcareous sands). We will examine soil water balance in areas with and without encroaching CTT to determine how shrubs dry soils. We will investigate the rooting depth profiles of Coast Banksia and CTT. Using an ecophysiological approach, we will examine tree stress (particularly over summer) in a natural experiment by quantifying leaf water potential, leaf gas exchange parameters (net photosynthetic rate and stomatal conductance) and chlorophyll fluorescence in areas with and without dense CTT. In a BACI experiment, we will remove encroaching CTT shrubs around Banksia and / or use supplementary watering to see if this changes the plant stress profile of Coast Banksia trees. Co-supervised with Dr Pete Green.

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