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

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