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
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
