Congratulations to Brad Farmilo

Brad Farmilo submitted his PhD thesis just before Christmas titled "The internal dynamics of forest fragments". Brad's been with me these last four years, and undertaken  a really neat study about the ecological mechanisms that change (e.g. herbivory, recruitment dynamics) when you grow pine forests around remnant eucalypt forest. He did this at the world's second longest experimental fragmentation study site: the Wog Wog Habitat Fragmentation Experiment, near Bombala in southern NSW.

Importantly, we think we've seen an interaction between climate drying and fragmentation as it affects plant species density. Brad's work lays the foundation for understanding how pine forest harvesting (which is due to occur soon) then subsequently affects patterns and processes in these forests.


You can check out his Research Blog here: http://wogwogfragmentationexperiment.blogspot.com.au/
It tracks his progress over the years, and provides some neat tips about undertaking a PhD.

Here's the Executive Summary of his thesis:

Virtually all of Earth’s ecosystems have been dramatically transformed via human actions leading to irreversible biodiversity losses. Global extinctions are expected to result as species richness declines towards an equilibrium determined by the amount of remaining habitat. This thesis uses the Wog Wog Habitat Fragmentation Experiment (the second longest running experiment of its kind) in temperate south-eastern Australia to investigate how patterns of plant species density vary with size of forest fragments (0.25, 0.88 and 3.06 ha), as well as identifying factors which may influence vegetation dynamics within a plantation landscape. Species density in small fragments was higher than continuous forest for both total and common species at small spatial scales. This finding contradicts much of the fragmentation literature suggesting that the mature plantation matrix may alter important within-fragment conditions, which are yet to be documented. Small fragments were also characterized as having higher soil moisture and canopy cover, and lower daily maximum temperatures, which is strongly influenced by the structure of the adjacent plantation. Rates of recruitment of the dominant shrub appear to be more pronounced within fragments, irrespective of size, than in areas of continuous forest (although not significant at alpha = 0.05). This finding, in concert with microclimatic changes in small fragments, may have caused an increase in structural complexity within fragments, which may also positively influence plant species density in small fragments. We also show that the affect of vertebrate herbivores on understorey seedlings is species-specific, but that their influence is largely uniform across the fragmented landscape and continuous forest areas. These findings have been generated from a single point in time and therefore, it is expected that due to the nature of the landscape (forest removal and a subsequent cycle of plantation development and harvesting) the long-term biodiversity in forest-plantation systems will be imperiled more so than traditional grass-forest systems because of profound ecological changes that are occurring not just in space, but in time.  In addition, many of our results suggest that there is a minimum size of fragment to be maintained in these landscapes below which ecological processes are disrupted and may therefore be of reduced value to native biodiversity.


 

Students completing in 2013

BEN ZEEMAN
Changes in the stand dynamics and composition of a long-unburned coastal woodland - effects of drought, fire and herbivory

My honours research assessed changes in vegetation structure and composition in a woodland at Ocean Grove, Victoria using data from three points in time (1971, 1996, 2012). Previous assessments of the site had documented the replacement of Eucalyptus with the mid-storey species Black She-Oak in the long absence of fire. In my study, changes in the continued absence of fire were assessed, as well as whether these changes could be reversed with the re-introduction of fire.

 

Long-unburned coastal grassy woodland at Ocean Grove Nature Reserve

I identified that in the continued absence of fire, Black She-Oak had consolidated dominance, with declines in tree density compensated for through an increase in basal area, while all other trees, as well as small shrubs in the understorey, declined markedly.  Where fire had been re-introduced, the structure of the woodland had opened up, creating large canopy gaps and killing many Black She-Oak trees. Surprisingly, trees did not recruit in open areas created by fire, most likely a consequence of wallaby browsing. Small shrubs that had declined in the absence of fire failed to recover with the re-introduction of fire, nor were these species found in the germinable soil seed bank. Changes that did occur with the re-introduction of fire were largely characterised by the proliferation of grass cover.

Burnt coastal woodland at Ocean Grove Nature Reserve. While the canopy has
opened up, fire did not recover once common native shrubs.

 

Thus, the changes that had occurred in the long absence of fire were found to be non-reversible with the re-introduction of fire.

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

The David Ashton Scholarship winner announced

Citra Jewson-Brown was recently awarded the David Ashton Scholarship. Congratulations!

The award recognises the most outstanding new Honours students undertaking research in the field of plant ecology in the Department of Botany at La Trobe University. It is named after Dr David Ashton, a Victorian plant ecologist who spent his entire working life trying to understand the regeneration and succesional dynamics of Mountain Ash forests. He also worked with students in the alpine regions of Victoria, so would be chuffed to know that Citra intends to focus her thesis on high mountain ecology.

Citra will work with Dr John Morgan on insect herbivory in high altitude populations of Snow Gum (Eucalyptus pauciflora). In particular, she is keen to quantify how herbivory varies within and between populations of Snow Gum. This will likely involve an interaction between environment (altitude) and "provenance".

Honours Project Overviews – for studies beginning in 2012

In the Morgan Plant Ecology Lab, we explore questions relating to species diversity, environmental gradients, vegetation dynamics, extinction processes, disturbance and land use. Much of our work is conducted in the threatened grassy ecosystems of lowland Australia, as well as alpine vegetation. We focus on the importance of plant demography and niche processes in community assembly, and use plant traits to predict vegetation responses to key drivers such as climate, habitat loss and invasions. I am interested to talk to students about their own ideas, but provide some general project themes as examples of projects in 2012.

Paying the extinction debt – what are the plant traits / attributes of species that have already paid the ‘debt’ in fragmented ecosystems relative to those species that have yet to do so?

Habitat loss and degradation pose a major threat to biodiversity. Extensive loss of habitat area can result in local extinction of specialist species. However, many species exhibit a delayed response to environmental changes due to the slow intrinsic dynamics of populations, resulting in an extinction debt. Repeat surveys can be used to directly assess changes in habitat characteristic species by comparing historical and current inventories in fragmented grasslands with the aim to characterize the species that constitute extinction debt. In communities in which extinction debt is already paid, locally extinct and persistent species might be characterised with different life-history trait values. If so, results can be applied to less degraded grasslands, where the extinction debt is not yet paid, to determine those species most vulnerable to future extinction.

Identifying resilience to a warming climate and capacity for adaptive management in Australian alpine plant species: a seed-based approach

The Australian Alps are heritage listed, one of 11 Australian centres of plant diversity, and one of the world’s 187 biodiversity hotspots. Already experiencing reduced snow cover, increased temperatures and elevated CO₂, they have been identified by the IPCC as critically vulnerable to climate change. Alpine areas occur in narrow altitudinal bands; thus, plant species and communities have limited scope for movement to cooler, wetter, refuges. One of the major determinants of how climate change will affect alpine plant species will be their ability to reproduce and recruit under novel environmental conditions.

We aim to identify resilience to a warming climate in alpine ecosystems by focusing on seed traits. We will collate baseline information on alpine seed regeneration requirements (physiological dormancy mechanisms, thermal germination niche breadth) to summarise current understanding and make predictions. We will expand knowledge on alpine seed and germination traits using key predictors of resilience such as life form (grasses, forbs, shrubs), habitat breadth (narrow versus broad), population size (rare, common), and phylogeny. We will select alpine species, contrasting one or more of the above characteristics, for assessment of seed production, dormancy (such as stratification requirements), thermal germination niche breadth (variation around optimal germination using temperature gradient plates) and variation in these traits among populations.

 

The role of dominant species in the structure and function of ecosystems

Many communities are characterized by uneven distributions of species. Understanding the processes underlying these patterns and their implications for community dynamics and ecosystem function is a central endeavor of ecology. Often in communities only a few species are very common (or dominant), whereas a majority of species occur at moderate or low abundance (subordinate or rare). Dominant species generally garner a disproportionate share of resources, contribute most to productivity and other ecosystem functions, and are consistently present in the community over time. Rare and uncommon species, on the other hand, are collectively the most diverse component of the community, but generally contribute less to ecosystem functioning (although there are exceptions, e.g., legumes) and often experience high levels of turnover.

Our research has shown that dominant species (i.e. C4 grasses like Kangaroo Grass) can strongly influence diversity, and it is through the impacts of disturbances on their abundance that variation in community attributes and ecosystem processes in space and time are observed. These dominant species likely play a central role in the maintenance of ecosystem function and the dominant species are important in determining resistance of communities to invasion. Our research seeks to (a) understand why these species are dominant (i.e. trait-based approaches) and (b) gain a more general understanding their role in ecosystems.

New Honours Student in the Lab

Citra Jewson-Brown has joined the Lab.

Citra will investigate how herbivory affects fitness in snow gum seedlings. Upslope advance of snow gums in the Australian alps are thought to be mostly due to increases in temperature, but we think herbivory also plays a role.

The basic starting point for this project is the observation that herbivory on eucalypt saplings varies dramatically in the high country. Some saplings (e.g. near treeline) have high levels of defoliation whereas other seedlings (in subalpine woodlands and snowplains) do not suffer as much. Why? Do ants ‘defend’ saplings against defoliation – many saplings have ant nests at the base of saplings and these tend scale insects. Hence, as elsewhere, perhaps the ants 'protect' the scale and in the process, defend saplings from defoliators.

There are three basics steps that will be undertaken in this project:

Step 1 – quantify the nature of herbivory across sites that vary in altitude, within a plant, within a season

Step 2 – quantify the abundance of ants and scale on saplings – and how this varies with altitude

Step 3 – experiment by excluding ants (and/or scale) from a number of saplings and compare to unexcluded saplings (where there is an obvious utilization)

What we hope to learn – controls on eucalypt ‘performance’  (a key species in the alpine) are driven by factors other than climate; one may be an interaction with another key species (ants) which may themselves be affected by climate and non-climate factors (scale).

Honours Students 2010/11

Two Honours students undertook their thesis in the Plant Ecology Lab under the supervision of Dr John Morgan in 2010/11. Below is a summary of their findings.

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Tara Angevin:

How does functional diversity change with land-use intensification?

Biodiversity loss, due to anthropogenic land use, is of increasing concern, as human activities have the potential to erode the ecosystem processes and services important to ecosystem functioning. While many studies have explored the impacts of disturbance on species richness, a neglected aspect of biodiversity studies is functional trait diversity (the degree to which species differ from one another in relation to their functional traits). Plant functional traits have been recognised as valuable tools for understanding the mechanisms driving community composition, as the range of functions provided by a plant community is thought to be dependent on the diversity of trait states and the species that express them.

Many studies assume that increasing disturbance will lead to a loss of species richness, in turn driving a loss of functional diversity, consistent with the sampling effect hypothesis. There is evidence to suggest that there are numerous trajectories possible for the species richness and functional diversity relationship, many of which deviate considerably from the typical sampling effect.

This trait-based study investigated the relationship between species richness and functional diversity using a space-for-time chronosequence method, to determine whether the loss of species richness would automatically result in the loss of functional diversity. Functional trait diversity and species richness were linked to one another using multi-dimensional trait amalgams. Three novel functional diversity indices, Functional richness (FRic), Functional evenness (FEve) and Functional divergence (FDiv) were applied to determine the level of functional space occupied by the plant community. Multi-trait diversity indices look at the interaction of traits in functional space, rather than just looking at the diversity of trait states.

In addition, the current study aimed to investigate which traits help underpin the changes observed across a disturbance gradient, through single trait analysis.

Floristic composition and functional trait signatures of both native and exotic species were compared between three disturbance treatments; disturbance categories were stratified according to information available based on time- since- disturbance and disturbance type. Lastly, this study aimed to determine whether plant functional traits are a useful currency to help underpin the patterns in species richness observed across the various disturbance gradients.

These studies provide evidence to suggest that species richness and functional diversity are not always correlated, and report that disturbance can lead to an increase in species richness (both native and exotic) yet no corresponding shift in species functional attributes. No significant differences in functional diversity was observed between low, moderate and high disturbance treatments when aggregated in multi-trait analysis, though results did show slight shifts in functional trait diversity, when analysed individually. Leaf area was reported to increase with increasing disturbance and plant height was shown to decrease with increasing disturbance. This type of relationship is not frequently reported in current literature and provides evidence that species richness and functional diversity can be decoupled and that novel communities may reassemble following disturbance events.

It was concluded that species richness and functional diversity are dependent on a number of factors, such as the size of the species pool, competitive interactions, conditions present within a specific type of a system (ie/site productivity) and the type of disturbance inposed onto a system. These studies also indicate that disturbance intensity was perhaps not severe enough to impact on environmental filters or there has been insufficient time to see a shift in functional diversity. 

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James Vincent
What evidence is there for upslope migration of the obligate-seeder Alpine Ash (Eucalyptus delegatensis) after fire?

Current models predict mountain species will migrate upslope in response regional climate warming. Evidence from the literature supports the upslope advance of species but also demonstrates that, in many cases, migration lags behind climate change. This study focused on changes in the upper distribution of Eucalyptus delegatensis (Alpine Ash) at the montane/sub-alpine after a recent landscape-scale fire in the Australian Alps.

Eucalyptus delegatensis only recruits via seed after crown-scorching fire and is considered a long-term occupant of a site 2 - 4 years after regeneration. Consequently, Alpine Ash can only track climate and migrate upslope following fire events. This study demonstrated the upper distribution of E. delegatensis shifted only 4 - 6 m in altitude following fire in 2003 (last burnt in 1939), despite a potential increase of 130 m in altitude based on local temperature increases. It is hypothesised that upslope establishment was constrained by either limited seed dispersal or unsuitable sites for regeneration above the boundary.

To untangle these potential mechanisms, a seed sowing (to overcome dispersal limitation) and transplant experiment (to determine effects of local site factors on early survival and growth) was conducted at Lake Mountain. Two age classes of Alpine Ash (<3 months and 18 months old) grew successfully, with low mortality, 100 m above the boundary. A slight non-significant trend toward greater growth was detected below the boundary. Therefore, it is proposed that Alpine Ash may be dispersal-limited in years favourable for growth but safe-site limited in years of more extreme climatic conditions. Further work is required, however, to substantiate this hypothesis.

In the context of the future migration potential of Alpine Ash, the species is unlikely to track changes in climate due to the requirement of fire for recruitment, coupled with long intervals between fire events, a poor dispersal ability, and reliance on favourable growing conditions after fire. It is proposed that the migration potential of a species’ may be ranked according to its climatic and edpahic requirements and traits such as dispersal ability, generation time and germination cues; specialists and species of low dispersal capacity and long generation time are more likely to lag behind changes in climate.