Tuesday, 10 May 2011

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.
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. 

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.