Our research focuses on the population dynamics of plants and how they are influenced by impacts of natural disturbances and global environmental change. We are particularly interested in the interactive effects of fire, grazing and drought in grasslands and woodlands in southern Australia, and how climate change, fragmentation and shrub encroachment affect ecosystems.

Wednesday, 17 August 2011

Assessing habitat condition – an old approach to an old problem

The drawing above, depicting a one yard by one yard quadrat, was published in 1936 (R.T. Patton Ecological studies in Victoria; Part IV – Basalt Plains Association. Proc. Roy. Soc. Vict., 48, 172–190). It is one of the first descriptions of the diversity in native grasslands near Melbourne. Historically, botanists tended not to focus on the area west of Melbourne. Von Meuller (the famed 19th century botanist) seldom visited the area. It was not until 1916 (Sutton) that the flora was reviewed and then only the Keilor Plains. By the time of John Stuwe’s review of native grasslands in western Victoria in 1986, he was only dealing with 0.15% of the original area of Themeda grasslands.

Such historical information is of immense importance when trying to determine how the composition and structure of native grasslands has changed in the almost complete absence of floristic information, and to identify remnants that most approximate the historic condition.

Despite the small samples size (n=1), we can gain many importance pieces of information from this 90 x 90 cm quadrat:
Native species richness = 12 (3 grasses – all perennial, 9 forbs – 1 annual, 8 perennial)
Exotic species richness = 1 (the annual grass Aira)
Themeda tussock density = 13 (comprising many small tussocks)

So how does a current day native grassland dominated by Themeda compares to one historic example we have?

Quadrat depicting current species density at Mt Cottrell
(Drawing by Hannah Forrester)

Recently, some students of mine re-drew grassland quadrats in a conservation reserve that is less than 3 km from Patton's original site. The grassland is dominated by native species . A typical example of the current day diversity is shown above.

Native species richness = 3 (the dominant perennial grass + 2 forbs)
Exotic species richness = 4 (1 annual grass, 1 annual legume, 1 Iridaceae, 1 perennial forb)
Themeda tussock density = 31 (comprising many small tussocks)

The grassland at Mt Cottrell looks like a high quality remnant
- but comparison with historical data suggests otherwise
(Photo: John Morgan)
It's clear that, despite the grassland looking like a native grassland from a structural perspective, profound changes have occurred. Invasions of non-native species are one obvious change - but they are largely sub-ordinate species and do not necessarily strongly influence the function of the grassland. Rather, it is the almost complete loss of interstitial native species that has been most profound. Where there might have been 11 (largely perennial) species in the inter-tussock spaces, our survey showed just two. And these occurred at incredibly low density.

It's likely that the loss of native species has had two principle drivers - the loss of palatable species during the period of stock grazing that preceeded the declaration of the reserve probably accounts for the absence of many typical grassland forbs unaccustomed to on-going and heavy herbivory. And some loss might have also occurred due to the lack of frequent burning. Themeda assumes monodominance at the site, and appears to strongly compete for light and space with interstitial species. Many temperate grasslands are burnt irregularly after conservation, leading to rapid declines in diversity, so similar processes might be at play here.

While the comparison we have made is very simple, and perhaps old fashioned, the historical data gives us something to aim for when considering the restoration objectives for the site. It tells us what sort of native species might be returned and at what densities. This is an incredible challenge, and not for the faint hearted. But at least our objectives are evidence-based and this is likely to lead to restoration that has a clearly defined end-point. It tells us that the re-establishemnet of interstitial forbs, not weed control, is our priority, and that to do this, reducing the dominance of Themeda is paramount.

Sunday, 7 August 2011

Global plant trait data now more accessible

Theophrastus - one of the first botanists!

The use of plant functional traits to describe patterns in ecology has a long history. Indeed, it was Theophrastus who, in about 300 BC, first categorised plants by their growth form: tree, shrub, herb. Ian Wright's paper on the Worldwide Leaf Economics Spectrum remains a classic for me because it showed how using a large dataset (in his case, >2500 species) could search powerfully for patterns in leaf traits and how these were shaped by climate drivers. Such studies are well-beyond the scope of the average researcher, but by collating and sharing data, such insights become possible.

The PFT field is flourishing - so well that a new database has just been launced to act as a repository for trait data. The unimaginatively named TRY Database looks like a real winner for ecologists interested in examining large-scale patterns in nature using the traits of plants that underpin their response to environment and disturbance. It's not a publicly accessible database - you'll have to provide datasets to get access - but I think it could act as an important repository for trait data that remains buried in Honours and PhD theses, and the recesses of Excel files.

Location of sites across the globe for which plant
trait data has been submitted to TRY

This database aims to gather datasets that cover a variety of biomes, geographic areas, and traits. Already, the database comprises about 2,400,000 trait entries for more than 64,000 plant species and about 1000 different traits. My own research group is busy collating the data we have assembled over the years - an impressive dataset of >500 species from the temperate and alpine grassy ecosystems of southern Australia. In the spirit of co-operation, we hope to submit our data to TRY so that others can use our hard-won data.

For further information on TRY, a couple of recent papers have just been published:

Kattge et al. (2011) TRY - a global database of plant traits. Global Change Biology 17, 2905-2935

Kattge et al. (2011) A generic structure for plant trait databases. Methods in Ecology and Evolution 2, 202-213