Great Western Woodlands, Changes in Plant Diversity Indices, Composition and Cover in Eucalyptus salubris Woodlands Across Time Since Fire Chronosequence, 2012 

The data set contains information on plant diversity indices, species composition, vegetation cover and edaphic properties from the Eucalyptus salubris woodlands, Great Western Woodlands site. The data represents changes in plant diversity due to disturbance with time since fire in a chronosequence. 

We at TERN acknowledge the Traditional Owners and Custodians throughout Australia, New Zealand and all nations. We honour their profound connections to land, water, biodiversity and culture and pay our respects to their Elders past, present and emerging.

Funding: (1) Australian Supersite Network, part of the Australian Government’s Terrestrial Ecosystems Research Network https://portal.tern.org.au/, a research infrastructure facility established under the National Collaborative Research Infrastructure Strategy and Education Infrastructure Fund - Super Science Initiative - through the Department of Industry, Innovation, Science, Research and Tertiary Education. (2) A biodiversity and cultural conservation strategy for the Great Western Woodlands, Western Australian Department of Environment and Conservation; Terrestrial Ecosystems Research Network. 

Disturbances are important ecosystem processes affecting patterns of species diversity (including species richness, diversity and evenness) and community composition. Determining appropriate disturbance regimes for particular ecosystems is thus an important issue for natural resource management. There have been few studies of the response of plant species composition and diversity to fire in ‘fire-sensitive’ Mediterranean-climate woodlands, where the dominant overstorey trees are typically killed by fire, resulting in dense post-fire recruitment. The Great Western Woodlands (GWW) region of south-western Australia supports the world’s largest remaining area of Mediterranean-climate woodland, which in mosaic with mallee, shrublands and salt lakes cover an area of 160,000 km². Eucalyptus woodlands in this region are typically fire-sensitive, and fire return intervals recorded over recent decades have been much shorter than the long-term average. This has lead to considerable conservation concern regarding the loss of mature woodlands, and has highlighted a need to better understand how plant species composition and diversity changes with time since fire. We measured changes in diversity indices and floristic composition in Eucalyptus salubris woodlands with increasing time since fire at 72, 50 x 50 m plots using a space-for-time approach. To estimate stand ages for this study we used satellite imagery, growth ring counts and relationships between growth ring counts and plant size, resulting in an estimated time since fire range sampled of 3 to 370 years. 

(1) Floristic sampling:- For each plot we recorded the vascular plant taxa present and estimated their abundance by systematically placing a 12.5 mm diameter pole vertically at 50 points per plot, each 3 m apart, and recording the identity of all plants with live parts intercepting the pole. Sixteen of these points were placed along each of the two sides of the 50 x 50 m plot commencing at the north-west corner, with the remaining 18 points placed along the diagonal starting in the same corner. This technique provided an objective measure of abundance reflecting but not equivalent to protective cover. Species that were present but not recorded at point intercepts were allocated a nominal proportional abundance of 1%.

(2) Diversity indices:- PRIMER analysis software (Version 6.1.11) was used to derive diversity indices for floristic plot data. We tallied total species number per plot (species density), and using cover data, calculated the Shannon diversity index (logex) and Pielou’s evenness index.

(3) Soil sampling: (a) A single bulked sample of the top 10 cm of soil was taken from aggregation of multiple 2 cm diameter sub-samples collected from throughout each of 52, 50 x 50 m plots sampled in spring 2010. Samples were stored at ~4°C until delivery to the CSBP Futurefarm analytical laboratories (Bibra Lake, WA), where they were thoroughly mixed, air dried at 40°C, and ground to pass through a 2 mm sieve.

(b) Analyses were undertaken on each bulked sample as follows (where given, method numbers apply to Rayment GE & Higginson FR 1992, Australian Laboratory Handbook of Soil and Water Chemical Methods. Inkata Press, Melbourne): available phosphorus (Colwell method, bicarbonate-extractable phosphorus - manual colour, 9B1), potassium (Colwell method, bicarbonate-extractable potassium, 18A1), ammonium and nitrate (measured simultaneously using Lachat Flow Injection Analyser, soil:solution ratio 1:5, 1M KCl, indophenol blue, Searle 1984, Analyst 109:549-568; and with copperized-cadmium column reduction), organic carbon (Walkley and Black method, 6A1), extractable sulphur (40°C for 3 hours, 0.25M KCl, measured by ICP; Blair et al. 1991, Aust J Soil Res 29:619–626), pH (1:5 soil/0.01M CaCl₂, 4B2) and conductivity (1:5 soil:water extract, 3A1).

(4) Sampling Study Extent: Plots were sampled on the date at which they were established. Two times since fire are shown in plot details for all plots: 1) Time since fire as determined from analysis of Landsat imagery. This truncated the true time since fire for plots last burnt that were more than ~ 60 years ago. 2) Estimated time since fire of plots burnt > 38 years ago based on growth ring counts and growth ring-size relationships, using Model 2 of Gosper et al. (in press). Further detail on methods to determine the time since fire of plots can be found in: Gosper, C.R., Prober, S.M., Yates, C.J. and Wiehl, G. (2013) Estimating the time since fire of long-unburnt Eucalyptus salubris (Myrtaceae) stands in the Great Western Woodlands. Australian Journal of Botany 61, 11-21.

(5) Sampling description: Each of the 72 plots was 50 x 50 m, with sides aligned north-south and east-west and with a steel dropper placed in the north-west corner. Plots were placed in relatively uniform vegetation within 1 km of vehicular tracks on public land; Nature Reserves, Unallocated Crown Land or Unmanaged Reserves. Plots were spaced at least 250 m apart, and at least 500 m apart for plot of the same time since fire. Further detail on the sampling can be found in: Gosper, C.R., Yates, C.J. and Prober, S.M. (2013), Floristic diversity in fire-sensitive eucalypt woodlands shows a ‘U’-shaped relationship with time since fire. Journal of Applied Ecology doi: 10.1111/1365-2664.12120