To identify the properties of habitat mosaics produced by fire that enhance the persistence and status of plants in eucalypt-dominated mallee habitats.
Key research questions
- How well do the current Key Fire Response Species serve as surrogates in reflecting the state of the floristic and structural composition of tree mallee communities?
- Are there other species of plants that would be better Key Fire Response Species? What attributes do they share?
- Does a high number of seral stages within a mosaic equate to high floristic and structural diversity?
- What are the thresholds of burning frequency which, if crossed, lead to effectively irreversible changes in floristic and structural composition of plants communities?
Methods – pilot study – spring 2006
Before sampling was undertaken at all sites in all mosaics, a pilot study was conducted to identify the most appropriate methods to gather data to address the botanical questions listed above, as well as provide detailed habitat data for the faunal components of the study.
Initially mosaics to be sampled were subdivided between northern and southern landscapes, as aridity increases to the north. Thirty sites were chosen based on topographic position with an attempt to get an even spread of dune vs. swale within each time-since-fire category. The Time Since Fire categories were 'old' (pre-1970s), 'intermediate' (1980s), and 'recent' (2004-2006). For the pilot study, 10 sites were studied for each TSF category. The sites used were located beside the pitfall lines used for the reptile and mammal surveys. The quadrats used were 5x5m, 10x10m, 20x20m, 30x30m, 40x40m and 50x50m in a nested formation.
Within each quadrat the following were recorded:
- All new species as they occur
- Number of individuals present for key species e.g. eucalypts, Triodia and shrubs
- Number of eucalypt stems and their DBH in the 20x20m quadrat.
One 100m transect was carried out at each site in order to quantify percentage cover and height of key species. The point intercept method was used to measure cover and height of species along the transect. Height classes will be used.
Habitat variables also measured included:
1. Structure – height classes along a line transect
- stem density and DBH of eucalypts within a 20x20m quadrat
- cover values for each height class along a line transect
2. Litter – estimate amount/measure depth
- descriptive information e.g. centred around eucalypts or evenly distributed etc
- separate into size classes e.g. fine (<6mm) or coarse (>6mm)
- collect for fuel load estimation (summer 2008)
- presence/absence of logs (within certain size classes)
3. Bare ground – percent cover along a line transect (or within a quadrat)
4. Triodia measurements – number of clumps
- estimate cover
- size measurements e.g. circumference
5. Identification of dominant (and/or all) species within an'x*x'm quadrat (size of quadrat to be determined from the pilot study)
6. Habitat complexity score
Seed bank studies
Plant biodiversity does not include only those species that are present above-ground but must also include those species present in the soil seed bank. Some species have very long-lived soil seed banks and thus there absence from the above-ground community does not necessarily equate to an absence from future communities if a relevant environmental cue occurs (e.g. rain, increase in accessible light). Do certain species (e.g. fire ephemerals) drop out of the seed bank as time-since-fire increases?
Sample of soil were collected within a subset of very old, intermediate and very young sites across time-since-fire categories.
We collected ten 5cm soil cores at each site within a 10x10m quadrat. These samples were pooled within a site before establishing glasshouse trials. Samples were subdivided across the topographic gradient (i.e. dune vs. swale), soil type (i.e. deep vs. shallow sand) and vegetation communities (i.e. loamy sands vs. woorinen sands). Germination was stimulated using cues such as smoke water, charcoal and heat for fire, and watering for a set period to simulate a large rainfall event. Control samples with no treatment except water were also used.