Conserving Plant Diversity in Banksia Woodlands

Final report on the project

Dr William R Loneragan
The University of Western Australia

This project aims to establish the relationship between community composition, the soft seed bank and fire history in an area of urban remnant Banksia Woodland near Perth, Western Australia.

Sixteen sampling sites were chosen within areas that had remained unburnt for 3, 21, 39 and >48 gears. Sixteen sites were randomIy selected, four from each ‘unburnt’ group. At each site soil cores were extracted to a depth of 19 cm and divided into litter, humus, 9 5 cm and 5 18 cm lagers. These samples were used to compare estimates of species composition and seed density in the soil seed bank following treatment by heat (80ºC for 15 min), smoke (1 hour exposure using the traditional seedling emergence method and a method involving prior seed concentration through centrifugation.

Preliminary trials, using the traditional seedling emergence method, were carried out, smoke, heat, heat plus smoke and untreated (control). Smoke treatment resulted in significantly more seed germinating than the heat treatment, and a greater (though non significant) seed density estimate than the heat plus smoke or control treatments.

A second germination trial was undertaken following concentration of the soil samples by sieving, mixing with salt solution and centrifugation. The centrifugation method was shown to extract ~ 85% of all seed < 1.0 mm from the mineral soil fractions. Estimates of seed density and species richness for some depth fractions were Increased in comparison to the conventional seedling emergence method.

The relationship between soil seed bank composition and the above ground vegetation during post fire succession was explored through multivariate analysis (DECORANA). The concentration method, unlike the traditional emergence method, was shown to be well correlated with the above ground vegetation. This similarity is thought to be indicative of the presence of persistent resprouter species and reduced seeder seed numbers in the later successional sites. Analysis of these data is proceeding.

Further details: Smith, M. A. Bell, D. T. Loneragan, W. A. (1999) Comparative seed germination ecology of Austrostipa compressa and Ehrharta calycina (Poaceae) in a Western Australian Banksia woodland. Australian Journal of Ecology. 1999. 24: 35-42