Spatial distribution and dynamics of populations of the introduced annual Emex australis in south-eastern Australia.
The population dynamics of the annual weed Emex australis are described for 3 sites in south-eastern Australia. A graphical test showed a random spatial distribution of emerged and dead plants. Mortality was greatest in the seedling stage and in a year when there were high seedling densities and high rainfall. However, there was no correlation between nearest neighbour distance and mortality for a given year or site. There was a significant negative density-dependent relationship between the number of shoots and seeds produced/plant and plant density in terms of nearest neighbour distances. Most seed production came from the earliest accession of plants each season, apparently due to the suppression of later accessions. There was a relative constancy in the numbers of seeds present at the end of each season for each site even though seed production varied greatly. This demonstrates the importance of seed storage in the soil as a factor buffering above-ground plant dynamics.