Patterns of native and exotic species establishment in banksia woodland after fire

摘要

Plant invasions have become a worldwide problem as the introduction of aliens often cause negative effects on ecosystem structure and functioning. Plant-recruitment models are useful to make quantitative predictions of the impact of the aliens on native floras. One such model is the lottery. This study investigated whether lottery or non-lottery mechanisms might explain how exotic species are able to replace native species recruiting together in Banksia woodlands in Western Australia. The demographyof the nineteen studied species (ten native and nine exotic) was assessed on a plot basis from number of initial seeds and seedlings (emerged germinants), survivors per month, survivors at the end of the growing season and number of seeds produced per species. The study was conducted in three unrelated sites that had recently been burnt. Variables were measured in plots within the burnt area and in adjacent non-burnt plots over ten consecutive months and at the end of the next growing season. We hypothesised that recruitment after fire of native and introduced species follows a lottery pattern. We showed that both groups followed biased lotteries, with abundance of exotics exceeding that expected by chance alone, and abundance of native species less than expected, based on their numbers of seeds. Most of the exotics produced seeds by the end of the growing season but none of the natives had. These processes help provide a mechanism to explain how exotics are gradually replacing natives in a system subjected to recurrent fire.