S. C. Navie

The soil seedbank of pasture communities in central Queensland invaded by Parthenium hysterophorus L.

ABSTRACT A study examining the composition and dynamics of the soil seedbank was conducted at two locations in central Queensland between December 2007 and May 2009. These two grassland communities were infested with parthenium weed (Parthenium hysterophorus L.), which had been present at both sites for at least 25 years. During the period of study, the seedbank varied between 5 962 and 16 206 seeds/m2 at the Clermont site and between 6 795 and 24 862 seeds/m2 at the Moolayember Creek site. Parthenium weed exhibited a very abundant and persistent seedbank, accounting for 80–87% of the seedbank at the Clermont site and 3–26% of the seedbank at the Moolayember Creek site. The species richness and species diversity of the seedbank, as well as the seed abundance of several native and introduced species, were higher at the Moolayember Creek site than at the Clermont site. The domination of the seedbanks by parthenium weed, especially at Clermont, suggests that the weed is having a substantial negative impact on seedbanks of native plant communities. The diversity of the seedbank at the Clermont site was found to be lower in comparison with that observed during an earlier study in 1995–1996, while the diversity at Moolayember Creek was found to have increased. Hence, the prolonged presence of parthenium weed may have substantially reduced the diversity of the seedbank at the Clermont site, while improved management practices may have increased diversity at the Moolayember Creek site.

Soil seed bank dynamics in response to an extreme flood event in a riparian habitat

A significantly increased water regime can lead to inundation of rivers, creeks and surrounding floodplains- and thus impact on the temporal dynamics of both the extant vegetation and the dormant, but viable soil-seed bank of riparian corridors. The study documented changes in the soil seed-bank along riparian corridors before and after a major flood event in January 2011 in southeast Queensland, Australia. The study site was a major river (the Mooleyember creek) near Roma, Central Queensland impacted by the extreme flood event and where baseline ecological data on riparian seed-bank populations have previously been collected in 2007, 2008 and 2009. After the major flood event, we collected further soil samples from the same locations in spring/summer (November–December 2011) and in early autumn (March 2012). Thereafter, the soils were exposed to adequate warmth and moisture under glasshouse conditions, and emerged seedlings identified taxonomically. Flooding increased seed-bank abundance but decreased its species richness and diversity. However, flood impact was less than that of yearly effect but greater than that of seasonal variation. Seeds of trees and shrubs were few in the soil, and were negatively affected by the flood; those of herbaceous and graminoids were numerous and proliferate after the flood. Seed-banks of weedy and/or exotic species were no more affected by the flood than those of native and/or non-invasive species. Overall, the studied riparian zone showed evidence of a quick recovery of its seed-bank over time, and can be considered to be resilient to an extreme flood event.

Impact of an invasive weed, Parthenium hysterophorus , on a pasture community in south east Queensland, Australia

Parthenium weed is a highly invasive alien species in more than 40 countries around the world. Along with severe negative effects on human and animal health and crop production, it also causes harm to ecosystem functioning by reducing the native plant species biodiversity. However, its impacts on native plant species, especially in pasture communities, are less known. Given parthenium weed causes substantial losses to Australian pastures’ productivity, it is crucial to estimate its impact on pasture communities. This study evaluates the impact of parthenium weed upon species diversity in a pasture community at Kilcoy, south east Queensland, Australia. Sub-sites containing three levels of parthenium weed density (i.e. high, low and zero) were chosen to quantify the above- and below-ground plant community structure. Species richness, diversity and evenness were all found to be significantly reduced as the density of parthenium weed increased; an effect was evident even when parthenium weed was present at relatively low densities (i.e. two plants m−2). This trend was observed in the summer season as well as in winter season when this annual weed was absent from the above-ground plant community. This demonstrates the strong impact that parthenium weed has upon the community composition and functioning throughout the year. It also shows the long-term impact of parthenium weed on the soil seed bank where it had displaced several native species. So, management options used for parthenium weed should also consider the reduction of parthenium weed seed bank along with controlling its above-ground populations.