Examining the impact of control over time on the seed bank of Mimosa pigra on Top End, Australia floodplains (original) (raw)
Related papers
2012
A monitoring site on a floodplain was established to assess seed bank decline following the complete removal of a c. 250 hectare stand of the invasive introduced shrub Mimosa pigra. The site was revisited ten years after control. During this time, germinating plants were actively controlled, preventing local addition to the seed bank. Seed input from off-site is not quantifiable but is believed to be minimal. Despite time since control, there were still 109 (±25.8) viable seeds m-2. The aim was to evaluate M. pigra seed bank persistence and inform weed management decisions. The results indicate that M. pigra seeds can remain viable under grass cover for over a decade unless work is performed to break seed dormancy in some way. This should be taken into consideration when devising management strategies including type of control, stocking rates and duration of follow-up control of seedlings. Keywords Seed bank, Mimosa pigra, seed dormancy, integrated control.
Assessing soil seed bank persistence in flood-meadows: The search for reliable traits
Journal of Vegetation Science, 2004
To assess seed bank persistence of target species in endangered flood-meadows (alliances Cnidion and Molinion), we investigated established vegetation and soil seed bank of 46 plots for 3 yr and 2 yr, respectively. As traits of seed persistence we calculated various continuous indices that refer to the frequency and abundance of species in above-ground vegetation and at different soil depths. Furthermore, we tested the significance and soundness of easily observed traits such as maximum seed density per plot and seed attributes (mass, size and shape) as predictors of soil seed bank features.
Resilience of soil seed banks to site degradation in intermittently flooded riverine woodlands
Journal of Vegetation Science, 2010
Questions: (1) What is the recovery potential of soil seed banks of intact, average and degraded floodplain woodlands? (2) Will soil seed banks of different functional groups (native and exotic, dryland and wetland) display contrasting responses to site degradation? Location: Semi-arid, seasonally flooded woodland of eastern Australia. Methods: Diversity, abundance and composition of soil seed banks were assessed using a glasshouse study. Surface soil samples were taken from a total of nine sites with three levels of degradation (intact, average, degraded) from three microsites (subcanopy, canopy edge, open). Results: A total of 26 662 individuals of 82 species germinated. Seed abundance increased tenfold from intact to degraded sites, but there was no effect on richness. Species composition of all functional groups varied significantly among degradation states. Seeds of native wetland and exotic dryland species were more abundant in degraded than in intact sites. However, the abundance of native dryland germinants did not differ among degradation classes and no seeds of exotic wetland species were observed. Richness of exotic dryland species was significantly higher in degraded sites. Conclusions: Increasing disturbance promoted seed banks of exotic but not native dryland species and native but not exotic wetland species. Unexpectedly, disturbance promoted the abundance of native seeds more than exotics, although this was driven by a single species. Our results suggest that the dryland phase of the floodplain community is more resilient to degradation than predicted.
Cover photographs: Plants that germinated in the seed bank trial. Centre: seed bank samples in sand-bed, upper left: liverwort Ricca cavernosum, upper right: Sedge Cyperus difformis, lower left: Gratiola pedunculata, lower right: Damasonium minus Disclaimer: The work reported here has been undertaken to the best of my ability, and with the best available knowledge, within time constraints, and is reported in good faith. Charophyte Services (Michelle T. Casanova) is not responsible for management arrangements or decisions made with reference to this work.
Plant Ecology formerly `Vegetatio', 2000
Persistent soil seed banks are presumed to play a significant role in bridging and exploiting the effects of major flood disturbances in riparian systems. However, presently there is little empirical data on the correlation between flooding and seed bank dynamics. The objective of this study was to assess the impact of inter-annual flooding variation on soil seed bank dynamics in flood-meadows. We analysed seed bank composition at 46 plots along the northern Upper Rhine River, Germany, after two periods with contrasting flooding conditions ͑1996-1997: low and rare flooding; 1998-1999 high and very frequent flooding͒. Between both sampling occasions the total number of seedlings emerging from the seed bank decreased by 50% and average species-richness per sample by 30%, irrespective of the sampling depth. Similar decline occurred in mesophytes and wetland species as well as over different functional groups, with the exception of legumes. Considerable compositional changes in the seed bank were also indicated by shifts in DCA ordination and by the comparison of similarity matrices from both years with the Mantel test. The Mantel test also confirmed that compositional changes were more pronounced in the seed bank than in aboveground vegetation. There was poor correlation between the decline in total seed densities and species in the soil seed bank and environmental variables such as flooding duration and ecological groupings such as floodplain compartment and seed bank community types. Further distinct patterns of decline and persistence were evident only at the species level. While 21 species displayed a significant decline, only two species increased. Annual arable weeds and perennial ruderals with high temperature or nutrient requirements to break dark dormancy were amongst the most significantly declining species. In contrast, there was no decline in typical winter annuals and certain perennials that preferably germinate in autumn and fall into dormancy at the beginning of the warm period. Generally, differences in germination requirements and dormancy cycles of species gave the best explanation for the patterns of decline and persistence after intense flooding. Given these findings, the heavy depletion of the persistent soil seed bank we observed is most likely attributed to a post-flood germination flush due to very favourable recruitment conditions prevailing during the draw-down period after early summer flooding in 1999. The results of our study suggest that persistent soil seed banks are of outstanding importance to bridge and exploit the highly variable hydrological conditions that are typical of flood-meadows. Thus, they play a significant role in maintaining the floristic diversity of this habitat type over time and space.
Soil seed bank dynamics in response to an extreme flood event in a riparian habitat
Ecological Research, 2014
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.
Rupestrian grasslands over ironstone outcrop, locally named canga, are montane ecosystems with restricted distribution known to harbor an unusually a large number of endemic plant species. These communities are highly threatened due to their high sensitivity to habitat conversions and extreme low resilience derived from anthropogenic pressure. Ecological restoration attempts on degraded rupestrian grassland areas have not yet been successful. Mimosa calodendron is an endemic canga shrub thought to play a facilitator role and, therefore, may enhance seedling recruitment in degraded areas. Since dormancy and slow germination are key factors of the biology of seeds and may hamper their use in ecological restoration, this study aimed to investigate the environmental control of seed dormancy and germination of M. calodendron seeds. We tested the effect of mechanical scarification, light and different incubation temperatures on seed germination. The effect of scarification on water uptake by seeds was also measured. M. calodendron seeds have physical dormancy and scarification was an effective treatment to promote high and rapid germination. Heat treatment also increased germination percentage of non-scarified seeds, but was less efficient than scarification. Once water uptake occurred, germination took place under a broad thermal gradient, regardless of light condition. Therefore, the germination profile of M. calodendron seems to be suitable for uncomplicated use in restoration projects, requiring only a pretreatment for dormancy release.
Seed bank dynamics of two exotic grass species in Australia's northern savanna
2004
The control of two exotic grasses, Andropogon gayanus Kunth. (gamba grass) and Pennisetum polystachion L. Schult. (mission grass) represent a major management challenge in Australia's tropical savannas. Understanding the size and longevity of the soil seed bank can assist in understanding the management requirements for these species, such as ongoing control requirements. This study assessed the seed longevity of mission and gamba grasses, and the seed bank in sites densely invaded by either gamba or by mission grass, and compared them with uninvaded sites. The germinable seed bank of the exotic grasses declines markedly from the dry season to the early wet season, whereas the germinable native seed bank increases during this time. Longevity trials suggest that the proportion of exotic seeds carried over is low, approximately 2.3% and 0.1% for gamba and mission grass respectively. The carryover of the exotic seedbank demonstrates the importance of ongoing control. The seed bank of native species in the invaded sites was higher than the exotic seedbank, and it represents a natural source of seed for rehabilitation following control.