Many studies have investigated the effects of human disturbances on floodplain propagule banks, but few have examined how these propagule banks change down the soil depth profile. Changes in soil propagule banks with depth can indicate the state of past vegetation and potentially demonstrate the effects of different land uses on the soil profile. Here, we examined changes in soil propagule banks down the soil-depth profile in an Australian floodplain wetland with five different land-use histories, ranging from a, in this case, relatively minor disturbance (clearing) through to more major disturbance (continuous cultivation). Land use had a larger influence than floodplain geomorphology on the propagule distribution of wetland plant-group numbers. An observed decrease in individuals over the depth profile also altered terrestrial plant groups in fields with longer land-use histories. Overall, soil-propagule profiles for terrestrial plants were not as affected by land use as were those of wetland plants. The geomorphological position on the floodplain also altered the soil propagule bank, with areas subject to the most flooding having the highest number of wetland species and retaining more of these species with greater depths. In conclusion, land-use impacts alter soil-propagule banks down the profile, despite most studies focussing on the top few centimetres.

Summary Restoration of degraded plant communities requires understanding of community assembly processes. Human land use can influence plant community assembly by altering environmental conditions and species’ dispersal patterns. Flooding, including from environmental flows, may counteract land use effects on wetland vegetation. We examined the influence of land use history and flood frequency on the functional composition of wetland plant communities along a regulated river. We applied fourth corner modelling to determine species’ trait‐based responses to flooding and land use by combining data on (i) the occupancy and abundance of species in propagule banks and standing vegetation, (ii) species traits, and (iii) environmental conditions of 22 standing vegetation and 108 soil propagule bank study sites. We used analysis of deviance to test how well each dataset characterised trait–environment interactions, and generalised linear models to identify traits related to species’ responses. The occupancy and abundance of native species in the propagule bank and standing vegetation increased with flood frequency and decreased with duration of agricultural land use. Species in standing vegetation with water‐borne propagule dispersal (hydrochory) showed similar trends. In contrast, species with higher specific leaf area were associated with longer land use duration. Identifying trait‐based differences in the propagule bank and standing vegetation can help disentangle effects of dispersal and environmental filters. The occupancy and abundance of hydrochorous species in standing vegetation were negatively related to land use duration, but hydrochorous species were positively related to land use duration based on their abundance in the propagule bank. This suggests that land use does not limit plant dispersal, but acts as an in situ abiotic filter, limiting species present in standing vegetation. Synthesis and applications. Land use duration and flood frequency have opposite effects on plant community traits in floodplain wetlands of the Macquarie Marshes, Australia. Legacies of agriculture can impede restoration of plant communities. Environmental flows that increase flooding may alleviate these impacts, especially in areas that have been used for agriculture for over 20 years, by providing dispersal and environmental filters that favour native wetland species. More flooding will likely be required to restore floodplains with longer histories of agricultural land use compared to floodplains less impacted by agriculture.

This study examined the assisted natural restoration of native vegetation in an Australian floodplain wetland where flows were reinstated and the river was reconnected to the floodplain, following cessation of agricultural cultivation. Extant vegetation was surveyed three times during an inundation event at plots with different land-use histories. Restoration rate was more influenced by past land use than long-term inundation frequency and success decreased with antecedent land-use intensity. Prolonged land-use history (>3years cultivation) restricted restoration success. Sites with longer cultivation histories tended to have fewer aquatic species, more terrestrial species and exotic species. For example, amphibious responders with floating leaves were found only in reference plots and less frequently in farmed treatment plots. In this scenario, increased persistence of exotics and dryland species suggested alternative trajectories. Fields with a short land-use history (1-3years of clearing and cultivation) resembled undisturbed floodplain communities, consistent with a field of dreams' hypothesis.Although river-floodplain reconnections can restore wetlands, legacy effects of past land use may limit the pace and outcomes of restoration.

QuestionHow do contrasting influences of inundation and historical land uses affect restoration of soil propagule bank composition in floodplain wetlands?LocationNorthern Nature Reserve (large ephemeral floodplain), Macquarie Marshes, New South Wales, Australia.MethodsWe conducted germination assays on soil samples collected from fields with different land-use histories, stratified along an inundation gradient. We used GLM to determine whether native and exotic species richness and abundance varied along gradients of inundation and land use.ResultsSpecies richness and plant abundance in soil propagule banks were positively related to inundation and negatively related to intense historic land use. The abundance of native species was significantly higher in more frequently inundated areas. Abundances of exotic and ruderal species were higher in areas of intense prior land use. Overall species richness was generally similar across land-use histories.ConclusionsLand-use legacies compromised the ability of propagule banks to rejuvenate native vegetation in this floodplain wetland, especially in less frequently flooded parts of the floodplain, which harboured more ruderal and exotic species. Negative effects of prior land use may be alleviated by increased inundation. Native soil propagule banks were remarkably intact, providing a reservoir for restoration of wetland vegetation, even in soils highly disturbed by up to 20yr of agricultural cropping. With appropriate inundation, soil propagule banks in less degraded areas of the Macquarie Marshes can provide diverse mixtures of desired species in high abundance but, in highly degraded areas, full restoration may be delayed.

1. In dryland environments, freshwater ecosystems often suffer extensive degradation through habitat modification and water regime changes. The Macquarie Marshes are located in the Murray-Darling Basin in south-eastern Australia. They are an example of an ecosystem that has experienced significant degradation in recent decades owing to upstream water diversions. Recent reforms of water management in the Murray-Darling Basin have attempted to balance environmental needs against consumptive uses of water.2. This paper examines the role a protected area has played in conserving the Macquarie Marshes freshwater ecosystem and discusses how Murray-Darling Basin water reform, together with social expectations of public land managers, have had impacts on the management of the Macquarie Marshes Nature Reserve.3. Protected areas may limit adverse impacts on habitat associated with local-scale agricultural production but struggle without formal water management arrangements to protect water-dependent ecosystems from threats operating at a catchment scale. Protected area managers balance demands from stakeholders to address local issues, such as fire management and geomorphic changes, against contributing to the achievement of environmental goals in a water planning system that operates at the catchment scale.4. European settlement and water resource development has marginalized local Aboriginal people from any role in land and water management activities. The water reforms have given them more opportunities for involvement in decision-making processes, but opportunities for increased access to water for cultural and spiritual purposes remain limited. Protected areas offer a means of providing greater access for Aboriginal people to their ancestral lands.5. The strategies and processes developed to maintain and enhance the Macquarie Marshes exemplify the evolution in understanding of freshwater ecosystem protection in Australia, and are relevant globally to water resource management in complex social-ecological systems. Copyright (C) 2016 John Wiley & Sons, Ltd.

Wetlands worldwide are becoming increasingly degraded, and this has motivated many attempts to manage and restore wetland ecosystems. Restoration actions require a large resource investment, so it is critical to measure the outcomes of these management actions. We evaluated the restoration of floodplain wetland vegetation across a chronosequence of land uses, using remote sensing analyses. We compared the Landsat-based fractional cover of restoration areas with river red gum and lignum reference communities, which functioned as a fixed target for restoration, over three time periods: (i) before agricultural land use (1987–1997); (ii) during the peak of agricultural development (2004–2007); and (iii) post-restoration of flooding (2010–2015). We also developed LiDAR-derived canopy height models (CHMs) for comparison over the second and third time periods. Inundation was crucial for restoration, with many fields showing little sign of similarity to target vegetation until after inundation, even if agricultural land uses had ceased. Fields cleared or cultivated for only one year had greater restoration success compared to areas cultivated for three or more years. Canopy height increased most in the fields that were cleared and cultivated for a short duration, in contrast to those cultivated for >12 years, which showed few signs of recovery. Restoration was most successful in fields with a short development duration after the intervention, but resulting dense monotypic stands of river cooba require future monitoring and possibly intervention to prevent sustained dominance. Fields with intensive land use histories may need to be managed as alternative, drier flood-dependent vegetation communities, such as black box (Eucalyptus largiflorens) grasslands. Remotely-sensed data provided a powerful measurement technique for tracking restoration success over a large floodplain.

Responsibility for solving collective action problems in invasive species control has conventionally been assigned to government. The large continuing costs arising from invasive species demonstrate the limitations of government-centred (monocentric) approaches to governance in this domain, and indicate a need for polycentric alternatives which complement government capacities with those of laildholders and their community organisations. We sought to add to existing knowledge about collective action problems for invasive species management, and to explore the potential for community-based, polycentric approaches to improve management in this domain, through workshops and a survey of landholders regarding the weed serrated tussock (Nassella trichotoma) in two regions of New South Wales, Australia. Serrated tussock threatens the private interests of a substantial proportion of landholders in the two regions. Private landholders recognise how management of this weed on their (win properties poses a collective action problem, where success is dependent on the diligent control efforts of neighbouring private and public landholders. They are more likely to consider issues relating to horizontal social capital (e.g. relationships with public and private neighbours) as barriers to effective serrated tussock control on their own property, than issues relating to information and education about this species. Community-based approaches to this weed have the potential to improve its management across the landscape, and a great majority of private landholders appear willing to participate in such a program. Such an approach will require the active participation of public land managers, continued coercion of non-cooperative landholders, and can be developed from the foundation of existing institutional arrangements for land management, taking into account unique regional relationships and characteristics. It should complement and build on, rather than replace existing legislative, research, and extension approaches. Crown Copyright (C) 2016 Published by Elsevier Ltd. All rights reserved.

We examined the effects of grazing exclusion over a period of 14 years on the species richness and community composition of three plant communities with different dominant species and water regimes in the Gwydir Wetlands in eastern Australia. Responses to grazing exclusion varied among the three plant communities, and were most likely to be evident during dry periods rather than during periods of inundation. In frequently flooded plant communities, there was an increase in phytomass following exclusion of domestic livestock, but changes in plant community composition and species richness due to livestock exclusion varied depending on the morphological attributes of the dominant plant species. In a plant community where tall sedge species were dominant, livestock exclusion further increased their dominance and overall species richness declined. In contrast, where a prostrate grass species such as Paspalum distichum was dominant, species richness increased following livestock exclusion, due to an increase in the abundance of taller dicotyledon species. However, livestock exclusion in a community where flooding was less frequent and native grass species have been largely replaced with the introduced species Phyla canescens, resulted in no significant changes to phytomass, species richness or community composition among the grazing exclusion treatments over time. Our results indicate responses to exclusion of domestic livestock are dependent upon the dominant species within the plant community and will likely vary over time with the extent of wetland inundation. Grazing exclusion alone, without increased flooding, is unlikely to restore floristically degraded floodplain plant communities.

Effective control of invasive weeds such as serrated tussock (Nassella trichotoma) requires collective action by land managers across the landscape. We explored the impediments to adoption of weed control practices amongst private and public land managers, and the potential of collective action programs to overcome these impediments. A case study approach was adopted, involving serrated tussock control in two contrasting grazing regions of NSW, the Northern Tablelands and the Southern Tablelands. Although there are important barriers to adoption of serrated tussock control practices, collective action has potential to improve adoption amongst public and private land managers alike. An effective collective action program requires trust and willingness to reciprocate to develop between participants. Existing landholder networks may be employed to ensure ongoing success over the longer term. Concurrent enforcement may be required so that that non-participants also attempt to control serrated tussock on their land.