1. In most cases, the most important determinant of wetland vegetation is the water regime. Although water regime is usually described and managed at the scale of whole wetlands, the patterning of vegetation is likely to be determined by water regimes that are experienced at much finer spatial scales. In this study, we assess the significance of internal heterogeneity in water regimes and the role that this heterogeneity plays in vegetation patterning. 2. The effects of water regime on wetland plant species richness and vegetation structure were studied at Dowd Morass, a 1500 ha, Ramsar-listed wetland in south-eastern Australia that is topographically heterogeneous. Data on plant variables and water depth were collected along 45 (50 m) transects throughout the wetland and related to water regimes assigned individually for each transect. Wetland plants were assigned to plant functional groups (PFG) that describe the response of plants to the presence or absence of water at different life stages. 3. The classification of water depth data indicated four distinct water regimes in the wetland that were differentiated primarily by the duration of the dry period. Representatives of all PFGs co-existed over small spatial scales where topographical variation was present, and the richness and cover of understorey species declined as transects became more deeply and permanently flooded. Some PFGs (e.g. amphibious fluctuation tolerator-low growing and amphibious fluctuation responder-morphologically plastic) were eliminated by extended periods of flooding, which increased the cover but not richness of submerged plants. Species richness and foliage projective cover declined as water regimes shifted from shallow and frequently exposed conditions to regimes typified by deeper and longer inundation. Cover of the structurally dominant woody species was compromised by deeply flooded conditions but vegetative regeneration occurred despite high water levels. 4. Internal topographical variation generates mosaics of water regimes at fine spatial scales that allow plant species with different water regime requirements to co-exist over small distances. Deep water and an absence of dry periods result in decreased cover of plants and an overall loss of species richness in the understorey. Water regimes are described that promote regeneration and cover of structurally dominant taxa and increased species richness in the understorey. The study demonstrates a strong association between vegetation and the diverse water regimes that exist within a single wetland, a pattern that will be useful for modelling the effects of modified water regimes on wetland vegetation.

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1. Reinstating more natural water regimes is often a priority intervention to rehabilitate wetlands that have been degraded through anthropogenic changes to their natural wetting and drying cycles. Hydrological interventions are often made in chronically desiccated wetlands but less commonly in wetlands that have been permanently inundated and that require a drawdown phase for rehabilitation. Reports on the effectiveness of reinstating a drawdown phase in chronically inundated wetlands are particularly rare. 2. We undertook a landscape-scale, experimental drawdown of water levels at Dowd Morass, a large, Ramsar-listed, brackish-water wetland in south-eastern Australia that had been artificially flooded for 30+ years. During the hydrological manipulation, c. 500 ha of the wetland was drawn down and re-flooded, and the remaining c. 1000 ha was used as a control site. Fringing areas with a fluctuating water regime were used as a reference site. Results were analysed in terms of gradient analysis, by classifying the different water regimes created by the hydrological interventions. The response of wetland vegetation was measured along replicated transects over a 4-year period, before, during and after drawdown. Wetland plants were assigned to plant functional groups for analysis. Assembly theory and knowledge of life-history traits were used to predict that drawdown would promote recruitment of plant species that required exposed sediment for germination and seedling establishment. 3. Within-wetland microtopography interacted with the hydrological interventions to generate three distinct water regimes, which were differentiated by the spatial extent of exposed sediment and duration of the dry period. Drawdown promoted limited recruitment of some plant species, and the survival of cohorts then depended strongly on the extent and duration of the dry period. Species richness and vegetation cover (understorey and overstorey) continued to decline in constantly flooded areas of the wetland. Increased salinisation of sediments and surface waters reduced the effectiveness of the drawdown and dramatically affected species richness and cover of aquatic vegetation, which did not recover fully when fresher conditions returned. 4. The capacity of vegetation to respond to the reinstatement of a drawdown cycle following chronic inundation was constrained by abiotic (e.g. salinity) and biotic (e.g. depauperate seedbanks) factors. Reinstating a dry phase in chronically inundated, brackish-water wetlands is complex and risky and may not effectively improve vegetation Correspondence: P.I. Boon,

Wetlands dominated by Swamp Paperbarks (Melaleuca spp., Myrtaceae) are common in coastal regions across Australia. Many of these wetlands have been filled in for coastal development or otherwise degraded as a consequence of altered water regimes and increased salinity. Substantial resources, often involving community groups, are now being allocated to revegetating the remaining wetland sites, yet only rarely is the effectiveness of the rehabilitation strategies or on-ground procedures robustly assessed. As part of a larger project investigating the condition and rehabilitation of brackish-water wetlands of the Gippsland Lakes, we overlaid a scientifically informed experimental design on a set of community-based planting trials to test the effects of water depth, microtopography, plant age and planting method on the survival and growth of seedlings of Melaleuca ericifolia Sm. in Dowd Morass, a degraded, Ramsar-listed wetland in south-eastern Australia. Although previous laboratory and greenhouse studies have shown M. ericifolia seedlings to be salt tolerant, the strongly interactive effects of waterlogging and salinity resulted in high seedling mortality (>90%) in the field-based revegetation trials. Seedlings survived best if planted on naturally raised hummocks vegetated with Paspalum distichum L. (Gramineae), but their height was reduced compared with seedlings planted in shallowly flooded environments. Age of plants and depth of water were important factors in the survival and growth of M. ericifolia seedlings, whereas planting method seemed to have little effect on survival. Improved testing of revegetation methods and reporting of success or otherwise of revegetation trials will improve the effectiveness and accountability of projects aiming to rehabilitate degraded coastal wetlands.

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