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.

1. Dispersal of propagules by waterbirds is thought to be important for wetland plants because of the abundance of birds and their frequent movements among aquatic habitats. Differences in bird characteristics (size, movement, feeding ecology) were expected to lead to different outcomes for plant dispersal. 2. We investigated heterogeneity in plant dispersal by ducks (Anas superciliosa, Anas gracilis, Anas castanea). We calculated the probability of transport of viable seeds by germinating propagules retrieved from feathers and feet (epizoochory) and the contents of the oesophagus, gizzard and lower gut (endozoochory). 3. The abundance and richness of seeds carried internally and externally did not differ among sympatric bird species. We used estimates from the literature of movements of Anas species to approximate dispersal kernels for the transport of plant propagules. 4. Heterogeneity in the abundance and movement ecology of disperser species will result in differing patterns and degrees of connectivity for wetland plant metacommunities. Sedentary waterfowl are likely to have an important role in replenishing propagules and connecting aquatic metacommunities over small distances. Nomadic waterfowl may facilitate long-distance dispersal. We discuss the implications of differences between duck species in movement patterns for connectivity of aquatic plant metacommunities across landscapes.

Shallow urban lakes are often subject to chronic nutrient enrichment and their submerged plants are sometimes harvested to facilitate recreational use. The theory of alternative stable states predicts that: (i) low levels of nutrient enrichment should have little effect on the existing communities of submerged macrophytes in such lakes; but (ii) harvesting the plants should facilitate a shift to phytoplankton dominance. These two predictions were tested with large (3000 L), replicated mesocosms in a shallow urban lake densely colonized by the submerged angiosperm, Vallisneria americana Michaux. Harvesting V. americana substantially increased light penetration through the water column, but did not significantly increase phytoplankton biomass. Vallisneria americana regrew rapidly after harvesting and Chara species, which were previously absent, appeared in the harvested mesocosms. Chronic low-level nutrient enrichment significantly increased phytoplankton biomass (>100 µg chlorophyll a L -1 ) but not epiphyte biomass on the leaves of V. americana or on plastic leaf surrogates. The aboveground biomass and leaf area index of V. americana were not affected significantly by nutrient enrichment. The theory of alternative stable states successfully predicted the resilience of the submerged angiosperm community to low-level nutrient enrichment, but did not accurately predict the response to plant harvesting. The response of the lake vegetation to higher levels of nutrient enrichment is reported. M F 0 2 0 0 2 P l a n t r e s p o n s e s t o h a r v e s t i n g a n d e u t r o p h i c a t i o n K . M o r r i s e t a l .

No abstract

Aerial seed banks are potentially the main source of sexual recruitment for woody wetland plants. Whilst the importance of soil seed banks for the persistence and recruitment of wetland plants has been examined in many studies, the role of aerial seed banks has been largely neglected. We used seed traps and the seedling emergence technique to quantify the seed rain from aerial seed banks of the Swamp Paperbark Melaleuca ericifolia Sm. (Myrtaceae) in Dowd Morass, a Ramsar-listed, brackish-water wetland in south-eastern Australia. Nine plant species germinated from material collected in seed traps over 2004-2005, but emergents were dominated (80-97%) by M. ericifolia. The mean number of M. ericifolia emergents ranged from \1 to \100 seedlings m -2 day -1 , and showed a peak in the summer-autumn period. Regression analysis showed a significant negative correlation (r 2 = 0.738) between the number of M. ericifolia emergents and water depth. Water depth and salinity were negatively correlated (r 2 = 0.819), and increases in the number of M. ericifolia emergents as water levels fell were also associated with high salinities. Increasing air temperature and vapour pressure deficit also stimulated seed release during periods of drying. This study is one of the first to demonstrate the importance of aerial seed banks for sexual recruitment in woody wetland plants and the release of seed in relation to environmental factors. Aerial seed banks warrant consideration alongside soil seed banks for the establishment and long-term survival of woody plants in wetlands.