Floodplain vegetation of the River Murray in 1987–1988: an important pre-drought benchmark for subsequent studies.

One way to investigate seedling establishment under controlled (or partially controlled) conditions is<br>through mesocosm studies. Mesocosm studies provide a powerful means of quantifying causal<br>relationships in a controlled environment. This study will focus on the responses of seedlings to a<br>sequence of flooding and drying treatments. Work will be undertaken within<br>experimental/laboratory set-ups, so there will be no specific work undertaken at MDB (Murray–<br>Darling Basin) EWKR research sites.<br>Four woody floodplain species, River Red Gum (Eucalyptus camaldulensis Dehnh.), Black Box<br>(Eucalyptus largiflorens F.Muell.) and Coolibah (Eucalyptus coolabah Blakely &amp; Jacobs), and one<br>native floodplain shrub species, Tangled Lignum (Duma florulenta Meissner), were identified as the<br>key target species (Burns &amp; Gawne 2014). Seedling-specific literature reviews were undertaken to<br>assess and collate existing information about the recruitment of seedlings of the four key species<br>(Durant et al. 2016). The information collated from the literature review, as well as expert<br>discussions and input through workshops, teleconferences and emails, forms the basis of this<br>experimental design.<br>The experiment will focus on addressing the primary question:<br>‘What is the relationship between flow parameters such as duration, frequency and interflood-dry<br>period (sequential, cumulative events) and establishment?’

In the floodplains of the lower River Murray (Australia), riparian open forests and woodlands dominated by River Red Gum (Eucalyptus camaldulensis Dehn.), Black Box (E. largiflorens F. Muell.) and River Cooba (Acacia stenophylla A. Cunn. Ex Benth.) have been severely impacted by salinization and drought. The ‘Bookpurnong Experiment’ was developed to test the hypothesis that watertable lowering combined with groundwater freshening would reduce tree water stress and improve floodplain vegetation health. Tree water use and water stress following groundwater freshening were examined using measurements of sapflow, pre‐dawn leaf water potentials and stable isotope composition of xylem water. Water use and water stress varied markedly across the floodplain. The open mixed forest lining the bank of the River Murray, with access to fresh groundwater, used five times more groundwater over the measurement period and maintained greater canopy vigour than the open mixed woodland at inland sites. The River Cooba trees approximately 80 m from the river responded to watertable lowering of 0·65 m and to groundwater freshening by increasing transpiration. Black Box trees at the same site experienced reduced plant water stress, with no increase in transpiration. However, at a third site, approximately 170 m from the river, where the saline watertable (total dissolved solids = 36 300 mg l−1) was lowered by 1 m, no change in plant water stress or pattern of plant water use was observed. These results indicate that groundwater lowering combined with groundwater freshening can provide an accessible water source for water‐stressed floodplain vegetation. Copyright © 2009 John Wiley &amp; Sons, Ltd.

SummaryGlobally, floodplain and riparian forests are rapidly declining ecosystems due to anthropogenic influences coupled with a changing climate. In the Murray‐Darling Basin, Australia, little is known about the demographic structural status and recruitment of floodplain and riparian tree species. The aim of this study is to provide a baseline assessment of the current demographic structure of the ecosystem‐defining tree species: River Red Gum (Eucalyptus camaldulensis), Coolibah (Eucalyptus coolabah), Black Box (Eucalyptus largiflorens) and River Cooba (Acacia stenophylla) within the basin in Queensland. Tree size data were collected from 131 plots of 0.25 ha located along major waterways and the abundance of individuals at the seedling, young tree, mature and senescent life cycle stages was determined. The diameter size distribution for the four species approximated a negative exponential distribution (reverse J‐curve). Low tree abundance in the &lt; 10‐cm diameter class in all the species relative to the reverse J‐curve suggested low recruitment and possible early evidence of a decline in the sustainability of the populations according to the Law of de Liocourt. This low abundance of young trees was more pronounced in Black Box and extended to the &lt; 20‐cm diameter class, but this species was not well replicated, and more data are required. In addition, the low abundance of recruitment trees occurred concurrently with the observed below average rainfall and erratic rainfall distribution in the last two decades relative to long‐term totals. These results suggest a need for management interventions to foster seedling recruitment such as grazing management and tree planting programmes to ensure species establishment and survival along basin waterways.

A conceptual model of tree behaviour improves the visual assessment of tree condition

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 &gt;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.

Summary For decades the floodplain forests of the River Murray have endured the effects of prolonged water stress. This has resulted in significant crown dieback and loss of condition. The Living Murray (TLM) initiative aims to restore the ecological health of six Icon Sites along the River. The two eucalypts River Red Gum (Eucalyptus camaldulensis) and Black Box (Eucalyptus largiflorens) that dominate the forests at five of the six Icon Sites are undergoing widespread decline. To enable effective management and restoration of these forests, we developed a standardised tree condition assessment method. Named the TLM tree condition assessment method, it utilises visual assessment of a range of tree crown variables (extent and density of the foliage in the crown, epicormic growth, new tip growth, reproductive activity, leaf die‐off, mistletoe infestation) and measurements of bark condition, diameter at breast height and dominance class. This article describes the TLM tree condition assessment method and assesses it for consistency between multiple observer teams after limited training. The level of observer agreement between six teams each comprised of two observers was assessed for seven of the ten variables. Intra‐class correlation was used to compare scores of 30 River Red Gum trees assessed on Gunbower Island on the River Murray. The level of agreement for all variables was statistically significant with six of seven variables having correlation coefficients over R = 0.5. The TLM tree condition assessment method was found to provide accurate estimates of a range of tree variables that can be used to determine tree condition. The TLM tree condition assessment method provides a valuable monitoring tool that can be used to assess management interventions, such as management flooding and silvicultural thinning.

Floodplains provide important ecological, hydrological, and geomorphic functions within river corridors. During overbank flows, complex hydrodynamic conditions occur as water exits and re‐enters the channel and interacts with hydraulically rough floodplain vegetation. However, the extent to which floodplain vegetation influences channel‐altering hydrodynamic forces and thus bedform topography and sediment transport is poorly understood. We address this knowledge gap and present the results of flume experiments where we measured bedform topography under varied floodplain vegetation conditions at two overbank flow relative depths. The experiments were conducted in a 1‐m wide meandering compound channel inset in a 15.4 long, 4.9‐m wide basin. The channel bed was a mobile sand‐and‐gravel mixture with a median sediment size of 3.3 mm, and sediment transport occurred only within the channel. We tested bare and vegetated floodplain conditions with 2.7‐cm diameter rigid emergent vegetation elements at spacings of 3.0 and 12.1 units m−2. We performed a moving‐window analysis of topographic surface metrics including skewness, coefficient of variation, and standard deviation, as well as topographic patch analysis of area and contagion to measure changes in bedform heterogeneity as flow depth and vegetation density were varied. Our results show that both greater density vegetation and larger flows can increase bedform topographic heterogeneity. These findings suggest that floodplain vegetation and natural hydrologic regimes that include overbank flows can enhance stream habitat complexity. Designing for the effects of established vegetation conditions and prioritizing floodplain vegetation planting may be useful for river managers striving to achieve successful biomic river restoration.

There is widespread concern about population decline in a number of woodland-dependent birds in southern Australia. Of all declining species, approximately half forage on the ground. This study examined the avifaunal assemblages of temperate woodlands of the Northern Plains, Victoria, to investigate the importance of woodland habitats for ground-foraging species. Four main types of woodland were surveyed (white cypress-pine, black box, grey box and river red gum) and, in total, 89 bird species were detected. All four woodland types differed in habitat structure and, in turn, supported significantly different avifaunal assemblages. Forty of the 89 species (45%) foraged, at least in part, on the ground. Species richness and abundance of ground-foragers differed significantly between woodland types, being highest in white cypress-pine and black box. There was a greater richness of ground-foragers during the breeding than non-breeding season, but abundance did not vary seasonally. Overall, ground-foraging birds comprised a greater proportion of species (&gt;55%) and individuals (&gt;60%) in white cypress-pine and black box woodland than in grey box and river red gum (42–48% of species, &lt;50% individuals). Those ground-foragers regarded as declining also occurred in greatest richness in white cypress-pine woodlands, one of the most depleted habitats in the region. The lowest richness of ‘declining’ ground-foraging species was in river red gum woodland, the most widespread woodland type. Throughout Australia, the proportion of ground-foraging species in bird assemblages tends to be greater in temperate, semi-arid or arid woodlands than in moist forests and rainforests. However, in many regions woodland habitats are severely depleted and their open ground layer is particularly vulnerable to degradation. The extent of suitable habitat for ground-foraging birds in temperate woodlands may be much less than is apparent from current measures of tree cover. Sustainable management of drier (non-riverine) temperate woodlands is required to conserve this important element of the Australian avifauna.

Velocity distribution characteristics in meandering compound channels with one-sided vegetated floodplains

For populations to persist, recruitment must keep pace with mortality. In variable environments, opportunities for reproduction occur patchily in time and space, and favourable conditions must occur sufficiently often to allow growth to maturity (hence ‘recruitment’). The risks of local extinctions may be increased by anthropogenic factors. This scenario is illustrated by two tree species, river red gum (Eucalyptus camaldulensis) and black box (E. largiflorens), on the floodplain of the River Murray, South Australia. Fixed area plots were established at Banrock Station, where large, mature trees are common, although red gum outnumber black box by about four to one. Trunk diameter was measured as a surrogate for tree age. The smallest diameter (0–10 cm) black box are nearly as common as seedlings of that species, whereas the smallest diameter red gum (0–10 cm) are 10 times more abundant than seedlings. Small trees of both species occur in localized clumps, and the respective size‐class distributions exhibit series of peaks and falls, suggesting episodic recruitment and opportunistic survival. Population viability calculations suggest that more than 100% of existing saplings need to survive to maintain the local black box population (i.e. there are too few saplings). The red gum population apparently requires a smaller proportion of survivors, but the calculations may be biased by the clumped distribution of the saplings. Based on population structure and viability estimates, black box at this site appear to lack sufficient regeneration to compensate for adult mortality while red gum appear to have a much better balance. The methods established here may be useful for assessment of stands of these species in other areas. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Summary Recent studies suggest that river red gum health is declining across much of the Murray floodplain. Some anecdotal reports assert that localised but severe declines in river red gum health are related to the increased abundance of the hemi-parasitic shrub dwarf cherry. To investigate this, river red gum health was measured by canopy cover in 548 trees on the Murray floodplain downstream from Swan Hill, in areas with varying amounts of dwarf cherry. Trees were slightly but significantly less healthy where dwarf cherry was present. However, river red gums in poor health were widespread in the study area, suggesting that decline is largely due to broad-scale ecological changes. Dwarf cherry appears, at most, to play a secondary role in localised river red gum decline.

Summary A field trial has been established near Kerang, in north-central Victoria, to provide information on methods and effects of growing trees on salt-affected land. The experimental site comprised a saline sodic clay soil overlying highly saline groundwater within two metres of the surface. Measures taken to enable tree establishment included ploughing, gypsum incorporation, drip irrigation and sub-surface drainage. High mortality of planted seedlings occurred in the first and second years after planting as a result of salinity, frost and other site factors. Eucalyptus camaldulensis (river red gum) was the most successful of 22 species planted in terms of both survival and height growth. E. astringens (brown mallet), E. brockwayi (Dundas mahogany), E. largiflorens (black box), E. leucoxylon (yellow gum), E. occidentals (swamp yate), Leptospermum lanigerum (woolly tea-tree) and Melaleuca lanceolata (moonah) also grew satisfactorily. Analysis of soil samples collected at intervals during the study showed a substantial improvement in site conditions in the first two years after planting, including decreasing salinity of the surface soil and upper profile, and an increase in exchangeable calcium content to 25 cm depth. These effects were attributed to the site treatments rather than the trees, although the trees might exert an ameliorative effect on the soil and groundwater in future years. The establishment methods used in the trial are applicable to tree establishment on similar sites in the irrigation areas of northern Victoria.

Wetlands are among the most valuable ecosystems in the world and are crucial in supporting biodiversity. They also provide space for storing surface waters, where intense biological processing occurs that helps improve water quality. Human activities, particularly irrigated agriculture and urban developments instigating water diversions from rivers, have altered the hydrology of most wetlands. The Lower Murrumbidgee wetland, located in the Murrumbidgee River Catchment, is an example and is one of the significant wetlands across the Murray Darling Basin of Australia. Historic estimates show the volumes of water ranged from none in dry years to about 300 to 400 GL (1 GL = 10(9) L) in an average and wet year, respectively. The flows reaching the Lower Murrumbidgee wetland have been drastically reduced by at least 60% because of the upstream diversions introduced during the last century. These reductions have adversely affected the health of natural vegetation and agricultural crops in the Lower Murrumbidgee floodplain. This article presents the results of the quantification of total water consumption of various land uses in the Lower Murrumbidgee floodplain using the remote sensing-based Surface Energy Balance Algorithm for Land (SEBAL) modeling approach. The spatial analysis of actual evapotranspiration (ETa) shows that ETa rates are the highest (13-26%) for the red gum (Eucalyptus camaldulensis) forests both in summer and winter days. However, in terms of total ETa volume, lignum (Muehlenbeckia florulenta) constitutes the most significant part, which is around 14-30% of the total ETa volume for the area. Actual evapotranspiration from winter cereal cropping areas following the summer ponding is the third highest consumer of water after the river red gum and lignum. Actual evapotranspiration from the fallow land is also significant, representing 5-28% of total ETa from the region. In view of the extent of the unaccounted flows in the overall water balance of the system, there is a need to upgrade measuring and reporting infrastructure by strengthening the institutional and management arrangements to better gauge the efficiency of environmental and consumptive water use. The state-of-the-art technology of remote sensing-based SEBAL modeling proved to have potential for measuring actual water use with reliable accuracy and can be used for assessing the environmental and productive use of water from wetlands in other regions of Australia.

Plant communities on the River Murray floodplain, South Australia, are degraded by flow regulation and salinization, with up to 95% of eucalypt trees being dead or dying from water stress. This paper describes the floodplain seed bank and its capacity to respond to floods or managed ‘environmental flows’. The soil seed bank contained mainly annual native species, particularly chenopods, whereas the dominant trees, river red gum and black box (Myrtaceae: Eucalyptus camaldulensis, E. largiflorens), retained most of their seeds in a canopy seed bank (‘serotiny’). In healthy trees, seed release peaked in summer (December– February for river red gum, October–March for black box), but variable volumes suggested cyclical patterns in seed crops. Seed release, viability and germination rates did not appear to limit recruitment. In water‐stressed trees, however, seed release was up to nine‐fold less. Germination requires water from floods or local rainfall. Flow regulation has reduced flood frequencies and delayed timing, so that germination now is likely to be followed by relatively hot, dry conditions (summer). Following managed watering events, seeds accumulated in high‐water strandlines, where they germinated readily under a mulch of organic litter, but survival was limited. The importance of local rainfall as a complementary water source was demonstrated, and survival rates were higher for rain‐triggered germinants, compared to seedlings germinating in strandlines created by managed watering. Seedling survival would be greater if environmental flows were delivered to complement local rainfall or to extend the effect of short flood events. Copyright © 2008 John Wiley &amp; Sons, Ltd.

The native riparian vegetation communities on the Chowilla floodplain in the lower River Murray in South Australia are suffering severe declines in health, particularly the Eucalyptus camaldulensis Dehnh. (red gum) and Eucalyptus largiflorens F.Muell. (black box) communities. The primary cause of the decline is salinisation of the floodplain soils caused by increased rates of groundwater discharge and hence increased movement of salt up into the plant root zone. The salinity is driven by a lack of flooding and rising saline groundwater tables. Rises in the naturally saline groundwater levels are due to the effects of river regulation from Lock 6 and high inflows from regional groundwater levels increased by Lake Victoria to the east. River regulation has also led to reduced frequency and duration of the floods that leach salt from the plant root zone and supply fresh water for transpiration. The frequency of medium-sized floods occurring on Chowilla has been reduced by a factor of three since locking and water extractions were commenced in the 1920s to provide reliable water for urban and agricultural use. The soil salinisation on the floodplain was modelled by using a spatial and temporal model of salt accumulation from groundwater depth, groundwater salinity, soil type and flooding frequency. The derived soil water availability index (WINDS) is used to infer vegetation health and was calibrated against current extent of vegetation health as assessed from fieldwork and satellite image analysis. The modelling work has shown that there is a severe risk to the floodplain vegetation from current flow regimes. This paper estimates that 65% (5658 ha) of the 8600 ha of floodplain trees are affected by soil salinisation matching a field survey of vegetation health in 2003 (Department of Environment and Heritage 2005a), compared with 40% in 1993 (Taylor et al. 1996). Model results show that the best management option for Chowilla is lowering the groundwater down to 2 m below current levels, which predicts an improvement in the health of the floodplain tree species from 35 to 42%.