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

Abstract

Abstract:As part of a wider study of floodplain vegetation along the River Murray, we carried out a field survey in 1987-1988 involving collection of floristic and vegetation condition data from 335 sample plots (each 400 m 2 in area), between Hume Dam and Lake Alexandrina (including the Edward-Wakool anabranch system). The floodplain vegetation is dominated by just two tree species, River Red Gum (Eucalyptus camaldulensis) and Black Box (Eucalyptus largiflorens), but the composition of the understorey shows much greater variation, both along the river and across the floodplain. A total of 499 plant species, subspecies and varieties were recorded from the survey plots, of which 316 (63%) were native and 183 (37%) were exotic. From analysis of the floristic data we identified 37 vegetation communities, not including the vegetation of permanent wetlands and cleared areas; 21 communities were distinguished in the River Red Gum zone, 12 communities in the Black Box zone, and 4 communities on rises within the floodplain. The main floristic division among the River Red Gum communities was between Riverine Plain/ Headwaters Zone communities of the upper Murray, and Mallee Zone communities of the lower Murray. Among the Black Box communities, the main floristic division was between inner floodplain communities and outer floodplain communities, with a further division between South Australian communities and New South Wales/Victorian communities. Major factors influencing the floristic patterns included flooding frequency/duration and soil salinity.Eucalypt health declined steadily downstream and was poorest in the lower reaches of the river below the Darling Junction, where 60% of the trees were healthy, 18% unhealthy (at least 40% of the canopy dead) and 22% dead. By comparison, at the upper end of the river, above Tocumwal, 84% of the trees were healthy, 14% unhealthy and only 2% dead. Overall, the condition of Black Box trees (44% unhealthy or dead) was worse than the condition of River Red Gum trees (29% unhealthy or dead). Eucaypt regeneration was also poorest below the Darling Junction, with regenerants present in 77% of plots upstream of the Darling but only 35% of plots downstream. The findings of poor tree health and sparse regeneration below the Darling coincide with the most heavily regulated part of the Murray, where the reduction in flooding due to upstream storages and water extraction, mainly for irrigation, has been greatest. Black Box regeneration was much sparser overall than River Red Gum regeneration (regenerants present in 69% of River Red Gum plots but only 29% of Black Box plots). The poor condition of the Black Box trees, coupled with their poor regeneration, suggests that the long-term future of this species along the Murray, particularly below the Darling Junction, is tenuous, even though it is a dominant component of the vegetation.The integrity of floodplain vegetation along the Murray has been severely compromised by weed invasion. Weeds were common throughout the survey area, but were most ...

Do grazing intensity and herbivore type affect soil health? Insights from a semi‐arid productivity gradient

“…and corresponded to low, moderate and high productivity, respectively. The least productive blackbox sites occurred on upper level floodplains that receive floodwater infrequently (10–40 years; Smith & Smith ). The soils are relatively deep, with a high proportion of fine sediments (silt + clay; Eldridge, Koen & Harrison ; Appendix S2).…”

Livestock activity increases exotic plant richness, but wildlife increases native richness, with stronger effects under low productivity

“…Our sites were selected based on the overstorey dominance of three focal tree species: white cypress pine ( Callitris glaucophylla ), blackbox ( Eucalyptus largiflorens ) and river red gum ( Eucalyptus camaldulensis ). At the least productive end of the gradient (based on NPP data from MODIS imagery: 0.64 g C m −2 days −1 ) are sites located within the blackbox community (Table ), which is generally found on higher level floodplains that receive floodwater very infrequently (10–40 years; Smith & Smith, ). The soils have uniform and deep profiles and contain relatively high levels of silt (56%) and clay (19.3%, Eldridge, Koen, & Harrison, , Table ).…”

Introduced and native herbivores have different effects on plant composition in low productivity ecosystems

“…The soils have gradational profiles consisting of Quaternary colluvium and aeolian deposits, and are generally low in C, N and P. The understorey in these communities varies according to soil type and disturbance (fire, grazing) history. The Black box community occurs on upper level floodplains of inland rivers, lakes and swamps that receive infrequent flooding (10–40 years; Smith & Smith, ). Their soils have a deep uniform profile and are relatively high in silt and clay (Eldridge, Koen, & Harrison, ).…”