Effects of livestock on riparian zone vegetation in an Australian dryland river

Robertson, Alistar; Rowling, R.W.

doi:10.1002/1099-1646(200009/10)16:5<527::aid-rrr602>3.0.co;2-w

Cited by 79 publications

(24 citation statements)

References 23 publications

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“…Herbivores are attracted to the receding waters where there is more food. Floodplain forests in semi-arid regions are more prone to elevated browsing than adjacent upland vegetation because herbivores concentrate near water, particularly during droughts (Robertson & Rowling 2000). Water stress can make seedlings more nutritious to herbivores, particularly insects (Crawley 1983).…”

Section: N T E R a C T I O N O F F L O O D I N G A N D B R O W S I N Gmentioning

confidence: 99%

“…Reduced flooding frequency increases water stress on seedlings, and vulnerability to drought and browsing mortality. Infrequent and restricted flooding in dry periods can lead to the concentration of herbivores into areas with water (Robertson & Rowling 2000). Extensive clearance of vegetation in many arid river basins alters hydrological balance and raises saline water-tables.…”

Section: Introductionmentioning

confidence: 99%

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Recruitment of a keystone tree species must concurrently manage flooding and browsing

Horner

Cunningham

Thomson³

et al. 2016

Journal of Applied Ecology

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Summary Multiple pressures (land‐use change, water extraction and climate change) interact to influence biodiversity and ecosystem processes, but direct evidence for interactions among multiple pressures is limited. Floodplain forests are an acute example of how interacting pressures (river regulation, water extraction, decreasing rainfall and mammal browsing) interact to degrade native ecosystems. We conducted a 2‐year field experiment to determine how flooding, browsing and sediment salinity interacted to determine in situ seedling survival and growth of the keystone floodplain tree species (Eucalyptus camaldulensis Dehnh.). On semi‐arid floodplains of southern Australia, 1‐year‐old seedlings were planted on the banks of six ephemeral creeks, three of which were flooded with management flows before planting while the others remained dry. Four plots were established at each creek, two open to browsing and two fenced to exclude mammal herbivores. Flooding had a strong positive effect on seedling survival and height, but browsing had strong negative effects. Sediment salinity (a covariate rather than a designed effect) had a weak negative effect on seedling survival and height. The positive effects of flooding were largely offset by the negative interaction with browsing and, to a lesser extent, sediment salinity. Although flooding has been restored to some degraded floodplain forests subjected to river regulation and a drying climate, the long‐term success of such actions is likely to be undermined by persistent browsing. Synthesis and applications. Management actions that focus on single pressures (e.g. infrequent flooding) and processes (e.g. mature tree survival) while ignoring other pressures are unlikely to sustain populations of keystone species, suggesting that complementary strategies (managed flooding with herbivore control) are necessary to sustain recruitment and, therefore, ensure the future health of these essential ecosystems.

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Section: N T E R a C T I O N O F F L O O D I N G A N D B R O W S I N Gmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Recruitment of a keystone tree species must concurrently manage flooding and browsing

Horner

Cunningham

Thomson³

et al. 2016

Journal of Applied Ecology

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“…Sites were selected where some native remnant vegetation was present, along with a bridge to which drift nets could be attached to enable sampling. Sites were avoided where willows or blackberries were dominant, or there was livestock access, as these factors can profoundly affect riparian vegetation (Robertson & Rowling, 2000;Meeson, Robertson & Jansen, 2002).…”

Section: Study Areamentioning

confidence: 99%

Flow regulation affects temporal patterns of riverine plant seed dispersal: potential implications for plant recruitment

Greet¹,

Cousens²,

Webb³

2012

Freshwater Biology

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Summary 1. Changes to the natural flow regime of a river caused by flow regulation may affect waterborne seed dispersal (hydrochory), and this may be an important mechanism by which regulation affects riverine plant communities. We assessed the effect of altered timing of seasonal flow peaks on hydrochory and considered the potential implications for plant recruitment. 2. We sampled hydrochory within five lowland rivers of temperate Australia, three of which are regulated by large dams. These dams are operated to store winter and spring rains and release water in summer and autumn for agriculture. At three sites on each river, hydrochory was sampled monthly for 12 months using passive drift nets. The contents of the drift samples were determined using the seedling‐emergence method. 3. More than 33 000 seedlings from 142 taxa germinated from the samples. In general, more seeds and taxa were observed in the drift at higher flows. By altering the period of peak flows from winter–spring to summer–autumn, flow regulation similarly affected the period of peak seed dispersal. The effect of regulation on seed dispersal varied between taxa depending on their timing of seed release and whether or not they maintain a persistent soil seed bank. 4. Hydrochory in rivers is a product of flow regime and the life history of plants. By altering natural flow regimes and thus hydrochorous dispersal patterns, flow regulation is likely to affect adversely the recruitment of native plant species with dispersal phenologies adapted to natural flow regimes (such as many riparian trees and shrubs) and encourage the spread of non‐native (exotic) species. 5. Changes to hydrochorous dispersal patterns are an important mechanism by which altered flow timing affects riverine plant communities. Natural seasonal flow peaks (in this case spring) are likely to be important for the recruitment of many native riparian woody taxa.

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“…Regeneration of the dominant riverine trees, E. camaldulensis and E. largiflorens, is strongly episodic, with dense and widespread regeneration pulses after major floods (Dexter, 1978;Cunningham et al, 1981). Moreover, tree regeneration in riverine areas is widely constrained by heavy livestock grazing (Robertson & Rowling, 2000;Jansen & Robertson, 2001), and stocking levels have declined in many riparian ecosystems on private and public land over the past 30 years (ECC, 2001;Price & Lovett, 2002). The increase in cover we detected may include regeneration during the study period as well as canopy growth of older saplings and trees.…”

Section: Riverine Woodlandsmentioning

confidence: 99%

How widespread is woody plant encroachment in temperate Australia? Changes in woody vegetation cover in lowland woodland and coastal ecosystems in Victoria from 1989 to 2005

Lunt

Winsemius

McDonald

et al. 2010

Journal of Biogeography

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Aim Encroachment or densification by woody plants affects natural ecosystems around the world. Many studies have reported encroachment in temperate Australia, particularly in coastal ecosystems and grassy woodlands. However, the degree to which published studies reflect broad-scale changes is unknown because most studies intentionally sampled areas with conspicuous densification. We aimed to estimate changes in woody vegetation cover within lowland grassy woodland and coastal ecosystems in Victoria from 1989 to 2005 to determine whether published reports of recent encroachment are representative of broad-scale ecosystem changes.Location All lowland grassy woodland and coastal ecosystems (c. 6.11 · 10 5 ha)in Victoria, Australia. Four major ecosystems were analysed: Plains woodlands, Herb-rich woodlands, Riverine woodlands and Coastal vegetation.Methods Changes in woody vegetation cover from 1989 to 2005 were assessed based on state-wide vegetation maps and Landsat analyses of woody vegetation cover conducted by the Australian Greenhouse Office's National Carbon Accounting System. The results show changes in woody cover within mapped patches of native vegetation, rather than changes in the extent of woody vegetation resulting from clearing and revegetation.Results When pooled across all ecosystems, woody vegetation increased by 18,730 ha from 1989 to 2005. Woody cover within Riverine woodlands and within Plains woodlands each increased by >7000 ha. At the patch scale, the mean percentage cover of woody vegetation in each polygon increased by >5% in all four ecosystems: Riverine woodlands (+9.2% on average), Herb-rich woodlands (+7.6%), Plains woodlands (+6.7%) and Coastal vegetation (+5.9%). Regression models relating degree of encroachment to geographic and climatic variables were extremely weak (r 2 £ 0.026), indicating that most variation occurred at local scales rather than across broad geographic gradients.Main conclusions At the scale of observation, woody vegetation cover increased in all lowland woodland and coastal ecosystems over the 16-year period. Thus, published examples of encroachment in selected coastal and woodland patches do appear to reflect widespread increases in woody vegetation cover in these ecosystems. This densification appears to be associated with changes in land management rather than with post-fire vegetation recovery and is likely to be ongoing and long-lasting, with substantial implications for biodiversity conservation and ecosystem services.

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Effects of livestock on riparian zone vegetation in an Australian dryland river

Cited by 79 publications

References 23 publications

Recruitment of a keystone tree species must concurrently manage flooding and browsing

Recruitment of a keystone tree species must concurrently manage flooding and browsing

Flow regulation affects temporal patterns of riverine plant seed dispersal: potential implications for plant recruitment

How widespread is woody plant encroachment in temperate Australia? Changes in woody vegetation cover in lowland woodland and coastal ecosystems in Victoria from 1989 to 2005

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