These guidelines have been created to help riparian ecological restoration projects in the Greater Sydney region. The guidelines were created as part of a grant from Sydney Water 2022 Community Grants awarded to Hornsby Shire Council to initiate platyplus eDNA testing in the Hornsby Shire. Our sincere thanks to all of the authors who contributed to the Principles for Riparian Lands Management published by Land & Water Australia 2007 where most of this material has been derived. We are in the process of adding in case studies as time permits.
What is Riparian Land?
Riparian land is defined as any land which adjoins, directly influences, or is influenced by a body of water. The body of water could be a creek or stream (even if it flows only occasionally), a river, a lake, reservoir, large farm dam or a wetland.
Riparian land is important because it is often the most fertile and productive part of the landscape, in terms of both agricultural production and natural ecosystems. It often has deeper and better quality soils than the surrounding hill slopes due to past erosion and river deposition and because of its position lower in the landscape, often retains moisture over a longer period.
Riparian land generally supports a higher diversity of plants and animals than the surrounding hill slopes. This is a result of its wide range of habitats and food types, its proximity to water, its less extreme microclimate and its ability to provide refuge. Many native plants are found only, or primarily, in riparian areas, and these areas are also essential to many animals for all or part of their lifecycle. Riparian land provides a refuge for native plants and animals in times of stress, such as drought or fire.
From an aquatic perspective, vegetation in riparian land regulates in-stream primary production through shading (reduced light and water temperature); supplies energy and nutrients (in the form of litter, fruits, terrestrial arthropods and other organic matter) essential to aquatic organisms; and provides essential aquatic habitat by way of large pieces of wood that fall into the stream and through root-protection of undercut banks.
In addition to being productive, riparian land is often a vulnerable part of the landscape – being at risk of damage from cultivation or over-grazing and from natural events such as floods. The combination of productivity and vulnerability means that careful management of riparian land is vital for the conservation of Australia’s unique biodiversity.
In the Past
The important linkages between land and water in riparian areas were not well recognised in the past by Australian land users or governments. There was a widespread belief that streams and rivers could be used as drains – removing problems from the adjacent land. However, it is now understood that rather than being seen as drains, waterways should be likened to arteries supporting the land around them. Similarly, because of its position, riparian land can be seen as a ‘last line of defence’ for aquatic ecosystems against potential negative effects from surrounding land use.
It is now recognised that riparian land has the capacity to:
- Trap sediment, nutrients and other contaminants before they reach the waterway and reduce water quality for downstream users
- Lower water tables
- Reduce rates of bank erosion and loss of valuable land
- Control nuisance aquatic plants through shading
- Help ensure healthy stream ecosystems
- Provide a source of food and habitat for stream animals
- Provide an important location for conservation and movement of wildlife
- Help to maintain agricultural productivity and support mixed enterprises
- Provide recreation and maintain aesthetically pleasing landscapes and
- Provide cultural and spiritual enrichment for people
The range of benefits provided by riparian land can be referred to as ‘ecosystem services’.
Degradation of Riparian Land
Because riparian land is a particularly dynamic part of the landscape, it can change markedly – even under natural conditions. Fires, unusually severe frost, cyclones and major floods can all have huge impacts on riparian land and result in major changes to channel position, shape and associated riparian vegetation. Although relatively infrequent, these events can cause large changes to riparian land.
In contrast, human impact since European settlement has been at a lower intensity than these extreme natural events, but it has been continuous over time and has resulted in widespread and large-scale degradation of riparian areas. In southern Australia, the degradation has been largely as a result of the wide-scale removal or non-regeneration of riparian vegetation due to clearing and un-managed grazing of domestic stock. In northern Australia, feral animals and plants have also had a major impact on riparian areas.
The major impacts are summarised below:
- Removing riparian trees increases the amount of light and heat reaching waterways. This favours the growth of nuisance algae and weeds.
- Clearing native riparian plants remove the natural source of leaves, twigs, fruits and insects that underpins the aquatic food web.
- Under natural conditions, trees would occasionally fall into the river, and the large woody pieces provide important habitat for aquatic organisms. Removing riparian vegetation takes away the source of large branches and trunks and disrupts aquatic ecosystems.
- Continuing agriculture to the top of stream banks by cropping or unrestricted stock access increases the delivery of sediments and nutrients to streams. Large volumes of fine-grained sediment smother aquatic habitat, while increased nutrients stimulate weed and algal growth. Increased nutrient load also affects estuaries and marine life beyond the river mouth.
- Removing riparian vegetation destabilises stream banks, often resulting in massive increases in channel width, channel incision and fully erosion. This erosion of the channels often delivered more sediment than human activity on the surrounding land.
- Removing vegetation along channels, and of large wood in channels, can allow water to travel downstream at a faster rate, sometimes contributing to increased flooding and erosion of lowlands.
- Removing vegetation throughout the catchment can lead to raised water tables and salinisation of land which, as salt-saturated water drains into rivers and streams, ultimately results in saline waterways.
It is important to recognise that the impacts of these disturbances are not just cumulative; they often exacerbate each other. For example, clearing riparian vegetation from upland streams multiplies, many times, the impact of increased nutrients from surrounding land use. This is because clearing also results in extra light and higher water temperatures, conditions needed to enable nuisance weeds and algae to flourish and dominate the aquatic ecosystem.
The National Land and Water Resources Audit publication Catchment, River and Estuary Condition in Australia (2002) lists the following as key management actions, required to improve the condition of rivers and wetlands:
- Protective management of good condition riparian lands and wetlands
- Revegetation of disturbed riparian lands
- Reduction in the barriers to fish passage
- Rehabilitation and re-establishment of wetlands and
- Provision of environmental flows.
Many landholders in Australia are now implementing improved management techniques. Fencing and other methods used to control and manage the access of stock to riparian areas are a high priority in many parts of the country. Landholders are reporting that the cost of fencing and off-stream watering can be more than recouped over time because, for example, fenced riparian land can be used for growing higher value crops, because grazing can be managed to improve pasture composition and production, or because the health and productivity of animals grazed there is improved due to reduced disease transmission and improved water quality. In recognition of the fact that improved riparian management provides public as well as private benefits, there are now many forms of community and government support available to defray the cost of durable riparian fencing.
Diversity and Dynamics of Riparian Vegetation
Given it broad definition a diverse array of habitats can be considered ‘riparian’. From a vegetation perspective, however, these can be classified into four major types:
- Channel habitats
- Channel bank habitats
Riparian Plant Diversity
Riparian vegetation throughout much of Australia is dominated by a relatively small number of plant species (Cole 1986) and can be characterised as having low species diversity but with locally high individual species abundance (fielding & Alexander 1996).
A wide range of life forms are represented including trees, shrubs, monocots (i.e. grasses and sedges) and forbs, the latter two groups of which include perennial, annual and ephemeral species. Of the non-vascular plants, many Bryophytes (mosses, liverworts and hornworts) are restricted to the riparian zone and submerged charophytes (green macro-algae) are also frequently encountered in channel and wetland habitats. Amongst vascular plants, ferns and fern allies have a limited occurrence in riparian zones, e.g. Marsilea spp. (nardoo) (Capon 2003) with angiosperms generally comprising the dominant component of riparian flora.
Plants persisting in riparian habitats usually exhibit adaptations that allow them to survive through periodic episodes of fluvial disturbance. These can be either physiological or morphological adaptations that enable plants to tolerate the stresses associated with flooding in time or space.
Common morphological adaptations amongst flood tolerant plants include the ability to rapidly elongate stems and petioles upon submergence, allowing plants to emerge from the low light conditions of floodwaters. The development of aerenchyma (a form of plant tissue with large spaces between cells in which gases are stored and diffused ) in stems and roots, facilitating better gas exchange, is another widespread response to flooding amongst tolerant plants. Many riparian plant species also develop adventitious roots or initiate increased branching of lateral roots when flooding occurs. Physiological adaptations may include the ability to switch to alternative metabolic pathways during flooding so respiration can continue under anoxic conditions (Hook 1984).
Riparian plant species may also display a variety of life history adaptations to flooding, including, for instance, timing significant reproductive events to coincide with regular flood pulses. Some species may delay flowering and seed production until seasonal floodwaters have receded (Blom et all 1990) while others might flower prior to seasonal floods but have dormant seeds which germinate in response to conditions occurring during floodwater recession (Pautou & Arens 1994). Plants that release seeds before or during a flood may be dispersed widely by floodwaters through hydrochory (Nilsson et al. 1991). Many annual and ephemeral riparian monocots and forbs are likely to maintain large persistent soil seed banks that enable plants to persist within a habitat as dormant propagules until conditions suitable for their germination and establishment occur (Leck & Brock 2000). Germination cues (e.g. temperature, light and oxygen availability) in wetland plant species are often related to flooding (Leck 1989). Furthermore, annual plant species and some perennial monocots and forbs, frequently exhibit extremely rapid life cycles maximising opportunies for replenishment of the soil seed bank prior to further flooding or the onset of through (Blom & Voesenek 1996). The ability of riparian trees to generate depends on a set of conditions that allows seed dispersal, germination and establishment.
Plant Functional Groups
A useful approach for considering relationships between a plant species and their habitats, and how these contribute to temporal and spatial vegetation dynamics, is to classify plants into functional groups. Naiman and Décamps (1997) describe four broad functional groups of riparian plants bases on their adaptations and response to fluvial disturbance:
- Invaders that colonise alluvial sediments via large quantities of wind-and-water-dispersed weeds
- Endurers that can resprout from stems or roots following damage by flooding, fire or grazing
- Resisters that are tolerant to disturbances such as flooding or fire and
- Avoiders that lack specific adaptations to disturbance and do not survive in unfavourable habitats.
Threats to Riparian Vegetation
Hydrological change – changes to natural flooding regimes through flow regulation and water extraction, pose one of the greatest threats to vegetation communities in riparian zones throughout the world.
Weeds – Weeds are a serious threat to ecological integrity and productivity of many Australian vegetation communities (Grice & Brown 1999) and riparian zones are highly susceptible to weed infestation (Grace 2004). Weed infestations are often the result of disturbance or the build-up of nutrient levels caused by fertilisers or grazing animals. Primary disturbances include vegetation clearance, fire and stock grazing. Altered flooding regimes may also enable the establishment of weed species in riparian zones (Stromberg 2001). Some weeds are able to infest undisturbed and intact riparian vegetation in which case the weeds are able to outcompete the native species with regards to light, space, nutrients and moisture. Throughout Australia many weeds now dominate riparian areas, their dominance perpetuated by grazing activities, associated impacts, and ineffective land management practises. The cost of weed eradication and/or control is high, and if weeds are neglected and become dominant, the productivity and diversity of native riparian vegetation can seriously decline. Although the riparian zone occupies only a small proportion of the landscape, it exerts an influence that affects most of the adjacent landscape, and the presence of weeds limits critical catchment processes and reduces productivity.
Grazing – grazing is the dominant land-use in Australia (Steward 1996) and the riparian zone is often severely impacted upon by the activities of domestic stock.
Excellent Video on Creating Healthy Farm Dams
The following are a list of management principles for protecting, maintaining and rehabilitating riparian vegetation.
- First identify and protect area of existing riparian vegetation assessed to be in good condition. Areas can be compared with local undisturbed or reference sites, and/or assessed for their capacity to provide crucial riparian zone functions and to self-regenerate. Identify threats and act to remove or mitigate them.
- The next priority is to promote natural regeneration or recolonisation where this is possible. This may require checking for availability of seed in the soil or on plants, removal of threats such as grazing animals or weeds, and sometimes deliberate action to promote regeneration (e.g. use of fire).
- Replanting , whether by tubestock or direct seeding, is more expensive and requires careful attention to site preparation, specially for weed management and removal of other threats. Species selection, based on reference to undisturbed sites and local knowledge, is required for different parts of the riparian zone, and for different stages of revegetation succession (e.g. early colonisers versus slow-growing climax spp). If early support (e.g. artificial watering) is needed to ensure success, it may be best to replant small areas sequentially.
- Revegetation activities need to be timed according to season and growth periods, as well as for the likelihood of floods and other disturbances. Plan for follow-up work after the planting, especially to maintain stock exclusion and weed control until ‘new’ vegetation is fully established. Make use of the detailed guides to revegetation that are now available for most parts of Australia (e.g. through Greening Australia, government agencies and catchment and community groups).
Riparian vegetation shades streams, decreasing the amount of direct and diffuse sunlight reaching the water surface and reducing daily and seasonable extremes of water temperature
Shading controls primary productivity within the stream to a greater extent than nutrients levels, as the growth of most aquatic plants is regulated by light availability. At sites with elevated nutrient levels, shading can therefore control the effect of nutrient enrichment.
In cleared streams water temperature can exceed the lethal limit for aquatic fauna, directly influencing local biodiversity and at lower temperature levels, the growth and development of aquatic plants and animals.
The temperature tolerance of Australian aquatic macroinvertebrate fauna is similar to that measured elsewhere in the world. In temperate systems, a target of 21°C is recommended and in northern systems, 29°C for stream water temperature.
The degree of shade created by riparian vegetation is influenced by several factors, including canopy height, foliage density, channel width and orientation, valley topography, latitude and season. The effect of shading on the structure and function of stream ecosystems is greatest in small streams.
Typically, riparian replanting is best conducted in the upland streams of a catchment, particularly those oriented east-west, as this will have a flow-on effect for temperature in the lower reaches. However for cooler-water refugia in large rivers, replanting tributaries close to the confluence can have considerable benefits for native fish.
Stream shade has three components – macrotopographic shade (provided by nearby hills), bank shade and vegetation shade. Any restoration activities need to recognise the differential effects of those components.
Colder waters contain higher dissolved oxygen concentrations compared to warmer waters (Horne & Goldman 1994). For example, a 10°C increases in temperature (a change commonly recorded in streams following riparian clearing) can reduce oxygen concentration by over 2.5mg/L (-1)? which may represent a quarter of the total oxygen present. Elevated water temperatures generally raise ecosystem respiration and consequently oxygen consumption. Following riparian clearing, the combined effects of a lowering in oxygen saturation and increased respiration can drive systems anoxic, particularly at night (Bunn & Davies 1992, Davies et al. 2004a).
Sub-lethal Impacts of Elevated Water Temperature
Water temperature, including elevated temperatures can have the following direct effects on aquatic fauna:
- Effects on growth and development of most aquatic organisms (such as algae, invertebrates, fish, reptiles and amphibians).
- Control of larval development
- Influencing egg development, timing of hatching, and emergence of adults
- Premature emergence of adults, possibly at times when climatic conditions in the terrestrial environment are unsuitable for adult survival or when few mates from adjacent forested sites are present
- Overall reduction in fecundity because larvae mature at smaller sizes in warmer water and smaller insects produce fewer eggs
- Modifying the trigger for migration, spawning, egg development and hatching of many fish species
Assessment of aquatic food webs has shown that micro-algae such as diatoms are more readily consumed by organisms higher up the food chain than are larger plants such as filamentous algae and macrophytes (Bunn et al. 1998). Lower light inputs to streams (caused by shade and/or turbidity) and lower water temperatures enhance the productivity of palatable food material (Bunn et al. 1998,2000). Furthermore, excessive growth of macrophytes and filamentous green algae in stream channels, when stimulated by high light intensity and high nutrient levels, cause major changes in aquatic habitat and can reduce oxygen levels through plant respiration and the decomposition of accumulated organic matter. At high light levels, there is a shift in plant growth to macrophytes (Bunn et al. 1998) which do not readily enter aquatic food webs. In this case, macrophytes encroach the channels, increasing the incidence of localised flooding. Shading alone, independent of nutrient status, was found to control invasive macrophytes that had choked the channels of open streams in the tropical canelands of far north Queensland and streams in the subtropics.
The previous discussion demonstrates that variations in productivity and composition of aquatic plant groups, which often reflect changed light availability (e.g. following clearing of riparian vegetation) can lead to dramatic changes in the structure and function of stream ecosystems. At one extreme, productive diatom communities in cool, shaded streams can represent a high-quality source of food for primary consumers. At the other extreme, prolific growth of filamentous green algae and invasive macrophytes in the open stream channels can lead to loss of aquatic habitat and severe water quality problems.
In rainforest streams 75% cover can be achieved by mature vegetation on channels about 8-10metres wide or less; which translates to sub-catchments of 8-10 km2 or less. Note that these relationships will vary with latitude. At higher latitudes (for example, southern Victoria and Tasmania) the canopy cover required to prevent excessive growths of filamentous algae is less than this due to the lower intensity of incoming solar radiation. In more open-forest types, effective shading (75% cover) may be achieved along only smaller streams. Nevertheless, this shade is important as most of the total catchment area is made up of such streams.
Riparian vegetation, which influences the amount of light reaching streams and also water temperatures, has the ability to affect the growth of aquatic plants and animals, water quality, aquatic habitat and ecosystem function. Controlling the light and temperature environment by maintaining or replanting riparian vegetation is, therefore, an important consideration in the management of riparian areas. The following guiding principles are important for setting priorities for riparian restoration to meet temperature and light targets (see Davies et al. 2004b)
- Restore upland (lower order) streams before higher order streams (however for thermal refugia for fish in major rivers, revegetation of tributaries is recommended near the confluence.
- Restore reaches with negligible riparian vegetation before trying to improve low density vegetation
- Restore streams on north-west aspects before those on south-west aspects.
- Preferentially restore reaches where soil properties favour the establishment of replanted vegetation. (See Land & Water Australia’s River and Riparian Management Technical Guideline number 5 ‘Managing high in-stream temperatures using riparian vegetation’ which provides a step by step process that can be used where restoration efforts need to be focussed.
Aquatic Food Webs
Carbon from aquatic and terrestrial sources is directly consumed by invertebrates and some fish and decomposed by aquatic fungi and bacteria. Aquatic insects represent much of the biodiversity, abundance and biomass of animals in streams and rivers and are major consumers of organic matter (Bunn1992). In turn, these smaller primary consumers are essential elements of the food web, which supports predatory invertebrates, fish, other aquatic vertebrates, terrestrial and semi-aquatic consumers in the riparian zone.
Although riparian inputs of leaves and detritus may be an important food source for forest stream invertebrates, they are rarely eaten directly by aquatic vertebrates (Garman 1991). In contrast, terrestrial invertebrates and fruits falling from riparian land are important to the diets of many freshwater fish and other freshwater vertebrates. These terrestrial sources are easily accessed by fish in small streams, where there is overhanging vegetation and numerous bank eddies. Similar conditions can be found at the margins of larger streams where overhanging vegetation and large woody pieces cause eddies (Cloe & Garman 1996).
Consequences of riparian clearing for stream ecosystem function
Riparian vegetation clearly plays an important dual role in stream ecosystems, regulating in-stream primary production (through shading) and supplying energy and nutrients. The importance of these functions becomes most apparent when riparian vegetation is removed. To a limited extent, slight increase in light and nutrients associated with land clearing could have a positive effect on productivity in rivers, in that they stimulate high-quality algal sources. It is important to distinguish between algal sources (such as diatoms and some benthic cyanbacteria) that are preferentially eaten and other aquatic plants that are not. The former groups appear to require low light conditions of shaded, forested streams or warm, turbid river pools, while the latter require much higher light conditions and are more likely to proliferate in the absence of riparian shade.
The influence of riparian management on stream erosion, remember the phrase “Please Think” — PLS –T.
1. PROCESS — Managers will be most effective in targeting riparian revegetation if they first understand the erosion mechanisms (the processes) that are acting in a particular stream or river reach.
2. LEVERAGE — Once we understand the erosion mechanism, then we can understand the influence (the leverage) that specific revegetation or other riparian management will have on that mechanism.
3. SCALE — Size is everything! Where you are in a catchment and the size (scale) of the channel influences both the erosion processes that operate, and the leverage that riparian vegetation and management have over those mechanisms.
4. TIME — the interaction between the vegetation and the erosion mechanisms will change with time as the vegetation grows, and as the vegetation alters other aspects of the system.
Riparian management, particularly in the form of the very popular riparian revegetation, can influence and control stream bed and bank erosion. But the effectiveness of vegetation varies greatly depending upon the particular processes driving erosion, the position within the catchment, the type and location of the vegetation, and the scale of both the erosion and the revegetation. Time is the other important variable to consider. There is little point attempting to understand the role of vegetation in bank erosion mechanisms if we do not understand bank erosion processes and rates, so this should be the first step taken by river managers. Once the processes and rates at a site or within a reach or catchment have been identified, then the most effective management options can be determined.
Field monitoring has confirmed that riparian vegetation generally has a second order impact on bank erosion processes, but this leverage can still be important in slowing erosion to an acceptable rate. The ways in which vegetation can influence subaerial loosening, fluvial scour and mass failure, the three key erosion processes, are now better understood.
Scale should be considered next, in terms of catchment position, channel and bank size, and hence the scale of vegetation required to have the desired effect. The location of revegetation, both within the catchment to maximise cost-effectiveness, and at the specific reach or site (top and/or toe of bank, planting width and spacing), should be considered now. Past changes within the catchment and reach are part of the time considerations — are there responses to past change still working through the stream network?
Time for replanted or regenerating vegetation to grow and exert its maximum leverage on erosion is also important. Field data shows that the initial response to riparian revegetation can be the opposite of what was expected, for example an initial increase in sediment yield, and this needs to be planned for and explained. Some specific issues to keep in mind are:
- Riparian vegetation is very effective at preventing or reducing the subaerial processes that loosen bank soil and make it available for removal by fluvial scour – unmanaged grazing by domestic, native or feral animals will reduce this effectiveness.
- Effects on erosion by mass failure remain the most important influence of tree roots on the stability of cohesive stream banks.
- Isolated trees along a bank are doomed to fail, but trees at a spacing of about half their mature canopy radius (so that their root plates overlap) protect each other.
- Plant roots do not particularly alter the inherent erosion resistance of cohesive stream banks to fluvial scour. But trees will begin to affect rates of fluvial scour when the stream bank is within half a canopy width of the tree (which is usually 5–6 times the tree trunk diameter) due to physical protection by roots.
- If grass establishes itself in the bed or lower bank of a stream, it will resist almost any shear stress that is likely on many streams.
- Grazing significantly reduces the resistance of grass along stream beds and banks to shear stress and erosion.
Wood and Other Aquatic Habitat
- Riparian vegetation increases stream channel complexity and directly contributes to aquatic habitat through inputs of logs and branches. In turn, the provision of complex habitat has a major influence on aquatic biodiversity.
- Logs and branches can enhance stream stability, regulate sediment transport and exert significant control on channel complexity in bedrock rivers and channel geomorphology in alluvial rivers.
- Logs contribute to the formation of physical features in streams, such as scour pools and channel bars, which serve as habitat for in-stream biota.
- Logs provide physical habitat for biota at all levels of the food chain, ranging from microscopic bacteria, fungi and algae, to macroinvertebrates, fish and turtles.
- Logs also provide sites where bacteria, fungi and algae can process carbon and other nutrients such as nitrogen and phosphorus, thus contributing to ecosystem processes such as productivity and respiration.
- In alluvial rivers, logs can modify surface water/ground water exchange and enhance nutrient processing.
- Logs from Australian riparian zones are relatively immobile. Our streams tend to have a low average stream power, the wood has a high density and many riparian trees have a complex branching structure that ensures they are easily anchored in position.
- Although vast amounts of wood have been removed from many Australian rivers, what does remain provides important habitat for microbes, invertebrates, fish and other animals.
- Retention and reinstatement of logs should be a priority for river rehabilitation, instead of removal or even realignment.
Riparian Wildlife and Habitats
Riparian lands are among the most productive ecosystems on earth. They occupy only a small proportion of the landscape but frequently support a greater variety and abundance of animal life than adjacent habitats.
Important habitat components include vegetation (often taller, denser, more diverse, and more complex in riparian lands), food, standing water, shelter from predators, sites for nesting and roosting, and a local microclimate with less extreme temperatures and more humid conditions than adjacent areas.
Wildlife species differ in their dependence on the riparian zone: some are confined to it throughout their lives; others may use it only occasionally, although their long-term persistence depends on access to intact riparian habitats.
Riparian areas are often corridors for wildlife movement. This occurs naturally in dry regions, where stream-side vegetation forms distinctive networks across the landscape.
In regions where most native vegetation has been cleared for human use, vegetated riparian zones also provide habitat for many species.
Impacts of Land Management Practices on Riparian Land
Land management practices on and surrounding riparian land can lead to its degradation if they are not compatible with its special properties and functions. Land uses on riparian land, whether for agriculture, other commerce, or for urban development, need to be planned and managed carefully.
When allowed uncontrolled access to riparian land, domestic stock can degrade riparian vegetation by grazing and trampling, leading to consequent increases in rates of erosion, to changes in floral communities by way of preferential grazing, and to invasion by exotic weeds.
Uncontrolled grazing, especially by cattle which favour riparian areas, often results in increased stream turbidity, as well as increased input of nutrients and bacteria into the stream. Such disturbance of the stream has deleterious effects on aquatic ecosystems and on the quality of water available to downstream users.
Exclusion of stock from riparian land can allow riparian vegetation and riparian habitats to recover, although a return to pre-disturbance conditions does not always occur.
Altered fire regimes also have major impacts on the functioning of riparian ecosystems.
Degradation of riparian lands by clearing and grazing has negative impacts on a range of wildlife species which depend on these riparian areas.
Restoration of riparian lands, including fencing to exclude livestock and re-instatement of native vegetation, can lead to improved riparian habitat for a variety of wildlife species.
There may also be benefits to other aspects of farm productivity, such as reduced impacts of pest species.
The Problem with Willows in Riparian Areas
In many high rainfall areas, willows have been used extensively to help stabilise many stream banks.
Willows establish easily, grow rapidly, produce fine matted roots ideal for stabilising soil, and require little attention after planting. However, over time the consistent use of willows (and the planting of male and female plants of most species that successfully spread by seed), has caused changes to the ecology and flows of rivers and streams. Some southern rivers are now completely choked by invasive willows.
Willows have displaced native riparian species and colonised sand and gravel bars in streams, diverting floods and causing erosion on vulnerable banks. The soft textured leaves that are all dropped at the same time do not provide a year-round food source for native in-stream animals. This, together with the extreme shade provided by willows has reduced biodiversity wherever willows dominate riparian areas.
Willows are also prodigious users of water, and en masse can reduce natural water flow. Some of these features also apply to other invasive species found in the riparian zone including poplars, she-oaks, olives and desert ash. Willows are now listed as a weed of national significance.
For many people, an important deterrent to changing stock management in riparian areas is the fear that they will become havens for weeds and pest animals, as well as posing a fire risk. These are issues that must be taken into account in planning the management of riparian areas. Fortunately many landholders have found ways to improve their management of riparian areas without significant invasion or establishment by weeds.
An important principle of weed management is that most weed species find it difficult to invade and establish into intact riparian vegetation. In general, if vigorous pasture and healthy native vegetation is maintained or established in riparian areas, weeds will find it harder to compete and establish. Managing grazing so that plant cover of established pasture and native vegetation is maintained is the key management practice to prevent weeds becoming a problem.
On riparian land that has become degraded by past land use and management, and on areas that are affected by flood, frost, or wildfire, it is vital to promote natural regeneration or to deliberately revegetate as soon as possible after the disturbance, otherwise weed invasion is almost certain and it will be much harder to bring the area back to a natural condition. However, even with this careful approach to management, some weed species especially suited to riparian areas may become established.
Weeds can be brought in through wind dispersal of seeds, seeds passing through the droppings of birds and other animals, or seeds and pieces of vegetation arriving from upstream during peak flows. Where these invaders are successful, carefully-managed and selective grazing in the riparian area can be used, as well as selective control with herbicide or hand-weeding. Pulling individual weeds out by hand or grubbing out with a hoe can be effective when numbers are low.
In many regions, riparian areas have already been invaded by woody weeds. These plants, which might include willows, pepper trees, olives, desert ash, tamarisk and other species, may provide some benefits (for example, they may shade the stream or help strengthen banks against erosion), but overall their influence is negative, and in the long run they should be replaced with local native species. Willows, for example, will gradually grow into the stream, blocking the channel, and causing additional flooding. They can be highly aggressive, and now that both sexes in most species are present in Australia there have been some huge seeding events, with millions of seedlings becoming established downstream, completely choking some channels. Willows also use a lot of water, and are harmful to native in-stream animals as they drop all their leaves at once into the stream where they decompose and create anoxic (no oxygen) conditions.
Monitoring and Evaluation in Riparian Land Management
Monitoring and evaluation (M&E) should be seen as an integral part of any riparian management project. M&E at a project or output level is straightforward, and methods for this are well developed. M&E at the outcome level, to determine whether, and the extent to which the project has met its objectives, is a more complex proposition and is likely to be expensive to undertake properly.
Effective evaluation requires consideration of the scale and frequency of measurement and potential difficulties of separating treatment effects from natural variability. Statistical comparison with control or reference sites is the preferred approach, but is not always possible. A before-and-after (BACI) approach requires adequate baseline data before treatments are imposed.
Selection of indicators for monitoring programs should reflect the questions being asked in the evaluation, and the level of accuracy and precision therefore necessary
Methods for the rapid appraisal of riparian condition have been developed to meet the increasing need to assess whether riparian management is being effective, and to further adapt it if not.
Principles for Riparian Lands Management – Published by Land & Water Australia 2007
The source of Provest Creek is storm water run off from the urban area of Hornsby Heights and this small tributary flows into the much larger Berowra Creek which ultimately flows in to the Hawkesbury River.
At the top of the catchment is Montview Oval which was created from an old landfill site. A quarry operation mining clay shale and fireclay was also in operation from 1960 to 1975. Since that time the area has been largely undisturbed. The vegetation community is a Peppermint-Angophora Forest. The area is quite weedy but surveying revealed an amazing variety of wildlife. The ecological restoration project was very careful not to impact the existing wildlife.
The creek is lined with Arum Lilies Zantedeschia aethiopica and they were removed from a small area as well as other weeds such as Senna, Blackberry, Privet and Crofton. The Arum Lilies in the water are very deep rooted and were virtually impossible to fully remove. Subsequent heavy rains washed away areas of the river bank where removal had taken place.
The small areas where the Arum Lilies were fully removed left the bank vulnerable to erosion. It would have been more effective to cut the Arum Lilies at the base so that they can still hold the river bank but not seed and plant into the creek grasses seen in the local area. In this case Gahnia sieberiana and Lomandra longifolia were subsequently planted to hold the bank in place.
Large Small-leaved Privets (Ligustrum sinense) lined parts of the creek. These were left in-situ and using a drill 3-4 holes angled downwards were created in the trunk and glyphosate was placed in the holes. Only about half of the privets were treated initially and 6 months later the rest were treated. Privets are an important food source for birds so we were reluctant to remove them too quickly. The privets died but were still able to hold the bank in place which reduced erosion until other plants such as Callicoma serratifolia were able to start replacing them.
If removing an entire privet remember that they coppice fairly easily if not treated properly. Small ones can be removed by pulling their roots up but larger ones need to be cut fairly near the base, leaving no room to coppice and then 100% glyphosate placed on the cut.
Native Mammals Detected During Surveying at Provest Creek
- Ring-tailed Possum – Pseudocheirus peregrinus
- Brush-tailed Possum – Trichosurus vulpecula
- Swamp Wallaby – Wallabia bicolor
- Bush Rat – Rattus sp.
- Sugar Glider – Petaurus breviceps
- Feather-tail Glider – Acrobates pygmaeus
- Whitestriped Free-tail Bat – Austronomus australis
- Eastern Horseshoe Bat – Rhinolophus megaphyllus
- Wattled Bat species – Chalinolobus sp.
- Bentwinged Bat – Miniopterus sp.
- Greyheaded Flying Fox – Pteropus poliocephalus (Vulnerable sp. NSW)
- Red Fox – Vulpes vulpes
- Cat – Felis catus
- Red-bellied Black Snake – Pseudoechis porphyriacus
- Eastern Water Skink – Eulamprus quoyii
- Eastern Water Dragon – Intellagama lesueurii lesueurii
- Eastern Snake-necked Turtle – Chelodina longicollis
- Bleating Tree Frog – Litoria dentata
- Common Eastern Froglet – Crinia signifera
- Dwarf Tree Frog – Litoria fallax
- Spotted Marsh Frog – Limnodynastes tasmaniensis
- Striped Marsh Frog – Limnodynastes peronii
- Broad-palmed Frog – Litoria latopalmata
- Peron’s Tree Frog – Litoria peronii
- Smooth Toadlet – Uperoleia lavigata
- Ewing’s Tree Frog – Litoria ewingii
- Leaf-green Tree Frog – Litoria phyllochroa
- Red-crowned Toadlet – Pseudophryne australis (Vulnerable sp. NSW)
Other Aquatic Species
- Eel sp. (short finned or long finned) – Anguilla reinhardtii
- Spiny Freshwater Crayfish – Euastacus spinifer
- Damselfly – Zygoptera order
- Darner Family Dragonfly – Aeshnidae family
- Australian Brush Turkey – Alectura lathami
- Australian Golden Whistler – Pachycephala pectoralis
- Australian King-Parrot – Alisterus scapularis
- Australian Magpie – Gymnorhina tibicen
- Little Raven – Corvus mellori
- Australian Wood Duck – Chenonetta jubata
- Black-faced Cuckooshrike – Coracina novaehollandiae
- Brown Cuckoo-dove – Macropygia phasianella
- Brown Thornbill – Acanthiza pusilla
- Brown Gerygone – Gerygone mouki
- Crimson Rosella – Platycercus elegans
- Eastern Whipbird – Psophodes olivaceus
- Eastern Spinebill – Acanthorhynchus tenuirostris
- Eastern Yellow Robin – Eopsaltria australis
- Grey Butcherbird – Cracticus torquatus
- Grey Fantail – Rhipidura albiscapa
- Grey Shrikethrush – Colluricincla harmonica
- Laughing Kookaburra – Dacelo novaeguineae
- Lewin’s Honeyeater – Meliphaga lewinii
- Little Wattlebird – Anthochaera chrysoptera
- New Holland Honeyeater – Phylidonyris novaehollandiae
- Noisy Friarbird – Philemon corniculatus
- Noisy Miner – Manorina melanocephala
- Olive-backed Oriole – Oriolus sagittatus
- Pied Currawong – Strepera graculina
- Pilotbird – Pycnoptilus floccosus
- Rainbow Lorikeet – Trichoglossus moluccanus
- Red-browed Finch – Neochmia temporalis
- Red Wattlebird – Anthochaera carunculata
- Rufous Whistler – Pachycephala rufiventris
- Satin Bowerbird – Ptilonorhynchus violaceus
- Silvereye – Zosterops lateralis
- Spotted Pardalote – Pardalotus punctatus
- Striated Thornbill – Acanthiza lineata
- Sulphur-crested Cockatoo – Cacatua galerita
- Superb Lyrebird – Menura novaehollandiae
- Superb Fairy-wren – Malurus cyaneus
- Variegated Fairy-Wren – Malurus lamberti
- Welcome Swallow – Hirundo neoxena
- Willie Wagtail – Rhipidura leucophrys
- White-eared Honeyeater – Nesioptilotis leucosis
- White-browed Scrubwren – Sericornis frontalis
- White-cheeked Honeyeater – Phylidonyris niger
- White-throated Treecreeper – Cormobates leucophaea
- White-headed Pigeon – Columba leucomela
- Wonga Pigeon – Leucosarcia melanoleuca
- Yellow-tailed Black Cockatoo – Calyptorhynchus funereus
- Yellow-faced Honeyeater – Caligavis chrysops
- Yellow Thornbill – Acanthiza nana
- Common Blackbird – Turdus merula
- Red-whiskered Bulbul – Pycnonotus jocosus