Riparian zone restoration
Riparian zone restoration is the ecological restoration
Restoration ecology
-Definition:Restoration ecology is the scientific study and practice of renewing and restoring degraded, damaged, or destroyed ecosystems and habitats in the environment by active human intervention and action, within a short time frame...

 of riparian zone
Riparian zone
A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the fifteen terrestrial biomes of the earth. Plant habitats and communities along the river margins and banks are called riparian vegetation, characterized by...

* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

of stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...

s, river
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

s, spring
Spring (hydrosphere)
A spring—also known as a rising or resurgence—is a component of the hydrosphere. Specifically, it is any natural situation where water flows to the surface of the earth from underground...

s, lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

s, floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...

s, and other hydrologic
Hydrology is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability...


Riparian zone
Riparian zone
A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the fifteen terrestrial biomes of the earth. Plant habitats and communities along the river margins and banks are called riparian vegetation, characterized by...

s have been degraded throughout much of the world. The unique biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...

 of riparian ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

s and the importance of riparian zones in preventing erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

, protecting water quality, providing habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

 and wildlife corridor
Wildlife corridor
A wildlife corridor or green corridor is an area of habitat connecting wildlife populations separated by human activities . This allows an exchange of individuals between populations, which may help prevent the negative effects of inbreeding and reduced genetic diversity that often occur within...

s, and maintaining the health of in-stream biota
Biota (ecology)
Biota are the total collection of organisms of a geographic region or a time period, from local geographic scales and instantaneous temporal scales all the way up to whole-planet and whole-timescale spatiotemporal scales. The biota of the Earth lives in the biosphere.-See...

 (Aquatic organisms) has led to a surge of restoration activities aimed at riparian ecosystems in the last few decades. Restoration efforts are typically guided by an ecological understanding of riparian zone processes and knowledge of the causes of degradation. They are often interdependent with stream restoration
Stream restoration
Stream restoration or river restoration, sometimes called river reclamation in the UK, describes a set of activities that help improve the environmental health of a river or stream. Improved health may be indicated by expanded habitat for diverse species and reduced stream bank erosion...


Causes of riparian zone degradation

Riparian zone disturbance falls into two main categories: hydrologic modifications that indirectly impact riparian communities through changes in stream morphology
Channel types
A wide variety of river and stream channel types exist in limnology. All these can be divided into two groups by using the water-flow gradient as either low gradient channels for streams or rivers with less than two percent flow gradient, or high gradient channels for those with greater than a 2%...

 and hydrologic processes, and habitat alterations that result in direct modification of riparian communities through land clearing or disturbance.

Dams and diversions

Dams are built on rivers primarily to store water for human use, generate hydroelectric power, and/or control flooding. Natural riparian ecosystems upstream of dams can be destroyed when newly-created reservoirs inundate riparian habitat. Dams can also cause substantial changes in downstream riparian communities by altering the magnitude, frequency, and timing of flood events and reducing the amount of sediment and nutrients delivered from upstream. Diverting water from stream channels for agricultural, industrial, and human use reduces the volume of water flowing downstream, and can have similar effects.

In a natural riparian system, periodic flooding can remove sections of riparian vegetation. This leaves portions of the floodplain available for regeneration and effectively “resets” the successional timeline. Frequent disturbance naturally favors many early-successional (pioneer) riparian species. Many studies show that a reduction in flooding due to dams and diversions can allow community succession to progress beyond a typical stage, causing changes in community structure.

Changing flood regimes can be especially problematic when exotic species are favored by altered conditions. For example, dam regulation changes floodplain hydrology
Hydrology is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability...

 in the southwest U.S. by impeding annual flooding cycles. This modification has been implicated in the dominance of saltcedar (Tamarix chinensis) over the native cottonwood (Populus deltoids). Cottonwoods were found to be competitively superior to saltcedar when flooding allowed seeds of both species to cogerminate. However, the lack of flooding caused by altered hydrology creates more favorable conditions for the germination of saltcedar over cottonwoods.

Groundwater withdrawals

Riparian zones are characterized by a distinct community of plant species that are physiologically adapted to a greater amount of freshwater than upland species. In addition to having frequent direct contact with surface water through periodic rises in stream water levels and flooding, riparian zones are also characterized by their proximity to groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

. Particularly in arid regions, shallow groundwater, seeps
Seep (hydrology)
A Seep is a moist or wet place where water, usually groundwater, reaches the earth's surface from an underground aquifer.-Description:Seeps are usually not of sufficient volume to be flowing beyond their above-ground location. They are part of the limnology-geomorphology system...

, and spring
Spring (hydrosphere)
A spring—also known as a rising or resurgence—is a component of the hydrosphere. Specifically, it is any natural situation where water flows to the surface of the earth from underground...

s provides a more constant source of water to riparian vegetation than occasional flooding. By reducing the availability of water, groundwater withdrawals can impact the health of riparian vegetation. For example, Fremont cottonwood
Populus fremontii
Populus fremontii, the Fremont cottonwood or Alamo cottonwood, is a cottonwood poplar native to western North America, in California and east to Nevada, Utah, Arizona, and New Mexico, and south into Sonora in northwestern Mexico...

 (Populus fremontii), and San Joaquin willow
Salix gooddingii
Salix gooddingii is a species of willow known by the common name Goodding's willow, or Goodding's black willow. It was named for its collector, Leslie Newton Goodding....

 (Salix gooddingii), common riparian species in Arizona, were found to have more dead branches and experienced greater mortality with decreasing groundwater levels.

Plant community composition can change dramatically over a gradient of groundwater depth: plants that can only survive in wetland conditions can be replaced by plants that are tolerant of drier conditions as groundwater levels are reduced, causing habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

 community shifts and in some cases complete loss of riparian species. Studies have also shown that decreases in groundwater levels may favor the invasion and persistence of certain exotic invasive species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....

 such as Saltcedar
Tamarix chinensis
Tamarix chinensis is a species of tamarisk known by the common names Chinese tamarisk and five-stamen tamarisk or saltcedar. It is native to China and Korea, and it is known in many other parts of the world as an introduced species and sometimes an invasive noxious weed. It easily inhabits moist...

 (Tamarix chinensis), which do not appear to show the same degree of physiologic water stress as native species when subjected to lower groundwater levels.

Stream channelization and levee construction

Stream channelization is the process of engineering straighter, wider, and deeper stream channels, usually for improved navigation, wetland drainage, and/or faster transport of flood waters downstream. Levee
A levee, levée, dike , embankment, floodbank or stopbank is an elongated naturally occurring ridge or artificially constructed fill or wall, which regulates water levels...

s are often constructed in conjunction with channelization to protect human development and agricultural fields from flooding. Riparian vegetation can be directly removed or damaged during and after the channelization process. In addition, channelization and levee construction modify the natural hydrology of a stream system. As water flows through a natural stream, meanders are created when faster flowing water erodes outer banks and slower flowing water deposits sediment on inner banks. Many riparian plant species depend on these areas of new sediment deposition for germination and establishment of seedlings. Channel straightening and levee construction eliminate these areas of deposition, creating unfavorable conditions for riparian vegetation recruitment.

By preventing overbank flooding, levees reduce the amount of water available to riparian vegetation in the floodplain, which alters the types of vegetation that can persist in these conditions. A lack of flooding has been shown to decrease the amount of habitat heterogeneity in riparian ecosystems as wetland depressions in the floodplain no longer fill and hold water. Because habitat heterogeneity is correlated with species diversity, levees can cause reductions in the overall biodiversity of riparian ecosystems.

Land clearing

In many places around the world, riparian zones have been completely eliminated as humans have cleared land
Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use....

 for raising crops, growing timber, and developing land for commercial or residential purposes. Removing riparian vegetation increases the erodibility of stream banks, and can also speed the rate of channel migration. In addition, removal of riparian vegetation fragments the remaining riparian ecosystem, which can prevent or hinder dispersal of species between habitat patches. This can diminish riparian plant diversity, as well as decrease abundances and diversity of migratory birds or other species that depend on large, undisturbed areas of habitat. Fragmentation can also prevent gene flow between isolated riparian patches, reducing genetic diversity.

Livestock grazing

Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...

 have a propensity to aggregate around water, which can be detrimental to riparian ecosystems. While native ungulate
Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...

s such as deer are commonly found in riparian zones, livestock
Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...

 may trample or graze down native plant
Native plant
Native plant is a term to describe plants endemic or naturalized to a given area in geologic time.This includes plants that have developed, occur naturally, or existed for many years in an area...

s, creating an unnatural amount and type of disturbance that riparian species have not evolved to tolerate. Livestock grazing
Grazing generally describes a type of feeding, in which a herbivore feeds on plants , and also on other multicellular autotrophs...

 has been shown to reduce areal cover of native plant species, create disturbance frequencies that favor exotic annual weeds, and alter plant community composition. For example, in an arid South African ecosystem, grazing was found to cause a reduction of grasses, sedges, and tree species and an increase in non-succulent shrubs.


Mining stream channels for sand and gravel can impact riparian zones by destroying habitat directly, removing groundwater through pumping, altering stream channel morphology, and changing sediment flow regimes. Conversely, mining activities in the floodplain can create favorable areas for the establishment of riparian vegetation (e.g., cottonwoods) along streams where natural recruitment processes have been impacted through other forms of human activity. Mining for metals can impact riparian zones when toxic materials accumulate in sediments.

Invasive exotics

The number and diversity of invasive exotic species
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...

 in riparian ecosystems is increasing worldwide. Riparian zones may be particularly vulnerable to invasion due to frequent habitat disturbance (both natural and anthropogenic) and the efficiency of rivers and streams in dispersing propagules. Invasive species can greatly impact the ecosystem structure and function of riparian zones. For example, the higher biomass of dense stands of the invasive Acacia mearnsii and Eucalyptus species causes greater water consumption and thus lower water levels in streams in South Africa. Invasive plants can also cause changes in the amount of sediment that is trapped by vegetation, altering channel morphology, and can increase the flammability of the vegetation, increasing fire frequency. Exotic animals can also impact riparian zones. For example, feral burros along the Santa Maria river strip bark and cambium off native cottonwoods, causing tree mortality.

Methods of riparian zone restoration

Methods for restoring riparian zones are often determined by the cause of degradation. Two main approaches are used in riparian zone restoration: restoring hydrologic processes and geomorphic features, and reestablishing native riparian vegetation.

Restoring hydrologic processes and geomorphic features

When altered flow regimes have impacted riparian zone health, re-establishing natural streamflow may be the best solution to effectively restore riparian ecosystems. The complete removal of dams and flow-altering structures may be required to fully restore historic conditions, but this is not always realistic or feasible. An alternative to dam removal is for periodic flood pulses consistent with historical magnitude and timing to be simulated by releasing large amounts of water at once instead of maintaining more consistent flows throughout the year. This would allow overbank flooding, which is vital for maintaining the health of many riparian ecosystems. However, simply restoring a more natural flow regime also has logistical constraints, as legally appropriated water rights may not include the maintenance of such ecologically important factors. Reductions in groundwater pumping may also help restore riparian ecosystems by reestablishing groundwater levels that favor riparian vegetation; however, this too can be hampered by the fact that groundwater withdrawal regulations do not usually incorporate provisions for riparian protection.

The negative effects of channelization on stream and riparian health can be lessened through physical restoration of the stream channel. This can be accomplished by restoring flow to historic channels, or through the creation of new channels. In order for restoration to be successful, particularly for the creation of entirely new channels, restoration plans must take into account the geomorphic potential of the individual stream and tailor restoration methods accordingly. This is typically done through examination of reference streams (physically and ecologically similar streams in stable, natural condition) and by methods of stream classification based on morphological features. Stream channels are typically designed to be narrow enough to overflow into the floodplain on a 1.5 to 2 year timescale. The goal of geomorphic restoration is to eventually restore hydrologic processes important to riparian and instream ecosystems. However, this type of restoration can be logistically difficult: in many cases, the initial straightening or modification of the channel has resulted in humans encroaching into the former floodplain through development, agriculture, etc. In addition, stream channel modification can be extremely costly.

One well-known example of a large-scale stream restoration project is the Kissimmee River Restoration Project in central Florida. The Kissimmee River was channelized between 1962 and 1971 for flood control
Flood control
In communications, flood control is a feature of many communication protocols designed to prevent overwhelming of a destination receiver. Such controls can be implemented either in software or in hardware, and will often request that the message be resent after the receiver has finished...

, turning a meandering 167 km of river into a 90 km drainage canal. This effectively eliminated seasonal inundation of the floodplain, causing a conversion from wetland to upland communities. A restoration plan began in 1999 with the goals of reestablishing ecological integrity of the river-floodplain system. The project involves dechannelizing major sections of the river, directing water into reconstructed channels, removing water control structures, and changing flow regimes to restore seasonal flooding to the floodplain. Since the completion of the first phase of restoration, a number of improvements in vegetation and wildlife communities have been documented as the conversion from uplands back to wetlands has begun to take place.
Breaching levees to reconnect streams to their floodplains can be an effective form of restoration as well. On the Cosumnes River in central California, for example, the return of seasonal flooding to the floodplain as a result of levee breaching was found to result in the reestablishment of primarily native riparian plant communities.

Stream channels will often recover from channelization without human intervention, provided that humans do not continue to maintain or modify the channel. Gradually, channel beds and stream banks will begin to accumulate sediment, meanders will form, and woody vegetation will take hold, stabilizing the banks. However, this process may take decades: a study found stream channel regeneration took approximately 65 years in channelized streams in West Tennessee. More active methods of restoration may speed the process along.

Restoration of riparian vegetation

The revegetation of degraded riparian zones is a common practice in riparian restoration. Revegetation can be accomplished through active or passive means, or a combination of the two.

Active vegetation restoration

A lack of naturally-available propagules can be a major limiting factor in restoration success. Therefore, actively planting native vegetation is often crucial for the successful establishment of riparian species. Common methods for actively restoring vegetation include broadcast sowing seed and directly planting seeds, plugs, or seedlings. Reestablishing clonal species such as willows can often be accomplished by simply putting cuttings directly into the ground. To increase survival rates, young plants may need to be protected from herbivory with fencing or tree shelters. Preliminary research suggests that direct-seeding woody species may be more cost-effective than planting container stock.

Reference sites are often used to determine appropriate species to plant and may be used as sources for seeds or cuttings. Reference communities serve as models for what restoration sites should ideally look like after restoration is complete. Concerns about using reference sites have been raised however, as conditions at the restored and reference sites may not be similar enough to support the same species. Also, restored riparian zones may be able to support a variety of possible species combinations, therefore the Society for Ecological Restoration recommends using multiple reference sites to formulate restoration goals.

A practical question in active vegetation restoration is whether certain plants facilitate the recruitment and persistence of other plants (as predicted by theories of succession), or whether initial community composition determines long-term community composition (priority effects). If the former applies, it may be more effective to plant facilitative species first, and wait to plant dependent species as conditions become appropriate (e.g., when enough shade is provided by overstory species). If the latter applies, it is probably best to plant all desired species at the outset.

As a critical component of restoring native riparian communities, restoration practitioners often have to remove invasive species and prevent them from reestablishing. This can be accomplished through herbicide application, mechanical removal, etc. When restoration is to be done on long stretches of rivers and streams, it is often useful to begin the project upstream and work downstream so that propagules from exotic species upstream will not hamper restoration attempts. Ensuring the establishment of native species is considered vital in preventing future colonizations of exotic plants.

Passive vegetation restoration

Active planting of riparian vegetation may be the fastest way to reestablish riparian ecosystems, but methods may be prohibitively resource-intensive. Riparian vegetation may come back on its own if human-induced disturbances are stopped and/or hydrologic processes are restored. For example, many studies show that preventing cattle grazing in riparian zones through exclusion fencing can allow riparian vegetation to rapidly increase in robustness and cover, and also shift to a more natural community composition. By simply restoring hydrologic processes such as periodic flooding that favor riparian vegetation, native communities may regenerate on their own (e.g., the Cosumnes River floodplain). The successful recruitment of native species will depend on whether local or upstream seed sources can successfully disperse propagules to the restoration site, or whether a native seed bank is present. One potential hindrance to passive vegetation restoration is that exotic species may preferentially colonize the riparian zone. Active weeding may improve the chances that the desired native plant community will reestablish.

Restoring animal life

Restoration often focuses on reestablishing plant communities, probably because plants form the foundation for other organisms within the community. Restoration of faunal communities often follows the “Field of Dreams” hypothesis: “if you build it, they will come”. Many animal species have been found to naturally recolonize areas where habitat has been restored. For example, abundances of several bird species showed marked increases after riparian vegetation had been reestablished in a riparian corridor in Iowa.
Some riparian restoration efforts may be aimed at conserving particular animal species of concern, such as the Valley elderberry longhorn beetle in central California, which is dependent on a riparian tree species (blue elderberry, Sambucus mexicana) as its sole host plant. When restoration efforts target key species, consideration for individual species’ needs (e.g., minimum width or extent of riparian vegetation) are important for ensuring restoration success.

Ecosystem perspectives

Restoration failures may occur when appropriate ecosystem conditions are not reestablished, such as soil characteristics (e.g., salinity, pH, beneficial soil biota, etc.), surface water and groundwater levels, and flow regimes. Therefore, successful restoration may be dependent on taking a number of both biotic and abiotic factors into account. For example, restoration of soil biota, including symbiotic myccorhizae, invertebrates, and microorganisms may improve nutrient cycling dynamics. Restoration of physical processes may be a prerequisite to the reestablishment of healthy riparian communities. Ultimately, a combination of approaches taking into account causes for degradation and targeting both hydrology and the reestablishment of vegetation and other life forms may be most effective in riparian zone restoration.

See also

  • Buffer strip
    Buffer strip
    A buffer strip is an area of land maintained in permanent vegetation that helps to control air, soil, and water quality, along with other environmental problems, dealing primarily on land that is used in agriculture. Buffer strips trap sediment, and enhance filtration of nutrients and pesticides by...

  • Constructed wetland
    Constructed wetland
    A constructed wetland or wetpark is an artificial wetland, marsh or swamp created as a new or restored habitat for native and migratory wildlife, for anthropogenic discharge such as wastewater, stormwater runoff, or sewage treatment, for land reclamation after mining, refineries, or other...

  • Drainage system (agriculture)
    Drainage system (Agriculture)
    An agricultural drainage system is a system by which the water level on or in the soil is controlled to enhance agricultural crop production.-Classification:Figure 1 classifies the various types of drainage systems...

  • Environmental restoration
    Environmental restoration
    Environmental restoration is a term common in the citizens’ environmental movement. Environmental restoration is closely allied with ecological restoration or environmental remediation...

  • Infiltration (hydrology)
    Infiltration (hydrology)
    Infiltration is the process by which water on the ground surface enters the soil. Infiltration rate in soil science is a measure of the rate at which soil is able to absorb rainfall or irrigation. It is measured in inches per hour or millimeters per hour. The rate decreases as the soil becomes...

  • Land rehabilitation
    Land rehabilitation
    Land rehabilitation is the process of returning the land in a given area to some degree of its former state, after some process has resulted in its damage...

  • Limnology
    Limnology , also called freshwater science, is the study of inland waters. It is often regarded as a division of ecology or environmental science. It covers the biological, chemical, physical, geological, and other attributes of all inland waters...

  • Restoration ecology
    Restoration ecology
    -Definition:Restoration ecology is the scientific study and practice of renewing and restoring degraded, damaged, or destroyed ecosystems and habitats in the environment by active human intervention and action, within a short time frame...

  • Revetment
    Revetments, or revêtements , have a variety of meanings in architecture, engineering and art history. In stream restoration, river engineering or coastal management, they are sloping structures placed on banks or cliffs in such a way as to absorb the energy of incoming water...

  • Riprap
    Riprap — also known as rip rap, rubble, shot rock or rock armour or "Rip-rap" — is rock or other material used to armor shorelines, streambeds, bridge abutments, pilings and other shoreline structures against scour, water or ice erosion.It is made from a variety of rock types, commonly granite or...

  • Watertable control
    Watertable control
    Watertable control is the practice of controlling the water table in agricultural land by subsurface drainage with proper criteria to improve the crop production.- Description and definitions :...

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