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Vegetation Components of Riparian Health

Vegetation Components of Riparian Health

Vegetation Components of Riparian Health:

Riparian Vegetation Age-Class and its Role in Health

The Role of Age Class in Riparian Health. For a riparian-wetland area to recover or maintain itself, it has to have more than one age class of riparian-wetland plants. Most riparian areas will recover or maintain themselves with two age classes, as long as one of the age classes is young (for recruitment), and the other is middle-aged (for replacement). Older, mature age classes usually take care of themselves, as they are well-attached to existing water tables. Older age classes can usually persist even with degraded conditions, so they are not a good indicator of a healthy riparian area.

Age Class Distribution Relationships. Expanding populations generally have a pyramid shape of age distribution, with many young plants forming a wide base, fewer middle-aged, and very few old at the top. Stable populations are more bullet shaped, with somewhat equal young and middle-aged groups forming the base and middle, and then gradually diminishing to the oldest individuals. Diminishing populations are more urn shaped, with a narrow base of young, widening toward the older age classes, and then sharply narrowing with the oldest individuals. An indicator of diminishing populations is low proportions or missing classes of young and/or middle aged individuals.

Plant age can be difficult to establish, especially in the Southwest. The USDA Forest Service uses age class in reference to woody species only and establishes a procedure based on number of stems and proportion of live stems for determination of age.

For herbaceous species such as sedges, the term age-class distribution can be somewhat misleading, but the intent is to identify indicators of expanding, stable, and diminishing populations through recruitment and reproduction. While often hard to observe, seedlings of perennial plants indicate recruitment and young sedges colonizing a fresh sediment deposit may be seen as a line of plants tapering in size toward the youngest emerging plants.

Warning Signs. Some warning signs that the age class distribution is out of balance, which may be indicative of declining health or unraveling of riparian areas include:

  • A lack of seedlings and saplings of woody species. Riparian areas that require woody vegetation should have evidence of new and young plants, especially in places where they normally establish such as point bars.
  • Woody plants that browsing keeps from escaping. When willows or other woody plants cannot gain sufficient leader growth to get tall enough to be beyond reach of browing animals, they may not recruit new reproducing individuals into the population.
  • Scattered, individual stems of herbaceous species such as sedges and rushes. Herbaceous species help protect the riparian area by forming dense stands with even denser root masses. In order to be effective, these species should be forming dense mats.

In those few channels where vegetation doesn’t contribute to bank stability, the diversity of age-class of riparian species doesn’t need to be evaluated.

References

  • Surber, G., B. Ehrhart. 1998. Stream and Riparian Areas Management: A Home Study Course for Managers. Montana State Extension Service. Information also available at http://www.animalrangeextension.montana.edu/range/riparian-habitat.html#
  • USDI Bureau of Land Management. 1998. Riparian Area Management: A User Guide to Assessing Proper Functioning Condition and the Supporting Science for Lotic Areas. Technical Reference TR 1737-15. 124 pp. More Information available at: http://www.blm.gov/or/programs/nrst/index.php
  • Winward, A. H. 2000. Monitoring the vegetation resources in riparian areas. Gen. Tech. Rep. RMRSGTR-47. Ogden, UT: U.S. For. Serv., Rocky Mountain Res, Sta. 49 pp. available at https://globalrangelands.org/dlio/14490

Species Diversity

Why Species Diversity is Important. For a riparian area to maintain itself, or to recover, a diverse composition of vegetative species is required. Although all potential plants won’t always be present in a riparian area, it is important that at least two species of the required functional groups are present. The presence of only one species makes a site vulnerable to disease or extreme climate events, which may result in degradation of an area. Composition needs to also be diverse enough to accommodate substantial shifts in the water table or zone of saturation that may occur with drought cycles.

Warning Sign. The presence of only one species. A lack of diversity is a sign that riparian health may be declining. There are some areas that canonly support one species, but they are uncommon and usually limited as a result of a unique soil property, vegetative characteristics, or water regime.

References

The Relationship Between Vegetation and Soil Moisture Characteristics

Vegetation can be an indicator of a water table. The presence of riparian-wetland vegetation can be one way of looking for evidence that the water table level is being maintained or is moving toward its potential extent. The maintenance or recovery of an existing water table is vital to the maintenance or recover of a riparian wetland area.

Categories of Riparian Plants. Riparian-wetland species are divided into categories relative to the likelihood of their occurrence in wetlands or non-wetlands. These categories are:

  • Obligate Wetland. Occurs almost always (estimated probability 99%) under natural conditions in wetlands.
  • Facultative Wetland (FACW) -- Usually occurs in wetlands (estimated probability 67%-99%), but occasionally found in non-wetlands.
  • Facultative (FAC)-- Equally likely to occur in wetlands or non-wetlands (estimated probability 34%-66%).
  • Obligate Upland (UPL)-- Occurs in wetlands in another region, but occurs almost always (estimated probability 99%) under natural conditions in non-wetlands in the regions specified. If a species does not occur in wetlands in any region, it is not on the National List.
  • Facultative Upland (FACU)-- Usually occurs in non-wetlands (estimated probability 67%-99%), but occasionally found on wetlands (estimated probability 1%-33%).

Definitions from USDA Plants Database

Plants that occur in wetlands are hydrophytes, and they have to be in contact with the water table, which is why they can be used as indicators of soil moisture characteristics.

Warning Sign. The site is dominated by facultative or obligate upland plants which could indicate declining health or “unraveling” of the riparian area. These types of plants don’t have the root mass needed to hold streambanks and dissipate energy, as well as maintain the water table.

Some intermittent systems, depending on duration of flow, could be somewhat different, as their potential may be facultative plants.

References

Root Masses and Bank Stability

Having the Right Roots. Vegetation is important in slowing flow velocity, stabilizing streambanks, and reducing erosion. Streambanks dominated by vegetation without extensive root masses are undercut during high flow events and collapse. This collapse results in a change in the active channel’s width/depth ratio, gradient, and sinuosity, which reduces a riparian-wetland area’s ability to dissipate energy. The best soil stabilizers and streambank holders are woody species such as willows and cottonwoods, and herbaceous species such as sedges, and rushes. The extensive root systems of these species are especially effective in the development of overhanging banks, which provide habitat for fish and other aquatic organisms. These types of plants are known as Obligate Wetland of Facultative Wetland plants.

Annual herbaceous species and those species that indicate uplands generally lack sufficiently dense, deep root systems to provide much protection. These species are known as Facultative Upland or Upland plants.

When Vegetation Doesn't Play a Role in Stability. There are exceptions where riparian vegetation with root masses capable of withstanding high flow events is not required. These include high gradient, bedrock, or boulder/cobble stream types. In these systems, vegetation contributes little, if any, to bank stability.

Warning Signs: When vegetation with shallow root systems dominates an area, such as the Kentucky bluegrass dominated system above, the riparian area is incapable of withstanding high flow events and maintaining the stability of the banks. Some warning signs that the vegetation present lacks root masses capable of holding banks, which may be indicative of declining health or “unraveling” of riparian areas include:

  • Undercut Banks. Streambanks that are continually undercutting and shearing off indicate the plants present don’t have the root masses needed.
  • Presence of upland plants in the riparian area. Species such as Kentucky bluegrass, redtop, blue grama, (most grasses) and sagebrush, do not have the root masses capable of withstanding high flow events. If these plants dominate plant communities along the streambank, it’s an indicator that the stream is in need of better vegetation.

References

Plant Vigor

The Role of Vigor in Riparian Health. Looking at the vigor of riparian plant species will help to ascertain if plants are healthy and robust or are weakened or stressed and leaving the area. What is happening aboveground is a reflection of the condition belowground and the ability for riparian-wetland species to hold an area together. As riparian vegetation weakens or leaves an area, the area is subject to degradation.

Determining Vigor, or the Lack of Vigor. Vigor is difficult to quantify, possibly because the relative health of plants within a community is expressed in many morphological and physiological forms. It is helpful when evaluating vigor to separate woody plants and herbaceous plants. The reproductive indicators explained in Riparian Health - Understanding Riparian Vegetation Age-Class and its Role in Health, as well as plant size, leaf area and size, seed production, and root growth are all associated with relative plant health or vigor. Reduced height or reduced leaf area (production) and signs of stress, such as chlorosis, have traditionally been used as indicators of reduced vigor in herbaceous species. Growth form, leader length, and the amount of dead or dying limbs are indicators of vigor for shrubs and trees.

Warning Signs. Some warning signs that plant vigor is low or in decline, which may indicate declining health or “unraveling” of riparian areas include:

  • High amounts of dead limbs in woody species. A loss of vigor and the subsequent loss of a plant altogether, is a sign that vigor in the plant is declining. This could be a sign of old age.
  • Willow leaves turning yellow during the growing season. This decrease in vigor usually occurs as a result of water being removed or added to a system, which stresses the plants. This can also indicate a disease or soil nutrient problem or climate factors.
  • Herbaceous species such as sedges occurring as isolated plants or broken clumps. Sedges exhibiting high vigor in their systems usually form dense communities which form mats along riparian areas. Low vigor may be exhibited by an inability to form these communities.
  • Narrow leaves of sedges. Some sedges, such as Nebraska sedge tend to have wide leaves (~ thumb width) just up from the base when vigorous. Narrow leaves (~ pencil width) indicate stress from lack of moisture, excess grazing pressure or some other cause.

References

  • Surber, G., B. Ehrhart. 1998. Stream and Riparian Areas Management: A Home Study Course for Managers. Montana State Extension Service. Information also available at http://www.animalrangeextension.montana.edu/range/riparian-habitat.html#
  • USDI Bureau of Land Management. 1998. Riparian Area Management: A User Guide to Assessing Proper Functioning Condition and the Supporting Science for Lotic Areas. Technical Reference TR 1737-15. 124 pp. https://globalrangelands.org/dlio/62740

Is Adequate Vegetation Present?

The Connection Between Stream Energies and Vegetation. Streambank erosion is a physical process that occurs along virtually all natural channels. Not only is it a normal part of channel evolution and meander migration, but it is also essential for creating and maintaining a variety of aquatic and riparian habitats. When bank erosion becomes excessive, it can destroy significant channel and floodplain habitats. This occurs as these areas are excavated and sometimes buried under massive amounts of sediment. The best protection against excessive erosion is the preservation of adequate, desirable vegetative cover to dissipate the erosive forces acting upon the channel banks during periods of high stream flow.

Bank erosion occurs when the eroding force (shear stress) of water moving along the bank exceeds those forces in the bank that are resisting the shear force. Shear force on the bank is directly proportional to the rate at which velocity increases when moving away from the bank. Due to friction, the highest water velocity in a stream is about 1/3 of the way down from the water’s surface. This puts more of the energy against the streambank at about 1/3 of the depth. Thus, if velocity increases very rapidly in the near-bank region, the velocity gradient is steep and shear stress is high. Conversely, if velocity increases slowly or not at all in the near bank region, shear stress of the bank will be minimal or negligible. With either situation, the energies associated with the stream’s velocity are being exerted under the surface against the streambanks. Adequate vegetation will ensure that the riparian vegetation root masses are present and capable of withstanding the energies. Root masses are a key factor due to the fact that they increase the tensile strength of the bank. Particularly in noncohesive soils and sediments, the presence of vegetation may greatly increase binding forces in bank material. Tensile strength provided by root masses of riparian vegetation may be the primary source of resistance in the alluvial sediments of many Western streams. Tensile strength will be dependent upon both the kind of vegetation present and the extent and density of root masses in the sediments. Determination of root-mass adequacy is site specific, as less cohesive sediments will require greater root mass to achieve the same level of stability as more cohesive sediments elsewhere.

Vegetation also has the potential to influence the balance of energy by the occurrence of living or dead vegetation (or any other cover, for that matter) that extends into the flow of the stream/river. It has the potential to reduce near-bank velocities, thus reducing erosive shear forces acting upon the bank. In an ideal situation, vegetation along the bank is sufficient to produce a zone of near-zero velocities near the bank, effectively moving the velocity profile away from the bank so that shear stress is dissipated in turbulent eddies in the flow. A similar process occurs in the over-bank region when density of vegetation is sufficient to produce near-zero velocities in overbank flow during flood events.

Looking at the Vegetation. The following characteristics should be assessed regarding riparian species to determine if the vegetation in a channel is adequate:

  • Age-class distribution
  • Diversity
  • Species
  • Root masses, and
  • Plant vigor

If each of these items is evaluated and found to be healthy and doing well, then the vegetation present is adequate. If any of these items are absent or minimal, then there is some question as to whether or not the vegetation is adequate.

Warning Signs. Some warning signs to look for that may be indicative of inadequate vegetation include:

Bareground. Soil that is not covered by vegetation, litter or duff, downed woody material, or rocks--is highly susceptible to erosion. It may contribute both to overland sediment flow and to the erosion of streambanks. In both cases, it can affect water quality as well as contribute to the loss of valuable soil and acreage. Bare stream banks are also prime areas for invasion of noxious weeds or other undesirable plant species. Bare ground increases the possibility of compaction or bank shearing by hoofed animals, vehicles, or people. This reduces the water-holding capacity of the soil.

Riparian species present, but inadequate. If riparian plant species appear to be low in vigor, losing diversity and species, or not producing the root masses needed, there might not be adequate vegetation to sustain the riparian area and protect it during high flows.

Upland plants in the riparian area. Upland plants in a riparian area are indicative of an unhealthy riparian area. Upland species do not have the root masses capable of holding a streambank together and resisting the energies within the stream. 

References

The Role of Large Woody Material in Riparian Areas

Large Woody Material - A Specific Attribute in Specific Places. Some riparian wetland systems, mainly those in the Pacific Northwest, require large woody material (LWM) that falls into the stream to capture bedload, aid floodplain development, and dissipate energy. In these systems, it is important to determine if the streamside and upland plant communities are producing the size of woody material over time that can fulfill this need. Without coarse and/or large wood to dissipate energy, these systems cannot handle the normal high-flow events that occur. The LWM in the system needs to be large enough to stay for a period of time that allows it to operate as a hydrologic modifier.

Large Woody Material Plays a Specific Part in Very Complex Systems. The complexity of forest riparian environments has led researchers to study the hydrology, sediment delivery, vegetation, and biology of these systems to determine how each component, including LWM affect specific products, such as water quality and fish. To visualize forest riparian/stream processes, it is necessary to consider each point of interest as interrelated to the whole stream continuum. The location of interest may be anywhere from the headwaters to the ocean. The way each part of the system functions changes as the streams merge and grow larger, and the enormous variety of stream slope, geology, hydrologies, vegetation types, etc., adds to the difficulty of describing how the whole system functions.

The Role of Large Woody Material (LWM). In order to understand the role of LWM, a knowledge of stream hydrology, forest ecology, fisheries, and climate is also required. To cover all of these aspects would be too lengthy and in depth to write here. The following are some key points that are important to remember regarding the role of LWM in a stream:

  • LWM and living trees are essential to the development and maintenance of some forested riparian stream ecosystems from their headwaters to the downstream end of the forest stream continuum.
  • The riparian/stream continuum is in a state of dynamic stability when it is functioning properly and the movement of LWM down the stream system is normal and necessary. The function of LWM in the stream and on the floodplain changes from the headwater to the wider downstream valleys.
  • Floods, fires, windthrow, torrents, landslides, and normal tree mortality are essential delivery mechanisms needed to maintain and restore the riparian stream system’s functionality.
  • The temporal processes of the forest riparian /stream system must be measured in decades and centuries.
  • The spatial location of LWM is continually shifting during annual and episodic events. This spatial movement replenishes materials that are broken down or flushed out of the system.

Warning Signs. Two warning signs that not enough LWM is present for the stream and may be indicative of declining health or “unraveling” of riparian areas are: 1) There is an absence of large wood near the stream. Without living mature trees present that will access the stream in the future the stream is without a source of LWM. 2) Only isolated pockets of trees exist near the stream. The stream needs to have adequate trees as a source of LWM. Isolated pockets of trees does not fulfill this need.

Reference

  • USDI Bureau of Land Management. 1998. Riparian Area Management: A User Guide to Assessing Proper Functioning Condition and the Supporting Science for Lotic Areas. Technical Reference TR 1737-15. 124 pp. More Information available at: http://www.blm.gov/or/programs/nrst/index.php
Sarah Noelle

Hydrologic Components of Riparian Health

Hydrologic Components of Riparian Health

Hydrologic Components of Riparian Health:

The Function of Floodplains

What is a Floodplain? Schmudde provides three definitions of floodplain: 1) Topographically, it is flat and lies adjacent to a stream. 2) Geomorphically, it is a land form composed primarily of unconsolidated depositional material, or sediments, derived from the stream. 3) Hydrologically, it is a land form subject to periodic flooding by the stream.

Floodplains develop over time as the result of flood inundations. The water moving over a floodplain travels at a lower velocity than the channel flow, and as flow velocity decreases, sediment is deposited. Over time, these deposits of nutrient-rich sediment are built up in layers. The sediment also brings nutrients to the riparian vegetation which is growing upon it.

Function of Floodplains. Schmudde provides a good summary of the functional purpose of the floodplain: “Thus, the floodplain is seen as an integral part of the stream system and the adjustment mechanism needed to meet the requirement of discharge and load imposed by the basin it serves.”

When evaluating a riparian area, it is important to determine if frequent floodflows are capable of spreading out on a floodplain adjacent to the stream thereby providing for energy dissipation, sediment deposition, and periodic flooding of vegetation.  Stream systems that are not highly confined generally support a floodplain landform that is flat and adjacent to the stream. However, if the channel is downcut and floodflows can no longer access the floodplain, it no longer provides those important hydrologic functions.

The floodplain provides the additional capacity for the stream system to transport and store water and sediment. The magnitude and significance of the additional capacity depends on the spatial extent of the floodplain along with basin and stream system characteristics. Vegetation often is an important player in the efficiency and longevity of floodplain function. Periodic flooding of the floodplain is often necessary to promote and sustain riparian vegetation and therefore is a key factor in determining the functional condition of the riparian system.

Understanding Bankfull. The floodplain is functional if it is normally connected to the stream at the bankfull discharge point of the channel. Wolman and Leopold (1957) suggest there is an annual flood that normally reaches the floodplain every year or so. Gebhardt, et al., (1989) call this area of inundation the “active floodplain” to distinguish floodplain activity form floodplain inactivity. Thus, an active floodplain would see some inundation every year or so, and the spatial extent of the inundation would increase over the floodplain as the magnitude of the flood increases. In other words, the larger the flood, the more floodplain will be used. The loss or reduction in the ability of the floodplain to dissipate energy and transport water and sediment are key factors in contributing to loss of functionality.

Evaluation of bankfull discharge is key in determining whether the topographic floodplain feature is connected to the stream. Water enters the floodplain when flows begin to exceed bankfull discharge. Bankfull discharge is significant for riparian resource management in that it represents a measure of interaction between the stream and it's adjacent valley bottom; thus, it strongly influences the geomorphic and biological characteristics of the riparian environment. Bankfull discharge on the majority of streams in the world has a recurrence interval between one and three years; one and a half years is considered a reasonable average. Hence, the floodplain will be accessed in relatively frequent events.

Bankfull stage, or elevation of water surface, can be identified in the field through several observable features: top of point bar, changes in vegetation, topographic break in slope, change in size, staining, or color of substrate material, and change in the nature and amount of debris deposits (Leopold, 1994)

It is best to have more than one indicator present, as just one -- for example, vegetation -- can be indicative of more short-term events than the channel-forming flows.

Bankfull discharge for a channel may be determined through the use of one or more surveyed cross-sections and a number of hydraulic models. These are best done by trained professionals who use the data that are collected from them. Your local Extension Agent can help you find a trained person.

Warning Signs. Some warning signs that the floodplain is not being inundated, which may be indicative of declining health or “unraveling” of riparian areas include:

  • Oversized Channels. Channels have widened to the point that the floodplain is not accessed fairly frequently.
  • Downcut/Incised Channels. Channels that have downcut are incapable of accessing their floodplains and will begin the process of establishing a new floodplain at it's lower levels, if possible.

Exceptions to the Rules. There are situations in which floods do not reach the floodplain due to flows being regulated -- either through reservoirs or diversions. The regulation of flow keeps the stream from having to dissipate energies on a floodplain regularly.

References

  • Gebhardt, K., C. Bohn, S. Jensen, W.S. Platts. 1989. Use of hydrology in riparian classification. In Practical Approaches to Riparian Resource Management – An Educational Workshop. Bureau of Land Management. Billings, MT. pp. 53-59.
  • Leopold, L.B. 1994. A View of the River. Harvard University Press, Cambridge, Massachusetts. 298 pp.
  • Schmudde, T.H. 1968. Flood plain. In The Encyclopedia of Geomorphology, edited by Fairbridge, R.W. Reinhold Book Corporation, NY. Pp. 359-362
  • Wolman, M.G. and L.B. Leopold, 1957. River floodplains: some observations on their formation. USGS Professional Paper 282-C.

The Role of Beavers in Riparian Areas

Benefits of Beaver. Beavers are key agents of riparian-wetland succession because their dams act as hydrologic modifiers. When a beaver dam is constructed, a flowing stream can be changed to a pond overnight. This in turn can lead to aggradation of the channel, establishment of floodplains, and raising groundwater levels. Elevated water levels also help to keep water in areas that would be otherwise dry during summer months and also during times of drought. This helps to sustain plant and animal life. The key to whether or not a beaver dam is beneficial is its stability. Beaver dams built with the correct, stabilizing woody vegetation, where there is enough additional woody vegetation to maintain the dam once built, are considered stable. Some beavers, known as “mudders,” also pack their dams with mud. The mudders’ construction technique creates a better basis for vegetation to capture a dam, thus helping to stabilize it.

Disadvantages of Beaver. Although beaver dams can be a benefit, they can also be a hazard. Beaver dams that are not stable unleash tremendous energies when they fail that often results in degradation and stream adjustments, including channel widening, lowering, and lateral migration. For this reason, it is important to note when evaluating riparian health whether beaver dams that are present are being actively maintained.  A dam that isn't being maintained, or has not used mud in the construction, or is not captured by vegetation will breach at some point.

Warning Signs. Poorly constructed beaver dams, or those made from the wrong materials, such as the sagebrush dam in the above picture, will breach easily and can lead to degradation of the current channel. Some warning signs that a beaver dam is unstable and may lead to a breach and subsequent decline in health of the riparian area include:

  • Lack of sufficient woody vegetation. Is there sufficient woody vegetation present for dam construction and maintenance? If not, there will be little vegetation to maintain the dam once built and may cause beaver to abandon the dam.
  • Beaver dams with breaks or leaks. This may be a sign that a breach of the dam is forthcoming.
  • Beaver dams which lack captured vegetation. Captured vegetation growing within and among a beaver dam helps to stabilize it and prevent breaching.

References

Is the Channel in Balanced with the Landscape?

Streams and their Landscapes - Understanding the Connection. The way a stream appears and the way water flows through the system is related to the landscape within which it exists. Streams in narrow, high mountain valleys are often steep with little sinuosity. Energies are dissipated with step/pools and with large boulders and debris within the channel. Streams that occur in wide valleys tend to move slowly, have only gradual slopes, and use sinuosity to further slow down and control the flow. Thus, the attributes of sinuosity, width/depth ratio, and gradient all play an important and related role in how well a stream dissipates energy. The landform in which a stream occurs will determine what the sinuosity, width/depth ratio, and gradient should be. To be in balance, a stream's attributes should match its landscape. If one of these attributes is out of balance, it often leads to the others being out of balance as well. For example, when there is a decrease in sinuosity, it results in a higher stream gradient, which increases velocities. Increased velocities accelerate erosion, which alters sinuosity, gradient, floodplain access and width/depth ratios.

Determining Balance. Determining a stream’s balance requires classification of stream length. Channel classification tools such as Rosgen’s (SEE ROSGENS) describe a range of characteristics for specific channel types and make it easier to understand this balance. Classifying the stream will also help to describe the stream’s position in the landscape and the expected range of variability for composition of bed and bank materials and for parameters related to channel size, shape, and pattern. Classification of the stream reach under consideration -- as well as adjacent reaches in both upstream and downstream directions -- and evaluation of recent channel evolution will provide a great deal of information for determining if the sinuosity, width/depth ratio and gradient of a stream are in balance with the landscape settings.

Warning Signs. Some warning signs that sinuosity, width/depth ratio, and gradient are out of balance, indicative of declining health or unraveling riparian areas include:

Stream is becoming wider and shallower - Stream channels get wider and shallower when something causes the banks to break down or when the amount of sediment in the channel exceeds the capacity of the water to move it through the system. An aggrading channel may find an alternative route and suddenly switch locations. Also, as the stream becomes shallower, stream temperatures may rise, which can increase bacteria, algae, and other organisms that respond to sunlight penetration and that may reduce water quality. Stream temperatures which exceed tolerance levels also adversely affect fish habitat. These levels differ from species to species.

Sinuosity is reduced, channel is straightening – Sinuosity differs depending on the type of stream that is being dealt with. If sinuosity is out of balance, water velocity is increased. This can lead to downcutting and/or bank shearing. Bank shearing may be the channel trying to widen to re-establish its sinuosity.

References

Riparian Areas and Water Storage

Storing Water in a Riparian Area. A healthy riparian area includes much more than just the channel in which the water flows and the vegetation on the banks near it. Healthy riparian areas often spread out across floodplains and farther through the water table. Riparian areas have the ability to store and release water over a long period of time. This water is stored by the soil in the streambanks, floodplain, and substrate under the channel which acts as a sponge to retain water. This water can extend out beyond the banks, sometimes spreading to include entire valley bottoms. The water is held here until later in the year, when the stored water slowly seeps out of the “sponge.” As it seeps out, it is either percolated downward to recharge underground aquifers or moves back into the stream channel, thus extending the availability of surface water later into the year.

Bringing Water Storage Back into a Riparian Area. When a riparian area degrades, it loses its ability to store water, and water tables are lowered or lost altogether. A degraded riparian area recovers by capturing sediment, called "aggradation," which aids floodplain development and improves flood-water retention. This recovery is often most evident by the increase in riparian-wetland vegetation. For example, a change in species composition from upland species like sagebrush to riparian-wetland species like Nebraska Sedge in the floodplain and near the stream is a good indication that the riparian zone is once again capturing and storing water. Aerial photos are a great tool for documenting these changes near a channel.

Warning Signs. Some warning signs that a riparian area may be starting to degrade and lose its ability to store water, which may lead to a decline in health or unraveling of riparian areas include:

  • Increase in upland vegetation in the riparian areas. Upland vegetation growing next to the stream and replacing riparian vegetation is a sign that less water is being stored in these areas.
  • Downcutting. Vertical instability or incision of a stream causes the floodplain to get flooded less often or for shorter periods. Much less water flows into the valley bottom aquifer through the banks then used to flow in through the floodplain surface. Water also drains faster out of the aquifer into the lowered stream. As the banks dry, the vegetation changes and fewer roots allow streambank soil to erode. Deep and fast floodwaters prevent the stream from capturing sediment (to build a new sponge) until the incision gets very wide.

Restoring water storage. After streams incise a little but before they get past a depth of no return, they may come back up with renewed balance in the sediment supply, more roughness from riparian vegetation or woody debris, or a lower gradient from restored or reformed meanders. When the stream floods its floodplain frequently (between 1 and 3 years on average), water from floods can again be stored under the floodplain. Streams that cut down too deeply lose their ability to reverse incision. High stress on the channel bed tends to increase erosion and incisions may become very deep. These channels widen because weakened banks allow rapid erosion. Eventually, wide shallow flows in the bottom of the gully cannot transport their load like they could when they were narrow and deep. Then bars begin to form and vegetation can help them stabilize into a new smaller and lower floodplain. As aggradation continues, water storage generally increases.

Exceptions to the Rules. Not all channels are capable of widening and spreading water out into adjacent floodplains and streambanks. For channels that are steep, deeply entrenched and confined, such as Rosgen’s A1 channel type, the channel is incapable of widening and little water is stored within the banks. Also, in these channels, vegetation is not needed for bank stabilization, and the landform dictates much about channel shape and water and sediment movement.

References

How Uplands Contribute to Riparian Health

Uplands and Riparian Areas Are Related. A riparian area and the stream that flows through it is the drainage point for the watershed they inhabit. Therefore, the condition of the uplands is going to influence the condition of the riparian area. When a riparian area undergoes a sudden change in its ability to function, the source of the problem could lie in the uplands, where an important change in sediment or water supply has caused riparian degradation.

If there has been a change in the water or sediment being supplied to a riparian-wetland area without any obvious changes occurring in the riparian area, the uplands should be investigated for possible causes. These could include road construction, fire, logging, urbanization, woodland expansion, and mudslides, as well as anything else that might alter the sediment or water that is delivered to the stream.

Warning Sign. One warning sign to look for that may be indicative of problems related to uplands is an excess of sediment in the system. This could be manifested through: braiding, mid-channel bars, overloading of point bars, fan deposits that alter sinuosity, cementing of a stream's substrate.

References

  • Surber, G., B. Ehrhart. 1998. Stream and Riparian Areas Management: A Home Study Course for Managers. Montana State Extension Service. Information also available.
  • USDI Bureau of Land Management. 1998. Riparian Area Management: A User Guide to Assessing Proper Functioning Condition and the Supporting Science for Lotic Areas. Technical Reference TR 1737-15. 124 pp. More Information available. 
Amber Dalke

Riparian Health

Riparian Health

Two of the three attributes used to assess rangeland health are 1) hydrologic function and 2) soil/site stability.

1. Hydrologic function refers to the site's capacity to capture, store, and safely release water from rainfall, run-on moisture, and/or snowmelt (where relevant). Two important components of hydrologic function are the site's ability to resist a reduction in it's hydrologic function following a disturbance or management action, and the site's ability to recover it's hydrologic capacity following degradation.

2. Soil/site stability refers a site's capacity to limit redistribution and loss of soil resources (including nutrients and organic matter) by wind and water.

The best way to protect hydrologic function and site stability is to maintain the proper amount and kind of vegetation on the site. This should be a primary management goal, or at least at a minimum, a major consideration for any rangeland vegetation management project. When a site lacks proper hydrologic function and soil/site stability, it can lose fertile topsoil, which ultimately reduces the areas productivity and resource value. 

Evaluating a Healthy Stream

1. A riparian area is considered healthy, or properly functioning, when it contains adequate vegetation, proper landform, or large woody debris which will:

  • Dissipate stream energy associated with high water flow thereby reducing erosion and improving water quality
  • Filter sediment, capture bedload, and aid floodplain development
  • Improve flood-water retention and ground-water recharge
  • Develop root masses that stabilize stream banks against cutting action

2. Develop diverse ponding and channel characteristics to provide the habitat and the water depth, duration, and temperature necessary for fish production, waterfowl breeding, and other uses, and

 3. Support greater biodiversity.

Not All riparian Areas Are Equal. It is important to remember that not all riparian areas are created equal. As stated above, “adequate vegetation, land form, or large woody debris” or any combination of these may be required to keep a riparian area functioning and healthy. For example, in most western Oregon riparian areas, large woody debris, or fallen trees, must be present to dissipate energy, capture bedload, and aid floodplain development. However, many areas in the Great Basin do not have the potential or require large woody debris to dissipate stream energy. Where they do, the wood is generally smaller; instead this is accomplished through the presence of vegetation such as willows, sedges, and rushes.

The Right Components Bring about the Right Characteristics. When the components necessary are present to dissipate energy associated with high flows, a number of physical characteristics or changes are evident. These include:

  • Reduced erosion
  • Sediment filtering or deposition
  • Improved floodwater retention

As these physical attributes of the system begin to function, they start the process of developing ponding and channel characteristics that provide habitat for fish, waterfowl, and other uses. It is important to note that the physical attributes have to be in working order to sustain the channel characteristics that provide the habitat for these resource values.

When these physical aspects are not present, changes have to be made that allow them to recover. A change such as acquiring vegetation leads to other physical changes, which allows the systems to begin to function. Recovery starts with acquiring the right elements to dissipate energy, which begins to put the physical processes into working order and they provide the foundation to sustain desired condition.

Water and soil conditions provide the basic structure of a riparian area, and as long as this basic structure has not been seriously altered, the maintenance and even improvement of a riparian area are often relatively easy. Without them, plants lose their resilience and systems fall apart. Then, little stresses can keep them from recovery.

Attributes That Are Warning Signs. Some specific attributes may indicate that a riparian area is “unhealthy” or “unraveling.” The primary physical features to consider in determining this are:

  • Evidence of channel downcutting
  • Evidence of channel widening
  • Amount, location, and causes of bare ground and
  • Amount of fine materials on the bottom of the channel

Vegetation Is the Easiest Attribute to See. Vegetation plays a critical part in the health of a riparian area. It is also important for management because plant communities often provide the first indicators of changes to the system. Important factors to consider when looking at riparian vegetation include:

  • The types and amounts of plants present,
  • How well they are fulfilling riparian functions,
  • The amount of foraging and browsing pressure being exerted on certain plants, and
  • The mix of age classes of woody species, if present.

If these attributes, or lack of them, are issues in a riparian area, it could indicate that the riparian area is in need of management changes to bring it back into a healthy and functioning condition.

For more information, or help in determining the health of a stream, contact:

  1. Your local Cooperative Extension agent
  2. Land management agencies that administer the land, such as the Bureau of Land Management or U.S. Forest Service
  3. Natural Resources Conservation Service personnel for riparian areas on private property.

References

Sheila Merrigan

Introduction to Riparian Areas

Introduction to Riparian Areas

Riparian Areas:

What is a Riparian Area?

The term “riparian” is defined as "vegetation, habitats, or ecosystems that are associated with bodies of water (for example streams, springs or ponds) or depend on perennial or intermittent surface or subsurface water." Put more simply, riparian areas are the green ribbons of trees, shrubs, and herbs growing along watercourses. Some riparian features we enjoy include the cottonwood groves where we like to picnic along sandy riverbeds, the green, shady areas next to the stream where we like to fish, and wetlands with ducks, tadpoles and dragonflies.

Riparian areas occur in a wide range of climatic, hydrologic, and ecological environments. Different latitudes and altitudes can support very different riparian communities. This is caused primarily by differences in soil, water and temperature. In the western United States, riparian areas occur from high elevation montane meadows or forests through intermediate elevation woodlands to low elevation shrublands and desert grasslands.

Riparian Areas are Ecosystems. An ecosystem is a functional system that includes both a biotic part in the organisms, such as the plants and animals, and an abiotic part, which factors in their immediate environment such as soil and topography. These organisms interact both with each other and with their environment. Each ecosystem is unique because the organisms and the environment differ from other ecosystems.

The three main characteristics that define riparian area ecosystems are hydrology, soils and vegetation. These reflect the influence of additional moisture compared to the adjacent, drier uplands. Riparian areas are the transition zones between aquatic (water-based) systems and terrestrial (land-based) systems, and usually have characteristics of both. These characteristics make it habitat for a larger number of species of plants and animals.

Because riparian areas are at the margin between water and land, their soil was most likely deposited by water and could be washed away by water. Protecting soil, streambanks, or water edges from excess erosion is an important function of riparian plants. Thus, properly functioning riparian areas absorb the water, nutrients, and energy from big events and use them to recover from disturbances while improving water quality. The toughness of riparian plants with dense, strong root systems, stems that slow floodwaters, and maybe woody debris that forms pools, adds to riparian stability and habitat diversity.

Some riparian areas, especially those not functioning properly or in high energy - high sediment locations are very dynamic and disturbance-driven. Plant communities may be susceptible to rapid change, if soil and water conditions change dramatically. These changes might include:

Flooding or lack of flooding either temporary or more long term, as caused by beavers, or man-made structures;

  • Deposition of sediment on streambanks and across floodplains;
  • Dewatering of a site by a variety of means; and
  • Changes in channel location or elevation

Where are Riparian Areas Found? Riparian areas are found at every elevation and in all landforms, and differ depending on local physical conditions (water, soil, temperature, etc.) and their location (elevation, valleys, canyons, etc.). High mountain riparian areas may be narrow and in deep ravines or canyons, while lowland floodplains in wide valleys may have large meanders. Desert washes may be sandy and only have water for a short time each year. These differences in vegetation, landform, and geology have led to a wide variety of terms used to denote riparian areas. These include riparian buffer zones, cottonwood floodplains, alluvial floodplains, floodplain forests, bosque woodlands, cienegas, and meadows.

Significant differences in water availability due to precipitation between the eastern and western United States has led to major differences in these regions’ riparian areas (See Figure 1). In the eastern United States, precipitation is much greater and riparian areas can maintain more lush vegetation than the arid regions of the western United States. Because of the higher precipitation received in the eastern United States, even the terrestrial upland ecosystems can maintain lush vegetation. As a result, it is difficult to define the boundaries between riparian areas and terrestrial uplands in the eastern United States. In contrast, in most of the western United States and particularly in the southwest, the transition between riparian and upland terrestrial systems is easily identifiable. This distinction is abrupt because the surrounding terrestrial habitat is much drier than the riparian area (Figure 1). Riparian areas in the arid western United States have different plant composition but are also more lush than their adjacent uplands. Another important difference between the eastern and western United States that influences riparian areas are the pathways that water follows to reach streams. In the eastern United States, more water infiltrates the soil resulting in more subsurface flow reaching the stream and thus, more soil moisture (Figure 1). In the western United States, there is more overland flow reaching the stream (Figure 1).

Riparian Areas: Different but the Same: Although riparian areas can differ greatly, they all have several things in commons. They are shadier, cooler, and moister than the adjacent upland environments. A wide variety of animals are attracted to these areas including insects, amphibians, reptiles, fish, birds, and mammals. Suitable habitat (food, water, and shelter) is often provided in riparian areas to support these animals which may not occur in surrounding drier areas.

In the western United States, riparian areas compromise less than 1 percent of the land area, but they are among the most productive and valuable natural resources, rivaling our best agricultural lands. They are particularly efficient at storing water, dissipating flow energies, improving water quality, trapping sediment, building and maintaining banks, and converting of solar energy. Such an important resource requires awareness on our part, and a need to learn and understand the landscapes around us.

References

  • Arizona Riparian Council. 1994. Riparian. Arizona Riparian Council Fact Sheet No. 1.
  • Chaney, E., W. Elmore, W.S. Platts. July 1993. Managing Change. U.S. Environmental Protection Agency.
  • Marti, E., S.G. Fisher, J.D. Schade and N.B. Grimm. 2000. Flood frequency and stream-riparian linkages in arid lands. In: Jones, J.B. and P.J. Mulholland (eds.), Streams and Ground Water. Academic Press. New York, NY. pp. 111-136.
  • Fisher, T. Grazing Riparian Areas in the Spring. A Home Study Course for Managers. Montana State Extension Service.
  • USDA-NRCS. August 1996. Riparian Areas Environmental Uniqueness, Functions, and Values. RCA Issue Brief #11.
  • Zaimes G. 2007. Defining Arizona's Riparian Areas and their Importance to the Landscape. In: Zaimes G. (editor), Understanding Arizona's Riparian Areas. University of Arizona Cooperative Extension, Publication # AZ1432. pp.1-13.

Types of Riparian Areas

Written by Mindy Pratt, Utah State University

Lentic or Lotic? The water of riparian areas makes them different from the adjacent terrestrial uplands. Water bodies can be natural such as streams, rivers, or lakes, or they can be man-made such as ditches, canals, ponds, or reservoirs. When riparian areas are part of a system with flowing water, such as streams or rivers, they are called lotic systems. In contrast, if the water in the system is stationary or moves only slowly without wind or at a spillway, such as lakes, ponds or seeps, the riparian area is referred to as a lentic system.

Lotic Systems. Lotic systems have two main divisions – natural and man-made systems. Natural systems include rivers and streams, while man-made systems include ditches and canals. Because man-made systems are quite variable and are managed solely to transport water to other areas, they do not share many characteristics with natural systems, and are not looked at as “healthy” or “unhealthy”. On the other hand, streams and rivers that occur naturally require certain characteristics in order to function, and can therefore be managed for those characteristics. In referring to lotic systems from this point on, the term will be referring to those natural systems that occur throughout the landscape. One way to classify these lotic systems is by the length of time water flows in the channel throughout the year. These can be divided into perennial, intermittent, and ephemeral systems.

Perennial streams/rivers have flow in the stream channel throughout the year. The sources of these systems include springs as well as substantial flow inputs from ground water. Stream flows can vary widely from year to year and may even dry up during severe droughts, but the ground water level is always near the surface. Perennial streams are found in both mesic (humid) and arid (dry) regions.

Intermittent streams/rivers are also connected to ground water, but flow in the stream channel typically occurs for a period of longer than a month, but shorter than a year. The majority of the water in these systems comes from some surface source such as melting snow or springs. The ground water is immediately below the streambed even when there is no flow in the channel. In many cases the flowing or drying of these streams can be predicted by seasonal precipitation or snowmelt patterns. Typically, these streams are associated with arid and semiarid climates, but are also common in mesic regions. There are two types of intermittent streams, spatially and temporarily intermittent, and these often occur along the same watercourse.

  • Spatially Intermittent or Interrupted– water appears above the streambed in some places, while it remains below the streambed in other places.
  • Temporally Intermittent – water appears above the streambed only after a rainfall or snowmelt event. These rainfall and snowmelt events recharge the stream and water typically rises above the streambed in part because the ground water is close to the streambed surface.

Ephemeral streams/rivers only flow for a few hours or days, and normally do not flow for 30 consecutive days. Flow is most commonly in response to rainfall or snowmelt events that are of sufficient magnitude to produce overland flow. The streambed of ephemeral streams is generally well above the water table, and these systems are often known as washes or arroyos. It is easy to confuse intermittent and ephemeral streams in the arid and semiarid western United States. The primary distinguishing factor between the two is the presence or proximity to ground water. In ephemeral streams it is minimal to nonexistent.

Are Ephemeral Streams really Riparian Areas? Whether or not to include ephemeral streams as riparian areas is a main point of disagreement among scientists. The main argument against including them as riparian areas is that ephemeral streams/rivers do not have the potential to perform the entire spectrum of riparian ecological functions. The main argument for including ephemeral streams/rivers is that these areas have “many” of the characteristic ecological functions that define riparian areas. For example, these areas are frequently disturbed and unstable, they are areas of soil transport and deposition, and there is usually a higher density of vegetation along ephemeral streams/rivers. They also serve as corridors that disperse plants and serve as animal transportation routes similar to other riparian areas.

Lentic Systems A lentic ecosystem is one such as a lake or pond that contains standing water. These can also be natural or man-made, but unlike lotic systems, the two types of systems are very similar in their characteristics. In lentic systems, water generally flows into and out of the lake or pond on a regular basis. The rates at which inflow and outflow occur vary greatly and can range from days, in the case of small pools, to centuries, in the case of the largest lakes.

References

  • Surber, Gene and Bob Ehrhart. 1998. Stream and Riparian Area Management. Montana State University Cooperative Extension Service.
  • USDI Bureau of Land Management. 1998. Riparian Area Management: A User Guide to Assessing Proper Functioning Condition and the Supporting Science for Lotic Areas. Technical Reference 1737-15. National Applied Resources Sciences Center, Denver, CO. 127 pp.
  • Zaimes G.N. (ed). 2006. Arizona’s Riparian Areas. University of Arizona Cooperative Extension.

Stream and River Classification

Classifying stream and rivers helps managers to understand to expected in specific stretches of stream. The two main methods used are:

The Strahler Classification Method or stream ordering assigns numbers to streams, with streams having no tributaries being 1st order and the numbers rising as tributaries join the stream/river flows farther from the source.

The Rosgen Classification Method takes into account a stream or river's slope, sinuosity, width/depth ratio, the degree of entrenchment, and the particle size of the streambanks and channel bottom to determine the stream type. It is more detailed than the Strahler method, and it is independent of size.

Riparian Vegetation

Riparian Vegetation is Specific Plants with a Specific Purpose. The vegetation that occurs in a healthy riparian area is both unique and important to the functionality of the riparian areas. Stabilizing types of riparian vegetation have root masses capable of withstanding most high flow events that occur in our streams and rivers. These root systems are important for the bank stability they provide. These root systems are mainly found in members of the sedge family (Cyperaceae), rush family (Juncaceae) and willows (Salicaceae). Few grasses have these capabilities. Abundance of species other than stabilizers may indicate a riparian area that is not working effectively. Some of the species that indicate this are: noxious weeds, tap-rooted herbs, annuals, Kentucky bluegrass, small clovers and plantain. Too many of these species would be a red flag that something within the riparian system is out of balance.

Other Functions of Riparian Vegetation. Riparian vegetation also influences other functions of a riparian system. Vegetation interacts directly with flowing water by providing resistance as water flows past stems and among leaves and branches. This slows the flows and affects the shape and pattern of the channel by reducing erosion and allowing deposition along the channel. The relatively stiff stems of woody vegetation may create high turbulence as flow travels around the stem and produces local pockets of erosion. Sedges, rushes and grasses, as well as other fine-stemmed vegetation, may simply bend as flow passes over them, contributing to channel roughness and capturing sediment. Riparian vegetation also traps nutrients in addition to the sediments, and reduces water and soil temperature and evaporation.

How to determine if a Riparian Area's Vegetation is Correct and Healthy. Because vegetation plays a vital role in a riparian system, not only does the correct type of vegetation need to be present and healthy, but it also needs to show evidence that vegetation is being replaced or is increasing in extent. In order to determine if this is occurring, the following items need to be evaluated:

  • Is there a diverse age-class distribution of riparian species?
  • Is there a diverse composition of riparian species?
  • Do the species present indicate that riparian-wetland soil characteristics are being maintained?
  • Is the vegetation present comprised of plants or plant communities that have root masses capable of withstanding high streamflow events?
  • Does the riparian vegetation present exhibit high vigor?
  • Is there enough riparian vegetation cover present to protect banks and dissipate energy?
  • In systems where it is needed, is there an adequate source of coarse and/or large woody material?

Understanding the riparian vegetation that should be present within a riparian area as well as the functions it should provide are important to any management plan or decision that will be made.

References

  • Dickard, M., M. Gonzales, W. Elmore, S. Leonard, D. Smith, S. Smith, J. Staats, P. Summers, D. Weixelman, and S. Wyman.. 2015. Riparian Area Management: Proper Functioning Condition Assessment for Lotic Areas. Riparian area management-proper functioning condition assessment for lotic areas (Technical Report No. 1737‐15 v. 2). Denver, CO: USDI, Bureau of Land Management.
  • Zaimes, G.N. (editor). Understanding Arizona’s Riparian Areas. University of Arizona Cooperative Extension, Publication #AZ1432.

Water Quality Regulations

  • Arid West Water Quality Research Project: Created to address concerns that the water quality criteria developed under the Clean Water Act - on which state water quality standards are based - may not be appropriate for arid and semi-arid ecosystems.
  • Impaired Waters and Total Maximum Daily Loads: A clickable map linked to state-specific TMDL information. Information on specific rivers and streams with enviro-mapper capabilities.
     
  • National Water Quality Assessment Data Warehouse: The U.S. Geological Survey (USGS) began its NAWQA (National Water Quality Assessment) program in 1991, systematically collecting chemical, biological, and physical water quality data from study units (basins) across the nation.

Watershed and Riparian Basics Resources

  • ARS Watershed Research USDA Agriculture Research Service (ARS) scientists maintain a national network of 14 research watersheds across the United States to address critical issues relating to water quantity and quality on our nations agricultural and rangelands.
     
  • California Watershed Information Technical System The goal of the Watershed Information Technical System (WITS) is to provide the information and tools to support local watershed planning, restoration, monitoring, and education via the CERES Web. CERES and its project WITS are programs of the California Resources Agency.
     
  • Managing Arid and Semi-arid Watersheds A cooperative project between the USFS Rocky Mountain Research Station and the University of Arizona: the basics of watershed management, information about riparian ecosystems of the Southwest, a searchable bibliography of resources.
  • Southwest Watershed Research Center Basic and applied research in global change, hydrology and water resources, erosion and sedimentation, water quality, and development of improved decision support systems.
     
  • Surf your watershed This EPA site allows the user to locate local watersheds and drinking water sources and provides access to watershed information of all kinds from per capita use to real-time stream flow data, indicators of watershed health, toxic releases, hazardous wastes and local citizen-based work on behalf of the watershed.
  • Watersheds Defines a watershed as "the area of land that catches rain and snow and drains or seeps into a marsh, stream, river, lake or groundwater." This site provides information and services for protecting and restoring water resources.
  • Irrigation and Water Use: Economic Research Service Briefing Room publication which investigates water allocation, water conservation, and water management issues facing irrigated agriculture.
Sheila Merrigan

Riparian Areas

Riparian Areas

Much of the West's water supply originates as rainfall or snowmelt on rangeland watersheds. In addition, the riparian areas along Western rangeland streams and rivers provide vital habitat for wildlife, fish, and plants. The running water and lush vegetation of these areas often serve as focal points for livestock and for recreation. Concurrently, sparsely vegetated rangelands may be susceptible to erosion. Upland activities that significantly diminish vegetative cover can lead to increased runoff and sedimentation. Heavy use of riparian areas can destroy aquatic habitat and undermine the ability of these systems to filter pollutants.

As a result of rising concern over non-point source pollution, the Environmental Protection Agency through the Clean Water Act has begun monitoring Western rangeland waterways and looking for ways to improve water quality. Encouragingly, many local communities have proactively come together to address watershed problems. Here we provide information about riparian areas and links that introduce the terminology and basic principles involved in watershed and riparian management, discuss the major issues related to grazing in riparian areas, describe how the Clean Water Act is being applied, and cover the issues involved in riparian area monitoring.

Mitch McClaran

Additional Resources

Additional Resources

Additional References

Related Links

Mark Thorne

How to Control Invasive Plants

How to Control Invasive Plants

You can help control invasive plants in several ways. First, learn how to identify the invasive plants in your area and report occurrences to private and public land managers or owners. In Arizona, for example, keeping weeds from becoming established should continue to be a very high priority. The proverbial axioms, “an ounce of prevention is worth a pound of cure” and “the easiest weed to control is the one you don’t have yet” certainly hold true here. It is critical to detect and, if possible, eradicate incipient infestations before they have a chance to spread onto un-infested land. Once a plant sets seed, takes root, and becomes well established, the amount of effort to manage the plant greatly increases.

Second, you can control problem weeds on your own property so that your weeds do not become your neighbor’s problem. There is no “cookbook” or “silver bullet” approach to controlling invasive weed infestations. Management options will vary with each weed species, the scale of the problem, and the ecological conditions unique to the area (soil type, depth of water table, timing and amount of precipitation, topography, etc.). Annual and biennial weeds can sometimes be effectively managed during the early stages of infestation with pulling or cultivation, whereas well-established perennial weeds may require timely application of herbicides that are registered for the targeted weed. When weed infestations become well entrenched, integrated management will be necessary to combine the appropriate set of tools for the targeted plant and ecological site. Possible tools for weed management include mechanical (e.g., hand pulling, grubbing), chemical (e.g., herbicides), and biological (e.g., insects, targeted grazing) methods. Keep in mind that many invasive plants have spines and/or toxic or irritating substances. When controlling weeds manually by hand-pulling, or by applying herbicides, be sure to take safety precautions by wearing the appropriate protective clothing (gloves, boots, safety glasses, etc.). Before using herbicides, always read the label and follow instructions.

Lastly, you can volunteer to help with inventories, mapping, and eradication of invasive plant species in your area. Contact your local county extension office for more information on how to control specific invasive weeds or to get more involved in weed management efforts. Go to the Invasive Species 101 webpage to learn more about what you can do to control invasive plants.

Heidi Diedrich

Non-natives, weeds, & noxious weeds

Non-natives, weeds, & noxious weeds

Learn about non-natives vs. weeds vs. noxious weeds:

Not all Non-native Plants are Harmful

It is very important to be concerned about the damage that non-native, invasive plants can cause.  However, it is also important to recognize that while most invasive plants are not native to the United States, not all non-native plants are invasive or harmful. Of the thousands of plants that have been purposely introduced into North America, less than 10% have become problematic invaders. Although there are plenty of “horror stories” involving introduced plants, many non-native, domesticated plants have proven to be beneficial to society as crops (e.g., corn and wheat), for landscaping, and for revegetation efforts on degraded or weed-infested lands.  On the other hand, some native plants and animals can become invasive in certain settings (feral animals, mesquite, and juniper for example). 

The term ‘naturalized’ is conventionally used to describe non-native plants that are capable of surviving and reproducing without human intervention for an indefinite period of time.  Naturalized plants may or may not become invasive.  Such plants that spread into new areas, survive, and that have a harmful impact to human health, economics, or ecosystem services are often referred to as invasive plants.

Weeds vs. Noxious Weeds

What is a weed and how does it differ from a noxious weed?  Consider these 2 plants:

invasive weed
The plant on the left is one that most of you are probably familiar with -- common dandelion (Taraxacum officinale).  On the right, is a noxious, invasive weed -- yellow starthistle (Centaurea solstitialis).  While dandelions have certainly been problematic for anyone who has tried to maintain a ‘weed-free’ lawn, they have not impacted millions of acres as yellow starthistle has done in California.  The point is, a weed to one person may be a desirable plant to another person – how a weed is defined really requires a value judgment.  In order for a weed to be classified as “noxious” it must be regulated by law. This video Plants Out of Place provides a better understanding of weeds, noxious weeds, invasive plants and their impacts.

Important historical pieces of legislation concerning noxious and invasive plants in the U.S. are the Noxious Weed Act of 1974 (as amended by the 1990 Farm Bill), the 1999 Executive Order on Invasive Species, and the 2000 Plant Protection Act.  Go here for a list of weeds that are designated as noxious in Arizona, for an example.  For additional reading on definitions, check out a ‘white paper’ located here (click on the first link under ‘Invasive Species Information’).

Kim McReynolds

Basics of Invasive Species

Basics of Invasive Species

Learn about the basics of invasive species:

Origins of Introduced Invasive Plants

Some of the most problematic invasive plants (weeds) in the United States were introduced from Europe or Asia (Eurasia), Africa, and the Mediterranean region either purposely or by accident.  Some invasive plants were introduced as ornamentals or with the intention of solving an environmental problem such as excessive soil erosion during the 1930’s, while others likely inadvertently hitched rides in ship ballasts, hay bales, or in agricultural seed.  For more information on the origins and impacts of invasive plants watch the video Dangerous Travelers.

Common Characteristics of Invasive Plants

The reasons why some plants become invasive while others do not are extremely complex and depend on characteristics of the plant as well as the unique abiotic and biotic idiosyncrasies of the ecosystem where the plant grows.  However, invasive plants often share one or more of the following characteristics:

  1. fast growth
  2. rapid reproduction
  3. high seed production and dispersal ability
  4. tolerance of a wide range of environmental conditions
  5. aggressive and prolific vegetative reproduction (massive root systems)
  6. association with humans or human activities (land management practices). 

Also, non-native invasive plants may not have the natural predators in their new environment which helps them to proliferate unchecked.

Invasive Plants act as Environmental Pollutants

Nearly 20 years ago, Dr. Steven Dewey, a weed scientist (now retired) from Utah State University, suggested that invasive plants act as environmental pollutants, to wit:

  • The pollutant weakens and kills native vegetation with endangered species being especially vulnerable.
  • The pollutant spreads naturally in water, wind, and/or soil, but is also spread by wildlife, livestock, and recreationists.
  • Affected lands cannot “heal” themselves over time - once polluted, always polluted.
  • The effects of the pollutant are not usually apparent until the spread is already out of control.

Some common environmental and economic impacts of invasive plants include:

Environmental

  • Degraded watersheds.
  • Decreased biodiversity.
  • Decreased forage and habitat for livestock and wildlife.
  • Decreased soil moisture.

Economic

  • Decreased land values.
  • Poisonous plant problems for livestock.
  • Increased erosion.
  • Control costs.

The video Hunters and Anglers Against Invasive Species provides more detailed information on the many negative economic and ecologic impacts that invasive plants can have on the environment.

Exponential Growth Associated with Invasive Plants

howery graph image

Infestations that were initially just a few plants can increase rapidly to become several thousand acres.  Invasive plants can sometimes lie “dormant” for decades, and then explode exponentially. One striking example of this phenomenon is yellow starthistle in California.  This Eurasian plant is believed to have been inadvertently introduced into California in the mid-1800’s.  By 1958, yellow starthistle had expanded its range to 1 million acres.  It had expanded its range by another 7 million acres by 1985, and over the next 20 years it more than doubled its acreage to >15 million acres.

Exponential growth is just one of the many insidious characteristics of invasive plants.  The cost of controlling invasive plants increases and the probability of successful control decreases as you move from left to right on the x-axis of the above figure.  Unfortunately, humans tend not to get too excited about invasive plants until it is too late to effectively manage them ecologically or economically.  Like so many things in life, the longer we wait to do something about it, the more damage it causes and the more expensive it becomes!

Invasive plant species have numerous effects on the ecosystem goods and services provided by rangelands. Those goods and services have value to society. In general, the invasive species will affect the quantity or quality of those goods and services.

On rangelands, most of the concern related to invasive species focuses on plants. Invasive plant species are discussed elsewhere on the website. This section will look at some of the economic considerations related to these plants.

Different authors have shown how invasive plants may affect native plant production, water quality, erosion rates, and recreation values and reduce livestock and wildlife forage and habitat, among other such impacts. In many cases, these effects have not been quantified, especially for different amounts of the invasive plant. For example, we would ideally want to know how wildlife habitat quality changes as a particular plant species increases.

From an economic standpoint, there are two types of economic effects. First are the change in values from each of the impacts. For example, if domestic forage is reduced, the animal numbers will either need to be reduced or alternative feed sources found. Either of those will likely reduce the net income to the rancher. Second are the costs associated with managing the invasive species. These costs include detection, control, and monitoring of the population.

Economic aspects have been measured in two different ways. The first is a cost-benefit type of analysis where the costs of controlling the species is compared to the change in value of the ecosystem goods and services being affected. The second, but related, way to look at economics is to evaluate how society spends money on control and the related impacts and then calculating how those values affect the regional economy.

In both methods, the cost of control is fairly straightforward. If chemical, mechanical, prescribed burning, or hand pulling is used, there will be a definite cost to the landowner. In a cost-benefit analysis, that cost is simply compared to the change in benefits. In the economic impact, the cost is calculated as money spent in different sectors — for example, chemicals purchased from a chemical company. In this case, the money spent circulates through the economy.

Benefits should include both market and nonmarket goods and services. Market goods and services include those things that are traded and have a cash value. An example of a market good is domestic livestock forage. Nonmarket goods and services are generally not traded and don't have a readily available monetary value associated with them. While a cost-benefit analysis should include both kinds, generally only market-valued benefits are included. For the economic impact analysis, only market-based values are considered.

The U.S. Department of Agriculture Natural Resources Conservation Service publishes average treatment costs for most states in their electronic Field Office Technical Guides (eFOTG) available from their website.

Examples -- Invasive Grasses

The objective of this section is to discuss key characteristics of the following invasive grasses that occur in the western United States: Buffelgrass, Fountain Grass, Cheatgrass, and Red Brome (scientific names appear below).  Each of these grasses have the potential to become ‘ecosystem transformers’ due to their unique invasive properties.  The following information will be discussed for each invasive grass species: 1) Impacts, 2) Key Characteristics for Site-Identification, and 3) Management Considerations.

Buffelgrass

Impacts

Buffelgrass - Key Characteristics for Site-Identification

  • Common Names: buffelgrass, African foxtail grass, pasto buffel, zacate buffel
  • Scientific Name:  Pennisetum ciliare (L.)
  • Family: Poaceae (Grass)
  • Origin:  Africa, Asia, the Middle East
    buffelgrass

Description:  Buffelgrass is a perennial warm-season (C4) bunch grass that can reproduce by seed, rhizomes, and stolons.  It was introduced into the southwestern U.S. from South Africa in the 1930s as a forage for cattle and to control erosion.   It is a very robust grass that may grow over 3-feet tall and wide.  Bristly flower heads range from 1.5 to 5 inches long and can be purple, gray, or yellowish, turning a distinctive golden-brown color when dry.  Spikes are dense with bristly fruit which are actually burs without hardened spines.  Although buffelgrass is a perennial it is an extremely prolific seed producer.  Inflorescences may emerge whenever soil moisture is available.  New plants produce seed in as little as six weeks.  Older plants branch profusely and densely at nodes giving mature plants a “messy” appearance.

Buffelgrass - Management Considerations: Buffelgrass is extremely drought tolerant and reestablishes and expands its range quickly after fire.  The Southern Arizona Buffelgrass Coordination Center (SABCC) has suggestions on the pros and cons for controlling buffelgrass using biological, chemical, cultural, prescribed fire, and mechanical control methods (click on the Control tab at the SABCC website).  There are also interesting news releases concerning the use of aerial spraying to control buffelgrass that can be found by clicking on the In The News tab at the SABCC website.  The Sonoran Desert Weed Wackers have been working hard to physically remove buffelgrass and other invasive grasses in and around Tucson for over a decade.  

Fountain Grass

Impacts

Fountain Grass - Key Characteristics for Site-Identification

  • Common Name: fountain grass, crimson fountain grass
  • Scientific Name: Pennisetum setaceum (Forsk. Chiov)
  • Family: Poaceae (Grass)
  • Origin: Africa, southwest Asia, the Middle East.

fountain grass image

Description:  Fountain grass is a coarse, perennial, warm-season (C4) bunchgrass that grows 2 to 3.5 feet tall.  Tufted culms grow in dense, usually large, clumps.  Red, rosy to purple, bristly, spike inflorescences are 2 to 4-inches long, and 0.75-1-inch wide.  The 0.25-inch long spikelets are solitary or in clusters of 3 on white-hairy branches attached below the bristles.  Flower heads are prominent, nodding, feathery, and attractive.  Seeds can remain viable for up to 6 years and plants can live for up to 20 years.  The cultivar 'Cupreum' is reported to be sterile (does not set seeds.)

Fountain Grass - Management Considerations: Fountain grass is found along roadways in southern Arizona, for example, and is expanding into rangelands as well as riparian areas.  Palatability to wild and domestic herbivores is low which facilitates its competition with native plants.  Like buffelgrass, it rapidly reestablishes after fire, is very difficult to control once established, but is manageable in areas where just a few spot infestations occur.  The key is to rapidly control new infestations while they are still small.  Click here to learn how land managers in California are dealing with this invasive grass (scroll down to ‘How Can I Get Rid Of It’).  

Cheatgrass and Red Brome

Impacts

Overview:  These two cool season (C3) annual grasses are discussed together because they are very similar in biology, ecology, and history and are separated mostly by prevailing temperature and elevation (although they do overlap in some areas).  Both species respond favorably to cool season precipitation and tend to be more prevalent in disturbed areas.  However, they are also found in areas with minimal disturbance across the western U.S.  When cool season precipitation is favorable, massive amounts of cheatgrass and red brome biomass can accumulate in the natural open spaces between native plants and increase fine fuel loads in both cold deserts (cheatgrass) and warm deserts (red brome).  Wet-dry cycles can dramatically increase the probability of unwanted wildfires after these species dry out and perpetuate the ‘annual grass-fire cycle’.  These non-native annual grasses are adapted to respond quickly to the release of competition for space and nutrients following a burn.  Also, hot fires can severely damage some native plant species that are not adapted to fire.  Plant communities infested with these species burn much more often and hotter than before they were infested (e.g., every 5-10 years instead of every 100 years).  Plant communities that are repeatedly burned become much more homogeneous (i.e., lower biodiversity), more susceptible to reinvasion, and provide fewer habitat values and ecosystem services.

Cheatgrass - Key Characteristics for Site-Identification

  • Common Names: cheatgrass, downy brome, June grass, bronco grass, downy chess
  • Scientific Name: Bromus tectorum (L.)
  • Family: Poaceae (Grass)
  • Origin: Eurasia, Mediterranean region.

cheatgrass image
Description:  Cheatgrass can grow between 2 inches to 2 feet tall (depending on site conditions and the timing and amount of cool season precipitation).  Like most annual plants, it is a prolific seed producer.  It germinates during cooler temperatures and rapidly grows and sets seed before most other species.  Seedlings are bright green with conspicuously hairy (downy) leaves, sheaths, glumes and lemmas.  Seed heads are open, drooping, multiple-branched panicles with moderately awned spikelets.  Auricles are absent.  At maturity the foliage and seed heads often turn purplish before drying and then turn a brown or tan color after drying. 

Red Brome - Key Characteristics for Site-Identification

  • Common Names: red brome, foxtail chess
  • Scientific Name: Bromus rubens (L.)
  • Family: Poaceae (Grass)
  • Origin: Eurasia, Mediterranean region.
    redbrome image

Description:  Red brome grows 8 to 20 inches tall (depending on site conditions and the timing and amount of cool season precipitation) with several to numerous stems from an erect to spreading base.  Seed heads are reddish-purple as they ripen and form a dense, compact panicle (similar to a spike) that is 2-3 inches long.  As seed heads dry they turn a tawny to brown color.  Leaf blades are short, narrow, flat and hairy, with prominent veins.  Leaf sheaths are papery.  Red brome occurs on disturbed and undisturbed sites in various soil types but is typically found in warmer climates and lower elevations than is cheatgrass, a close relative. 

 

Kim McReynolds

Invasive Plants

Invasive Plants

Humans have both intentionally and accidentally introduced many non-native plants and animals to Western rangelands. Some of them have produced benefits for humans while remaining under management control. Others have escaped and “gone wild” with unintended negative consequences. While we can debate the degree to which any particular exotic plant or organism has a right to exist on Western rangelands, one thing is for certain. Some of these plants and animals are spreading like wildfires and have become serious threats to the environment, human health, and economic well being.

Invasive species are plants, animals, or insects that have evolved elsewhere and have been purposely or accidentally moved to a new location. Some have invaded habitats by themselves. However, human exploration, colonization, and commercial trade have dramatically increased the diversity, scale, and impact of the invasions. Introduced species often find no natural enemies in their new habitat and therefore spread quickly and easily.

Invasive species are damaging to both the environment and the economy. The economic costs of non-native species invasions in the United States reaches billions of dollars each year. They disrupt the areas they invade by: replacing native species, reducing biological diversity, changing vegetation or animal productivity, placing other species at increased risk of extinction, altering wildfire intensity and frequency, and closing foreign markets to U.S. products from infested areas.

Users of natural resources — including hunters, ranchers, managers, hikers, campers, and any other outdoor enthusiasts — should do all they can to prevent the introduction and/or spread of invasive species. Information about invasive species in your area can be obtained from local Cooperative Extension offices or from the field offices of various federal and state land management agencies.

Although invasive species can come from both the plant and animal kingdoms, this module focuses on non-native, invasive plants. 

Kim McReynolds
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