Why are riparian forests disappearing

Rivers act as highways through the forest, carrying species, nutrients and organic matter across the landscape. Trees play an important role in regulating those roadways, both drawing up water and nutrients and depositing organic matter in the form of leaves, seeds, and fruit.

Clear the forest, and the traffic patterns for those nutrients will change. KathiJo Jankowski, a research ecologist at the United States Geological Survey, conducted research with Woodwell on the question of whether maintaining riparian buffers successfully mitigated that change.

Are they processing carbon differently? And are they processing nutrients differently? Jankowski asks. She waded through the streams at Tanguro Ranch, collecting data—dissolved oxygen levels, leaf litter, temperature measurements—to answer these questions. When she compared data from agricultural streams with riparian buffers to intact forests, she found only subtle shifts in basic ecosystem functions.

As long as those buffer forests remained, the streams mostly continued to flow as they always had. Jankowski said. One difference Dr. Jankowski did observe, however, was in the amount of leaf litter present in the streams.

Less overall vegetation on the landscape led to less organic matter in agricultural streams, a small change that can impact the wider food web. Nubia Marques was conducting complementary research around the same time as Dr. Jankowski, but her research focused on the animals that rely upon the ecosystem functions Dr. Jump to Navigation Skip to main content. Plants and trees along the water margins and banks are called riparian vegetation.

Potential impacts of reducing or removing riparian vegetation on water quality and mahinga kai Increased bank erosion - the loss of roots decreases the stability of the bank, increasing its vulnerability at times of flooding.

Increased water temperature - loss of shading from trees or overhanging streamside vegetation means waterways become more exposed and are more liable to fluctuate in temperature. Decreased dissolved oxygen through increased aquatic plant growth - plants and weeds growing within the waterway are more likely to thrive in unshaded waterways, potentially clogging and stemming flow, which can decrease oxygen levels.

FIGURE Differences in water movement in a non-tiled annual row-crop field and a perennial riparian forested buffer. More overland flow and less total evapotranspiration result in larger storm flow in the row-crop field while in the perennial riparian plant community, higher rates of infiltration and annual evapotranspiration reduce storm flow and increase baseflow.

Stream channels respond to these increased runoff frequency, volumes, and peak flow rates by increasing their cross-sectional area to accommodate the higher flows—either through widening of the stream channel, downcutting of the streambed, or both—similar to what is observed during channelization see Figure The altered hydrology characteristic of row-crop agriculture and some erosion control structures tends to concentrate overland flow within fields and transport it downslope in grass waterways or other ephemeral drainageways Schultz et al.

Although grass waterways are very effective in reducing gully erosion, transformation processes that could improve water quality are limited because the upland runoff enters the riparian area as concentrated flow.

Also, the increased overland flow over agricultural land promotes relatively high erosion. Over time, the upslope portion of the riparian area evolves into a terrace or berm that, if not managed via tillage, can hinder further inflow. When this occurs, runoff flows parallel to the riparian area until a low point or drainageway is reached. The diverted overland flow enters the riparian area as concentrated flow, which again reduces its effectiveness for water-quality protection.

Agricultural chemicals both pesticides and fertilizers in overland flow can also negatively impact fauna and flora located in riparian areas and downstream receiving waters. Edge-of-field pesticide losses are common, with 1—10 percent of the amount of pesticide applied being entrained in overland flow Wauchop, ; Baker, Similarly, fertilization can cause nutrient losses from the land to nearby streams to increase by an order of magnitude or more.

Healthy riparian areas often provide significant benefits to traditional agricultural activities. Riparian areas protect the quality of water resources used for agricultural and domestic purposes by trapping sediment, nutrients, and other pollutants. They stabilize stream channels and they promote the infiltration of overland flow. They increase groundwater resources by enhancing groundwater recharge in losing streams.

They can reduce wind erosion; trap snow, thus reducing drifting; protect livestock, wildlife, and buildings from excessive wind; and reduce noise and odors associated with some agricultural activities. Riparian areas can also be a potential source of income through their use for hunting and fishing and for timber and biomass production.

Unfortunately, these benefits have historically not played a role in agricultural management of riparian lands. The draining of water from urban and suburban lands for the purposes of improved crop production has been practiced since the s, spurred by the and Swamp Act and the subsequent organization of local drainage districts.

Farmers have relied on drainage to improve soil aeration, alter soil moisture conditions to allow earlier planting and easier fall tillage, and combat disease organisms that thrive in high-moisture conditions. Without drainage, many Midwest farmlands would be significantly reduced in productivity or simply unfarmable Fausey et al. Drainage occurs through subsurface tiles e. In practice, surface and subsurface systems often are used together.

For example, drainage tiles often intercept channelized streams or ditches created for the purpose of collecting tile outflow. Table shows the acreage of drained land in the most heavily affected regions of the United States.

Drainage impacts approximately In Illinois, the. Harvested Cropland 1, ha a. Drained Cropland 1, ha b. State Total Area 1, ha c. NAS also reports total cropland, which includes cropland used for pasture or grazing, land in cover crops, legumes, and soil-improvement grasses, land on which all crops failed, land in cultivated summer fallow, and idle cropland. In some highly drained areas, such as the Embarras River watershed of east central Illinois, tiles drain 70 percent to 85 percent of the cropland David et al.

Other areas such as the Southeast 6 million hectares and the Mississippi Delta 5 million hectares also have significant areas of drained cropland. Because drainage was traditionally a tool for managing soil moisture, the resulting water quality of receiving streams and other ecological factors were.

It is now known that drainage has had a dramatic impact on stream hydrology and water quality and on the functioning of riparian areas Evans et al. By concentrating flows and circumventing the biological processes that typically occur in riparian areas, drainage tile effluent can have greater peak flows, increased concentrations of nutrients, and either increased surface drainage or decreased some types of subsurface drainage sediment load.

Many of the effects of surface drainage are similar to those discussed above for channelization and traditional agriculture. The hydrologic differences among drained cropland, non-drained cropland, and undisturbed land have been investigated by Zucker and Brown Compared to non-drained cropland, tile-drained cropland has less erosion and phosphorus runoff because of limited overland flow.

However, in relation to non-cropped areas or cropped areas with various conservation practices, the environmental advantages of tile drainage are less clear or nonexistent. For example, studies in North Carolina have shown that compared to undisturbed sites, total outflow is increased by 5 percent with surface drainage and 20 percent for subsurface drainage Evans et al.

Evans et al. Depending upon conditions—such as antecedent soil moisture and storm intensity—surface and subsurface drainage were found to increase peak outflow rates by four and two times, respectively Figure This increased outflow often results in streambank erosion, channel incision, flooding, or other impacts.

Site is a natural, undrained site and Site is a surface drained and developed pocosin converted to agricultural use. Indeed, the changes in hydrology characteristic of extensively tiled areas can be so extreme that in many first- to third-order streams, flow from drainage tiles may constitute 90 percent of the baseflow during summer months Schultz et al.

Drainage also affects the transport of particles and chemical pollutants through riparian areas. As shown schematically in Figure , subsurface drainage can expedite direct transport of chemicals such as NO 3 -N from the soil zone to surface waters—often completely circumventing riparian areas.

Thus, approximately 37 percent of the cropped land in the Midwest is not afforded the beneficial nutrient absorbing and transforming processes of riparian areas. As a result, where nutrients are added to cropland, they often are delivered to the stream systems at highly elevated levels David et al. Surface drainage systems typically produce higher concentrations of phosphorus and sedi-. Drainage tiles typically bypass the functioning of riparian areas by conveying water directly from upland areas to the stream systems.

Tiles prevent riparian-related activities such as denitrification, and they enhance water conveyance, resulting in higher peak flows and greater total runoff. The short-circuiting of riparian areas via drainage is especially troubling in areas like the Midwest where soils are underlain by an impermeable aquiclude Schultz et al. In such places, the riparian area may constitute the only biologically active zone through which pollutants from cropland could be transformed.

The high nutrient loadings resulting from drainage networks have been implicated in the hypoxia in the Gulf of Mexico Turner and Rabalais, as described in Box The history of grazing by domestic livestock in much of the world has been one of large-scale degradation of native plant communities Chaney et al. Although domesticated livestock have played a.

The hypoxic zone in the Gulf of Mexico has increased in size since the s, nearly doubling in average size from — to — These and other waters in the northern Gulf of Mexico constitute approximately 40 percent of U.

The hypoxic zone has been caused by a complex mix of increased nutrient loads transported by the rivers and physical changes to the basins through activities such as channelization and loss of wetlands and riparian vegetation.

These factors produce a higher oxygen demand that, when coupled with water column stratification in the Gulf resulting from the freshwater—saltwater interface, can lead to hypoxic lower layers of water. It has been estimated that 90 percent of the nitrates entering the Gulf come from urban and agriculture runoff 56 percent from the Mississippi River Basin and 34 percent from the Ohio River Basin.

The first approach involves efforts to reduce nitrogen loads in streams and rivers in the basin through activities such as reducing fertilizer applications to recommended rates, increased use of conservation tillage systems, and improved sewage treatment.

The second involves enhancing denitrification and nitrogen retention within the Mississippi—Atchafalaya River Basins through restoration of ecological systems such as riparian areas and wetlands. One of the many programmatic indicators 22 were defined that will be used to track progress is the establishment of vegetative and forested buffers along rivers and streams in watersheds known to contribute significant quantities of nitrogen. Other estimates were also developed for wetlands acreage needed, fertilizer application options, tillage, and other possible remedies.

In the final assessment, however, it was recognized that no single approach would be completely successful and that a wide variety of approaches relying upon the many existing federal, state, local, and private programs will be needed to accomplish the changes necessary to solve the Gulf hypoxia problem EPA, As shown in Figure , primary grazing effects include the removal of vegetation, trampling of vegetation, destruction of biological soil crusts, compaction of underlying soils, redistribution of nutrients, and dispersal of exotic plant species and pathogens.

Secondary effects include. Long-term cumulative effects of domestic livestock grazing involve changes in the structure, composition, and productivity of plant and animal communities at community, ecosystem, and landscape scales. These tertiary effects often include overall declines in biotic richness or diversity of affected aquatic, riparian, and terrestrial areas.

In , the U. Department of Agriculture estimated that vegetation on more than half of all western rangelands had deteriorated to less than 40 percent of productive potential. Although this reflects changes principally in upland conditions, there is no doubt that the impacts to western riparian areas are likely to have been much more severe, for reasons described below.

Although upland range conditions reportedly have improved in many areas since , extensive field observations in the late s suggest that riparian areas remain in degraded condition Chaney et al.

The disproportionate impact of livestock on riparian areas is a product of both management and animal behavior. Although riparian areas comprise 1 percent or less of the arid land area of the 11 western states Belsky et al. Second, cattle in particular congregate in riparian areas and other wet areas because of the availability of water, shade, and more succulent forage—spending from 5 to 30 times more time in these cool, productive zones than would be predicted from surface area alone Belsky et al.

The grazing of riparian areas by domestic livestock involves the periodic removal of native streamside vegetation—particularly herbaceous plants, shrubs, or young trees. Along many streams and rivers, it has been a common practice to remove certain plants over time to create livestock pastures or hay fields or to convert the land to crop production. Grazing itself occurs over varying time periods e.

Characteristics of the riparian plant communities, such as composition, cover, density, or other measures of plant communities, are likely to show significant changes relative to ungrazed areas Kauffman and Pyke, In addition, a variety of effects on soils e.

Where riparian vegetation has been suppressed or removed via grazing over long periods of time, the root biomass along channel banks and the resistance to overbank flow may become sufficiently reduced such that channels become unstable. Channel widening and gullying as shown in Figure for channelization are common features of areas that have experienced the effects of season- or year-long grazing or other intensive grazing practices.

Intensive grazing of the arid southwest in the late nineteenth century is thought to have played a role in the extensive arroyo cutting observed in this area, although cycles of arroyo cutting and filling prior to the introduction of domestic livestock have also been documented Bull, ; McFadden and McAuliffe, ; Gonzalez, Season-long grazing commonly used throughout the West results in major impacts to riparian areas because a large proportion of plant biomass is removed, the remaining vegetation has little opportunity to recover, and the grazing is generally repeated year after year.

Grazing systems that employ rest-rotations or that result in less intensive utilization of riparian forage can potentially reduce these impacts, but these approaches have not been widely used and their potential ecological effects have received little study Elmore and Kauffman, Given the many impacts of grazing described above, it is no surprise that aquatic organisms and riparian wildlife have been profoundly impacted by historical grazing practices.

Two reviews have illustrated the adverse effect grazing has had on fisheries and wildlife. Federal land management agencies have often concurred with these assessments.

In , BLM and the U. The USFS concluded that livestock grazing is the fourth major cause of species endangerment nationwide, the second major cause of plant endangerment, and the number one cause of species endangerment in certain arid regions of the West, such as the Colorado Plateau and Arizona Basin Flather et al. Although there is limited evidence from more humid regions, Belsky et al.

Like livestock, native ungulates can modify riparian areas by eating plants, dispersing seeds, disturbing soil, and modifying channel morphology. Impacts on plants can include suppressed vigor, reduced reproductive output and regeneration, and increased mortality Opperman and Merenlender, For example, successful regeneration of white cedar in winter deeryards can be virtually nonexistent because of concentrated seasonal browsing Verme and Johnston, The effects of native ungulates depend on their populations, which fluctuate in response to predation, competition, weather, disease, and other influences Naiman and Rogers, White-tailed, mule, and black-tailed deer, elk, and moose have drawn attention when their numbers are particularly high or when their presence is concentrated temporally.

Such situations are most likely to occur as a result of human-induced changes in the landscape, or a change in predator—. Elk and moose browsing have caused damage e. Moose browsing on riparian willow thickets is believed to suppress both density and diversity of migrant breeding birds dependent on riparian vegetation Berger et al.

The extent and causes of this damage are controversial, though a lack of ungulate population regulation by either hunting or predation is considered at least partially to blame. In the Greater Yellowstone area, the extinction of grizzly bear and wolf populations has been linked to increases in moose density Berger et al.

In areas supporting both livestock and wild ungulates, livestock have been observed to do greater damage to forage resources. For example, native ungulates are scattered over their summer range, making their impact on forage resources minimal to moderate, while many domestic livestock graze on aspen-covered ranges in the West during the peak of the growing season and commonly use at least 50 percent of the annual production of palatable forage DeByle, Long-term studies in Utah and Nevada showed that aspen fails to regenerate or regenerates only at low stem densities when it is grazed by both livestock and native ungulates Kay and Bartos, ; Kay, In the absence of livestock, however, aspen regenerated successfully, provided that deer numbers were low.

In many human-modified landscapes, losses in the amount of available native habitat have concentrated herbivore pressure in an area that is already under stress. Hobbs and Norton used exclusionary fencing to show that deer were a limiting factor to the restoration of a riparian area that had been previously degraded by domestic livestock.

It was suggested that the site had reached a threshold of degradation beyond which recovery was not possible without exclusionary fencing to reduce ungulate browsing. Given the high populations of deer in many areas, particularly urbanized landscapes, exclusionary fencing or targeted population control may be needed to reduce herbivore pressure and assist in riparian area recovery. The removal of trees by forestry operations has the potential to alter longterm composition and character of riparian forests, and thus the structure and function of these systems Ralph et al.

If selection harvest methods are. However, where large portions of the standing timber are harvested or where the period between harvest operations is short, substantial changes to the composition, structure, and function of riparian forests almost certainly will result.

Figure shows the decline in virgin forest in the United States from to The location and construction of logging roads e. This figure shows an estimate of forests have never been cut. It does not show the current total area of forest. Upslope roads can increase hillslope erosion rates either surface erosion or landslides or materially alter flow pathways, for example via the interception of shallow subsurface flow into ditches and its rerouting to locations of instability Furniss et al.

Forest harvesting can occur in a variety of ways depending upon forest type, age, and density and upon topography, climate, and utilization standards. The impacts of forest harvest systems on riparian structure and function are much greater when forests are clearcut or harvested right up to streambanks and lake shorelines.

The total harvest of riparian vegetation and adjacent terrestrial forests can increase the amount of solar radiation reaching the water surface, which can increase water temperatures and affect aquatic primary production.

Temperature increases are of particular concern during summer when streams and rivers are naturally warmer. In addition, removal or alteration of the riparian vegetation changes the quantity and quality of terrestrial food resources for a stream, such as leaves, needles, and other forms of organic matter.

Removal of riparian forests and repeated harvest over short rotations e. Harvest of streamside forests also removes the vegetative cover that can slow the delivery of sediment into streams and retain nutrients, such as nitrogen and phosphorus. As discussed in Chapter 2 , riparian forests collectively provide for an array of sustainable processes and functions that make them exceptionally important for maintaining productive aquatic and terrestrial ecosystems Johnson et al.

Those functions, as measured by species richness and diversity, can be impaired by forestry operations. Studies have demonstrated the habitat value of uncut riparian areas for wood-peckers Conner et al. The red-shouldered hawk is associated with wooded bottomlands of major rivers Brewer et al. The hydrologic effects of timber harvesting, such as increased annual water yields, increased sediment production, and altered stream chemistry, have been documented from a large number of watershed studies in forested areas Ponce, ; Binkley and Brown, ; Adams and Ringer, ; Murphy, Such responses have not occurred universally and are typically dependent upon terrain conditions, the amount of timber removed, the type of logging system, post-harvest rainfall patterns, soil type, and other factors.

Although increased water yields are most common when large proportions of the forest are harvested, increases in peak flows have not occurred consistently Reiter and Beschta, ; Beschta et al. Increased sediment production is most likely in steep terrain where ground-based logging systems are employed or where soils are disturbed. Chapter 5 discusses how to diminish the potentially adverse effects of timber harvest upon aquatic and riparian resources by the use of various types of buffers or riparian reserves.

Even in cases where forestry has been moderated for restoration purposes e. Partial harvest often allows selective removal of larger or older trees, reducing ecological function more than width and targeted stem densities might reflect.

Streamside buffers are generally not designed to mirror the stand composition and dynamics of desired healthy riparian forests for a given age class, especially when harvest decisions are strongly governed by social concerns about economic impacts. Private holdings amount to million acres, of which 71 million are controlled by the forestry industry Coggins et al.

One of the major challenges in riparian management on public lands is the lack of a consistent scientific framework for determining widths of forested riparian areas that will sustain their desired structural and functional attributes. Differences in management between forest regions and individual national forests, between forests managed by the USFS and BLM, and among federal, state, and privately owned forests are more often based on policies, economic considerations, political pressure, and litigation than on differences in forest types, hydrologic regimes, climate, geology, physiographic provinces, or the ecological functions of riparian plant communities.

Significant protection and restoration of forested riparian areas across the United States are unlikely until a common framework is developed. Mining has historically been, and continues to be, an important land use in many portions of the United States, particularly on public lands. The General Mining Law of authorizes hardrock mineral extraction e. Approximately hectares million acres of public lands constituting 80 percent and 90 percent of all lands managed by the USFS and BLM, respectively are open to mining NRC, a.

Because only a small percentage of the U. However, local degradation can have major downstream effects, thus affecting aquatic and riparian resources. The mining of hillslopes and valley bottoms for minerals ranging from gold and silver to coal and gravel has involved a wide variety of approaches depending upon geology, topography, available technology, market value, and other factors. In hard-rock mining, the excavation of rock and soil to retrieve a mineral or ore of value to society often results in large amounts of waste rock or spoils.

The extent to which such materials influence riparian areas depends on the amount of spoils deposited along stream channels; in other situations the acidity of the spoils can be a major concern. Acid mine drainage is considered to be one of the major water pollution concerns associated with many mining operations Nelson et al. In addition, mining may introduce toxic metals such as arsenic, cadmium, chromium, copper, lead, mercury, and zinc, particularly when surface or groundwater is allowed to flow through waste piles.

Open-pit mining, where soils and rock overburden are excavated and embanked at a nearby location, is often employed when relatively low-grade ores or less valuable minerals are sought. The potential for riparian areas in or near these types of mining operations to be affected is often great. Depending upon the size and location of the mining operation, total hillsides can be excavated and their stream systems moved or buried.

This practice, which can bury and literally destroy streams, was ruled illegal in a federal district court decision. But since then, federal rule changes have been proposed that would again permit the practice under certain conditions. When a mining operation exposes large areas of bare ground, substantial increases in overland flow and sediment production can occur during rainfall periods.

Unless a well-designed and operated system of detention ponds is in place, such runoff may greatly increase sediment loading to nearby streams and rivers. Revegetation of embanked overburden and spoils is often a challenge for many open-pit mining operations. CAS Google Scholar. Weller SC: Structured interviewing and questionnaire construction.

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Marilda Mascarenhas provided us with logistical support. Fabricio Brito provided the map of the study area. Kate Proctor is acknowledged for commenting on the manuscript and James Welsh for the grammatical editing. You can also search for this author in PubMed Google Scholar. Correspondence to Guillaume Xavier Rousseau.

DC wrote the manuscript. All authors read and approved the final manuscript. Reprints and Permissions. Celentano, D. J Ethnobiology Ethnomedicine 10, 11 Download citation.

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Provided by the Springer Nature SharedIt content-sharing initiative. Skip to main content. Search all BMC articles Search. Download PDF. Abstract Background Riparian forests provide ecosystem services that are essential for human well-being. Methods This study takes place in a region presenting a complex history of human relocation and land tenure.

Results The local population depends primarily on slash-and-burn subsistence agriculture to meet their needs. Conclusions Slash-and-burn agriculture is the main source of livelihood but also the main driver of forest degradation.

Background In the tropics, riparian forests are essential for human well-being. Figure 1. Full size image. Results and discussion All informants belonged to the relocated community. Perception of well-being and livelihood in the agrovillages In their traditional lands, families used to live in adobe houses without electricity, water supply or a sewer system. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Conclusions In the present study an interdisciplinary research framework is proposed to design riparian forest restoration strategies based on ecological data, TEK and social needs.

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