Overstory #167 - Riparian buffer zone restoration for food security
Rivers, streams and creeks are attractive and valuable components of nature that provide beauty, enjoyment, recreation, inspiration and valuable resources for both urban and rural communities (Babb, 1996). From the beginning of human history riparian ecosystems have been one of the most intensively used ecosystems in the world. "Riparius" is a Latin word meaning "belonging to the bank of a river". It is the biotic community located at the bank of any kind of water body. All waterways have riparian zones whether they are tiny creeks or major rivers. This is the waterways buffer. It stretches along both sides of the waterway and is as wide as the area where annual or periodic flooding occurs.
Riparian areas were used primarily by early settlers for livestock grazing, fodder and firewood harvesting. Later intensive uses, including civil engineering works in the nineteenth century and hydroelectric developments in the twentieth century, have contributed to the decline of these valuable ecosystems. "Hydrologic modifications due to water diversions and dams; non-point source pollution and sediments from agricultural, forestry, and urban land practices; and vegetation removed by logging, cattle grazing all have damaged riparian ecosystems and have decreased their ability to support fisheries and wildlife, purify water, reduce flooding and perform other ecological functions" (Kentula, 1997).
This land/water boundary (ecotone) is greatly influenced by the vegetation, hydrology and geomorphology of a particular region. These factors also determine the structure, dynamics and economic importance of this zone. Although the ecological properties of riparian zones differ, they all share common characteristics that allow the application of certain restoration and rehabilitation principles to all riparian landscapes. The most important of these characteristics is extensive surface and subsurface connectivity of the ecotone with the adjacent upland and aquatic systems; diverse vegetation represented by a variety of age classes; and resilience in response to changes in the hydrologic and geomorphic characteristics of the boundary (Sedell et al., 1991).
Buffer zones for food security
A buffer zone can bring food security in many ways. The especially productive, protective, enriching and interactive nature of the riparian zone to adjacent habitats can be tapped for increased food production while still providing essential environmental services. As a transition area between land and water, buffer zones generally have an intermediate microclimate that allows for increased species richness. Designers can augment both the productive and protective roles of the buffer zone by incorporating habitat-modifying factors and specific components in stream bank stabilization bioengineering and by vegetating riparian buffer zone by multiple beneficial species. Vegetation in the riparian zone prevents the depletion of top fertile soil during water run off and thus enhances the fertility of adjacent farmlands. It also prevents the erosive action of floods if there is a tendency of flooding and thus protects the crops from floodwater velocity and erosive power, and blocks debris from entering the cropland.
Designing the buffer zone with multiple plant species can produce more microniches for animals to inhabit. The riparian habitat is a wildlife abode and a corridor in many cases, and thus attracts many animals and provides opportunities for hunting. Buffer zones can often be used by farmers for raising a few milk animals by controlled grazing.
Buffers may produce perennial crops such as hay, nuts, fruits and berries, lumber and veneer, and fiber (Dosskey et al., 2000). Fuelwood and mulching materials are other harvestable products from trees. Herbs can provide herbal medicines, handicraft items, edible parts, fodder for domestic animals and mulching materials. In Kerala, India, many local medicinal leaves are an essential part of the riparian vegetation.
Planting of Multiple Plant Species (Polyculture)
Plants that yield multiple products can be planted in the buffer zone (such as fodder grass, medicinal herbs and multipurpose trees). Species that are particularly valued by the local community can be selected. There are native trees in all localities suitable for the riparian zones and capable of yielding useful products. Some of the multiple functions and products to look for in a tree are wind resistance, erosion control, soil fertility and improvement, nitrogen fixation, shade, wildlife habitat, mulch or green manure, pest control, animal fodder, living fences, fuel wood, food (fruit, vegetables, root, shoot, oil), medicinal uses, tannin, dyes, soaps, cosmetics, bee forage for honey, crafts, carving, and timber. When choosing a tree for the riparian zone, consider the multiple uses and functions the species can provide (Wilkinson & Elevitch, 1998). When planting a multipurpose tree, a number of needs and functions can be fulfilled at once. It is said in India that planting a tree can be a more worthy act than giving birth to unworthy children (Reddy, 1998) and that one tree is equivalent to ten sons.
A recent report from a Black Creek, Iowa restoration project suggests that riparian zones can be designed to harvest products such as hay from switchgrass; sawtimber from oaks, black walnut, and ash; chip material for pulp; biomass for energy; landscape mulch from fast-growing species such as willow, cottonwood, or silver maple; salable native grass and forb seeds; nuts from species such as walnut and hazelnut; and berries from chokecherry, nakingcherry, and elderberry (Iowa State University Publications, 2006).
Food for Aquatic Organisms
The presence or absence of trees in the riparian zone is the most important factor affecting the macroinvertebrate and fish communities in the benthic zone of the streams. Manci and Schneller-McDonald (1989) have shown that loss of vegetative cover and undercut banks can decrease the amount of suitable habitat, thereby reducing stream productivity and fish carrying capacity. Streams and rivers alone are often low in productivity for a number of reasons such as the low rate of photosynthesis by aquatic organisms and downstream movement of nutrients by water flow. This causes aquatic ecosystems to depend heavily on adjacent terrestrial ecosystems for organic matter.
Naturally vegetated riparian zones along rivers and streams are an important component of a larger ecosystem that supports healthy coastal and freshwater shellfish populations (Cohen, 1997). Shellfishes including clams, oysters and mussels depend upon microorganisms for their food. The microorganisms in turn depend upon decaying leaves, twigs and other materials from the streamside vegetation. Mussel populations, important as food and as pearl producers (the shell for the production of buttons, ornaments, decorative articles and other curio items), can be enhanced by certain types of riparian vegetation. In 1910, more than 2600 commercial mussel fishers operated on the Illinois River; virtually none remain (Karr & Chu, 1999). This reduction in mussel fisheries is due to the absence of healthy, diverse, riparian buffer zones. Most of the shellfishes and stationary mollusks are filter feeders. The filter-feeding habits of these animals help to clarify water.
Seasonal flooding is another factor that influences aquatic biomass production. The extensive flooded riparian zone yields a wide variety of plant products including seeds, fruits, flowers, leaves, and feces and decaying terrestrial animals. As Welcomme (cited by Allan, 1995) has pointed out, large tropical rivers that have not been dammed have extensive lateral flood zones where much fish production occurs in seasonally inundated habitats. Fishes in such areas are specialized with many morphological and physiological adaptations to feed in flood zones and a greater part of their biomass production is dependent on these flood zone inputs.
Fruit trees planted along the shore not only provide food for humans but also serve as food for the fish and thus enhance fishery resources. In many tropical countries, fallen or discarded fruits from guava, papaya and avocado and leaves from Leucaena, pumpkin, wild vegetables and cowpea are used as fish feed. In small quantities, manure from cattle, sheep, goats, chickens and ducks are used as fertilizer for aquatic habitats. In some areas, trees like the mulberry are grown on the riverbank and the excreta of the silkworms grown on the mulberry are used as fish feed.
Habitats for Aquatic Organisms
Logs, coarse woody debris, stones, etc., introduced to the streams or stream banks significantly influence the generation and enhancement of instream fish habitats (Roni et al., 2002). Such objects aid in pool formation, provide structural materials for hiding, and provide cover, shade and habitat for various aquatic organisms (Kershner, 1997). The roughness of woody materials in the channel and floodplain system creates habitat heterogeneity. In streams with slopes greater than two percent, woody debris forms dams that act to modify sediment discharge, creating gravel storage areas and stable step-pools and enhancing side channel development and bank storage (Ministry of Natural Resources, 1994).
Protection of Water Resources
High quality water in adequate amounts is an essential asset for any community. Healthy riparian vegetation with extensive root system improves soil porosity and allows more surface runoff to soak into the ground. The flow of water through a healthy riparian zone is slowed by thick riparian vegetation. The high quantity of organic matter produced by the rich riparian vegetation increases microbial activity and the soil quality and thus the percolation of large amounts of water into the deeper aquifers. The organic matter on the ground turns the ground into a "sponge" to absorb more water and this enriches the most important agricultural resource base, the soil water. Diversely vegetated riparian zones help control moisture content of the atmosphere by plant transpiration. When selecting plant components for restoration, one major consideration must be the ability of the plant to resist erosive water flow.
Fertility of Agricultural Land
Multispecies buffer zones can protect agricultural land from erosion and from the loss of fertile topsoil. About ten million tons of sediment erodes from stream banks each year in Oregon and Washington (Manci & Schneller-McDonald, 1989). In the Indian state of Best Bengal, some 48,000 hectares of good farmland vanished over five years by the eroding power of the rivers Ganga and Bhagirathi (Bhaumik, 1998). This loss of land and fertile topsoil can be prevented by proper restoration of the riparian zone. Riparian vegetation cuts down soil erosion in many ways. The grass components together with the root systems of other plants physically bind and restrain sediment loads from the farmlands and also prevent bank erosion.
Raising Domestic Animals
A farmer who lacks adequate agricultural land can raise a few cows, goats or sheep in an appropriately vegetated riparian zone with light or controlled grazing. Suggestions are made by Kauffman and Krueger (1984) to consider riparian zones as "special use pastures". The Alberta Riparian Habitat Management Society's "Cows and Fish Program " is established to foster a better understanding on how improvements in grazing management on riparian areas can enhance landscape health and productivity. (Alberta Riparian Habitat Management Society, 2006). This program promotes a beneficial relationship between livestock and aquatic resources.
Protection of Farms and Farm Animals
A good standing riparian zone vegetation, especially trees, can protect farms and farm animals from wind, rain, frost and floods. Trees on farm borders can ensure many other protective measures for farm and farm animals. Planting deep-rooted, wind resistant plants as a 'living fence' in the riparian buffer zone (if the zone is in the prevailing wind direction) can help to protect the farm in many ways. In addition to protecting the buffer zone from erosion, such plantings can help prevent soil erosion by wind and also wind damage to crops.
Enhancement of Pollination
Planting trees that attract pollinators such as bees and other insects is another benefit of riparian restoration with multiple plant species. In the Himalayan region of India, the destruction of certain native trees along the boundaries of apple farms has lead to declining populations of pollinator bees. Farmers are now forced to keep other flowering plants in and around the farm to attract bees to their apple gardens.
Attempts to reintroduce floristic diversity into intensive agriculture have considerable effects on improving the biodiversity. Lys and Nentwig (1992), provide an example from Switzerland about a program of planting narrow strips of wild flower mixtures in cereal fields. These strips act as new habitats for increased insect diversity and later habitat for large animals such as the skylark, quail, hare etc. (Edwards & Abivardi 1997). These examples show that planting and protecting trees that support the growth of natural pollinators in the riparian zone is a good option for the farmers to achieve favorable pollination rates in their farms.
Riparian buffer zone restoration can enhance food security by improving fishery resources and providing opportunities for agricultural production. Vegetation along riparian zones also can help prevent soil erosion and undercutting of stream banks and keeps nutrients and soil where they belong. This in turn improves the agricultural resource base such as the quality and quantity of topsoil, and the amount of organic matter, fertility, and the water-holding capacity of soil, and thus enhances overall production. Multipurpose plants along the riparian zone provide opportunities for many products. Above all, a healthy riparian zone improves the beauty of the agricultural landscape by linking crops, animals, the living water and the living soil.
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This article is an original submission by the author. Recommended citation
Sebastian, M. 2006. Riparian buffer zone restoration for food security. The Overstory 167. Permanent Agriculture Resources, Holualoa, Hawaii. http//www.overstory.org
About the author
Mary Sebastian is a PhD candidate in the Biological Sciences Department of University of Windsor, Ontario, Canada. She has a Masters degree in Agroforestry and Sustainable Agriculture from the Faculty of Environmental Studies, York University, Ontario, Canada. Her work has focused on ecological restoration of riparian buffer zones. Email firstname.lastname@example.org
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Tags: Land restoration