52, November/December 2002
Special issue: Selected papers from the IALC Conference:
Assessing Capabilities of Soil and Water Resources in Drylands:
The Role of Information Retrieval and Dissemination Technologies
by Peter F. Ffolliott and Kenneth N. Brooks
"[This paper presents] a holistically conceived watershed management approach to land stewardship that is oriented toward producing, conserving, and sustaining the natural resources that can realistically be obtained on watersheds in arid and semi-arid environments"
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It is also necessary to appreciate that the nature and severity of these interactions are influenced by how people use these resources and the quantities of resources that they use. The effects of these interactions are more likely to follow watershed than political boundaries. Watershed management activities on the uplands of one political unit can significantly impact on the well-being of people living on a downstream political unit regardless of the respective land ownership, often resulting in unacceptable downstream or off-site effects. A watershed management approach to land stewardship accommodates the interests of the widest possible number of people. The approach examines the benefits obtained from good land stewardship by optimizing production and maintaining environmental integrity. It facilitates more effective conflict resolution from a sustainability perspective. A watershed management approach further recognizes that future generations of people deserve to inherit landscapes that are capable of producing the needed goods and services while maintaining ecosystem health and economic stability.
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Water limits much of what people can do. Sustainability of high quality water supplies is critical to the welfare and, ultimately, the survival of people living in dryland environments. It should not surprising, therefore, that the emphasis of watershed management practices in drylands is placed on developing and conserving supplies of water for both upland and downstream uses. Fortunately, numerous methods are used in developing water supplies in the absence of perennial streams or abundant groundwater (Brooks et al. 1997). Water harvesting is one example. Water harvesting systems involving the collection and storage of rainfall until the collected water can be beneficially utilized have been used to provide water for livestock production, forestry activities, or agricultural cropping for over 4,000 years in many dryland regions of the world. Interest in this technology continues to the present. Likewise, water spreading is a proven method of distributing intermittent water flows onto a landscape to enhance forage and crop production. Water harvesting and water spreading methodologies are used to increase both water supplies and productivity of the land that reduces the pressures of overgrazing by livestock, deforestation, and improper agricultural cultivation.
Water that is captured during periods of abundance can often be conserved for use at a later time through methods that reduce evaporation, transpiration, and seepage losses. Methods of reducing evaporation from stock tanks and other small impoundments include covering these water bodies with polystyrene, rubber sheeting, or floating blocks of wax. Aliphatic alcohols and other liquid chemicals that form monomolecular layers on the water surface have also been used to reduce evaporation on larger water bodies. Transpiration losses are reduced by replacing plant species that have high transpiration losses with species that have lower transpiration rates; removing plants with deep rooting systems that extract water from shallow water tables; and applying antitranspirants that either close stomata or form a film on leaf surfaces. Methods of reducing seepage losses from small reservoirs and earthen canals constructed in pervious soils include the compaction of the soil within these structures; the treatment of the soil surface with chemicals to break up aggregates; and lining the canals and bottoms of the reservoirs with impervious materials. This latter method can be too expensive for application on large reservoirs, however.
There can be adequate water to meet local needs in some instances, but its quality might be such that it is not suitable for its designated uses. Available water supplies, therefore, must be considered in the context of water that is suitable for a designated use. The quality of water flowing from upland watersheds is affected by geological-soil-plant-atmospheric systems and land uses. Water flowing from watersheds that are maintained in a good condition is usually high in its physical, chemical, and biological quality and, therefore, suitable to a wide array of designated uses. The reverse situation is the case when watersheds are in poor condition. Watershed condition is a term that indicates the health (status) of a watershed relative to its ability to process rainfall into streamflow and the watershed's capacity for sustaining plant growth (Brooks et al. 1997). Watershed management practices that maintain a watershed in good condition are those that sustain high rates of infiltration into the soil; do not contribute to excessive soil erosion; facilitate a relatively slow streamflow response to inputs of precipitation; and sustain baseflow between precipitation events on perennial stream systems.
Because evapotranspiration accounts for much of the disposition of precipitation falling on watersheds, vegetative changes that reduce evapotranspiration rates generally increase water flows from a watershed. Evapotranspiration is reduced by changes in the composition and structure of the vegetative cover on the watershed. Watershed studies worldwide have shown that water flows can be increased from 5 to 650 mm above pretreatment streamflow regimes when vegetation is converted from deep-rooted plant species to shallow-rooted species; a vegetative cover is changed from plant species with high interception capacities to species with lower interception capacities; or plant species with high transpiration losses are replaced by species with low transpiration losses (Bosch and Hewlett 1982; Whitehead and Robinson 1993). However, increases of water flows from vegetation manipulations in dryland regions are at the lower range of the above-reported increases. About 480 mm of annual precipitation is required for vegetation manipulations to cause a significant increase in water flows in the western United States (Hibbert 1979). Precipitation below this minimal amount is effectively used by the residual forest overstory and subsequent increases in herbaceous plant cover on the watersheds. The length of time into the future that water flows continue to exceed pre-treatment levels is influenced by the type of vegetation that regrows on the treated watershed and the rate of this regrowth.
Maintaining livestock is a traditional way of life of many rural societies that are indigenous to arid and semi-arid regions; therefore, implementation of proper livestock grazing practices on a watershed is necessary to sustaining livestock benefits. Dispersed livestock grazing on open rangelands or confined livestock grazing in small pasturelands or pens near homesteads are practiced. Many watersheds are able to sustain more than one type of ungulate, whether they are livestock or indigenous herbivores, with proper management of the lands that the animals graze. The production of milk, meat, or wool for a marketplace and, therefrom, higher economic returns to pastoralists are often obtained by grazing more than one type of livestock (sheep, goats, cattle, etc.) or combining management of livestock and indigenous wildlife species. Inclusion of sheep or goats with cattle, while complicating the management procedures, can increase total livestock production without adversely impacting the availability of forage, fodder, and water resources on the watershed. In doing so, a better distribution of animals can also be achieved, resulting in a more uniform use of natural resources.
A key to concurrently sustaining livestock grazing and flows of high quality water is retaining a vegetative cover on the watershed. The production of native forage and fodder species and a presence of natural occurring water sources often meet these joint requirements on watersheds in good condition. On other watersheds, however, it might be necessary to remove undesirable (noxious) plants to favor the establishment and growth of more desirable forage species; improve forage and fodder production by seeding of species suitable to the conditions encountered; or develop additional water sources by drilling wells and/or constructing water harvesting systems. Building small impoundments to trap and hold runoff water that would otherwise be unavailable to livestock can also be necessary. Attaining the goal of sustainable livestock production requires that the area to be grazed be stocked only with the number of livestock that can be supported on a sustainable basis; that livestock grazing be permitted only during the proper (often rainy) season when adequate forage resources are available; that the livestock be distributed appropriately and not be allowed to concentrate along streams or other watering sites where they can cause increased soil erosion, sedimentation, or other pollution; and that the kinds of livestock be stocked that are best suited to the condition of the watersheds. These managerial guidelines are necessary to sustaining a good condition of the watershed and preventing land degradation and, as a consequence, desertification.
Wood production and other forestry activities
Trees are a source of fuel, poles, and building materials for upland watershed inhabitants. The fruits, leaves, young shoots, and roots of trees also can be valuable food reserves for people in emergency situations. Trees are a source of fodder for livestock and browse for wildlife at times when herbaceous forage is not available. Trees can be planted in home gardens and parks, buffer strips along streets and sidewalks, and greenbelts around cities and villages to improve local environmental conditions. Trees play a vital role in maintaining the delicate ecological balance of arid and semi-arid environments. The roots of trees hold the often limited soil resources in place, control soil erosion, and help to stabilize steep slopes. Trees retained in windbreak plantings protect the site from accelerated aeolian erosion, lessen evapotranspiration rates, and moderate air temperature extremes. Multipurpose tree species are ideal for protecting and improving the fertility of soil while providing leaves and small branches for fodder without impairing agricultural cropping. Multipurpose trees often fix nitrogen in the soil in addition to providing benefits to local people and their livestock. The issue confronting managers is reconciling the needs of people living on the watersheds to harvest trees for fuel and other tree-based products with the ecological benefits obtained from the trees.
Trees in the woodlands and forests of the dryland regions of the world have often been mined more than managed as a renewable natural resource. Cutting of trees in excess of the sustainable production level in response to the growing needs of expanding human populations is likely to lead to a downward spiraling of available wood resources that is difficult to reverse. Converting woodlands and forests to livestock grazing lands or agricultural croplands compounds this problem. Incidences of wildfire and inadequately controlled fire set by people in this conversion process are other contributing factors. Applications of appropriate forestry practices are necessary to remedy this situation.
Applications of management practices to sustain wood production and other tree-based benefits require a knowledge of the inherent reproductive, growth, and survival characteristics of the trees in question. This knowledge has not always been available in the dryland regions of the world. Customarily applied forestry methods and techniques developed in the more humid regions of the world do not necessarily apply in dryland regions because of the inherently limited reproductive capacities, slow growth rates, and low yields of wood of the trees in these ecosystems. Nevertheless, ecosystems containing trees must be properly managed in the context of a watershed management approach to land stewardship to maintain acceptable growing stock levels. Much has been accomplished in this regard in recent years (Ffolliott et al. 1995). Natural and artificial reproductive methods, intermediate cuttings to achieve optimal tree growth, applications of fertilizers, and other cultural treatments are being incorporated into holistic silvicultural systems that are applicable to woodlands and forests of many dryland ecosystems. Prevention, protection, and, when necessary, control measures against wildfire, disease, and insects are also known in many instances. People are recognizing the need to invest labor, time, and other resources in implementing these systems and measures. Increased knowledge of growth rates and yields of wood have allowed rotational periods and cutting cycles to be identified for the sustainable use of many tree species valued for fuel, poles, and other products. It is important that the length of these periods be reconciled with the immediate priorities of people to use the trees in sustainable watershed management programs.
Small-scale, mostly rain-fed, and dispersed agricultural cropping is another common land use on watersheds in dryland regions. While small in their individual contributions to the overall agricultural economy of a region, the aggregate production of all agricultural cropping on upland watersheds can be comparatively large (Ffolliott, Brooks and Fogel 2002). Depending largely on the capacity of the land to produce agricultural crops and the level of capital available to do so, either subsistence or commercial farming might be practiced. The agricultural crops produced are utilized to meet the immediate needs of subsistence farmers, although the occasional surplus obtained might be sold at a local marketplace. Large-scale commercial farming is less commonly found on upland watersheds because of the likely need for large-scale irrigation facilities, more diversified marketplaces, and costly infrastructures for the transportation of managerial inputs and production outputs.
Small-scale farmers employ agricultural cropping systems that relate to the local climatological conditions, inherent soil capabilities, and their needs, abilities, and perceptions of agriculture in attempting to sustain themselves. While the agricultural cropping systems are endless in their strategies and methods of implementation, they can be grouped into categories of settled agriculture and shifting cultivation for discussion purposes. Settled agriculture is practiced where soil fertility and precipitation and temperature regimes allow crops to be grown in place on a more-or-less continuous basis. One crop a year is usually grown when rainfall amounts are sufficient. Shifting cultivation involves farmers moving from one site to another on a watershed once the potential of soil to produce agricultural crops at subsistence levels on the original site is lost. At higher elevations, cycles of shifting cultivation often include clearing trees on the site, burning the residual vegetation with the ash serving as fertilizer, and planting agricultural crops. When soil fertility declines to the point of limiting acceptable crop production, the farmer moves to repeat the cycle elsewhere, eventually returning to the original piece of land. As populations of people and their livestock increase, the lengths of fallow diminish, soil losses increase, and productivity of the land declines.
Farmers often engage in agricultural cropping on watershed lands that could also be used to grow forage and fodder for livestock production or trees needed for fuel and other wood products. Potential conflicts in land use can be encountered when this is the situation. However, small-scale agriculture can be compatible with watershed management objectives when it is practiced only on the sites suitable for agricultural cropping, considering both the land's inherent productivity potential and the economic returns of practicing agriculture on the land. One way by which sustained agricultural cropping is achieved on a watershed basis is through a geographic separation of agriculture from other land uses with the other watershed strata put to the use or uses to which they are most suited. Another option is to alternate or rotate agricultural cropping with other land uses of a watershed being managed to maintain water flows, livestock production, etc. This option can evolve into a shifting cultivation system. A third option of achieving combined production, the concurrent and continuous use of a watershed for agricultural cropping, livestock production, forestry activities, and other land uses, is generally not feasible in the dryland regions of the world.
There are land use, vegetative, and engineering measures that are available to maintain or increase the productivity of watersheds in terms of environmentally sound, small-scale agricultural cropping. Land use and vegetative measures include the establishment of windbreaks to protect sites vulnerable to excessive soil erosion and alley-cropping or other agroforestry schemes to optimize the site's productivity potentials and mitigate the risks of monocultures. Designating fallow periods of sufficient length of time to allow a recovery of the soil's fertility and, as a consequence, the land's productivity potential can be necessary. Engineering measures implemented for the same general purpose include the construction of bench or broad-based terraces, contour ditches, and gully control structures and protected waterways. Water harvesting, water spreading, and localized irrigation measures might also be considered.
Livestock grazing, forestry activities, and agricultural cropping often occur in varying combinations within a watershed boundary. Upland watersheds in many dryland regions are mosaics of these and other forms of land use. Some of the best opportunities for people to match their desired land uses with the capacities of a watershed to achieve productivity and benefits and, at the same time, attain downstream protection from flooding, sediment accumulations, and other detrimental and cumulative effects involve the integration of agroforestry practices into a watershed management approach to land stewardship. Agroforestry is a system of land use where trees or other woody plants are grown on the same piece of land as agricultural crops, livestock, or a combination thereof, either sequentially or simultaneously (Buck, Lassoie and Fernandes 1999). As such, agroforestry practices are effective combined production systems and, therefore, have a bearing on sustaining the welfare of watershed inhabitants.
Agroforestry practices in dryland regions are mostly agrosilvicultural, silvopastoral, and agrosilvipastoral in their structure. Agrisilvicultural practices are combinations of agricultural crops and forestry activities with the agricultural crops dominating. Silvopastoral combinations are forestry activities and livestock production with a dominate land-use of forestry. Agrosilvipastoral practices include agricultural cropping, forestry, and livestock production in varying combinations of dominance. Arrangements of the components of agroforestry can differ in space (random, alternate rows, or border-tree planting) and time (coincident, concomitant, or sequential). Agroforestry practices also differ in their function, that is, whether they function to produce one or more of the commodity needs of people, ameliorate microclimates, retain soil and water resources, or combinations of these and other protective functions. Agroforestry practices are subsistence, commercial, or intermediate from a socioeconomic standpoint, depending on whether the outputs meet the basic needs of the people, are made available for sale at a marketplace, or a combination of the two.
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Brooks, K. N., P. F. Ffolliott, H. M. Gregersen, and L. F. DeBano. 1997. Hydrology and the management of watersheds. Ames, Iowa: Iowa State University Press.
Brooks, K. N., P. F. Ffolliott, H. M. Gregersen, and K. W. Easter. 1994. Policies for sustainable development: The role of watershed management. EPAT/MUCIA Policy Brief No. 6. Washington, DC: U.S. Department of State.
Brooks, K. N., H. H. Gregersen, P. F. Ffolliott, and K. G. Tejwani. 1992. Watershed management: A key to sustainability. In Managing the world's forests: Looking for balance between conservation and development, ed. N.P. Sharma, 455-486. Dubuque, Iowa: Kendall/Hunt Pubs.
Buck, L. E., J. P. Lassoie, and E. C. M. Fernandes, eds. 1999. Agroforestry in sustainable agricultural systems. Boca Raton, Florida: Lewis Pubs.
Ffolliott, P. F., K. N. Brooks, and M. M. Fogel. 2002. Managing watersheds for sustaining agriculture and natural resource benefits into the future. Quarterly Journal of International Agriculture 41(1/2):23-40.
Ffolliott, P. F., K. N. Brooks, H. M. Gregersen, and A. L. Lundgren. 1995. Dryland forestry: Planning and management. New York: John Wiley & Sons.
Gregersen, H. M., K. N. Brooks, J. A. Dixon, and L. S. Hamilton. 1987. Guidelines for economic appraisal of watershed management practices. FAO Conservation Guide No. 16. Rome: FAO.
Gregersen, H. M., K. N. Brooks, P. F. Ffolliott, T. Henzell, A. Kassam, and K. G. Tejwani. 1996. Watershed management as a unifying framework for researching land and water conservation issues. Land Husbandry 2:23-32.
Hibbert, A. R. 1979. Managing vegetation to increase flow in the Colorado River Basin. USDA Forest Service, General Technical Report RM-66.
National Research Council. 1999. New strategies for America's watersheds. Washington: National Academy Press.
Whitehead, P. G., and M. Robinson. 1993. Experimental basin studies: An international and historical perspective of forest impacts. Journal of Hydrology 145:217-230.
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Peter F. Ffolliott, Professor, University of Arizona, School of Renewable Natural Resources, 220 Bio Sciences East, Tucson AZ 85719-9900, USA; Tel: 520-621-7276, Fax: 520-621-8801, Email: email@example.com
Kenneth N. Brooks, Professor, Department of Forest Resources, 115 Green Hall, 1530 Cleveland Ave North, University of Minnesota, St. Paul MN 55108, USA; Tel: 612-624-2774, Fax: 612-625-5212, Email: firstname.lastname@example.org
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