Watershed Planning and Management 3(2+1)

Lesson 23 Watershed Land Use/Land Cover

23.2 Agricultural Practices and LU/LC

Since the invention of agriculture, ~10,000 years ago, humans have modified or transformed the land surface. Agricultural production has caused greater environmental change to the biosphere than any other land use. It is estimated that 50% of the world’s land is used for agriculture and animal production while only 5% is unmanaged lands, parks and preserves. The major mode of human land transformation has been through agriculture. It is estimated that over the last 300 years, globally, 20% of forests and woodlands, 1% of grasslands and pastures (although most grasslands were converted to pastures) were lost while croplands expanded by 466%. Figure 23.1 illustrates these changes at a global scale. Although land-use practices vary greatly across the world, their ultimate outcome is generally the same: the acquisition of natural resources for immediate human needs, often at the expense of degrading environmental conditions.

 Fig. 23.1. World Wide Extent of Human Land Use and Land Cover Change. (Source: Foley, Jonathan A., et al. "Global consequences of land use." Science 309.5734 (2005): 570-574)

Land-cover changes also affect regional climates through changes in surface energy and water balance. Humans have also transformed the hydrologic cycle to provide freshwater for irrigation, industry, and domestic consumption. Furthermore, anthropogenic nutrient inputs to the biosphere from fertilizers and atmospheric pollutants now exceed natural sources and have widespread effects on water quality and coastal and freshwater ecosystems. Land use has also caused declines in biodiversity through the loss, modification, and fragmentation of habitats; degradation of soil and water; and overexploitation of native species. Although modern agriculture has been successful in increasing food production, it has also caused extensive environmental damage. For example, increasing fertilizer use has led to the degradation of water quality in many regions. In addition, some irrigated lands have become heavily salinized, causing the worldwide loss of ~1.5 million hectares of arable land per year, along with an estimated $11 billion in lost production. Up to ~40% of global croplands may also be experiencing some degree of soil erosion, reduced fertility, or overgrazing. The loss of native habitats also affects agricultural production by degrading the services of pollinators, especially bees. In short, modern agricultural land use practices may be trading short-term increases in food production for long term losses in ecosystem services, including many those are important to agriculture.

23.3 LU/LC Management of Watersheds

Land use can disrupt the surface water balance and the partitioning of precipitation into evapotranspiration, runoff, and groundwater flow. Surface runoff and river discharge generally increase when natural vegetation (especially forest) is cleared. Water demands associated with land-use practices, especially irrigation, directly affect freshwater supplies through water withdrawals and diversions. Agriculture alone accounts for ~85% of global consumptive use. As a result, many large rivers, especially in semiarid regions, have greatly reduced flows, and some routinely dry up. In addition, the extraction of groundwater reserves is almost universally unsustainable and has resulted in declining water tables in many regions.

Water quality is often degraded by land use. Intensive agriculture increases erosion and sediment load, and leaches nutrients and agricultural chemicals to groundwater, streams, and rivers. In fact, agriculture has become the largest source of excess nitrogen and phosphorus to waterways and coastal zones. Urbanization also substantially degrades water quality, especially where wastewater treatment is absent. The resulting degradation of inland and coastal waters impairs water supplies, causes oxygen depletion and fish kills, increases blooms of cyanobacteria (including toxic varieties), and contributes to waterborne disease.

Integrated watershed management, involves the adoption of a coherent management system for land, water and vegetation which can help to achieve the sustainable use of the natural resources within a watershed. This approach recognizes that such factors as urban and agricultural development, the loss of wetlands, land drainage schemes, forest clearance and other activities carried out in the watershed, even though well away from river channels can increase the volume and rate of run-off and worsen flood conditions. The watershed is the logical unit for coordinated land-use planning and management and effective and sustainable resource and environmental management. There is a clear association between land-use decision-making, natural resources utilization and the quality of the watershed environment - with a systems approach, the likely adverse consequences of mismanagement can be anticipated and appropriate precautions taken to minimize or avoid their effects.

The principles adopted for land-use planning at the watershed level may include the following components:

1. Integrated Utilization of Natural Resources

2. Sustainable Farming Systems

3. Interactive and Pro-active Community Farming Systems

4. Community Participation

5. Conservation Measures

6. Development of Models for Sustainable Land-use Systems

A sustainable farming system needs to focus on the social conditions, especially poverty alleviation, and may include the following components:

1. Food Component

2. Fodder Component

3. Fuel Component

4. Income Generation Component

23.4 Role of Cultural Practices as Land Management

Cultural land management practices can be classified into following basic categories.

1. Shifting Cultivation

2. Nomadic Pastoralism

3. Continuous Cultivation

4. Mixed Subsistence Farming

The insite about these cultural practices and their effect can be discussed as below.

23.4.1 Shifting Cultivation

Shifting cultivation, swidden or slash and burn agriculture is a common means of food production in the tropics. It is well suited to nutrient poor soils in areas of low population density. The natural vegetation is cut and burned, followed by up to five seasons of growing then several years of fallow. Once the area is allowed to go fallow, another area is chosen and the process repeated. The fallow usually lasts 20 years in humid areas and as few as 10 years in dryer areas. During the fallow period soil nutrients are regenerated and given long enough fallow, the cycle can be repeated indefinitely. Burning the natural vegetation makes nutrients stored in forest biomass more available in the form of inorganic ash. These nutrients usually decline rapidly with each successive crop and weeds and pests soon invade. Thus, crops can only be grown for a few seasons. Often the area is not completely abandoned, useful perennial plants (fruits plant) are left to mature and the area is revisited frequently to harvest the crop. This system gives very high yields per unit of cultural energy input. Unfortunately, with increasing population pressures and less available land, the fallow period has decreased. This leads to increased soil erosion and decreased species diversity. The shorter fallow associated with modern swidden agriculture makes the practice unsustainable.

23.4.2 Nomadic Pastoralism

Nomadic pastoralists raise domesticated relatives of wild undulates such as goats, cattle, camels and sheep. They live almost exclusively off animal product such as milk, meat and blood, though diets are often supplemented with plant products gathered in incidental foraging. The people tend to migrate extensively in search of water and pasture. This system allows humans to occupy areas unsuitable for rain-fed agriculture, although usually at low population densities. The animals are able to convert low quality plant food (grass), which are unusable by humans, into high quality foods such as milk and meat. The population of the animals varies considerably depending on rainfall. The populations are generally higher than those of wild relatives and can therefore feed more people than can otherwise be supported in these environments. Nomadic pastoralism is usually practiced in savannnas or areas otherwise unsuited for permanent rainfed agriculture. This form of subsistence is therefore most common in Africa, Northern Asia and Arabia. The Massai of Kenya is a well known group of nomadic pastoralists.

23.4.3 Continuous Cultivation

Under continuous cultivation, fields are used year after year with only brief fallow periods. Weeds, pests and losses of soil nutrients are frequent problems. Thus, a higher level of cultural energy input is required. Frequently, such areas are dependent on nutrient inputs from seasonal flooding or alluvial sediments in paddy water. In paddy fields, nitrogen can also be added by N₂-fixing cyanobacteria. The net energy gain for continuous cultivation is less than in shifting cultivation. This system can be very sustainable, much of the traditional farming, in India and Southeast Asia is based on continuous cultivation.

23.4.4 Mixed Subsistence Farming

The majority of farmers employ a combination of farming techniques. Mixed agriculture, with livestock and crops integrated into a single ecosystem, is very common in Asia, Africa and the Americas. Farmers are often highly dependent on animals as a key component of the farming system. The animals provide meat, milk, fuel, fertilizer, draft power, transportation and can be fed largely with agricultural waste products. Additionally, farmers are frequently engaged in a combination of agricultural and economic pursuits. They can barter for food or labor, sell agricultural products or work for others. The choice of cropping system can be based on several factors; climate, soil types, local economies, markets, availability of labor and land, knowledge base and traditions all influence the decision.

Common Characteristics

The following characteristics can be considered common and important features of traditional agricultural systems.

1. Focus on risk reduction

2. Year round vegetative cover of soils

3. System diversity: farm systems based on several cropping systems, cropping systems based on a mixture of crops, and crops with varietal and other genetic variability

4. Trophic complexity approaching natural systems. Multiple interactions between plants, weeds, pathogens and insects

5. High net energy yields because energy inputs are relatively low

6. Low levels of inputs and high degree of self-sufficiency

One of the key features of traditional farming systems is the interaction between domesticated varieties and their wild relatives. The promotion of natural hybridization and introgression has, over time, increased the genetic diversity available to farmers. Traditional farmers also experiment with new varieties and breed plants purposefully to create new strains. They generally plant experimental plots first and only integrate new varieties into their main crops once a variety has proven itself to be of value. This constant experimentation and breeding has created the diversity of crops upon which we now depend. Traditional farming systems also promote genetic diversity. The landscape in a traditionally farmed area is a patchwork of different vegetation types created by the farming methods. The result is a variety of ecological niches that encouraged biological diversity. The landscape, even in intensively managed areas, is a mosaic of cultivated, grazed, uncultivated, and successional areas. Evidence from tropical forests as well as desert areas in the Americas has shown that certain traditional agricultural activities increased the number of species present rather than decreased them. Some of the areas with the richest species diversity, such as tropical forests, have been managed by humans for centuries.

Keywords: Land Use Land Cover, Land Management, Watershed Management, Cultural Practices.

References

Foley, Jonathan A., et al. (2005). "Global consequences of land use." science 309.5734: 570-574.

Suggested Readings

• ESCAP-UN. (1997). Guidelines and Manual on Land-Use Planning and Practices in Watershed Management and Disaster Reduction, Economic and Social Commission for Asia and the Pacific, United Nations.

• Marten, G. (ed) 1986. Traditional Agriculture in Southeast Asia A Human Ecology Perspective. Westview Press,  Boulder, Colorado.

• DeFries, R. S., Asner, G. P.,  Houghton, R. A. (2004). Ecosystems and Land Use Change (Vol. 153, pp. 1-344). American Geophysical Union.

• Watson, R. T. (2000). Land Use, Land-Use Change, and Forestry: a special report of the intergovernmental panel on climate change. Cambridge University Press.