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Annual Review of Environment and Resources. Eric F. Lambin, 1 Helmut J. Geist, 2 and Erika Lepers 2. The review summarizes recent estimates on changes in cropland, agricultural intensification, tropical deforestation, pasture expansion, and urbanization and identifies the still unmeasured land-cover changes. Climate-driven land-cover modifications interact with land-use changes. Land-use change is driven by synergetic factor combinations of resource scarcity leading to an increase in the pressure of production on resources, changing opportunities created by markets, outside policy intervention, loss of adaptive capacity, and changes in social organization and attitudes.

The changes in ecosystem goods and services that result from land-use change feed back on the drivers of land-use change. A restricted set of dominant pathways of land-use change is identified. Land-use change can be understood using the concepts of complex adaptive systems and transitions. We argue in this paper that a systematic analysis of local-scale land-use change studies, conducted over a range of timescales, helps to uncover general principles that provide an explanation and prediction of new land-use changes.

In the mids, it was recognized that land-cover change modifies surface albedo and thus surface-atmosphere energy exchanges, which have an impact on regional climate 123. Decreasing the uncertainty of these terrestrial sources and sinks of carbon remains a serious challenge today.

Of primary concern are impacts on biotic diversity worldwide 7soil degradation 8and the ability of biological systems to support human needs 9. Understanding and predicting the impact of surface processes on climate required long-term historical reconstructions and projections into the future of land-cover changes at regional to global scales 11 Quantifying the contribution of terrestrial ecosystems to global carbon pools and flux required accurate mapping of land cover and measurements of land-cover conversions worldwide 1314 Many scientists, especially in the natural sciences, ly assumed that generating local- to global-scale projections of land change several centuries into the past and about years into the future would be easy.

Actually, many thought land changes consisted mostly in the conversion of pristine forests to agricultural uses deforestation or the destruction of natural vegetation by overgrazing, which le to desert conditions desertification. These conversions were assumed to be irreversible and spatially homogeneous and to progress linearly. Only the growth of the local population and, to a lesser extent, its increase in consumption were thought to drive the changes in land conditions.

A consensus is progressively being reached on the rate and location of some of the main land changes, but other forms of change, such as desertification, are still unmeasured and controversial. Understanding of the causes of land-use change has moved from simplistic representations of two or three driving forces to a much more profound understanding that involves situation-specific interactions among a large of factors at different spatial and temporal scales.

The richness of explanations has greatly increased, often at the expense of generality of the explanations. The last decade, however, has witnessed innovative methodological developments in the modeling of land-use change at local to regional scales 2021 Nevertheless, the recent progress in our understanding of the causes of land-use change still has to be fully integrated in models of the process. The main emphasis of the review is on tropical regions. Second, the complex nature of land-cover change is discussed to emphasize the need to integrate all scales and processes of change.

Third, a synthesis of recent case study evidence on the causes of land-use change is presented, with emphasis on the mode of interaction between diverse causes and dominant pathways of change. Fourth, the complexity of land-use change is described using the notions of complex adaptive systems and transition. Since humans have controlled fire and domesticated plants and animals, they have cleared forests to wring higher value from the land. About half of the ice-free land surface has been converted or substantially modified by human activities over the last 10, years.

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Agriculture has expanded into forests, savannas, and steppes in all parts of the world to meet the demand for food and fiber. Agricultural expansion has shifted between regions over time; this followed the general development of civilizations, economies, and increasing populations Two recent studies estimated historical changes in permanent cropland at a global scale during the last years by spatializing historical cropland inventory data based on a global land-cover classification derived by remote sensing, which used a hindcasting approach 11or based on historical population density data The area of cropland has increased globally from an estimated — million ha in to — million ha ina 4.

The area under pasture—for which more uncertainties remain—increased from around million ha in to around million ha in These increases led to the clearing of forests and the transformation of natural grasslands, steppes, and savannas.

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Forest area decreased from — million ha in to — million ha in Steppes, savannas, and grasslands also experienced a rapid decline, from around million ha in to — million ha in 1126 Table 1. Europe, the Indo-Gangetic Plain, and eastern China experienced first the most rapid cropland expansion during the eighteenth century. Starting in the nineteenth century, the newly developed regions of North America and the former Soviet Union followed suit.

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China experienced a steady rate of expansion throughout the last three centuries A very gradual cropland expansion occurred in Africa, south and Southeast Asia, Latin America, and Australia untilbut since then, these regions have experienced dramatic increases in cropland, especially during the second half of the twentieth century. The greatest cropland expansion in the twentieth century occurred in south and Southeast Asia The Corn Belt in the United States, the prairie provinces in Canada, the pampas grassland region in Argentina, and, a few decades later, southeast Brazil have also seen rapid expansion of permanent cropland early in the twentieth century Food and Agriculture Organization F.

On the basis of national statistics, inventory reports, estimates by experts, and a pantropical remote sensing survey for tropical forests only, the Global Forest Resources Assessment 29 estimated that the world's natural forests decreased by However, some natural forests were converted to forest plantations.

Gains in forest cover arose from afforestation on land ly under nonforest land use 1. The net global decrease in forest area was therefore 9. The total net forest change for the temperate regions was positive, but it was negative for the tropical regions. FAO estimated that tropical regions lost According to Achard et al. Forest regrowth ed for 1. The annual rate of net cover change in humid tropical forest was 0. A further 2. This figure does not include forests affected by selective logging.

Southeast Asia has experienced the highest rate Adger AL sexy women net cover change 0. Latin America, however, lost about the same area of forest as Southeast Asia during the — time period Forest degradation was most extensive in Southeast Asia 0.

Forest regrowth was more extensive, both in absolute and relative terms, in Southeast Asia than in the other humid tropical regions 0.

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These recent assessments of deforestation, as well as another remote sensing survey at a coarser spatial resolution but covering the entire tropical belt 31concur to estimate less deforestation in the s than was observed in the s. Still, it is unlikely that deforestation has ificantly slowed down, because differences in methods of assessment and definitions used may for at least part of the difference Moreover, deforestation in the dry tropical forests may often be underestimated.

In Latin America, large-scale forest conversion and colonization for livestock-based agriculture is prevalent, whereas cropland expansion by smallholders dominates in Africa. In Asia, intensified shifting agriculture, including migration into new areas, gradual change of existing areas toward more permanent agriculture, and logging explain most of the deforestation 2930 The largest deforestation front is the arc of deforestation of the Brazilian Amazon, which extends more recently outside Brazil, east of the Andes, and along the road from Manaus to Venezuela.

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More scattered areas of forest loss are detected in the Chaco and Atlantic forest areas in South America. Historically, humans have increased agricultural output mainly by bringing more land into production. The greatest concentration of farmland is found in Eastern Europe, with more than half of its land area in crop cover Despite claims to the contrary, the amount of suitable land remaining for crops is very limited in most developing countries 3839where most of the growing food demand originates.

Where there is a large surplus of cultivable land, land is often under rain forest or in marginal areas 38 The period after has witnessed a decoupling between food production increase and cropland expansion Table 3. The 1. Inmillion ha were irrigated Globally, the cropland area per capita decreased by more than half in the twentieth century, from around 0. Note, however, that national statistics in developing countries often substantially underreport agricultural land area 2838e. The mix of cropland expansion and agricultural intensification has varied geographically Tropical Asia increased its food production mainly by increasing fertilizer use and irrigation.

Most of Africa and Latin America increased their food production through both agricultural intensification and extensification. In western Europe and the northeastern United States, cropland decreased during the last decades, after abandonment of agriculture or, in a few cases, following land degradation mostly on marginal land. Globally, this change has freed million ha from agricultural use since Natural vegetation covers have given way not only to cropland but also to pasture —defined as land used permanently for herbaceous forage crops, either cultivated or growing wild The distinction between pasture and natural savannas or steppes is not always clear.

During the last decade, pastures increased considerably in nontropical Asia at an annual rate of 4. As eastern Africa recorded a large increase in head of cattle over this period [, additional head of cattle per year between andaccording to FAO 25 ], it is likely that many areas in pastoral use in Africa are classified as natural vegetation. Intowns and cities sheltered more than 2.

Urban population has been growing more rapidly than rural population worldwide, particularly in developing countries. According to the U. Population Division 43the of megacities, defined here as cities with more than 10 million inhabitants, has changed from one in New York to 17 inthe majority of which are in developing Adger AL sexy women. Urban form and function have also changed rapidly. For example, inthe 7 million inhabitants of Hong Kong were supported on as little as km 2 of built-up land However, urbanization affects land in rural areas through the ecological footprint of cities.

This footprint includes, but is not restricted to, the consumption of prime agricultural land in peri-urban areas for residential, infrastructure, and amenity uses, which blurs the distinction between cities and countryside, especially in western developed countries. Urban inhabitants within the Baltic Sea drainage, for example, depend on forest, agriculture, wetland, lake, and marine systems that constitute an area about times larger than that of the urban area proper Intotal nonfood material resources consumed in Hong Kong i.

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Fossil fuel energy consumed in this city i. Time series of global maps of nighttime lights detected by satellite 47 illustrate the rapid changes in both urban extent and electrification of the cities and their surroundings. A question still being debated is whether urban land use is more efficient than rural land use and, therefore, whether urbanization saves land for nature.

The most populated clusters of cities are mainly located along the coastal zones and major waterways—in India, East Asia, on the eastern U. The cities experiencing the most rapid change in urban population between and are mostly located in developing countries 48 Figure 2. It is estimated that 1 to 2 million ha of cropland are being taken out of production every year in developing countries to meet the land demand for housing, industry, infrastructure, and recreation This is likely to take place mostly on prime agricultural land located in coastal plains and in river valleys.

Note that rural households may consume more land per capita for residential purposes than their urban counterparts Other forms of rapid land-cover change that are thought to be widespread are still poorly documented at the global scale. Local- to national-scale studies, however, demonstrate their importance and ecological ificance.

Prominent among these are changes in the sub tropical dry forests e. The land cover is defined by the attributes of the earth's land surface and immediate subsurface, including biota, soil, topography, surface and groundwater, and human structures. These attributes are either a single land-cover category i.

The discrete representation of land cover has the advantages of concision and clarity, but it has led to an overemphasis of land-cover conversions and a neglect of land-cover modifications.

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