Background Image
Previous Page  40 / 104 Next Page
Information
Show Menu
Previous Page 40 / 104 Next Page
Page Background

40

About 2 billion ha of the world’s agricultural land have been

degraded because of deforestation and inappropriate agricul-

tural practices (Pinstrup-Andersen and Pandya-Lorch, 1998).

In spite of global improvements on some parts of the land,

unsustainable land use practices result in net losses of crop-

land productivity – an average of 0.2%/year. The combined

effects of competition for land from growing populations,

reduced opportunity for migration and rotation along with

higher livestock densities, result in frequent overgrazing and,

hence, loss of long-term productivity. Satellite measurements

show that between 1981 and 2003, there was an absolute

decline in the productive land area (as Net Primary Produc-

tivity) across 12% of the global land area. The areas affected

are home to about 1–1.5 billion people, some 15–20% of the

global population (Bai

et al

., 2007).

LOSS OF CROPLAND AREA FROM LAND DEGRADATION

A number of authors including den Biggelaar

et al

. (2004) estimate

that globally, 20,000–50,000 km

2

of land are lost annually through

land degradation, chiefly soil erosion, with losses 2–6 times higher

in Africa, Latin America and Asia than in North America and Eu-

rope. The major degrading areas are in Africa south of the Equator,

Southeast Asia, Southern China, North-Central Australia and the

pampas of South America. Some 950,000 km

2

of land in Sub-Sa-

haran Africa is threatened with irreversible degradation if nutrient

depletion continues (Henao and Baanante, 2006). In most parts

of Asia, forest is shrinking, agriculture is gradually expanding to

marginal lands and land degradation is accelerating through nutri-

ent leaching and soil erosion. In fact, about 20% of the agricultural

land in Asia has been degraded over the last several decades (Foley

et al

., 2005). The pace of degradation is much higher in environ-

mentally fragile areas, such as on the mountains.