IDSB02H3 Lecture 8: Dryland Environments Lecture Notes

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University of Toronto Scarborough
International Development Studies
Marney Isaac

IDSB02: Lecture 8 - Dryland Environments and Development. March 1st, 2017 Semi-arid Environments: ● Found between the tropical convergence zone and the great deserts. ● In the northern hemisphere, summer is a semi-arid wet season (within the ITCZ) and winter is the dry season under the STHPZ. ● Tropical grasslands with scattered trees. ● PET > Precipitation. Dryland Environments: ● Deserts, arid, or semi-arid lands. ● Occupy about 41% of global terrestrial area. ○ Home to 38% of the Earth’s population. ○ One of the world’s most heavily inhabited ecosystems. ● Defined by very low precipitation (< 1000 mm/yr). Precipitation of Regional climates: ● Arid (<200 mm/y). ● Semi-arid (200 - 1000 mm/y). ● Wet tropics (> 2500 mm/y). Dryland Management: ● Drylands are a large and important region, particularly in sub-Saharan Africa. ● Livelihoods are dominated by environmental constraints: ○ Low water availability/ water cycles. ○ Limited availability of soil nutrients. ○ Soil erosion. ● Highly developed, context specific, local bodies of environmental knowledge are needed to manage properly. Proximate Causes of Land Degradation in Semi-arid Environments: ● Rainfall and poor tillage practices. ● Changes in crop types: ○ Shift in production during climatic anomalies due to a few years of good rain. ○ Leads to degradation after the anomaly ends. ● Excessive growth of cattle herds ● Increased demand for fuelwood. Ultimate Causes of Land Degradation in Semi-arid Environments: ● Any combination of environmental, social, economic and political factors resulting in increasing sedentarization on lands not suited for it (environmental limits of growth), as well as: ○ Prolonged drought. ○ Increased population. ○ Loss of traditional ecological knowledge. ○ Effects of the good rainfall years. Forms of Dryland Livelihoods: ● Agriculture-based livelihoods. ● Pastoralism, nomadic livestock herding, animal husbandry. ● Key livestock species that are adapted to arid conditions are camels, goats, sheep, and cattle. ● Manage extreme spatially and temporally variable resources. ● The seasonal migration of animals/herders allows for the capture of moisture and soil fertility and then moving before resources are exhausted. Movement: ● Dominant reason for migration is to find better pasture. ● Requires very complex local knowledge. ○ Long-term experience of regional environmental variability. ● Access to different lands necessary to traverse during migrations. ● Navigating lands governed by various schemes, from common property to private ownership. ● Highly dynamic environmental-human systems. Desertification: ● Desertification: is a decrease in land quality that has become widespread in semi-arid/ arid regions. ● Initially blamed on exceeding the land’s “carrying capacity”. ● Soils have been sustainable for thousands of years, what’s changed? ● Western narratives suggest it’s strictly mismanagement. Drought x Wind - “The Dust Bowl”: ● In the early 20th century when a lot of the prairies can been settled, widely for agriculture. ○ The grasslands in the prairies were dug up and turned into crop rotations in large scales. ● Around this time there was the economic depression as well as decade long droughts. ○ This meant that farmers had years without crops or money. ● A lot of farmers stopped their agricultural businesses and abandoned their bare agricultural land. ○ Wind caused erosion of all this soil due to no protection of the bare soil. Conclusions From the “The Dust Bowl”: ● The dust bowl experience results in several conclusions about drylands in developing regions: ○ Degradation was a one-way trend from intact, “climax ecosystems” to deca
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