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Lecture 14

FOR201H1 Lecture 14: Lecture 14 - Causes of deforestation

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University of Toronto St. George
Sean Thomas

Causes of tropical deforestation Rainforest after logging - Intense forest degradation - Losses of sensitive species - Increases in erosion (esp. Near roads) - Increased potential for human access - But usually doesn’t result in complete deforestation Biodiversity in logged forests - For quite a few species, we don’t see huge effects - Species accumulation curves - Primary, once, twice logged are giving the same SA curves Most deforestation driven by land conversion (to agriculture) - Conversion for pasture land in Amazon - Drastic changes compared to logging Logging not equal Deforestation - Analyses of main drivers: - Cattle ranching (~60%) - Small-scale agriculture (30%) - Increasing contributions from large-scale commercial agriculture Deforestation trends - Brazil + Indonesia - In both cases, deforestation rates of tree-cover loss have leveled off - Increasing for a while - Big global picture of deforestation being shifted to other places - Wide diversity of areas are making up difference Cautions on deforestation statistics - How do they get numbers that say “every few minutes so much forest is lost” - Best data is from remote-sensing - But has uncertainty - Might not be able to pick up deforestation from partial logging - Can pick up large-scale deforestation - Self-reporting - FAO: But could be problematic - Might not have capacity to give the right numbers and also might not give the right numbers even if they have it - So remote-sensing data is the best - Problems with clouds - Challenge for remote-sensing to detect anything What drives tropical deforestation - Drivers are mostly socioeconomic factors - Most explanations: - Population growth - Increasing population = increasing pressure on forest - Economic development - If people have low economic status can’t have much impact on forest as they get some wealth, might have more impact (buying chainsaws) - But if economically-developed enough might invest in environmental services + conservation - Shifting cultivation - Agricultural conversion - Timber harvest - Interactions among forests Geographic distribution of tropical deforestation - Areas that have been completely deforested and other areas which have had minimal impact - Large parts of Asia were until recently, huge forested areas that are now gone - Large chunks of forest in Africa have disappeared but most of Congo Basin is there Population Pressure - Overlay map with population correspond well - Lots of people in India, coastal Africa Slide - Correspondence between net deforestation and population growth Economic development - Are places that have lots of people but still have good forest protection - Japan: - Has very high population density - 69% forest cover - Forest cover has been increasing in last 20 years - More old growth forests Economic development - Environmental Kuznets curve - At low rates of income and economic status, people might want to deforest areas but don’t have means to do that - As gain more wealth, have tools and incentive to deforest and utilize forest resources - Eventually if have high income, then they’ll have better things to do that extract forest resources + societal pressures to protect forests Does the Kuznets curve theory hold? - Data is pretty messy - Some weak evidence for this relationship - Clear that other factors are more important or can override economic status - Might be partly that world as a whole has moved past this stage - Some wealthy countries really choose to protect forests - But also some poor countries that protect their forests Shifting cultivators and shifted cultivators - Most traditional peoples engage in agriculture - Usually slash and burn - Stay in that area for some time, then move on when soil depleted - = shifting cultivation/swidden agriculture - At low population densities is really sustainable -
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