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Effects of Deforestation on Health

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Holzstaemme

Forests account for approximately 30% of the Earth’s land surface.[1] The soils and ecosystems that exist within these forests store around 1200 gigatonnes of carbon. With the earth’s atmospheric concentration of carbon dioxide (CO2) recently reaching 391 ppm (parts per million) in October of 2012,[2][3] more than a 100 ppm increase from the pre-industrial era[4] it is clear that the relationship between the Earth’s forests and atmosphere is critically important.[1] During the 1980s it became increasingly clear that the terrestrial biosphere played an important part in terms of the global atmospheric carbon balance. It became apparent that the conversion of land, most notably deforestation in the tropics, caused large terrestrial carbon losses into the atmosphere forcing other carbon sinks to compensate.[1]

Tropical Forests

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Tropical Forests account for just under 50% of the world's forests, however they contain as much carbon in their vegetation and soils as boreal and temperate type forests combined.[5] With trees in the tropics holding in general approximately 50% more carbon per hector than trees outside of the tropics, deforestation in these areas is more likely to lead to higher levels of carbon release.[5]

Amazon rainforest

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Slash and burn forest removal in Brazil increased dramatically in the 1970s and 1980s.

Forests currently play a major role in carbon uptake in the global carbon cycle.[6] The Amazon rain forest plays an important role by sequestering carbon under stable climatic conditions.[7] Forest fires are often not assigned a net emission of carbon as they are viewed as a bi-product of forest conversion for agriculture use, however accidental spread of fires beyond agriculture areas may contribute to increased carbon emissions. [8] If the carbon emissions from forest fires are due to a natural cycle of burning and regrowth, the net carbon balance is nearly zero.[8] However current forest-fire models suggest that forest fragmentation and climate change could shift the Amazon forest from a carbon sink to a source of atmospheric CO2.[7] Recurrent fires increase pyrophytic vegetation, such as bamboos and grasses which also increase forest flammability thus increasing potential emissions.[7] In 1997 and 1998 forest fires during the El Niño drought affected at least 20,000 km2 in the Amazon leading to large smoke episodes which halted air traffic in the area and caused ships to collide at sea.[9] The short-term effects on human health effects were irritations of the respiratory tract, skin and eyes, bronchitis, conjuctivitis as well as increased asthma attacks. [9]

The major drivers of deforestation and degradation in the Amazon are, forest conversions for shifting cultivation, croplands, pastures as well as industrial and fuel wood harvest.[8] When forests are converted to croplands all initial vegetation is replaced by crops causing a change in the carbon density.[8] Cropland conversion also causes a 25-30% soil carbon reduction.[8] Forest conversion to pastures for cattle is a major cause of deforestation in the Amazon, and although it does not cause the reduced soil carbon seen with croplands, it is still significant primarily due to its sheer magnitude.[8] The harvest of both industrial wood and fuel wood causes increased carbon emissions due to burning and decay of wood products as well as reduced carbon density of forests.[8] Tree plantations result in a carbon sink reducing atmospheric carbon dioxide in participating areas. However within tropical forests worldwide tree plantations have only accounted for an approximately 4% decrease in net carbon emissions.[8]

Southeast Asia

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By World War II approximately one-third of the tropical forests in Southeast Asia had been cleared, with declines continuing past the mid-century mark. [10] Over the past thirty years commercial logging for export has caused significant forest loss. [10] In the forested uplands of Indonesia, in order to extract timber, large forestry corporations constructed road systems to allow access to previously inaccessible areas. After having logged a given area the loggers moved on and small farmers settled along the roads and cleared additional forests.[10] Logging companies shifted from one concession to another, moving from country to country.[10] Increased market expansion for tropical timber along with inferior law enforcement, vested interests, and corruption, allowed for illegal logging operations to exist.[10] The lowland forests of Laos and Cambodia have been subjected to increasingly intense swidden cultivation and the majority of old-growth forests have ceased to exist in these areas.[10] Forests generally hold 20 to 50 times more carbon than the ecosystem which replaces them,[5] thus leading to a net increase of atmospheric C02.

Deforestation of the African Highland

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The Ethiopian Highlands

Environmental changes such as deforestation could increase local temperatures in the highlands thus could enhance the vectorial capacity of the anopheles.[11] Anopheles mosquitos are responsible for the transmission of a number of diseases in the world, such as, malaria, lymphatic filariasis and viruses that can cause such ailments like O'nyong'nyong virus.[11] Environmental changes, climate variability, and climate change are such factors that could affect biology and ecology of Anophelse vectors and their disease transmission potential.[11] Climate change is expected to lead to latitudinal and altitudinal temperature increases. Global warming projections indicate that the best estimate of surface air warming for a “high scenario” is 4 C, with a likely range of 2.4-6.4 C by 2100.[12] A temperature increase of this size would alter the biology and the ecology of many mosquito vectors and the dynamics of the diseases they transmit such as Malaria. Arthropods critically depend on ambient temperature for survival and development,[13] and their distribution range is limited by the temperature. Climate warming or any factor that alters the microclimate conditions of Anopheles mosquitos (e.g., Deforestation) in the highlands may facilitate the persistence of the mosquito population. [14] Climate warming can mediate mosquito physiology and metabolic rate because metabolic rate increases exponentially rather than linearly with temperature ectotherms.[15] Anopheles mosquitoes in highland areas are to experience a larger shift in their metabolic rate due to the climate change. This climate change is due to the deforestation in the highland areas where these mosquitos dwell. When temperature rises, the larvae take a shorter time to mature [16] and, consequently, there is a greater capacity to produce more offspring. Microclimatic changes in human homes caused by the effects of deforestation can also significantly shorten the duration of the mosquitoes' gonotrophic cycle by 1.7 days (4.6 vs 2.9 days)[17] The gonotrophic cycle is the period between the taking of a blood meal by a mosquito, including the digestion of the blood meal, until oviposition or egg laying. [18] The decrease of the gonotrophic cycles implies an increase of the biting frequency from an average of once every five days to once every three days. In turn this could potentially lead to an increase in malaria transmission when infected humans are available.

Deforestation for the purpose of logging and self-subsistence agriculture is a serious problem in the tropical regions of Africa. For Example, Malava forest, a tropical rainforest in kakamega district, Kenya, shrank from 150km2 in 1965 to 86km2 in 1997.In East African highlands, 2.9 million hectares of forest were cleared between 1981 and 1990, representing an 8% reduction in forest cover in one decade. [19] Land use and land cover changes may modify the temperature and relative humidity of malaria vector habitats in the highlands. For instance, deforestation in Cameroon caused the introduction of A. gambiae into the habitat that was previously dominated by A. moucheti.[20]

Deforestation of Mangroves

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A red mangrove, Rhizophora mangle

Mangroves are the salt-tolerant evergreen forests, found in the intertidal zones of sheltered shores, estuaries, tidal creeks, backwaters, lagoons, marches and mudflats of the tropical and subtropical latitudes. Mangrove systems are in continuous jeopardy, facing threats from human interventions. Human interference in mangrove forests has caused the system to shrink in an alarming way and at a faster rate than inland tropical forests and coral reefs.[21] It is predicted that small rise in sea level would be the greatest threat to the existing mangroves. [22] The mangrove forests are likely to be totally lost in the next 100 years, if current trends continues.[21] A healthy mangrove ecosystem provides vast benefits to the adjoining systems and mankind. Mangroves and associated soils can sequester 22.8 million metric tons of carbon each year, which is 11% of the total input of terrestrial carbon into oceans [23] and provides more than 10% of essential organic carbon to the global oceans. [24]Carbon sequestration potential of mangroves is 50 times greater than many other tropical forests. This is due to the high levels of below ground biomass and also the considerable storage of organic carbon in mangrove sediment soils. Failing to preserve mangrove forests may cause considerable carbon emissions and thus accelerate global warming. [25] The restoration of mangroves can be an ideal and natural counter-measure to global warming, and mangroves also play a key role in environmental security. This consists of mitigating the effects of tsunami, cyclones, floods and green house gas. In general, every ecosystem provides life supporting functions as well as other valuable services, many of which are interlaced with human welfare [26] Mangroves have a medicinal value aswell. Coastal ecosystems such as mangroves are as a potential site for new drugs. [27] Drug research groups have pointed out that mangroves possess an untapped source of new medicines and in the future this ecosystem will be the new frontiers for drug discoveries. [27]

Biodiversity

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The diverse forest canopy on Barro Colorado Island, Panama, yielded this display of different fruit

Deforestation is directly linked with a decrease in plant biodiversity.[28] This decrease in biodiversity has several implications for human health. One such implication is the loss of medicinal plants. The use of plants for medicinal purposes is extensive, with ~70 to 80% of individuals worldwide relying solely on plant-based medicine as their primary source of healthcare.[29] This dependency on plants for medicinal purposes is especially rife in developing countries that only consume 15% of manufactured pharmaceutical drugs, many of which are fake.[29] Local knowledge surrounding medicinal plants is useful for screening for new herbal medicines that may be useful for treating disease.[30] Villages and communities which reside continually in a single geographic area over time, create, transmit and apply widespread information surrounding the medicinal resources in the area.[30] Formal scientific methods have been useful in identifying the active ingredients used in ethnopharmacy and applying them to modern medicines. However, it is important that medicinal resources are managed appropriately as they become globally traded in order to prevent species endangerment[30].

Extinction of Indigenous Groups

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Deforestation is also a primary cause of dislocation and in some cases, extinction of indigenous people.[31] The Malaysian state Sarawak is an example where rampant deforestation has overrun many Dayak groups.[31] The indigenous Sarawakians relied on shifting agriculture, hunting and gathering in order to sustain their relatively low population density.[32] With the advent of modern logging technology the Sarawak forests entered 'mainstream' economic development.[31] This has lead to massive forced evacuations and relocation of the Dayak people causing a loss of their traditions and culture.[33]

References

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  2. ^ NOAA Mauna Loa dataset (reported online at: http://co2now.org/ )
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  5. ^ Dore, Sabina; Montes‐Helu, Mario; Hart, Stephen C.; Hungate, Bruce A.; Koch, George W.; Moon, John B.; Finkral, Alex J.; Kolb, Thomas E. (2012). "Recovery of ponderosa pine ecosystem carbon and water fluxes from thinning and stand-replacing fire". Global Change Biology. 18 (10): 3171–3185. doi:10.1111/j.1365-2486.2012.02775.x. PMID 28741823. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: date and year (link)
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  14. ^ Gillooly, J.F., Brown, J.H., West, G.B.,Savage, V.M.,Charnov, E.L. (September 2001). "Effects of Size and Temperature on Metabolic Rate". Science Magazine. 293 (5538): 2248–2251. doi:10.1126/science.1061967. PMID 11567137.{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link)
  15. ^ Munga, S., Minakawa, N., Zhou, G., Githenko, A.K., Yan, G. (September 2007). "Survivorship of Immature Stages of Anopheles gambiae s.l. (Diptera: Culicidae) in Natural Habitats in Western Kenya Highlands". Journal of Medical Entomology. 44 (5): 758–764. doi:10.1603/0022-2585(2007)44[758:SOISOA]2.0.CO;2. PMID 17915505.{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link)
  16. ^ Afrance, Y.A., Lawson, B.W., Githeko, A.K., Yan. G. (2005). "Effects of microclimatic changes caused by land use and land cover on duration of gonotrophic cycles of Anopheles gambiae (Diptera: Culicidae) in western Kenya highlands". Journal of Medical Entomology. 42 (6): 974–980. doi:10.1603/0022-2585(2005)042[0974:EOMCCB]2.0.CO;2.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  17. ^ Santos, R.L., Forattini, O.P., Burattini, M.N. (November 2002). "Laboratory and field observations on duration of gonotrophic cycle of Anopheles albitarsis s.l. (Diptera: Culicidae) in southeastern Brazil". Journal of Medical Entomology. 39 (6): 926–930. doi:10.1603/0022-2585-39.6.926. PMID 12495194.{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link)
  18. ^ Lindblade, K.A., Walker, E.D., Onapa, A.W.,Katungu, J., Wilson, M.L. (April 2000). "Land use change alters malaria transmission parameters by modifying temperature in a highland area of Uganda". Tropical Medicine & International Health. 5 (4): 263–274. doi:10.1046/j.1365-3156.2000.00551.x. PMID 10810021.{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link)
  19. ^ Manga, L., Toto, J.C., Carnevale, P. (March 1995). "Malaria vectors and transmission in an area deforested for a new international airport in southern Cameroon". Societes Belges Medicine Tropicale. 75 (1): 43–49. PMID 7794062.{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link)
  20. ^ a b Duke, N. C.; Meynecke, J.-O.; Dittmann, S.; Ellison, A. M.; Anger, K.; Berger, U.; Cannicci, S.; Diele, K.; Ewel, K. C.; Field, C. D.; Koedam, N.; Lee, S. Y.; Marchand, C.; Nordhaus, I.; Dahdouh-Guebas, F. (2007). "A World Without Mangroves?". Science. 317 (5834): 41–42. doi:10.1126/science.317.5834.41b. PMID 17615322. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: date and year (link)
  21. ^ Gilman, E., Ellison, J., Duke, N.C.,Field, C. (2008). "Threats to mangroves from climate change and adaptation options". Aquatic Botany. 89 (2): 237–250. doi:10.1016/j.aquabot.2007.12.009.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  22. ^ Jennerrjahn, T.C., Ittekot, V. (January 2002). "Relevance of mangroves for the production and deposition of organic matter along tropical continental margins". Naturwissenschaften. 89 (1): 23–30. doi:10.1007/s00114-001-0283-x. PMID 12008969.{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link)
  23. ^ Dittmar, T., Hertkorn, N., Kattner, G., Lara, R.J. (2006). "Mangroves, a major source of dissolved organic carbon to the oceans". Global Biogeochemical Cycles. 20: 7. doi:10.1029/2005GB002570.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  24. ^ Spalding, M., Kainuma, M., Collins, M. (2010). World atlas of mangroves (PDF). p. 319.{{cite book}}: CS1 maint: multiple names: authors list (link)
  25. ^ Farley, J., Batker, D., Del la Torre, I., Hudspeth, T. (September 2009). "Conserving Mangrove Ecosystems in the Philippines: Transcending Disciplinary and Institutional Borders". Environmental Management. 45 (1): 39–51. doi:10.1007/s00267-009-9379-4. PMID 19830480.{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link)
  26. ^ a b Regunathan, C., Kitto, M.R. (2009). "Drugs from the indian seas-- More Expectations". Current Science. 97: 1705–1706.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  27. ^ Muhammad, Ashraf (May 2012). "Strategies for conservation of endangered ecosystems" (PDF). Pakistan Journal of Botany. 44 (Special Issue): 1–6. Retrieved 25 November 2012. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: date and year (link)
  28. ^ a b Hamilton, Alan (2006). "2". Plant Conservation: An Ecosystem Approach. London: Earthscan. pp. 37–39. ISBN 9781844070831.
  29. ^ a b c Mirsanjari, Mir Mehrdad (May 2012). "The role of biodiversity for sustainable environment". International Journal of Sustainable Development. 4 (3): 71–86. SSRN 2054975. Retrieved 25 November 2012. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: date and year (link)
  30. ^ a b c Laurance, William F (1 December 1999). "Reflections on the tropical deforestation crisis". Biological Conservation. 91 (2–3): 109–117. doi:10.1016/S0006-3207(99)00088-9.{{cite journal}}: CS1 maint: date and year (link)
  31. ^ Kaur, Amarjit (February 1998). "A History of Forestry in Sarawak". Modern Asian Studies. 32 (1): 117–147. doi:10.1017/S0026749X98003011.{{cite journal}}: CS1 maint: date and year (link)
  32. ^ Goroh, Eleanor. "Update 2011-Malaysia". International Work Group for Indigenous Affairs. Retrieved 26 November 2012.
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