Deforestation local

Over virgin tropical forests, about 75% of incoming solar radiation is spent on evapotranspiration. Therefore, WTF deforestation will result in radical changes in energy exchange and global atmospheric circulation. Still more substantial will be changes in local climate, especially from the viewpoint of the rain rate which could decrease by as much as 65%. Another problem is that we still do not know the threshold level for WTF destruction. This level determines an ecosystem s ability to self-support. If, for instance, this level is 20%, then the threshold has already been exceeded. 

The use of locally mined, high-arsenic (>100 ppm) coals has caused arsenic poisoning in several villages in Guizhou Province, China (Fig. 17.2 Zhou et al, 1993). Although coal has been produced and used in this area for 100 years, only with the increase in population and subsequent deforestation have some villages and... 

To give an idea of how large a forest would need to be in order to supply such vast quantities of wood, let us assume a yield of 325 cord per acre, which for 515,000 trees would require a forest of 1,590 acres, or just short of 2.5 square miles. To put it more graphically, such a forest would have been 2.5 miles long and 1 mile wide. Is it really conceivable that the witnesses and the local residents could have failed to notice such a large deforested area The site would still be apparent today. 

Henderson-Sellers, A., R. Dickinson, T. Durbidge, P. Kennedy, K. McGuffie, and A. Pitman. 1993. "Tropical deforestation modeling local to regional scale climate change." Journal of Geophysical Research 98 7289-7315. 

Walker, G., Y. Sud, and R. Atlas. 1995. "Impact of the ongoing Amazonian deforestation on local precipitation A GCM simulation study." Bulletin American Meteorological Society 76 346-361. 

The relative magnitudes of the fluxes described in equation (2) can be compared graphically in Fig. 8.1. Although the erosion flux may be important on a local basis, it probably represents more a redistribution of carbon between the terrestrial and fluvial systems than a flux to the atmosphere. The dominant gas flux is from deforestation. Consequently, land uses that maintain forest cover and/or reduce the deforestation rate will have a major impact on the anthropogenic fluxes, thereby affecting the total... 

Fig. 8.2. Landsat TM image of the central portion of the Chico Mendes Extractive Reserve in eastern Acre, Brazil. The white line outlines the boundary of the reserve. North is to the top of the image, which covers about 90 km x 90 km. Xapuri is the local urban center. The light areas are deforested lands, principally large cattle ranches. The national highway BR-317 threads through the center of the deforested lands along the eastern side of the image. Data is from August 1989, TM bands 3, 4, and 5.

Reduced local precipitation could have severe effects in central Amazon, where there is already a distinct dry period. If a relatively small reduction in annual rainfall resulted in an extension of the dry period there could be serious consequences. Fearnside (1982) noted that in Manaus in 1979 there was a period of 73 days without rain. If this became common, then inevitably there would be marked ecological changes. There have been a number of attempts to model the effect of Amazon deforestation on precipitation and temperature, and we have recently reviewed them (Salati and Vose, 1983b and c), and concluded that the Henderson-Sellers (1981) suggestion of a decrease in rainfall of 600 mm yr" , and a small temperature increase is most valid of the current predictions. 

More data from remote sensing of general weather patterns, better and more detailed information of water vapour circulation patterns at local level, and improved modelling studies should eventually remove some of the uncertainty. In the meantime, the likelihood of at least local disruption of hydrological cycles seems sufficiently great that a conservative approach to tropical deforestation seems highly desirable. 

Graham, M. (2004). Effects of local deforestation on the diversity and structure of Southern California giant kelp forest food webs. Ecosystems 7, 341—357. 

A full appreciation of the toll of forced resettlement in Ethiopia extends far beyond the standard reports of starvation, executions, deforestation, and failed crops. The new settlements nearly always failed their inhabitants as human communities and as units of food production. The very fact of massive resettlement nullified a precious legacy of local agricultural and pastoral knowledge and, with it, some thirty to forty thousand functioning communities, most of them in regions that had regularly produced food surpluses. 

Vegetation and animal activity in soils play important roles in generating macropores, which locally focus recharge into the karst aquifer (e.g. Beven and Germann, 1982 Tooth and Fairchild, 2003). A reduction in evapo-transpiration by local deforestation could lead to an increase in seepage water in caves, which might be recognisable in palaeostudies by carbon isotope evidence. 

Werth, D. and Avissar, R. (2005) The local and global effects of African deforestation, Geophys. Res. Lett. 32(12), LI2704 (doi 10.1029/2005GL022969). 

---