Deforestation

W. DeForest, Photoresist Materials andProcesses, McGraw-HiU, New York, 1975. 

Human activity, particularly in the developing world, continues to make it more difficult to sustain the world s biomass growth areas. It has been estimated that tropical forests are disappearing at a rate of tens of thousands of hm per year. Satellite imaging and field surveys show that Brazil alone has a deforestation rate of approximately 8 x 10 hm /yr (5). At a mean net carbon yield for tropical rain forests of 9.90 t/hm yr (4) (4.42 short ton /acreyr), this rate of deforestation corresponds to a loss of 79.2 x 10 t/yr of net biomass carbon productivity. 

The manufacture of sugar was early understood to be an energy-intensive process. Cuba was essentially deforested to obtain the wood that fueled the evaporation of water from the cane juice. When the forests were gone, the bagasse burner was developed to use the dry cane pulp, called bagasse, for fuel. Bagasse was no longer a waste product its minimal value is the cost of its replacement as fuel. 

M. Klein and A. Deforest, Proc. Chem. Spec. Mfg. Assoc. 49th MidyearMtg, 1963, pp. 116—118. 

Runoff Water running down slopes rather than sinking in (again, result of poor humus content) Ex. erosion due to deforestation... 

The monograph by DeForest (1975) on photoresists is comprehensive, but does not cover the significant technological developments that have taken place since the mid-70s. More recent work has been discussed by Thompson et al. (1983) and by Turner and Daly (1989). 

A Semi-quantitative Approach Erosion and Deposition. Over the centuries the primary impact of human activity has been to deforest the surrounding countryside and increase the rate of erosion and deposition into rivers. This results primarily from the destruction of vegetation cover which stabilizes soil systems on gradient. The ecological impact of erosion has at present reached catastrophic proportions. The magnitude of continental erosion into rivers is illustrated in Figure 3. 

The nutrition needs of the future will be met with more limitations than in the past on the use of energy and restrictions on contamination of the environment. The maintenance of natural resources will receive much more attention than in the past. Concerns will increase regarding desertification, deforestation, urbanization, salinification, soil and water degradation, and atmospheric pollution. There is considerable difficulty in delineating these limitations, particularly as one considers the responsibilities and interests of developed and developing countries. The role of economics offers an additional challenge in working out these relationships. 

Introduction The Global Extent of Deforestation and Biomass Burning... 

Accurate estimates of deforestation on a global scale are largely unavailable, if not impossible, to ascertain. Since preagricultural times, temperate... 

Land use changes in the tropics have resulted in a landscape characterized as a mosaic of logged forests, cleared fields, and successional forests. This results in the transformation from extremely fire resistant rainforest ecosystems to anthropogenic landscapes in which fire is a common event (16, 17), Fires occur in disturbed tropical forests because deforestation has a dramatic effect on microclimate. Deforestation results in lower relative humidities, increased wind speeds, and increased air temperatures. In addition, deforestation results in increased quantities of biomass that are susceptible to fire. This biomass may be in the form of forest slash, leaf litter, grasses, lianas or herbaceous species (16, 18). 

Abusive forest practices are neither a recent phenomenon nor limited to developing tropical countries. Deforestation has brought about economic and social declines of civilizations for over 5,000 years 19). Postel and Ryan (1) estimated only 1.5 million ha of primary forests remain out of the 6.2 biUion ha... 

Deforestation, Biomass Burning and the Biogeochemical Balance of Forests... 

Figure 1. Generalized nutrient balance of ecosystems in the intervals between disturbance events. Natural disturbances such as wildfires, hurricanes, and floods as well as anthropogenic disturbances such as deforestation and biomass burning can dramatically influence nutrient inputs, internal cycles, and ecosystem outputs (losses).

Biomass Redistribution Associated with Deforestation and Fire. The influence of deforestation on biogeochemical cycles is dependent upon a number of factors associated with the unique characteristics of the ecosystem (climate, soils, topography, etc), the quantity of the total nutrient pool stored in aboveground biomass (Table II), and the level of disturbance (i.e. the degree of canopy removal, soil disturbance, and the quantity of wood or other forest products exported from the site). The quantity of biomass consumed by one or more slash fires following deforestation can also dramatically increase nutrient losses, influence post fire plant succession, and hence, postfire biogeochemical cycles. 

Figure 2. The carbon dynamics of a primary forest prior to and following deforestation and slash burning. Arrows represent the relative magnitude of C flux. In the primary forest (represented by the large box at the top of the figure), the C pool is in a dynamic equilibrium with inputs approximately equalling exports. With deforestation and fire, the balance is altered with exports far exceeding imports.

The maximum temperature and duration of heating during fires are important variables that influence the soil nutrient status, as well as the survival of residual vegetation following fire (Table III). Deforestation results in the presence of large quantities of wood debris in close proximity to the soil surface. Fires in this scenario result in soil temperatures and magnitudes of heat flux far in excess of those which occur in fires in uncut forests (Shea, R. W. Oregon State University, unpublished data). 

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