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PubMed2002

[Forest and population at Península de Osa, Costa Rica].

The research is focused on the relationship between population growth and conservation of the forest on the Osa Peninsula. Data of the geo-referenced censuses and information on land-use, derived from satellite images and aerial photography, were integrated into a GIS. We undertook an historical inventory of the changes in the population and the forest coverage, and the key events in the land tenure and economy of the region. Deforestation, reforestation, and fragmentation of the forest during the period 1980-1995 were analyzed. Relationships with the population potential, derived from the 1984 Costa Rican censuses, were identified, and the effects of third variables were controlled such as distances to the roads, rain, distances to the forest frontier, level of protection, etc. Both strong and significant associations between 1984 population potential and the three processes were detected. The probability of deforestation is null in unpopulated areas, 35% in areas with 25-30 potential farmers and to 65% in areas with 50 farmers and over. The probability of reforestation decreases from 100% to 28% and to 18% in these three categories. This kind of relationship persists in the multivariable analysis. An increase of 0.63% in the number of household, results in an increment of 1% in the risk of deforestation (elasticity). The elasticity in the chances of reforestation is -0.37 and 1% in fragmentation of the forest. An evaluation in the risk of deforestation for the period 1995-2005 was done. The most recent population data were used and it identifies several geographic areas with high deforestation risk.

Conservation of Natural Resources↗
PubMed1991

Tropical forests: present status and future outlook.

Tropical forests still cover almost 8 million km squared of the humid tropics but they are being destroyed at ever-more rapid rates. In 1989, the area deforested amounted to 142,200 km squared, or nearly 90% more than in 1979. Thus, whereas the 1989 amounted total to 1.8% of the remaining biome, the proportion could well continue to rise for the foreseeable future, until there is little forest in just a few decades. Deforestati on patterns are far from even throughout the biome. In much of the Southeast and Southern Asia, East and West Africa, and Central America, there is likely to be little forest left by the year 2000 or shortly thereafter. But in the Zaire basin, western Brazilian Amazonia, and the Guyana highlands, sizeable expanses of forest could persist a good while longer. The main agent of deforestation in the 'shifted cultivator' or displaced peasant, who, responding to land hunger and general lack of rural development in traditional farming areas of countries concerned, feels there is no alternative but to adopt a slash-and-burn lifestyle in forestlands. This person is now accounting for at least 60% of deforestation, a rapidly expanding proportion. However, he receives far less policy attention than the commercial logger, the cattle rancher, and other agents of deforestation.

Africa↗
PubMed1990

"Ghana faces ecological disaster".

The rate of deforestation in Ghana is alarming and urgent steps need to be taken to reverse the trend, Robert D. Mann, a British tropical agriculturist, has warned. He says, "There will be further disintegration of the local climate, deterioration of soil fertility and reduced food-crop production, if the present trend of denudation by felling trees and uncontrolled bush fires is not halted and reversed." Mann, who has conducted research on "deforestation, drought and famine in Africa" was in Ghana recently to speak on the "role of the Church in West Africa in stimulating action to combat desertification". Representatives of protestant churches in Ghana, Togo, Liberia, Gambia, Nigeria, Cote d'Ivoire and Sierra Leone attended the 3-day conference which was organized by the Overseas Department of the British Methodist Church. It was to enable participants to share perspectives on the nature, scale and seriousness of the deforestation problem. Participants also exchanged experiences on village-based projects for promoting tree planting and agro-forestry, and developed strategies for the rural development programs. Robert Mann noted that Ghana was not only affected by its proximity to the Sahel, but also by its own deforestation. The situation in Ghana, once renowned for her extensive forests and woodland, has now drastically changed. By 1980/81 the area of closed forest had been reduced to 17,000 sq km from 47,9000 sq km in 1937/38. He said in 1939 the volume of wood exported from Ghana was 42,450 cubic meters but it rose to 1,471,600 cubic meters by 1987. Such activities, Mann said, put severe strain on the environment and affected both the economy and sociocultural basis of the country.

Africa↗
PubMed2005

Effects of climate and land use changes on groundwater resources in coastal aquifers.

To estimate the freshwater loss in coastal aquifers due to salinisation, a numerical model based on the sharp interface assumption has been introduced. The developed methodology will be useful in areas where limited hydrological data are available. This model will elaborate on the changes in fresh groundwater loss with respect to climate change, land use pattern and hydrologic soil condition. The aridity index has been introduced to represent the variations in precipitation and temperature. The interesting finding is that the deforestation leads to increase groundwater recharge in arid areas, because deforestation leads to reduce evapotranspiration even though it favors runoff. The combined climate and land use scenarios show that when the aridity index is less than 60, the agricultural lands give higher groundwater recharge than other land use patterns for all hydrologic soil conditions. The calculated recharge was then used to estimate the freshwater-saltwater interface and percentage of freshwater loss due to salinity intrusion. We found that in arid areas, the fresh groundwater loss increases as the percentage of forest cover increases. The combined effects of deforestation and aridity index on fresh groundwater loss show that deforestation causes an increase in the recharge and existing fresh groundwater resource in areas having low precipitation and high temperature (arid climates).

Agriculture↗
PubMed2005

Human modification of global water vapor flows from the land surface.

It is well documented that human modification of the hydrological cycle has profoundly affected the flow of liquid water across the Earth's land surface. Alteration of water vapor flows through land-use changes has received comparatively less attention, despite compelling evidence that such alteration can influence the functioning of the Earth System. We show that deforestation is as large a driving force as irrigation in terms of changes in the hydrological cycle. Deforestation has decreased global vapor flows from land by 4% (3,000 km(3)/yr), a decrease that is quantitatively as large as the increased vapor flow caused by irrigation (2,600 km(3)/yr). Although the net change in global vapor flows is close to zero, the spatial distributions of deforestation and irrigation are different, leading to major regional transformations of vapor-flow patterns. We analyze these changes in the light of future land-use-change projections that suggest widespread deforestation in sub-Saharan Africa and intensification of agricultural production in the Asian monsoon region. Furthermore, significant modification of vapor flows in the lands around the Indian Ocean basin will increase the risk for changes in the behavior of the Asian monsoon system. This analysis suggests that the need to increase food production in one region may affect the capability to increase food production in another. At the scale of the Earth as a whole, our results emphasize the need for climate models to take land-use change, in both land cover and irrigation, into account.

Agriculture↗
PubMed2006

Condition and fate of logged forests in the Brazilian Amazon.

The long-term viability of a forest industry in the Amazon region of Brazil depends on the maintenance of adequate timber volume and growth in healthy forests. Using extensive high-resolution satellite analyses, we studied the forest damage caused by recent logging operations and the likelihood that logged forests would be cleared within 4 years after timber harvest. Across 2,030,637 km2 of the Brazilian Amazon from 1999 to 2004, at least 76% of all harvest practices resulted in high levels of canopy damage sufficient to leave forests susceptible to drought and fire. We found that 16+/-1% of selectively logged areas were deforested within 1 year of logging, with a subsequent annual deforestation rate of 5.4% for 4 years after timber harvests. Nearly all logging occurred within 25 km of main roads, and within that area, the probability of deforestation for a logged forest was up to four times greater than for unlogged forests. In combination, our results show that logging in the Brazilian Amazon is dominated by highly damaging operations, often followed rapidly by deforestation decades before forests can recover sufficiently to produce timber for a second harvest. Under the management regimes in effect at the time of our study in the Brazilian Amazon, selective logging would not be sustained.

Biomass↗
PubMed2005

Tropical forest cover change in the 1990s and options for future monitoring.

Despite the importance of the world's humid tropical forests, our knowledge concerning their rates of change remains limited. Two recent programmes (FAO 2000 Forest Resources Assessment and TREES II), exploiting the global imaging capabilities of Earth observing satellites, have recently been completed to provide information on the dynamics of tropical forest cover. The results from these independent studies show a high degree of conformity and provide a good understanding of trends at the pan-tropical level. In 1990 there were some 1150 million ha of tropical rain forest with the area of the humid tropics deforested annually estimated at 5.8 million ha (approximately twice the size of Belgium). A further 2.3 million ha of humid forest is apparently degraded annually through fragmentation, logging and/or fires. In the sub-humid and dry tropics, annual deforestation of tropical moist deciduous and tropical dry forests comes to 2.2 and 0.7 million ha, respectively. Southeast Asia is the region where forests are under the highest pressure with an annual change rate of -0.8 to -0.9%. The annual area deforested in Latin America is large, but the relative rate (-0.4 to -0.5%) is lower, owing to the vast area covered by the remaining Amazonian forests. The humid forests of Africa are being converted at a similar rate to those of Latin America (-0.4 to -0.5% per year). During this period, secondary forests have also been established, through re-growth on abandoned land and forest plantations, but with different ecological, biophysical and economic characteristics compared with primary forests. These trends are significant in all regions, but the extent of new forest cover has proven difficult to establish. These results, as well as the lack of more detailed knowledge, clearly demonstrate the need to improve sound scientific evidence to support policy. The two projects provide useful guidance for future monitoring efforts in the context of multilateral environmental agreements and of international aid, trade and development partnerships. Methodologically, the use of high-resolution remote sensing in representative samples has been shown to be cost-effective. Close collaboration between tropical institutions and inter-governmental organizations proved to be a fruitful arrangement in the different projects. To properly assist decision-making, monitoring and assessments should primarily be addressed at the national level, which also corresponds to the ratification level of the multilateral environmental agreements. The Forest Resources Assessment 2000 deforestation statistics from countries are consistent with the satellite-based estimates in Asia and America, but are significantly different in Africa, highlighting the particular need for long-term capacity-building activities in this continent.

Conservation of Natural Resources↗
PubMed2003

Modeling the production and uses of biological resources from the viewpoint of energy flow in a rural village in Sichuan, China.

This study aimed at clarifying the impact of deforestation and afforestation on the quality of life in a village in Sichuan Province, China. We devised a conceptual model of bioresource production and use based on quantified energy flow. The basic structure of the model has three sectors: production, use, and externals. We developed comprehensive methodology to quantify the model. Bioresource use per person in 1997 was 3.7 GJ for food, 10.2 GJ for fodder, 0.2-0.4 GJ for building material, 12.8 GJ for fuel, and 1.8 GJ for fertilizer, totaling 28.6-28.8 GJ. We used four environmental indicators to evaluate bioresource production and use: a biological productivity indicator, a use-efficiency indicator, a supply-demand balance indicator, and a self-sufficiency indicator. Use of these indicators showed that supply-demand balance of fuel was dramatically improved from 30% to 85% by afforestation, but 99% of bioresource use still depends on domestic products. Thus, it is necessary to improve biological productivity and promote the efficient use of bioresources to achieve sustainable living in the area. Massive deforestation in the 1950s caused a direct shortage of building material and fuel wood. The shortage of wood led to a stagnation in the rebuilding of houses, and fuel wood was substituted with crop residues. Because crop residues had been used for fertilizer and fodder, their use as fuel caused a shortage of fertilizer and fodder. This was an indirect impact of deforestation on people's quality of life.

China↗
PubMed2007

Overview and forecast on forestry productions worldwide.

Our world is largely dependent upon the forestry productions. Through the exploitation of forest reserves, we manufacture various industrial products, furniture, and obtain fuel and energy. Forestry productions should be conducted without large-scale deforestation and environmental degradation. In present study we perform a review and forecast analysis on forestry productions worldwide, with the objectives of providing an insight into the trend for several types of forestry productions in the future, and providing referential data for sustainable forestry productions and environmental management. Polynomial functions are used to fit trajectories of forestry productions since 1961 and forecasts during the coming 20 years are given in detail. If the past pattern continues, world fibreboard production would dramatically grow and reach 224,300,000 +/- 44,400,000 m(3) by the year 2020, an increase up to 240.7 to 408.9% as compared to the present level. Roundwood production of the world would change by -55.5 to 70.4% and reach 3,526,600,000 +/- 2,066,800,000 m(3) by 2020. In 2020 world production of sawlogs and veneer logs would change by -100 to 164.6% and reach 1,212,900,000 +/- 1,242,600,000 m(3). Global wood fuel production would change by -68.9 to 1.4% and reach 1,130,900,000 +/- 600,800,000 m(3) by 2020. Forestry productions in developed countries would largely surpass productions in developing countries in the near future. World forestry production grew since 1961 excluding wood fuel. Roundwood and wood fuel account for the critical proportions in the forestry productions. Wood fuel production has being declined and rapid growing of roundwood production has slowed in recent years. Widespread use of regenerative wood substitutes and worldwide afforestation against deforestation will be among the most effective ways to reduce deforestation and environment degradation associated with forestry productions.

Conservation of Natural Resources↗
PubMed2005

Modelling the conversion of Colombian lowland ecosystems since 1940: drivers, patterns and rates.

In biologically mega-diverse countries that are undergoing rapid human landscape transformation, it is important to understand and model the patterns of land cover change. This problem is particularly acute in Colombia, where lowland forests are being rapidly cleared for cropping and ranching. We apply a conceptual model with a nested set of a priori predictions to analyse the spatial and temporal patterns of land cover change for six 50-100 km(2) case study areas in lowland ecosystems of Colombia. Our analysis included soil fertility, a cost-distance function, and neighbourhood of forest and secondary vegetation cover as independent variables. Deforestation and forest regrowth are tested using logistic regression analysis and an information criterion approach to rank the models and predictor variables. The results show that: (a) overall the process of deforestation is better predicted by the full model containing all variables, while for regrowth the model containing only the auto-correlated neighbourhood terms is a better predictor; (b) overall consistent patterns emerge, although there are variations across regions and time; and (c) during the transformation process, both the order of importance and significance of the drivers change. Forest cover follows a consistent logistic decline pattern across regions, with introduced pastures being the major replacement land cover type. Forest stabilizes at 2-10% of the original cover, with an average patch size of 15.4 (+/-9.2)ha. We discuss the implications of the observed patterns and rates of land cover change for conservation planning in countries with high rates of deforestation.

Agriculture↗
PubMed1998

The geochemistry of mercury in central Amazonian soils developed on the Alter-do-Chão formation of the lower Tapajós River Valley, Pará state, Brazil.

In an oxisol-spodosol system developed on the terrestrial surface of the lower Tapajós Valley, the determination of total mercury (Hg), organic carbon (C), iron and aluminum oxy-hydroxide (Fe(cdb) and Al(cdb)) concentrations in the surface soil horizons are used to characterise the geochemical processes controlling the accumulation of Hg in soils under natural vegetation cover and in deforested and cultivated sites. Oxisols from the plateau have homogeneous and relatively high background Hg contents and burdens constituting an important natural reservoir of Hg for the region (90-210 ng/g dry wt. and 19-33 mg/m2 for the first 20 cm). The Fe(cdb) and Al(cdb) contents associated with the fine fraction (< 63 microns) of the soil suggest that oxy-hydroxides and, particularly Al-substituted Fe oxy-hydroxides, control the Hg concentrations observed in all of the soils of the study region. Consequently, the geochemistry of these minerals along the slopes governs the accumulation or the release of the Hg according to the natural evolution of the soil cover and/or following the degradation of soils by erosion after deforestation and cultivation. These observations have important implications for the interpretation of Hg contamination patterns observed in Amazonian aquatic systems that could be linked to different drainage sources of Hg from the terrestrial surface. The sandification and podzolisation that is characteristic of the evolution of numerous pedological systems in the equatorial Amazon could be responsible for exportation of the naturally accumulated Hg, as for other metals, by acidic complexation and migration to the black waters of the Amazon. In the central Amazon region, as a result of the fragility of the soil cover, deforestation and cultivation, affecting principally the superficial soil, promote the selective erosion of fine particles enriched in oxides and Hg. The erosion of soil could be responsible for an important release of Hg, transported in particulate form by drainage waters.

Aluminum↗
PubMed2005

Survivorship of Anopheles gambiae sensu stricto (Diptera: Culicidae) larvae in western Kenya highland forest.

The western Kenya highland has been experiencing dramatic landuse changes in the past three decades. Landuse change has been hypothesized to be one of the mechanisms for malaria epidemics in African highlands because it can alter the physical and chemical characteristics of mosquito breeding habitats. One important landuse change in western Kenya highland is deforestation. The current study examined the effects of forestation or deforestation on the survivorship of Anopheles gambiae larvae and colonization of other aquatic insects in larval habitats in Kakamega forest (elevation 1,500-1,700 m above sea level), western Kenya. We found that the survivorship of An. gambiae larvae was reduced from 55 to 57% in habitats fully exposed to sunlight (open habitats) to 1-2% in habitats with full forest canopy coverage (forest habitats) and partial canopy coverage (forest edge habitats) in two out of three trials. The average daily water temperature of the open habitats was approximately 3-3.4 degrees C higher than the forest habitats. Insect species in the orders of Diptera, Coleoptera, and Odonata colonized the larval habitats, but the three habitat types differed greatly in the animal assemblage. Canonical correspondence analysis found that water temperature and amount of leaf litter were the significant variables associated with animal assemblages. Redundancy analysis revealed that openness and the presence of predatory animals were significantly related to An. gambiae survivorship. This result suggests that deforestation facilitates the survival of the immature stage of An. gambiae in the highland.

Animals↗
PubMed2006

Land use change effects on forest carbon cycling throughout the southern United States.

We modeled the effects of afforestation and deforestation on carbon cycling in forest floor and soil from 1900 to 2050 throughout 13 states in the southern United States. The model uses historical data on gross (two-way) transitions between forest, pasture, plowed agriculture, and urban lands along with equations describing changes in carbon over many decades for each type of land use change. Use of gross rather than net land use transition data is important because afforestation causes a gradual gain in carbon stocks for many decades, while deforestation causes a much more rapid loss in carbon stocks. In the South-Central region (Texas to Kentucky) land use changes caused a net emission of carbon before the 1980s, followed by a net sequestration of carbon subsequently. In the Southeast region (Florida to Virginia), there was net emission of carbon until the 1940s, again followed by net sequestration of carbon. These results could improve greenhouse gas inventories produced to meet reporting requirements under the United Nations Framework Convention on Climate Change. Specifically, from 1990 to 2004 for the entire 13-state study area, afforestation caused sequestration of 88 Tg C, and deforestation caused emission of 49 Tg C. However, the net effect of land use change on carbon stocks in soil and forest floor from 1990 to 2004 was about sixfold smaller than the net change in carbon stocks in trees on all forestland. Thus land use change effects and forest carbon cycling during this period are dominated by changes in tree carbon stocks.

Agriculture↗
PubMed2004

Land-use systems and resilience of tropical rain forests in the Tehuantepec Isthmus, Mexico.

Land-cover types were analyzed for 1970, 1990 and 2000 as the bases for determining land-use systems and their influence on the resilience of tropical rain forests in the Tehuantepec Isthmus, Mexico. Deforestation (DR) and mean annual transformation rates were calculated from land-cover change data; thus, the classification of land-use change processes was determined according to their impact on resilience: a) Modification, including land-cover conservation and intensification, and b) Conversion, including disturbance and regeneration processes. Regeneration processes, from secondary vegetation under extensive use, cultivated vegetation under intensive use, and cultivated or induced vegetation under extensive use to mature or secondary vegetation, have high resilience capacity. In contrast, cattle-raising is characterized by rapid expansion, long-lasting change, and intense damages; thus, recent disturbance processes, which include the conversion to cattle-raising, provoke the downfall of the traditional agricultural system, and nullify the capacity of resilience of tropical rain forest. The land-use cover change processes reveal a) the existence of four land-use systems (forestry, extensive agriculture, extensive cattle-raising, and intensive uses) and b) a trend towards the replacement of agricultural and forestry systems by extensive cattle-raising, which was consolidated during 1990-2000 (DR of evergreen tropical rain forest = 4.6%). Only the forestry system, which is not subject to deforestation, but is affected by factors such as selective timber, extraction, firewood collection, grazing, or human-induced fire, is considered to have high resilience (2 years), compared to agriculture (2-10 years) or cattle-raising (nonresilient). It is concluded that the analysis of land-use systems is essential for understanding the implications of land-use cover dynamics on forest recovery and land degradation in tropical rain forests.

Agriculture↗
PubMed2006

A GIS-based assessment on the vulnerability and future extent of the tropical forests of the Congo Basin.

This paper examines the vulnerability of the Congo Basin's forests through a GIS platform, taking into consideration the variables of population growth, road density, logging concession, and forest fragmentation. The assessment indicates that the forests will continue to shrink towards the interior over the next 50 years. Current contiguous forests will fragment into three large blocks, including one on the west side of the Congo River and two in the Democratic Republic of Congo, while a large number of small forest patches will retain in the periphery of the large blocks. The study shows that integrated GIS assessment of the driving forces of tropical deforestation can shed light on the future forest distribution and provide a tool to address the broader implications of social and economic development for tropical deforestation.

Africa, Central↗
PubMed1994

Effects of pre-industrial human activities on climate.

Pre-industrial human activities which changed the atmospheric greenhouse gas or aerosol loading, or which modified the properties of the earth's surface, such as albedo, roughness, or vegetation cover, had the potential to modify the regional or even global climate. The primary activities which could have produced these effects were deforestation, burning, and agriculture. These activities were not independent, and often occurred together. Deforestation could have produced warming or cooling at the surface, and different effects on different scales, depending on the fate of the biomass removed and the new use of the land. Burning is much less now than it was in the past in some regions, which would have produced warming as the burning decreased. This may be a partial explanation for the Little Ice Age. While a thorough survey of such pre-industrial human activities is called for, current information indicates that regional climatic effects were large in some regions, such as western North America, and hemispheric or global effects were possible. Once these pre-industrial human climatic forcing factors are better quantified, existing numerical models of the climate can be used to examine the impacts on regional and global scales.

Agriculture↗
PubMed2006

Effects of land-use change on deposition and composition of organic matter in Frickenhauser See, northern Bavaria, Germany.

Characterization of bulk organic matter (OM) from lacustrine sediments of Frickenhauser See (northern Bavaria, Germany) reveals considerable variation during the last two millennia. Atomic C/N ratios and total organic carbon (TOC) content are positively correlated with arboreal pollen percentages which are used as an indicator of land-use intensity. Despite possible alterations of OM during early diagenesis, differences between three major lithological units are large enough to be interpreted as human impact on the sedimentation of OM in the lake. Sediments deposited prior to deforestation in the catchment area (unit C) are characterized by mean C/N ratios of 14.5, indicating a mixed composition of organic matter derived from lacustrine and terrestrial sources (forest litter). During a period of intensive soil erosion (ca. 1000 AD until 1870 AD; unit B), low C/N ratios of around 7.7 suggest that the relative proportion of forest litter decreased in favour of the lacustrine component and soil OM. Terrestrial plant detritus is only transported into the lake through numerous turbidite events. Deforestation and agriculture also coincide with a decreasing TOC content from an average value of 10.7% to 1.5%. This decrease is explained through a dilution effect due to the high input of minerogenic matter. Stable carbon isotopes indicate eutrophication of the lake due to the mobilization of nutrients through soil erosion. Starting around 1870 AD, organic-rich sapropelic sediments are deposited (unit A). A decline of turbidite events and increased wind shelter from trees due to reduced land-use intensity led to meromictic conditions. Consequently, negative excursions in the delta13C isotope record at the onset of unit A probably reflect methanogenesis under permanently anoxic conditions.

Carbon↗
PubMed2005

Tropical forests in a changing environment.

Understanding and mitigating the impact of an ever-increasing population and global economic activity on tropical forests is one of the great challenges currently facing biologists, conservationists and policy makers. Tropical forests currently face obvious regional changes, both negative and positive, and uncertain global changes. Although deforestation rates have increased to unprecedented levels, natural secondary succession has reclaimed approximately 15% of the area deforested during the 1990s. Governments have also protected 18% of the remaining tropical moist forest; however, unsustainable hunting continues to threaten many keystone mammal and bird species. The structure and dynamics of old-growth forests appear to be rapidly changing, suggesting that there is a pantropical response to global anthropogenic forcing, although the evidence comes almost exclusively from censuses of tree plots and is controversial. Here, I address ongoing anthropogenic change in tropical forests and suggest how these forests might respond to increasing anthropogenic pressure.

Journal Article↗