|DISforME||DISforME Homepage | DESERTLINKS Homepage | © DESERTLINKS 2004|
|Desertification Indicators System for Mediterranean Europe|
g Description of reasons for deforestation and why it is an issue in the context of desertification.
Introduction. A large area of the Earth's land surface is covered by forests, a very valuable resource to human populations, biodiversity, edaphic conditions, water storage, and the condition of the atmosphere. Human populations originally used forests only for timber, for shelter, as fuel for burning, and for other food- products. At that time the forests were used in a sustainable way, without excessive threat of extinction through over-exploitation. From these early times of the forest being used as a resource for people to modern times there has been a huge increase in the amount of timber being harvested daily, for a number of reasons such as:
Now forests are threatened by factors such as climatic hazards, diseases prompted by insects or pathogens, threats of a purely anthropogenic nature, fires, atmospheric pollution, deforestation and the increase in social pressure. Man is partly responsible for most of these threats. Indeed the mark of human actions is always present: it is relatively moderate concerning climatic disorder despite the emissions of greenhouse gases, responsible for important destructions; it is average in the sensitive growth of certain artificial forestry stands prone to parasitic attacks; it is preponderant in the phenomena of atmospheric pollution or of deforestation.
The estimated rates of global deforestation are astonishing. According to the World Resources Institute (http://pubs.wri.org/pubs_content.cfm?PubID=3018), more than 80 percent of the Earth's natural forests have already been destroyed (at a rate of about 40 million hectares per year). Up to 90 percent of West Africa's coastal rain forests have disappeared since 1900. Brazil and Indonesia, which contain the world's two largest surviving regions of rain forest, are being stripped at an alarming rate by logging, fires, and land-clearing for agriculture and cattle-grazing. Loss of habitats is among the obvious consequences of deforestation. (seventy percent of the Earth's biodiversity is present in forests. Rain forests help generate rainfall in drought-prone countries elsewhere. Studies have shown that destruction of rain forests in such West African countries as Nigeria, Ghana, and Côte d'Ivoire may have caused two decades of droughts in the interior of Africa. (http://pubs.wri.org/pubs_content.cfm?PubID=3018).
Deforestation may have catastrophic global effects as well. Trees are natural consumers of carbon dioxide-one of the greenhouse gasses whose build up in the atmosphere contributes to global warming. Destruction of trees not only removes these "carbon sinks," but tree burning and decomposition pump into the atmosphere even more carbon dioxide, along with methane, another major greenhouse gas.
Climatic conditions. Slightly more than one-half of the world's climates are classified as arid and semi-arid. Further sub-division of the arid and semi-arid areas is loosely defined. Generally speaking, deserts receive 100 mm or less of rainfall, arid lands receive between 100 and 300 mm and semi-arid, with the following classification:
Although all climatic areas are subject to desertification, the arid and semi-arid areas in general and the arid areas in particular, are highly susceptible, because they are only a few millimetres of rain away from being true deserts.
Weather Fluctuations. Arid and semi-arid areas have harsh climates made more hard by weather fluctuations. There are normally many more years of below average rainfall than average or above. Prolonged droughts occur frequently. Droughts occur so frequently in northeast Brazil, for example, that the area is called the drought polygon. Weather variation, per se, does not cause desertification, but it is an accelerator to desertification, especially when man continues land uses supportable only by average or above average rainfall. Failure to plan for the "bad" years and modify land use accordingly accelerates the desertification process. Although droughts increase the rate of land degradation, they are not the cause, nor does desertification have a direct relation to a nearby desert. Soil degradation may begin in any cultivated field.
All these microclimate changes also bring about ecological changes too. The ecosystem is being altered, in most cases adversely. Hence, these processes result not only in a loss of biological productivity but also in the degradation of surface microclimates. Phenomena such as global warming and the greenhouse effect, which have their origin in deforestation and desertification, among many other causes, are more serious, global in scope, and therefore potentially more threatening.
Drought tolerance of forests. Forests cover more than 30 per cent of the Earth's surface. They range from dry scrubby thickets in the African savannah to moist, dense tropical rainforests; from mangroves at the water's edge to hardy conifers on mountain tops. Each forest type has its own kind of trees which are best suited to the local climate. There are three broad types of forests in the world: Boreal, Temperate, Tropical.
The distribution of vegetation is controlled by several factors (regional climate, topography, soil parent material, time and organisms). However, at the broadest scale, the scale of biomes, global climate patterns are the primary factor determining the structure and distribution of vegetation. Aspects of climate that exert strong control over vegetation are temperature, precipitation, humidity, solar radiation, and wind. Each of these affects plant physiology directly (through effects on photosynthesis and respiration) or indirectly (through effects on nutrient availability via decomposition and soil development).
Drought is a crucial factor in the survival and growth of trees, especially in dry season areas. In recent decades, forest decline in several forest tree species has been attributed to recurrent droughts. Better adaptation of forest trees is important both for improved growth and because of the danger of climate change (it is likely that plant communities will - as a result of higher temperatures - have to face more severe drought conditions in the future).
Most plants, and particularly tree species, since they are so long-lived, are exposed to drought during their lifetime. In order to minimize the impact, and during severe drought, plants must have mechanisms in place to cope with the drought.
CO2 affects the sensitivity of trees to drought. An increase in CO2 content in the atmosphere reduces stomatal aperture, orifices found on the leaf surface by which plants absorb CO2 and release water vapour. This effect varies greatly from one species to another. In certain species, such as oak, the reduction in stomatal aperture is considerable, and this reduces water losses via leaf transpiration in the tree, and should thus reduce sensitivity to drought. In other species, such as maritime pine or beech, this "anti-transpiration" occurs to a lesser extent, or even not at all.
Forest destruction by fire. Every year, millions of hectares of the world's forests are being consumed by fires, resulting in billions of dollars in fire suppression costs as well as causing tremendous damage to the environment. The ecological and environmental impacts of forest fires are manifested in the degradation of the quality of vegetation, erosion of biodiversity, damage to the health of forest ecosystems, loss of wildlife habitat, air, river and estuarine pollution and overall ecological retrogression. Forest fires contribute to global climate change and warming. Biomass burning also destroys an important sink for atmospheric carbon. So fire is a factor reducing woods and accelerating soil deterioration, thus increasing hazards of desertification.
On average, only about 8-10% of the heat generated during a forest fire is radiated downward to the forest floor (Wells et al. 1979, DeBano et al. 1976, Raison et al. 1986, Steward 1989, Hungerford 1989). Yet this heating is responsible for all of the direct changes in physical and chemical soil properties caused by forest fire. Organic matter is destructively distilled into hydrocarbons between 175 °C and 315 °C (DeBano 1976). Hydrocarbons are vaporized at 300 °C and move downward precipitating around soil particles at the interface where soil temperatures are cooler. This waxy coating is water repellent, slowing infiltration. Water repellence may last from weeks to some years (Baker 1989, DeBano 1979).Overland flow from these areas can trigger rill erosion and mass erosion., thus inducing degradation and further processes which lead to desertification.
After low-severity fires, recovery to pre-fire conditions may take only as long as necessary for soil biota to re-establish and surface organic matter to re-accumulate. The changes listed above - especially the loss of organic matter from above and below ground - affect the chemical and physical nature of forest soil with consequences for post-fire regeneration as well as post fire water yield and soil loss via erosion. Following a severe fire, increased surface runoff during storms enhances the potential for surface erosion and shallow landslides, especially on sites in which roots and other organic structures that hold loose material on slopes were consumed or killed (Bitterroot National Forest 2000). Large, severe fires pose greater risks of erosion until vegetation cover develops and litter begins to accumulate. On slopes with scarce protective vegetation cover and debris after fire, soil can erode even without heavy rains, due to the sheer force of gravity.
Forest productivity. Maintaining the health and productivity of forest ecosystems is an important prerequisite to sound stewardship and the sustainable development of forested lands. Slow productivity of forests means reduced amount of biomass, consequently a forest cover less resistant and more prone to irreversible transformations. Forests have been, and continue to be, exposed to a broad range of natural and human-caused stressors. Natural stressors include weather extremes, forest insects and pathogens and catastrophic events. Human-caused stressors include activities such as land use change; improper or not sustainable timber harvesting practices; road building, which reduce the capacity of the site to persist as productive forest land; introduction of exotic pests and air pollution.
Altered ecological conditions caused by human activities or climate change can increase the susceptibility of forests to natural stressors such as drought, changes in the water table, pest epidemics and wildfires. The interaction of human stressors and natural stressors can accelerate the deterioration of forest health. The proximity of settlements and structures to forested land creates management challenges including those related to fire. Forest health problems that reduce the resiliency of forests' resiliency or that reduce the capacity of forests to support the needs of people and society should be addressed as strategic issues in forest management.
The increasing importance of forests make forest health efforts more timely and critical than ever before. But for forests to perform their vital environmental functions and to realize their enormous productivity potential, means that they must be managed. Silvicultural measures must be taken to improve the health of forests stands, to stimulate their production and to avoid the causes of poor stand health, in order to prevent the action of secondary organisms. The maintenance of species diversity and stand types is equally important for an efficient fight against biotic threats. Proper forest management technologies should be used more widely as the first steps in moving from merely exploitative logging to sustainable forest use. Although there are many unanswered questions about truly sustainable silvicultural systems for forests, there are many well-known practices that can be employed more extensively which could improve forest management and reduce the degradation of forests and their susceptibility to deforestation.
A recent assessment on the forest sector has provided an overview of gaps and priorities for promoting sustainable forest management and development. The following orientations have been highlighted: promotion of multifunctional objectives; strengthening of links between short-term and long-term strategies; monitoring based on criteria and indicators; promoting and motivating forest owners, forest enterprises and forest marketing; improving public administration; support to diversification of forest enterprises activities; strengthening of research, training and communication (EOFM, 2000).
The impact of grazing. Domestic animals reduce regeneration through overgrazing, browsing, and trampling. Large vertebrate herbivores are supposed to be an important structuring agent in terrestrial food chains, through their impact on plant diversity and plant nutritional value. In low productive systems, sustained heavy grazing by large vertebrates may change interplant relationships, e.g. inter-specific plant competition for light and nutrients and disturb important ecological processes such as the soil-plant nutrient cycle. Vertebrate grazing or browsing has, therefore, the potential to change biodiversity. In more productive systems, grazing may increase plant species richness by removing strong competitors, thus giving space for the growth of less competitive species. In contrast, in low productive systems, such as many alpine areas and on the arctic tundra, intense grazing can reduce plant species richness and species diversity. The ecological impact of ungulate grazing is not only determined by the productivity of the system, but also by the type of grazer, the degree of herbivory and the grazing history.
Overgrazing is often blamed for worldwide desertification, which is partly true and partly false, depending on the situation. It depends certainly on overgrazing intensity (such as slight, heavy, very heavy and destructive) and also overgrazing duration, which can be measured in months, years, decades or even centuries. Apart from prolonged droughts, acceptable and fixed stocking rates will cause temporary overgrazing in some years because of grazing capacity fluctuations. Damage to the vegetation, if any, is usually repaired by natural processes. Stocking rates and managerial systems that result in continual destructive grazing are a major cause of desertification on rangelands. The desertification process is accelerated when these practices are maintained during drought and certain seasons where plants are highly vulnerable to abuse. While it takes a long time, this will eventually result in desertified rangelands. Destructive grazing also causes poor livestock performance and many private landowners have learned this lesson. It is, therefore, not as common on private lands as it is on public or community grazing lands, where central control is lacking.
Role of forest management. The role of forest management is to maintain on appropriate enhancement of forest resources and encouragement of productive functions of forests (wood and non-wood). Forest management practices safeguard the quantity and quality of the forest resources in the medium and long term by balancing harvesting and growth rates and by preferring techniques that minimise direct or indirect damage to forest, soil or water resources. Appropriate silvicultural measures maintain the growing stock of resources at - or bring to - a level that is economically, ecologically and socially desirable. Forest management practices make the best use of natural structures and processes and use preventive biological measures wherever and as far as economically feasible to maintain and enhance the health and vitality of forests. Adequate genetic, species and structural diversity should be encouraged and/or maintained to enhance stability, vitality and resistance capacity of the forests to adverse environmental factors and strengthen natural regulation mechanisms.
The principal aim of forest management planning is:
Things going on in the wider world. Deforestation is the product of the interaction of the many environmental, social, economic, cultural, and political forces at work in any given region. In most cases, deforestation is a process that involves a competition amongst different land users for scarce resources, a process exacerbated by counter-productive policies and weak institutions. It creates wealth for some, causes hardships for others, and almost always brings serious consequences for the environment. Deforestation is an important contributor to global warming, however, its contribution relative to the other factors is not precisely known. The principal cause of global warming is the excessive discharges in industrialised countries of greenhouse gases, mostly from the burning of fossil fuels. It is thought that an additional 2,000 million tons or about 25 percent of the total carbon dioxide emissions are a consequence of deforestation and forest fires (WCFSD, 1997). At the regional level, deforestation disrupts normal weather patterns, creating hotter and drier weather.
Any effort to combat deforestation must be based on a complete understanding of who the agents of deforestation are and what its direct and underlying causes are. While forests will continue to be lost for decades to come, it is critically important that the fight against deforestation be done in the most rational way possible. Through improved protection and management of the remaining forests, through well-targeted socioeconomic development programs, and through policy and institutional reforms; deforestation can be brought under control (http://www.rcfa-cfan.org/english/issues.12-9.html).
Impact of human population. Rapid growth of the population and societies and increased demand for higher standards of living has brought about increased exploitation of the earths natural resources, which in turn has led to rapid destruction of the landscape. It is evident that through history mankind has put added stress on the land, starting from use of fire by prehistoric man in Palaeolithic times accidentally and intentionally burning large areas of forest for settlement and agriculture. (Pickering and Owen, 1997). Human impact on the land including clearance of natural vegetation, for settlement, urbanisation, reservoirs, mineral extraction, agriculture and tourism has led to a series of problems including:
Deforestation and a change in erosion risk. Deforestation in hilly areas often leads to decreased infiltration of water and consequently higher runoff and increased peak water discharges following rainfall events and reduced runoff during dry seasons. Most importantly, it results in increased soil erosion, gully and ravine formation, flooding risk, and siltation of reservoirs and irrigation schemes. For instance, deforestation in the Himalayas has been associated with a doubling in torrent width since 1990-and a downstream cost of more than US$1 billion (Government of India, 1983). Aforestation of denuded hilly land could reduce peak runoff; lessen the risk of flooding; conserve soils and prevent severe siltation, gully formation, and landslides. In experimental work, up to 500-fold differences in erosion rates between forest and cultivated cropland have been recorded (Maass et al., 1988). The presence of forest litter is critically important in facilitating infiltration rates and preventing soil/sediment movement by overland flow. Forests generally are expected to use more water (the sum of transpiration and evaporation of water intercepted by tree canopies) than crops, grass or natural short cycle vegetation. This effect may be related to increased interception loss - especially if tree canopies are wet for a large proportion of the year (Calder, 1990)- or, in drier regions, to trees' greater root system, which allows water extraction and use during prolonged dry seasons.
The Agri Basin, Italy . The Agri valley is one of the biggest hydrographic basins in the Basilicata Region of southern Italy. It follows a NW-SE direction extending from the eastern sector of the Lucanian Apennine Chain to the Ionian Sea (Ferrara et al., 1996). The Agri basin can be divided into three homogenous sub-areas (upper, middle and lower valley). These areas were identified by their physical-environmental characteristics as well as their socio-economic and demographic features. This division was also confirmed by the pattern of human settlements and land use.
The upper part of the Agri Basin is characterized by numerous slopes and cultivated terraces. It is well endowed with woods and vegetation that prevent and reduce the risk of erosion. Therefore, landslides are quite limited and localized (e.g. the municipality of Montemurro). Agriculture is characterized by specialized crops, such as fruit orchards and corn.
A key to the interpretation of land use change may be provided by the analysis of the interventions carried out on the territory in the last 60 years. The 1950s were characterised by the first initiatives of the special intervention for the South of Italy achieved by the CASMEZ (National Economic Body for the promotion of a huge programme of public works in the so-called "Mezzogiorno" of Italy). It was regarded necessary to "settle the southern regions, by means of land transformation, the realisation of public works, land reclamation and irrigation and protection in order to reduce the hydro-geologic instability". In this regard a strong point of the CASMEZ activity during these years was forestry, aimed at achieving water and soil protection and afforestation, favouring employment as well.
Up to the 1960s this policy granted "sustainable and balanced land management", which summoned forces that achieved a significant development project. However, land reclamation and transformation were not always positive. In some cases, such as at Policoro (Lower Agri Basin), the intensity of this reclamation, in association with the development of the coastal plains, coincided with the excessive deforestation of these areas for land conversion, so much that today only 500 ha of wood remain (Pantano Sottano Wood, the last remaining natural lowland forest in Southern Italy at sea level included in the list of Natura 2000 sites). Concerning deforestation, in the lower and middle part of the valley, where forest cover is already less widespread and the climatic conditions less favourable, it faces a slow and continuous reduction in extent. Forest is being replaced by farmland and is therefore becoming limited to a marginal area and role.
Actually the main cause of deforestation and forest degradation in Agri Basin is represented by forest fires. Fires, in terms of both frequency of occurrence and areal extent, are a serious problem in that environment, already subject to degradation and desertification phenomena. Just to give some information about the size of forest fires occurrence in the Agri Basin, in the period 1990-1995 about 1327 hectares of forest, mainly represented by high stands of broad-leaved, were affected by 304 fires. This means 3,88% of the total forested area of the valley and 13,41% of the total number of fires registered in the Region. Fires in Agri Basin, too, follow a clear pattern which is found in many other Mediterranean Regions and specifically, the highest number of fires are found in areas having the lowest forest index. In Agri Basin fires occur mainly in areas having forest indices up to 20%, corresponding seemingly to those areas dominated by coppices, i.e a rather poor productivity forest area.
The environmental hazards of desertification and deforestation, though distinct, provide mutual feedbacks and are far from being independent of each other. They consequently have similar implications and solutions.
Forests have always been crucial to human subsistence, food security, economic development and well-being. Today, the needs and demands facing the forest environment are more pressing than ever due to demographic growth, environmental concerns, socio-economic development, and appreciation of cultural and spiritual values. As the most important terrestrial ecosystem, forests sustain life through biodiversity, climate regulation (climate changes), water and soil conservation, and more. They have been deeply scarred by human activity during the last millennia, particularly by agriculture, urbanization and natural resource use. The processes of deforestation can therefore be affected by various factors related to physical environment, management and socio-economics characteristics of an area.
There are many causes for deforestation. The first and most important cause is wood extraction. Wood has always been a primary forest product for human populations and industrial interests. Since wood is an important structural component of any forest, its removal has immediate implications on forest health. Intensive, non sustainable harvest can lead to severe degradation, even beyond a forests capacity to recover. Forest fires too contribute to reduce the forest cover land and induce different ecological and environmental impacts, such as degradation of the quality of vegetation, erosion of biodiversity, damage to the health of forest ecosystems, loss of wildlife habitat, air, river and estuarine pollution and overall ecological retrogression.
Deforestation has many devastating effects. It affects climate significantly, in part because the forest plays a major role in the water cycle, recycling rain back into the clouds as it receives rainfall. As a result, when the land is cleared, flooding and drought become serious problems, as rainwater travels quickly through the ground without the forest to regulate it, thereby causing increased runoff and flooding in the wet season and water shortages in the dry season.
Burning and felling of the forests is also exacerbating the Greenhouse Effect. Burning releases carbon dioxide (CO2) into the atmosphere, fostering global warming. In addition, fewer trees means a lessening of the global forest's ability to absorb CO2.
Deforestation robs the world of countless species, destroying crucial biodiversity and losing species with potential uses in medicine, agriculture and industry. Biodiversity is important because it contributes to resiliency. A world without biodiversity would be more fragile and likely to amplify disturbance into catastrophe through the collapse of ecosystems that had lost keystone species. Thus, biodiversity reduction, combined with climate change, has the potential to spin out of control and to threaten the prosperity of human habitat.
The global effects of deforestation are the mainly reasons of worrisomely environmental process known like desertification. Among the main causes of soil degradation are in fact deforestation, overgrazing, over cultivation, water logging and salinization. Whether land will be deforested by natural or human causes can be predicted by assessing various indicators related to reduced vegetation cover and soil degradation, such as clearing forest land, forest fire, pastoral and agriculture activity, level of forest productivity, change climatic condition etc. Several of these indicators are interrelated and depend on local conditions.