This Ant is an "Aphid Rancher." (SE Costa Rica)
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While intense emphasis and coverage of this hot topic has slightly decreased, deforestation is a huge problem that the world faces in the near future. The three areas of highest concern in the world today are Asia, Africa and the Americas--where the tropics experience the highest pace of conversion at 10 million ha/year (Laurance, 1999). Deforestation is a non-random, unnatural process thus, not all forest types are equally endangered. The most vulnerable are accessible areas with relatively productive, well-drained soils and moderate topography--which are also most suitable for farming. Deforestation is the cutting, clearing, and removal of rainforest or related ecosystems, and subsequent conversion into other, less biodiverse, anthropogenic ecosystems such as pasture, cropland, or plantation (Kricher 1997).
Costa Rica has been a “poster child” for preservation of its resources. Currently Costa Rica has over 8,000 species of plants, but it has also lost over 60% of its forest cover. In 1970, as the cost of oil rose and the demand for coffee dropped, cattle ranching became a favored source of income, leading to the mass deforestation that Costa Rica has experienced. While Costa Rica is fighting to save all it has left, it serves as an excellent example for other countries experiencing the same type of economic difficulties. Costa Rica has converted large amounts of its land into national parks. While nature reserves and parks are necessary for sustaining current biodiversity, however they are inadequate in assuring maintenance of existing environments of tropical forests. Costa Rica is still undergoing heavy deforestation. In 1998 Costa Rica’s tropical forests were experiencing logging intensities of approximately 50 to 100 m3/ha (Putz et al. 2001). Logging (just one form of deforestation) is a problem, however, the greater ecological problems are the consequences of it, such as fragmentation, vulnerability to forest fires, increased hunting, land conversion, overall greater access to the forests. I hope to cover the causes of, and different means of deforestation, its long-term consequences, and the economic implications. I will discuss ecologically-friendlier forms of deforestation and several economic alternatives.
Causes of deforestation
There are many different hypotheses behind what drives deforestation. While to many there seems to be a simple answer--high population growth--the real reasons behind it are much moe complex. Geist and Lambin 2002 have identified and researched several reasons such as national policies which promote land use, the technological drive for mass production that exists in our world today, the economic drive for agricultural and wood production, the necessity for cattle pasture land creation and development which leads to road construction providing access to remote areas for natural resources, for attracting tourists, increasing colonization and much more. As the human population increases, so does poverty. As poverty increases, the governments do everything possible to stabilize their economies and bring income into their countries. The growing population of people need a place to live, thus they move out of the city and into rural areas, where trees are cut down to make room for homes, farms. Geist and Lambin 2002 have found that agricultural expansion is the leading form of land-use associated with deforestation (96%). The greatest of all reasons is pasture creation for cattle ranching because it is an excellent form of income. However, the nutrients of the land are quickly depleted and thus new rainforest land must be cleared to create new lands for grazing. It is important to note that nutrient-depleted pastures take many years to become restored to their prior state. In order to keep the economy going the governments have lowered the costs of land, labor, fuel or timber, thus many foreign companies invest in these areas. Since there is little or no government regulation of ecological factors such as pollution, it makes for an attractive investment. Another driver of deforestation is the mismanagement of land tenure agreements. For example, not only is wood extraction not controlled, often times other issues arise, such as that of road construction, which only leads to further forest fragmentation and deforestation. Often times policies are pro-deforestation in order to boost the economy with the state offering low taxes, legal land titling, credit and other incentives which leads to further road construction, extensions of pastures, etc. Increasing trade liberalization and international free-trade agreements are also promoting greater foreign investment, further promoting deforestation (Laurance, 1999). Other causes of deforestation include hydropower development, mining, oil and gas exploration, commercial hunting (which endangers many species with low reproductive rates) and more.
Methods of deforestation
There are many forms of deforestation. The two most often used are slash-and-burn, logging. The slash-and-burn method of deforestation leads to small pools of soil-N which are quickly depleted. Slash burning shows a dramatic short term increase in inorganic nitrogen and surface soil pH levels. The net nitrification and overall mineralization rates are lower (immediately after burning, nitrogen mineralization was higher than in undisturbed plots, but this increase was short term). High rates of soil erosion are common, the vegetation structure is altered. All of this leads to difficulties in overcoming these barriers during restoration, reforestation or alternative land uses (Ellingston, et al. 2000). Another danger is that once burned forests become increasingly prone to subsequent fires.
Logging is one of the most severe silvicultural interventions (wasteful logging practices) (Putz et al. 2001). Intensities of logging vary over time, however, it alters the composition of the landscape, thus influencing its inhabitants. Trees are not only cut down (much of which is done illegally), mortality rates of nearby damaged trees increase. Logging affects nutrient and hydraulic cycles and changes biogeochemical stocks (Putz, et al. 2001). Logging leads to networks of roads, which is just unnecessary tree mortality. This fragmentation makes the forest more vulnerable to forest fires, especially during droughts, which only increases deforestation levels. Logging leads to soil erosion and compaction. Grasses and vines invade the cleared areas. Clear lands experience soil fertility declines and then require many fallow years for nutrient recovery. Thus if new areas are not permitted to be cut, farmers will have to use quite heavily expensive fertilizers, further upsetting the nitrogen cycle.
Much of forest clearance in Costa Rica was for cattle ranchers (Park 1992). Nearly 2/3 of Costa Rica’s rainforest has been destroyed for cattle ranching. However what few realized before it was too late is that rainforest soil is not suitable for animal grazing or crop production because it quickly loses its fertility. Cattle grazing destroy the physical and chemical structure of the soil in just a few years. Land is cheap because government promotes farming, nutrient-exhausted farms are left behind and the deforestation process is started elsewhere (Park 1992).
Solutions/Alternatives
Conservation may be achieved through collaboration between loggers and environmentalists. For example the Debt-for-Nature-Swap program of 1987 was quite successful in saving forest lands (Park 1992). A great source of income is ecotourism which brings in more money than wood exports in Costa Rica. Another idea is well managed logging which can mimic natural disturbances and if hunting is kept to a minimum, populations will avoid bottlenecks (Laurance, 1999). Sustainable forestry (Park 1992) and sustainable agriculture are also wonderful options--such as changing from beef to dairy cattle in Costa Rica (Miller and Tangley 1991). Forest reserves such as La Amistad Biosphere Reserve, Costa Rica may not be equivalent to a natural untouched rainforest, but they are wonderful in preserving biodiversity (Miller and Tangley 1991). Another idea is growing forest from habitat fragments, for example the Guanacaste National Park, Costa Rica (Miller and Tangley 1991).
Long term consequences
We are experiencing three major global changes: increasing levels of carbon dioxide in the atmosphere, an increase in land use/land cover change and alteration in the biogeochemistry of the nitrogen cycle (Vitousek, 1994). These three have resulted and will lead to even more increased changes in climate and loss of biodiversity. Recently, we have undergone a sky-rocketing increase in atmospheric gases. These greenhouse gases have changed our climate by increasing surface temperatures, decreasing precipitation, decreasing humidity and changing atmospheric cycles. Zhang, et al. 2001 found that greenhouse gas warmed climate will lead to an increase in temperatures in the middle latitudes of northern and southern hemispheres. The may also lead to changes in large-scale atmospheric circulation, but it is not yet known what these changes will be.
It is important to note that an increase in CO2 levels is a result of fossil fuel combustion and not deforestation. However, deforestation has reduced the area and thus the effects of important carbon sinks, such as the Amazon basin. An increase in CO2 concentrations increases atmospheric longwave radiation (Zhang, et al. 2001). Plants respond to increased carbon dioxide levels in various ways. Some plants increase their growth rate, however the tissue they produce has lower nutrient concentrations, thus higher quantities must be consumed by herbivores to acquire sufficient levels of protein. Also increased levels of CO2 in seawater reduce oversaturation of aragonite -- a building block of coral reefs. (Vitousek, 1994). Undisturbed forests are a globally significant carbon sink, because new forests are only temporary carbon sinks only because they have lost so much carbon initially via deforestation. The newly cut rainforest will only turn into a source of greenhouse gas.
Recently we have experienced increased levels of nitrogen. By clearing land and burning forests humans have extracted nitrogen from long-term storage pools and released it into the atmosphere. This same rate of N fixation has also been noticed in an increase of atmospheric concentrations of nitrous oxide--another greenhouse gas (Vitousek, 1994). Enhanced nitrogen deposition has been noticed to cause forest dieback in European forests. The addition of nitrogen in the form of fertilizer seems to increase primary production and biomass however it seems to decrease species richness. Increased levels of nitrogen in plant tissues seem to favor consumers, the opposite of the effects of CO2. An experiment testing the slash-and-burn method on nitrogen levels found a short-term increases in inorganic nitrogen and soil pH, high levels of erosion of burned areas was also observed (Ellingson, et al. 1999). However, the potential rates of N mineralization were short-lived, and were significantly lower than those found in undisturbed rainforests. N and CO2 are not the only cycles experiencing a disruption or an increase. There are many other, including sulfur, whose change in cycle has led to sulfuric acid rain.
An increase in land use has had a significant change on land cover. Land cover change is the alteration of the physical or biotic nature of a site, such as the conversion of a rainforest to pasture land, while land use change involves alteration of the way humans use land, such as the conversion of low-input agricultural land to high-input uses (Vitousek, 1994). There is no global measure of land use change, nor is there any direct measure of deforestation. Land use change is one of the leading causes of increase in atmospheric concentrations of greenhouse gases. The slash-and burn method of deforestation has added high levels of nitric oxide, methane and carbon monoxide to the atmosphere. Locally this has led to increased temperatures and decreased humidity--characteristics of dryer climates--which may lead to susceptibility to fires and affect the rate of forest regeneration. A simulation model done by Lean and Warrilow, 1989, shows that if the entire Amazonian forest was converted to pastures, the area would experience increase in temperature, decrease in precipitation and alter the patterns of atmospheric circulation.
Deforestation leads to greenhouse warming of climate. Changes in tropical rainforest regions lead to large reductions in surface evapotranspiration and precipitation. Reduced evapotranspiration from large-scale deforestation could cause a 20% decline in rainfall. thus leading to a lower humidity, higher surface temperature and more severe dry-seasons (Laurance, 1998). This in turn may lead to the rainforests being replaced by drought-adapted deciduous forests or woodlands. Increases of surface temperature are not solely led by increases of CO2, but also by reduction of surface evapotranspiration and atmospheric longwave radiation (Zhang, et al. 2001). Surface albedo is increased, thus more short-wave radiation at the surface is absorbed. At the same time longwave radiation towards the surface and out to space is increased. Thus these radiation fluxes affect the surface moisture and thermal properties. Deforestation leads to reduction of evapotranspiration which leads to reduction of cloud cover. Reduction of cloud cover allows more radiation to reach the surface and reduces the effect of the increased surface albedo. It also changes the longwave radiation between the land-surface and the atmosphere allowing more longwave radiation to escape. This loss of surface latent heat of outgoing longwave radiation is offset by further reduction of cloud cover in order to maintain the increased surface temperature. Thus this vicious cycle continuous becoming worse each time. Tropical forests are more sensitive to soil water availability. Areas where dry seasons are very prominent will be in danger. These areas survive now because they have deep root systems which allows them to overcome droughts. However, reduction in soil water availability of an already threatened species may be quite detrimental (Laurance, 1998).
Why do we care?
The most important change of deforestation is the loss of biodiversity. The loss of species is permanent, while the level of biodiversity may be re-established after several billions of years, the combinations of genes will be lost forever. Tropical forests are not just incredible resources of biodiversity, they are homes to indigenous people who are the only one who know the uses of all the plants. Tropical forests are great supporters of the ecosystem they are a part of such as flood amelioration and soil conservation, they are crucial for maintaining stability of rivers and watersheds, they prevent soil erosion and much more. They are the most ancient, diverse and ecologically complex places on earth (Laurance, 1999).
Massive deforestation leads to severe weather patterns and climate changes. It is possible that further deforestation may lead to far more frequent El Ni–o events, such as the droughts of 1982-1983 and 1997-1998 and make them more severe, turn them into major catastrophes (Laurance, 1998).
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