Amazon rainforest case study 1. Physical factors and stores and flows in the water cycle in the Amazon Rainforest Characteristic Geology (rock permeability and porosity) Relief (slopes) Temperature Effect on the flood hydrograph Impermeable catchments (e.g. large parts of the Amazon Basin are an ancient shield area comprising impermeable, crystalline rocks) have minimal water storage capacity resulting in rapid run-off. Permeable and porous rocks such as limestone and sandstone store rainwater and slow run-off. Most of the Amazon Basin comprises extensive lowlands. In areas of gentle relief water moves across the surface (overland flow) or horizontally through the soil (throughflow) to streams and rivers. In the west the Andes create steep catchments with rapid run-off. Widespread inundation across extensive floodplains (e.g. the Pantanal) occurs annually, storing water for several months and slowing its movement into rivers. High temperatures throughout the year generate high rates of evapotranspiration. Convection is strong, leading to high atmospheric humidity, the development of thunderstorm clouds and intense precipitation. Water is cycled continually between the land surface, forest trees and the atmosphere by evaporation, transpiration and precipitation. 2. Physical factors affecting stores and flows of carbon STORES: Forest trees dominate the biomass of the Amazon Basin and are the principal carbon store. In total approximately 100 billion tonnes of carbon is locked up in the Amazon rainforest. Absorbing around 2.4 billion tonnes of CO2 a year and releasing 1.7 billion tonnes through decomposition, the rainforest is a carbon sink of global importance. 60 per cent of rainforest carbon is stored in the above ground biomass of tree stems, branches and leaves. The remainder is below ground, mainly as roots and soil organic matter. FLOWS: Carbon cycles between the forest and other living organisms, the soil and the atmosphere. Photosynthesis connects the rainforest to the atmosphere carbon stores. High temperatures, high rainfall and intense sunlight stimulate primary production. NPP averages about 2500 grams/m2/year. The Amazon Rainforest alone accounts for 15–25 per cent of all NPP in terrestrial ecosystems. Leaf litter and other dead organic matter accumulates temporarily at the soil surface and within rainforest soils. High temperatures and humid conditions promote rapid decomposition of organic litter by bacteria, fungi and other soil organisms. Decomposition releases nutrients to the soil for immediate take-up by tree root systems, and emits CO2 which is returned to the atmosphere. The geology of the Amazon Basin is dominated by ancient igneous and metamorphic rocks. Carbonates are largely absent from the mineral composition of these rocks…However, in the western parts of the basin, close to the Andes, outcrops of limestone occur... In the context of the slow carbon cycle they are significant regional carbon stores. 3. Human factors affecting stores and flows of water Deforestation in Amazonia averaged around 17,500 km2/year between 1970 and 2013. Since 1970 almost one-fifth of the primary forest has been destroyed or degraded (Figure 4.14), though in recent years rates of deforestation have slowed (Figure 4.15). In April 2014 devastating floods occurred on the Madeira River, the largest tributary of the Amazon River (Figure 4.16). At Porto Velho the river reached record levels of 19.68 m above normal. Vast expanses of floodplain were inundated; 60 people died; 68,000 families were evacuated; and there were outbreaks of cholera and leptospirosis. In the Upper Madeira: drainage basin human activity has modified stores and flows in the water cycle. Deforestation has reduced water storage in forest trees, soils (which have been eroded), permeable rocks (due to more rapid run-off) and in the atmosphere... At the same time fewer trees mean less evapotranspiration and therefore less precipitation. Meanwhile, total run-off and run-off speeds have increased, raising flood risks throughout the basin. Despite torrential rains in the upper basin of the Madeira River, the main driver of the floods was deforestation in Bolivia and Peru. Between 2000 and 2012, 30,000 km2 of Bolivian rainforest was cleared for subsistence farming and cattle ranching. Much of this deforestation occurred on steep lower slopes of the Andes. The result was a massive reduction in water storage and accelerated run-off. Deforestation has a huge impact on the water cycle and has the potential to change the climate at local and regional scales. Converting rainforest to grassland increases run-off by a factor of 27, and half of all rain falling on grassland goes directly into rivers. Rainforest trees are a crucial part of the water cycle, extracting moisture from the soil, intercepting rainfall and releasing it to the atmosphere through transpiration, as well as stabilising forest albedo and ground temperatures. This cycle sustains high atmospheric humidity which is responsible for cloud formation and heavy conventional rainfall. Deforestation breaks this cycle and can lead to permanent climate change. However, the impact of deforestation on water cycles is not just local. Projections of future deforestation in Amazonia predict a 20 per cent decline in regional rainfall as the rainforest dries out and forest trees are gradually replaced by grassland. Nor is it just deforested areas that experience a reduction in rainfall: disruption of the regional water cycle means that forests hundreds of kilometres downwind of degraded sites are affected too. 4. Human factors affecting carbon and nutrient flows and stores Present-day deforestation is most severe in the tropical rainforest. In primary rainforest, unaffected by human activity, the biomass of trees represents about 60 per cent of all the carbon in the ecosystem…The above ground carbon biomass in the rainforest is approximately 180 tonnes/ha. Most of the remaining carbon is found in the soil as roots and dead organic material. Deforestation exhausts the carbon biomass store. Croplands and pasture contain only a small amount of carbon compared to forest trees. For example the biomass of grasslands in areas of former rainforest is 16.2 tonnes/ha; and for soya cultivation it is just 2.7 tonnes/ha…At the same time deforestation drastically reduces inputs of organic material to the soil —> Soils, depleted of carbon and exposed to strong sunlight, support fewer decomposer organisms, thus reducing the flow of carbon from the soil to the atmosphere. In tropical rainforests, the principal store of plant nutrients such as calcium, potassium and magnesium is forest trees. Rainforest soils contain only a small reservoir of essential nutrients and the forest is only sustained by a rapid nutrient cycle. Deforestation destroys the main nutrient store – the forest trees – and removes most nutrients from the ecosystem. Nutrients no longer taken up by the root systems of trees are washed out of soils by rainwater; and soils, without the protective cover of trees, are quickly eroded by run-off. 5. Strategies to manage tropical rainforests: the positive effects on the water and carbon cycles The degrading or outright destruction of large areas of Amazon rainforest is an issue of international as well as national concern. This is because deforestation has implications for global climate change… Brazil is committed to restoring 120,000 km2 of rainforest by 2030. Indigenous people have lived sustainably in the rainforest for thousands of years, maintaining the water balance, carbon cycle and the forest’s biodiversity. These people survived as hunter gatherers and shifting cultivators. In stark contrast to exploitative commercial farming, logging and mining of the past 50 years, indigenous people pursued a way of life perfectly adapted to the limited resources and fragility of the rainforest. Modern strategies to manage the Amazon rainforest sustainably fall into three categories: Protection through legislation of large expanses of primary forest so far unaffected by commercial developments Projects to reforest areas degraded or destroyed by subsistence farming, cattle ranching, logging and mining Improving agricultural techniques to make permanent cultivation possible Since 1998, the Brazilian government has established many forest conservation areas. These Amazon Regional Protected Areas now cover an area twenty times the size of Belgium. By 2015: 44 per cent of the Brazilian Amazon comprised national parks, wildlife reserves and indigenous reserves where farming is banned. REFORESTATION Several reforestation projects, sponsored by local authorities, non-governmental organisations (NGOs) and businesses are underway, but so far progress has been slow. One such example is the Parica project in Rondônia in the western Amazon. This sustainable forestry scheme aims to develop a 1000 km2 commercial timber plantation on government-owned, deforested land. The plan is for 20 million fastgrowing, tropical hardwood seedlings, planted on 4000 smallholdings, to mature over a period of 25 years. Financial assistance is given to smallholders for land preparation, planting and the maintenance of plots. Tree nurseries provide them with seedlings. Timber will be exported along the Amazon and its tributaries through Manaus or Port Velho. Although this project is a monoculture and cannot replicate the biodiversity of the primary rainforest, it is sustainable. It also sequesters carbon in the trees and soil; reduces CO2 emissions from deforestation; re-establishes water and carbon cycles; and reduces run-off and the loss of plant nutrients and carbon from the soil. Also in Rondônia, the indigenous Suruí people participate in a scheme that aims to protect primary rainforest on tribal lands from further illegal logging, and reforest areas degraded by deforestation in the past 40 years. The Suruí plant seedlings bred in local nurseries in deforested areas around their villages. The native species planted are chosen to provide them with timber for construction, food crops and, through logging, a sustainable source of income. In 2009 the Suruí were the first indigenous group in Amazonia to join the UN’s Reducing Emissions from Deforestation and Degradation (REDD) scheme. This scheme provides payment to the tribe for protecting the rainforest and abandoning logging. It is a market-based approach involving granting of carbon credits to the Suruí. These credits can be purchased by international companies which have exceeded their annual carbon emissions quotas. In 2013, Natura, a large cosmetics transnational corporation (TNC), purchased 120,000 tonnes of carbon credits from the Suruí. This was the first carbon credit sale by indigenous people in Amazonia. Improved agricultural techniques Farming has been the main cause of deforestation in Amazonia. However, the low fertility of soils meant that permanent cultivation proved unsustainable. After a few years, smallholders abandoned their plots which were then converted to low quality grassland. Extensive ranching enterprises could scarcely support stocking levels of one head of cattle per hectare. One response to improve agriculture has been diversification —> Soil fertility can be maintained by rotational cropping and combining livestock and arable operations…Integrating crops and livestock could allow a fivefold increase in ranching productivity and help slow rates of deforestation. European explorers observed that the Amazon rainforest, as late as the sixteenth century, supported high population densities, and many large urban centres. This appears to contradict the view that natural resources for farming in the region are too poor to support settled, permanent cultivation. The explanation is thought to be human-engineered soils: so-called dark soils made from inputs of charcoal, waste and human manure. Charcoal in these soils attracts micro-organisms and fungi and allows the soils to retain their fertility long-term. Scientists are currently investigating these dark soils. If they can be successfully recreated they would allow intensive and permanent cultivation which would drastically reduce deforestation and carbon emissions.
