(give reason) forests help to maintain water table. [urgent please]

  • 0

The availability and quality of water in many regions of the world are more and more threatened by overuse, misuse and pollution, and it is increasingly recognized that both are strongly influenced by forests. Moreover, climate change is altering forests role in regulating water flows and influencing the availability of water resources (Bergkamp, Orlando and Burton, 2003). Therefore, the relationship between forests and water is a critical issue that must be accorded high priority.

Forested catchments supply a high proportion of the water for domestic, agricultural, industrial and ecological needs in both upstream and downstream areas. A key challenge faced by land, forest and water managers is to maximize the wide range of multisectoral forest benefits without detriment to water resources and ecosystem function. To address this challenge, there is an urgent need for a better understanding of the interactions between forests/trees and water, for awareness raising and capacity building in forest hydrology, and for embedding this knowledge and the research findings in policies. Similarly, there is a need to develop institutional mechanisms to enhance synergies in dealing with issues related to forests and water as well as to implement and enforce action programmes at the national and regional levels. In the past, forest and water policies were often based on the assumption that under any hydrological and ecological circumstance, forest is the best land cover to maximize water yield, regulate seasonal flows and ensure high water quality. Following this assumption, conserving (or extending) forest cover in upstream watersheds was deemed the most effective measure to enhance water availability for agriculture, industrial and domestic uses, as well as for preventing floods in downstream areas. Forest hydrology research conducted during the 1980s and 1990s (summarized by Bruijnzeel, 2004; Calder, 2005, 2007; Van Dijk and Keenan, 2007) suggests a rather different picture. Although the important role of upstream forest cover in ensuring the delivery of high-quality water has been confirmed, earlier generalizations about the benefits of upstream forest cover on downstream annual and seasonal flows were generally fallacious and misleading. Studies have shown instead that, especially in arid or semi-arid ecosystems, forests are not the best land cover to increase downstream water yield. Moreover, solid evidence has shown that in tropical ecosystems the protective role of upstream forest cover against seasonal downstream floods has often been overestimated. This is especially true in connection with major events affecting large-scale watersheds or river basins (FAO and CIFOR, 2005).

The International Year of Freshwater 2003 and the third World Water Forum (Kyoto, Japan, 2003) helped drive the incorporation of this understanding of biophysical interactions between forests and water into policies. The International Expert Meeting on Forests and Water, held in Shiga, Japan in November 2002 in preparation for these events, highlighted the need for more holistic consideration of interactions between water, forest, other land uses and socio-economic factors in complex watershed ecosystems. During the past five years, the Shiga Declaration has become a key reference for the development of a new generation of forest and water policies (see article by Zingari and Achouri, this issue). This article summarizes the state of current knowledge about forest and water interactions in watershed ecosystems. It summarizes some key issues that have emerged from discussion among forest hydrologists, other water-sector experts and policy-makers in the years since the Shiga Declaration, the third World Water Forum and the International Year of Freshwater.

  • 2

ISSUES IN CURRENT FOREST AND WATER POLICIES

Following the International Year of Freshwater 2003, discussion among forest hydrologists, other water sector experts and policy-makers has focused on three core issues: incorporation of forest hydrology knowledge in water policies; inclusion of forest-sector contributions in integrated water resource management policies; and payment for forest- and water-related environmental services.

Incorporation of forest hydrology knowledge in water policies

Despite the significant advances in scientific understanding of forest and water interactions, the role of forests in relation to the sustainable management of water resources remains, as elaborated in the previous section, a contentious issue. Uncertainty, and in some cases confusion, persists because of difficulties in transferring research findings to different countries and regions, different watershed scales, different forest types and species and different forest management regimes. Another difficulty is a gap between research and policy, which persists at least in part because of a general failure to communicate results of hydrological research effectively to policy-makers and to challenge conventional assumptions with scientific evidence. To address these issues, in 2006 the International Union of Forest Research Organizations (IUFRO) created a Task Force on Forests and Water Interactions. Its aim is to promote consensus in the forest hydrology community on the key issues concerning forest and water interactions, and to identify areas of scientific uncertainty on which to focus policy-relevant research. Seeking to generate and disseminate information that non-specialists can easily and safely use, the task force has produced a one-page fact sheet to convey key concepts in forest hydrology to policy-makers (summarized in the Box at right). FAO, similarly, has produced the booklet Why invest in watershed management to raise the awareness of policy- and decision-makers about the needs for and benefits of watershed management (see Box, next page). For the linking of research and policy related to forest hydrology, education has an important role. Scientific and technical education is generally highly sectoral. Education across disciplines is necessary to improve knowledge of forest and water interactions, e.g. to improve capacity to assess effects of afforestation and reforestation programmes on water quality and quantity, flood control and soil protection.

Inclusion of forestry in integrated water resource management

Development of integrated water resource management plans at the watershed and/or river-basin level was one of the targets set by the World Summit on Sustainable Development in 2002. These multisectoral plans should be aimed at ensuring water for people, food, nature, and industry and other uses (Global Water Partnership TAC, 2000). The need to include the nature for water dimension in these plans is increasingly recognized. The concept of nature for water takes into account the role of terrestrial ecosystems in enhancing water yields and water quality. For instance, the Lange Erlen forested area in Switzerland is flooded a dozen days a month with water from the Rhine to allow forest soil to filter the water to improve its quality and recharge the groundwater of the nearby city of Basel. As foresters are increasingly committed to the development of national forest programmes (NFPs) to implement sustainable forest management, there is scope for them to join forces with water experts to develop integrated water resource management plans and forestry programmes as part of a more comprehensive watershed/river-basin planning process. Similarly, management of transboundary watersheds and river basins should give greater consideration to the relationship between upstream forest cover and downstream water flows. For instance, the Program for the Sustainable Development of the Rhine (ICPR, 2001), a transboundary initiative, adopts afforestation and forest conservation measures to facilitate water retention and to prevent floods in nearby downstream areas. Protected forest area in the basin was 1200km2 in 2005 and is expected to reach 3500km2 by 2020. Many countries have begun to develop integrated water resource management plans at the national and/or watershed level. Their implementation is complicated by the number and variety of stake­holders within and beyond a watershed and their different and sometimes contrasting interests, as well as by overlap of the administrative responsibilities of different regional authorities in many countries. A step-by-step planning process is advisable to ensure buy-in for effective implementation of the plan. For example, the Water Framework Directive of the European Union foresees the development of river-basin management plans from a consultative process which will take place in 2008 and be finalized by 2009. This gives time for European foresters to cooperate with their water-specialist colleagues.

Payments for environmental services

In many countries, forest and water policies, plans and programmes are coming together through the increased popularity of payment for environmental services schemes (also called incentive-based cooperative agreements, stewardship payments, compensation schemes or performance payments) as financing mechanisms for watershed management, sustainable forest management and other sustainable development processes (see Box on Mexico). Payments do not necessarily involve money; often they take the form of services a community has been lacking, such as new or better roads, a school bus or weekly transport for farm produce. Forest stewardship by upstream populations, for instance, can be compensated by downstream water users through direct payment for the provision of forest hydrological services such as discharge regulation or protection of water quality. In developing countries, the ensuing hydrosolidarity between upstream forest managers and downstream water users is often mediated by public agencies. For instance, since 1996 the Government of Costa Rica has sponsored schemes to create economic incentives for conserving forests and to compensate those whose land or land uses generate environmental services. More sophisticated mechanisms involving subsidies generated by income taxes and other public-sector sources are being put in place in industrialized countries (see Box on Switzerland). The United Nations Economic Commission for Europe (UNECE) Convention on the Protection and Use of Transboundary Watercourses and International Lakes (2007) recently endorsed the concept of payments for ecosystem services including the conservation and development of forest cover.

Riparian forest buffer zones can greatly reduce or eliminate non-point source pollution from domestic, industrial and agricultural use (Suriname)
  • 1

Upstream and downstream, there is a need for more holistic consideration of interactions between water, forest, other land uses and socio-economic factors (forested watershed in India, irrigation in the Syrian Arab Republic) FORESTS AND WATER

Recent forest hydrology has focused on three topics that are particularly relevant for policy-making: the comparative advantages and disadvantages of forest cover in maximizing downstream water yields; the role of upstream forests in maintaining water flows during the dry season; and water-quality preservation. This section summarizes findings in these three areas (based on Hamilton, 2005). In the past, policy-making was often based on the assumption that the more trees, the more water. Current forest hydrology research challenges this assumption. The forest ecosystem is in fact a major user of water. Tree canopies reduce groundwater and stream flow, through interception of precipitation and evaporation and transpiration from the foliage. As both natural and human-established forests use more water than most replacement land cover (including agriculture and forage), there is no question that forest removal (even partial) increases downstream water yields. Consequently, removal of heavy water-demanding forest cover has sometimes been suggested, especially in semi-arid areas, as a means of preventing or mitigating drought. However, such a policy should be weighed against the consequent loss of the many other services and goods that forests supply, including erosion control, improved water quality, carbon fixation, recreation and aesthetic appeal, timber, fuelwood, other forest products and biodiversity. Such a practice should definitely be avoided in saline-prone areas, where forest removal would bring salts closer to the soil surface; and in mountain cloud forests, where tree foliage, epiphytic vegetative surfaces, twigs, branches, stems and shrubs provide a net to capture horizontal precipitation from fog or cloud. It is also well established that partial or complete removal of tree cover may accelerate water discharge and increase flood risk during the rainy season and may reduce river flow or even cause river beds to dry out in the dry season. However, the importance of forest cover in regulating hydrological flows has often been overestimated. Impacts of forest cover removal are evident only at the micro level and in association with short-duration and low-intensity rainfall events (which are usually the most frequent). As rainfall duration or intensity increases, or as distance of the rainfall area from the watershed increases, the influence of tree cover on flow regulation decreases. At the macro scale, natural processes in the upper watershed are more important than land management practices in the development of large floods. For instance, strong scientific evidence refutes the myth that deforestation in the Himalayas causes big floods in the lowlands of the Ganges and Brahmaputra; the large-scale floods result rather from a combination of simultaneous discharge peaks of the large rivers, high runoff from hills adjacent to the floodplains, heavy rainfall, high groundwater tables and spring tides, lateral river embankments and the disappearance of storage areas in the lowlands (Hofer and Messerli, 2006). Hence, although there are many good reasons for reforesting watersheds (e.g. reducing soil loss, keeping sediments out of streams, maintaining agricultural production, wildlife habitat and so forth), flood risk reduction or even control is not one of them. Reforestation to prevent or reduce floods is effective only at a local scale of a few hundred hectares. The complex relationships between forests and water in large river basins continue to be a matter of debate (see CIFOR, 2007), and it is clear that more work is needed for full understanding of these relationships. It is in maintaining high water quality that forests make their most significant contribution to the hydrological characteristics of watershed ecosystems. This is achieved through minimization of soil erosion on site, reduction of sediment in water bodies (wetlands, ponds, lakes, streams, rivers) and trapping or filtering of other water pollutants in the forest litter, particularly through the following mechanisms.

  • On sloping land, soil moves downhill mainly because of gravity and displacement by the splash action of raindrops. Natural forest cover provides the most effective barrier to splash-induced soil erosion, largely because of the contribution of the lower canopy leaves and the ground litter in reducing the force of splashing. Forest removal and replacement with other land use systems leads in most cases to higher and accelerated erosion unless great care in soil conservation is practised.
  • Erosion is generally associated with a higher sediment concentration in runoff and with siltation of watercourses. Good forest cover is more effective than any other kind of land cover in keeping the water as sediment free as possible. The surface cover, debris and tree roots trap sediments and stop their downslope movement. Moreover, deep tree roots stabilize slopes and help prevent shallow landslides.
  • In addition to sediment, various types of pollution depending on nearby land use and drainage to the watercourse can also impair water quality. Potential pollutants include excessive concentrations of organic matter (leading to water eutrophication) and agricultural or industrial chemicals. Forest is certainly an appropriate ground cover for drinking-watersupply watersheds, because forestry activities (with the exception of intensively managed plantations) generally use no fertilizers or pesticides and avoid pollution from domestic sewage or industrial processes. In addition, non-point source pollution (i.e. pollution from many diffuse sources) from domestic, industrial and agricultural use can be greatly reduced or even eliminated by maintaining adequate riparian forest buffer zones along watercourses. Such zones, however, will not prevent groundwater contamination. Moreover, where atmospheric pollutants are captured by trees because of their height and aerodynamic resistance, watershed forests will not protect water quality. This problem is most prevalent in mountain forests in industrialized countries.
Although forests can mitigate small, local floods, they do not appear to influence floods from extreme high-rainfall events like this one caused by a cyclone in Paznaun Valley, Austria in August 2005 Forests maintain high water quality by minimizing soil erosion and reducing sediment; deforestation generally increases erosion, resulting in higher sediment concentration in runoff and siltation of watercourses (Pakistan)
  • 1
What are you looking for?