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PU-GEC

Peri-urbanization and Global Environmental Change

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Ecosystem Service Evaluation

Last Updated: 2009-05-15

Taipei and its peri-urban areas have widely varying environmental characteristics. A conceptual urban ecological economic system of Taipei-Taoyuan area can be drawn by using the Odum energy diagram. Locally available renewable energy sources power natural ecosystems and human-subsidized agricultural production systems to provide important life-support services to urban system. Goods and services must be imported from economic system to transform and extract indigenous resources needed for life-support in urban areas.

Ecological economic system of Taipei-Taoyuan area

On the basis of land use and land cover maps, this study identified ten major peri-urban ecosystems which can generate ecosystem services for urban areas. The natural ecosystem includes forest and riparian wetland. The agricultural production system includes paddy rice field, crop land, orchard, and range farm. Water resources are another important system for generating various ecosystem services for urban areas.

   Ecosystem services of Taipei-Taoyuan areas

The biophysical evaluation of ecosystem services begins with an analysis of energy flows within the examined system. The conceptual energy system diagram of three natural ecosystems can be represented as following energy diagrams. For example, the agricultural areas in the Taipei-Taoyuan area include paddy rice field, crop land, orchard, range farm and fallow land. The energy flows of a typical agricultural production system explicitly incorporate renewable energy, agricultural land, crop biomass, soil, inflows of irrigated water and goods and services. The amount of renewable energies used by the agricultural production area depends on the size of agricultural field. In addition to renewable energy, this human-subsidized production system must feedback energy and materials (e.g. fertilizer, irrigation, labor, etc.) to match the renewable energy to enhance crop production. Food provision is the major ecosystem service offered by agricultural production area. Since large volumes of irrigated water are required to grow rice in paddy fields, the water contained in the soil can also recharge ground water. Agricultural production in peri-urban areas can also provide an aesthetic value to nearby urban dwellers. The major crops in the study area are rice and vegetables and due to the excess agricultural production in Taiwan, approximately 50% of the agricultural land in the study area is currently fallow and government subsidized.

  

Energy diagram of agricultural ecosystem

  

Energy diagram of forest ecosystem

Energy diagram of water resources in Taipei-Taoyuan area

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Accordingly, the flows of energy sources, outflows and internal processes of these three natural ecosystems were used to calculate their emergy values in 2006. Take the agricultural system as an example. Using emergy as an enumerative, rice paddy field, crop land and fallow captured most renewable energies. The emergy value of live stock production is 1.21 E21 sej/yr and higher than that of all crops due to the higher goods and services fed back from economic system to its production. The emergy value of rice production and vegetable crops are 1.31 E20 sej/yr and 1.24 E20 sej/yr, respectively. The paddy rice field requires more irrigated water (2.05 E20 sej/yr) to grow rice than to grow other crops and also function to recharge ground water (1.18 E20 sej/yr). The emergy evaluation of aesthetic value (cultural service) from agricultural production area is calculated by summing all emergy inflows to the system, which accounts to 8.06 E20 sej/yr.

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Emergy evaluation of agricultural production in 2006

The system components were entered into a symmetrical impact matrix, and the influences of each component on all other components were recorded to illustrate the connected flows between components. Assessments in a row indicate how one component influences other components, whereas assessments in a column indicate the influence of the other components on it. The components with high active sum (AS) include upstream rivers, soil nutrients and crop biomass of agricultural production area, and soil water in forest ecosystems. The upstream rivers, crop biomass and soil water in forest ecosystems also have high passive sum (PS), leading to their highest value of total sum (TS=AS+PS), and indicate their critical influence in the entire system. By calculating the activeness and passiveness of each system component, the components can be situated in a system grid.

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System grids showing systemic role of ecosystem services in Taipei-Taoyuan area

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The forest ecosystem can conserve water resources by storing excess runoff and discharging ground water to surface water. The component of soil water (A) thus provides a regulating service of water flow and plays a critical role in the entire system. The soil nutrients in the forest ecosystem (B) are an active component because they support biomass production. However, since harvesting timber is prohibited, no provisioning service is available from forest biomass (C), and its role is less active. Riparian wetland, however, tend to fall in the indifferent sector of the system grid due to its smaller area as compared to the other ecosystem. The high active sum and passive sum values of agricultural production system components (G, I) reveal the critical role of ecosystem services in agricultural production area of the study region. Given the topographic characteristics of the study region, reservoirs are used to designate water resource as upstream and downstream. The upstream rivers (J) provide provisioning services of surface water and hydroelectricity. These rivers are considered the most critical component and have an active role in the entire system. The downstream portion of the surface water (K) tends to receive runoff and discharge from other system; its role is less active than that of the upstream portion.

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