عنوان مقاله [English]
Use of land affects structure and function of ecological systems. Landscape transformations are the main causes of loss of biodiversity (Dale et al. 30). Effects of land transformation go far beyond the changed boundary and one-third to half of terrestrial areas is changed by human activities (Vitousek et al. 1997, 495). Land cover changes impact regional climate and hydrological cycles. In one hand, land uses provide natural resources and services for human society and on the other hand they cause degradation and destruction of ecosystems and their services (Foley et al., 571). Land use and management were the main source of environmental degradation along history. American Society of Ecology has determined five basic principles for land use management (Dale et al. 2000, 640): time, species, place, disturbance and landscape.
Urbanization trend in Europe is analyzed by Antrop (2004); relative areas of main land uses are including forest (33%), natural area and extensive agriculture (24%), arable land (24%), permanent farming (16%), grassland (2%), and Urban area (1%). Current rate of urbanization in the majority of European countries is more than 80% and this explosive process comes from urbanism driving force during the past decades. Historical information of land conversions can help restoration activities.
Environmental changes could be detected at numerous scales but scale of landscape has more important information for spatial planning (O’Neil et al. 1997, 514). Change of landscape directly affects ecological processes and spatial arrangement of elements influence horizontal flows and movements (Forman and Godron 1986, 54).
Land use refers to type of human activities taking place on the land but land cover refers to biophysical condition of land surfaces. Sometimes concept of land use and land cover may be mixed and confused resulting in wrong understanding of landscape structure and function. Based on V-I-S model (Gluch and Ridd 2010, 86) land covers could be classified into three main groups detected by remote sensing technique: vegetation, soil, and impervious surface.
More than 50% of the land in Iran is mountainous (Firouz 1974, 15). Current rate of urbanization in Iran is more than 70% (Tehran comprehensive Plan, 2007, 25); urbanization growth rate was more than 1.5 % during the last decade (Seyyed Akhlaghi 2012, 499). Mountain regions are fragile and susceptible to environmental changes (Korner 2007, 570). Majority of cities in Iran are placed on lowland plains. Therefore, these are our questions: How are mountain upland and lowland plains interacting? How does urban growth of Tehran and Karaj cities affect ecotonal piedmont zones in the middle? Ecotonal piedmont zones in the middle of upland-lowland continuum have the role to connect mountains to plains. It is our objective to monitor land cover changes in ecotonal zone of piedmont in the southern slopes of the central Alborz Region respecting sprawl growth of Tehran-Karaj metropolitan area.
2. Materials and Methods
Study area of this research is ecotonal zone of piedmont in the southern slopes of the central Alborz region (Figure 1). From north to south, Tehran Plain could be divided into two main geomorphologic zones; the piedmont zone in the north up to the mountain front, and the Tehran plain in the south down to Rey City and its suburbs (Jahani and Reyhani 2006, 115). Tehran plain (Tehran-Karaj area) is located on the southern piedmont zone of Alborz Mountain Range, in an area more than 5,000 km2 to Namak (salt) Lake Desert in the south. The average annual precipitation in Tehran is still less than the figure for the country and is about 230 mm (Jahani and Reyhani 2006, 116). Tehran, the capital megacity of Iran, with still-growing population of 10 million of permanent residents and two million non–resident commuters is not an exception to this general custom. The expansion of the city which has started from Qajar and its accelerated speed from 1970s has not clammed down yet (Saeednia 1989, 3). The city of Tehran with an increasing population of 10 million citizens lies between Shahre-Rey in the South and Alborz Mountains in the North (Yavari 2007, 327). The slope is ranged from 1.3 to 5 percent with north to south aspect (Saemian 2012, 13). The population of the Tehran has increased from 0.1 million in 1891 to 8 million in 2006, a drastic increase of 80 times (Jahani and Reyhani 2006, 117). We used four satellite images of Landsat 7 ETM+ (2000) and Landsat 8 OLI/TIRS (2013) to capture land covers (Table 1). Classification is done by supervised method and maximum likelihood algorithm using Erdas Imagine 8.4. Accuracy assessment for each of the four classified images was more than 80%. Upper limit of Ecotonal piedmont coincides with knick line separating mountain and pediment plain and lower limit is drawn below the foothills. Ecotonal piedmont is divided into four unit zones: (1) Northern Tehran; (2) Suburb of Tehran-Karaj; (3) Northern Karaj; and (4) Western Suburb of Karaj.
3. Results and Discussion
Results show that relative percentage of open spaces, built areas, and vegetation covers at 2000 were 53.43, 28.73 and 19.48 percent, respectively. But at 2000 the proportion was different for built areas (52.59%), open spaces (38.55%) and vegetation covers (8.53%). Ascending ranking of the zones relative area of built-ups at 2000 was zone 3 (47.86%), zone 1 (43.12%), zone 2 (20.26%) and zone 4 (7.69%). At 2013, the ranking became different with zone 1, 3, 2, and 4 by relative value of 74.96, 63.01, 58.59 and 23.74 percent, respectively (Table 2).
Respective vegetation covers at 2000, zone 1 was in the first rank with value of 30.92% but at 2013 zone 4 by 11.82% becomes the first rank. At 2000, open spaces decreased as zones 4, 2, 3 and 1 have values 79.21, 59.44, 37.61 and 25.67, respectively. But at 2013, the same ranking remained but with decreased values of 64.42, 34.28, 31.20 and 16.49 percent, respectively.
Our results indicate that 32.93 percent of the ecotonal piedmonts have changed during 13 years (2000 to 2013). Vegetation covers and open spaces were the major source of land cover conversions and built area was the ultimate rank of land cover conversions. This explosive trend of urbanization in the ecotonal zone of piedmont signifies that regional inter-relations within upland-lowlands continuum (Becker 2007, 62) have been disturbed. Peidmont as a middle connector zone in this continuum (Marstone 2008, 510) and as an indicator of environmental change at landscape scale (Farina 2010, 126) have to be monitored for restoration activities in network of life support systems (Yavari et al. 2007, 340). This ecotonal zone has significant roles in vital processes of air and water (Bogachev 2004, 79). The alluvial fans and the orchards placed in this zone are the main suitability features must be conserved.