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5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Land use-land cover and

Land use-land cover and normalized difference vegetation index changes in Wello confidences level, at the degree of freedom (df), n-2 = 11-2 = 9 and n = number of years. � If |to| � t0.25,9 = 0.703, then Acal is significantly different from zero at 75% confidence level � If |to| � t0.10,9 = 1.383, then Acal is significantly different from zero at 90% confidence level � If |to| � t0.05,9 = 1.833, then Acal is significantly different from zero at 95% confidence level 4.2.3 Ground truth data collection and LULC type identification In order to support image classification, ground truthing was done in two phases. First, reconnaissance assessment was done during the research site identification. The reconnaissance survey aimed to gain general information of the study area and existing biophysical conditions. In this phase, an unsupervised classification-based LULC map was used, and signatures of the major land uses were interpreted in the field. After the reconnaissance survey, tentative LULC types were defined. During the main field survey, the coordinates of the ground control points (GCPs) of the past and actual LULC types were collected using a global positioning system (GPS). The GCPs for the LULC of 2000 were collected based on information from elderly people and agriculture offices. A total of 250 GCPs were collected for each year through field survey and secondary information. In most cases, GCPs of the year 2000 and 2009 were the same except in cases where the respondents were not certain of the year 2000 changes. Before the reconnaissance survey, the LULC of the study area was mapped in twelve mapping units using unsupervised classification. After the main survey, the final land use/cover classification was done by maximum likelihood supervised classification using the training areas identified during the field survey. Due to the coarse resolution of the satellite images and low separability of the signatures, the LULC classes were reduced to five by aggregating some classes together. Cultivated land, settlements and bare land have very similar signatures with low separability. Thus, these classes were clustered to the same mapping unit. Similarly, forests and woodlands were aggregated as forestland. In the early period, exclosures are dominated by newly emerging grasses with little regenerating woody vegetation and have a similar signature to that of 38

Land use-land cover and normalized difference vegetation index changes in Wello grasslands. Thus, grasslands and woody grassland were classified as grassland/woody grassland. Accordingly, the LULC types were grouped in five major classes: i) cultivated land/others, ii) forest, iii) degraded woody vegetation, iv) grasslands/woody grasslands, and v) water bodies (Table 4.1). Table 4.1 Description of LULC types No. LULC type Description (i) Cultivated lands/others Includes wide range of LULC, mainly cultivated lands (irrigated and non-irrigated), settlements up to city level and bare lands. (ii) Forest Represents area covered by woody vegetation with more than 20% canopy cover. This includes forests, woodlands, (iii) Degraded woody vegetation (iv) Grasslands/woody grassland old exclosures and bush lands. Area with woody remnants and some scattered woody vegetation where the canopy and ground cover were less than 5% and 25%, respectively. These lands are used for free livestock grazing and have free access for firewood and construction wood collection. Includes grasslands and woody grassland. New exclosures were at first degraded woody vegetation, but due to exclusion from human and animal intervention the areas started to regenerate. Thus, the ground cover improved (> 25%), but the canopy cover is still low, between 5% and 20%. After two to three years of exclosure, the ground is largely covered by grasses, scrubs and shrubs. (v) Water bodies Includes lakes (Hayk, Hardibo and Maybahr), swamps (Hara Swamp), ponds and water accumulated at some points within wide river courses. 4.2.4 Digital elevation model In order to compare the LULC and NDVI change against land-use policy, which is based on slope, the study area was classified into slope classes using a 30-m resolution gridded elevation data in digital elevation model (DEM). The land-use policy demarcated land use based on three slope classes, i.e., less than 30%, 30% to 60% and over 60% slopes. The policy determined land use as i) land allowed for cultivation and grazing, ii) land where perennial crops such as fruits, coffee and others annual crop cultivation is allowed, and iii) land where cultivation and grazing are prohibited in the above mentioned slope ranges (Anonymous 2005; 2006). The policy urges appropriate 39

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