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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
assessment. With 1:250,000 DEM data, ArcGIS hydrology tool 
was used to extract the area border, and 19 sub-watersheds were 
got as the final assessment units with administrative map as 
reference (Figure 1). 
3. METHODS 
3.1 Conceptual framework of ecosystem health assessment 
For the requirement of environmental management and decision 
making, scientist designed numerous conceptual frameworks. In 
all of these frameworks, the Pressure-State-Response (PSR) 
model (OEDC, 1993) reached the most extensive agreement and 
was widely used in wetland ecosystem assessment (Mai, et al. 
2005), evaluation of land use (Zhou, et al. 2002), ecological 
security assessment (Zuo, et al. 2002) for its clarity causal 
relationship. But the PSR model also has shortage, for instance, 
it can not classify the entire index clearly, and the response 
indicators are difficult to quantify etc. Furthermore, PSR model 
is founded for environmental problem, it is not suitable to social 
issue. Therefore, the “Driving forces-State-Response” model 
(OEDC, 1993) and the “Driving forces-Pressures-State-Impacts- 
Response” model (EEA, 1998) were developed on the basis of 
PSR model. 
Based on current situation and needs we required, we revised 
the PSR model (Figure 2) and regarded it as our conceptual 
framework. “Effect” index was introduced in the revised model, 
“Effect” shows the ability of self-recovery within an ecosystem, 
it contains resilience and nature response. In this way, we took 
the ecosystem’s self-recovery into account when calculated the 
response index. At the same, the pressure index was subdivided 
into nature pressure and artificial pressure, the state index was 
subdivided into vigor and organizational structure. So, the 
revised model has a better pertinence in indicator selection and 
accords with the conception of ecosystem health well. 
+ 
DongSheng city 
Nature Artificial Social 
Pressure Pressure Response 
Organization Vigor Nature Resilience 
Structure Response 
Figure 2. The revised PSR model 
3.2 Establishment of assessment indicator system 
Based on the concerned principles and methods of establishing 
ecosystem health assessment index system, the assessment 
indicator system was established (Table 1). 
Assessment indicator 
Pressure 
Nature 
pressure 
Area ratio of damaged land 
Desertification index 
Artificial 
pressure 
Population density 
Traffic impact index 
Ratio of theoretical and practical 
stocking rates 
Human footprint index 
State 
Vigor 
Vegetation coverage 
Annual precipitation-evaporation ratio 
Net Primary Productivity 
Organization 
structure 
Distribution of grassland pattern 
Landscape diversity index 
Patch density index 
Effect 
Resilience 
Difference of NDVI 
Land use/land cover evaluation 
Nature 
response 
Soil erosion index 
Ratio of grassland degradation 
Soil and water conservation index 
Response 
Social 
response 
Area ratio of natural reserve 
Afforestation index 
GDP per capita 
Table 1 Assessment indicator system 
3.3 Evaluation Standard 
Generally speaking, there are two methods to quantify the 
... evaluation of objects: relative method and direct evaluation 
method. Since structure and function of grassland ecosystem is 
extremely complex, and absolute value researches of many 
Figure 1. Result of sub-watershed extraction in Ordos city indicators are immature. The relative evaluation method was 
adopted here, and the study areas were ranked as I to V from 
good to bad with final ecosystem health indexes. 
3.4 Evaluation Method 
Ecosystem is a complex organization and open system, which 
has close and inseparable relations and functions to external 
environment, so the method combined with qualitative and