Since ecosystem services vary considerably, evaluation of ecosystem functions at a regional scale has
usually been limited by the methods used, and the fact that data has often been difficult to obtain.
Currently, assessment methods that use mathematical models combined with GIS data are the focus of
ecological research.
InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs Tool) is a model developed by the
Natural Capital Project of Stanford University, the University of Minnesota, the World Wildlife Fund
(WWF) and The Nature Conservancy (TNC). It is designed to assist in decision-making about natural
resource management and/or conservation [11, 12]. In the present study the InVEST model was used to
evaluate the change in ecosystem regulating services before and after the earthquake, focusing on water
retention, soil conservation and carbon storage. The reason for choosing these three ecosystem services
was that: 1) the chosen ecosystem services are important to both the earthquake-affected area and the
Upper Yangtze River Basin; and 2) these services can be quantified and the results compared.
The details of the assessment methods are set out below.
Soil conservation
Based on the Universal Soil Loss Equation (USLE), the InVEST model modifies the slope length–
gradient (LS) factor equation. The rainfall and runoff erosivity factor (R) was calculated by the
Richardson formula[13]. Soil erodibility was calculated using the EPIC model, and the vegetation cover
and soil conservation measures factor were obtained from research results[14]. The soil conservation
function (Ac) was calculated as the difference between potential and actual erosion:
Ac = Ap – Ar (1)
where Ap is the potential erosion (t/ha·a), and Ar is the actual erosion (t/ha·a).
The potential soil erosion is defined as the soil erosion capacity without regard to land cover or land
use.
Water retention
Ecosystem water conservation is composed of the water retention capacity of vegetation and soil. The
soil layer is the major contributor to water conservation. Only the water retained by the soil was
considered in the InVEST model, the main aim being to calculate the average amount of water retained
by different ecosystems in one year, taking into account different land usage, soil permeability differences,
and the effect of topography and surface roughness on runoff.
Carbon storage