Ecological Modelling 220 (2009) 2503–2511
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Ecological Modelling
journal homepage: www.elsevier.com/locate/ecolmodel
Coupling a land use model and an ecosystem model for a crop-pasture zone
Xia Xu a,∗, Qiong Gao a, Ying-Hui Liu a, Jing-Ai Wang b, Yong Zhang a a State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, College of Resources Science and Technology, Beijing Normal University, Beijing 100875, China b School of Geography, Beijing Normal University, Beijing 100875, China article info abstract
Article history: This paper describes the development of a land use model coupling ecosystem processes. For a given Received 12 November 2008 land use pattern in a region, a built-in regional ecosystem model (TESim) simulates leaf physiology of Received in revised form 24 April 2009 plants, carbon and nitrogen dynamics, and hydrological processes including runoff generation and run-on Accepted 27 April 2009 re-absorption, as well as runoff-induced soil erosion and carbon and nitrogen loss from ecosystems. The Available online 13 August 2009 simulation results for a certain period from 1976 to 1999 were then used to support land use decisions and to assess the impacts of land use changes on environment. In the coupling model, the land use type for a Keywords: land unit was determined by optimization of a weighted suitability derived from expert knowledge about Coupling model Land use change the ecosystem state and site conditions. The model was applied to the temperate crop-pasture band in Ecosystem process and function northern China (CCPB) to analyze the interactions between land use and major ecosystem processes and Soil erosion functions and to indicate the added value of the feedbacks by comparing simulations with and without The northern China crop-pasture band the coupling and feedbacks between land use module and ecosystem processes. The results indicated (CCPB) that the current land use in CCPB is neither economical nor ecologically judicious. The scenario with feedbacks increased NPP by 46.78gCm−2 a−1, or 32.23% of the scenario without feedbacks, also decreased soil erosion by 0.65 kg m−2 a−1, or 23.13%. Without altering the regional land use structure (proportions of each land use type). The system developed in this study potentially benefits both land managers and researchers. © 2009 Published by Elsevier B.V.
1. Introduction enced; and estimating the speed of land use and land cover change. By using certain suppositions, the LUCC model can also be used to Optimal land use planning is a leading issue for terrestrial explore future land use patterns. ecosystem management in the world (Brody, 2003; Bousquet and Le A number of land use models have been developed in the Page, 2004). The multiple objectives of land use decisions can lead last decade based on methods of systems analysis (De Wit et al., to substantially different consequences in terms of ecosystem evo- 1988; Rabbinge and van Latesteijn, 1992; Kruseman et al., 1995; lution (Haberl et al., 2001; Krausmann, 2001; Verburg et al., 2004; Kuyvenhoven et al., 1995; Penning de Vries et al., 1995). Some mod- Krausmann et al., 2004). Policy makers and stakeholders have both els address urbanization and agricultural intensification (Brown et a current and a future right to decide on the use of land (FAO, 1995). al., 2000; Engelen et al., 1995; Hilferink and Rietveld, 1999; Lambin They thus require enhanced understanding of the opportunities for et al., 2000), by simulating land use changes either as a function and limitations to regional development. Spatially explicit dynamic of land use in the neighborhood and user’s expertise, or based models, that integrate land use changes and ecosystem processes on the empirical relationship between land use and driving fac- and functions, are important tools for the design, analysis and quan- tors (Pijanowski et al., 2000; Pontius et al., 2000). The Conversion titative understanding of future spatial patterns and impacts of land of Land Use and its Effects (CLUE) model is capable of simulating use change (Veldkamp and Lambin, 2001; Rutherford et al., 2008). multiple land use types simultaneously using competition between Lambin (1994) pointed out that the LUCC (Land Use and Land Cover land use types, without incorporation of the environmental effects Change) model can help scientists to make suppositions and to on land use (Veldkamp and Fresco, 1996; Verburg et al., 1999, 2002, answer major questions in land use research, including: elucidat- 2006). ing the socio-economic and biophysical variables explaining land The choice of model may have important implications in terms use and land cover change; determining the concrete area influ- of specific aspects of the resultant land use changes. Castella and Verburg (2007) applied two different LUCC modeling frameworks to the same research site. The integration of land use change ∗ Corresponding author. with ecosystem processes to improve future land use manage- E-mail address: [email protected] (X. Xu). ment remains an important subject that deserves more advanced
0304-3800/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.ecolmodel.2009.04.043 2504 X. Xu et al. / Ecological Modelling 220 (2009) 2503–2511 research. Spatially explicit landscape models have been developed understanding of the relationship between land use change and to address the impacts of spatial variation on ecosystem processes ecosystem processes. (Higgins et al., 2000; Curnutt et al., 2000; Gao et al., 1996; Gao and The region has a history of land use research and modeling: An Reynolds, 2003). Spatially explicit landscape models link a process- et al. (2002) reconstructed the land use structure of the CCPB; Liu based ecosystem model to a geographic information system (GIS). and Tong (2003) investigated the land use changes in the past 50 An example is the project NELUP (Watson and Wadsworth, 1996), years and estimated the effect of the changes on the quality of the in the United Kingdom, in which ecological models have been built eco-environmental system; Zhan et al. (2004) estimated the envi- within a GIS environment as a part of a computerized decision ronmental effects of land use change in the Inner Mongolia part of support system (DSS). NELUP integrates models based on eco- the CCPB; Shu et al. (2006) simulated the optimal land use patterns nomics, ecology and hydrology in one modeling framework with with the model LUOS basing on GLP (Grey Linear Programming) and a common database and user interface. Weber et al. (2001) linked CA (Cellular Automata) methods; and finally Gao et al. (2007) sim- three simulation models from agricultural economic, ecological and ulated the impacts of soil erosion and climate shift on the regional hydrological sciences, via GIS and examined land use changes in a carbon balance with a spatially coupled regional ecosystem model, peripheral German region and their effect on ecology and hydrol- TESim. ogy. More recently, similar approaches have been taken in the As the core of International research projects “Global Change following studies: Gao et al. (2003) introduced land use as a limiting and Terrestrial Ecosystems (GCTE)” and “land use/land cover change factor for dynamic vegetation development during their simulation (LUCC)” had relatively independent in-depth study from natural of primary production; Fu et al. (2003) analyzed the dynamic effect ecosystems and the change of terrestrial surface process under of five land use structures and seven land use trends on soil mois- human activities, as the deepening of research about these two ture; Ozaki et al. (2008) simulated effects of alteration of river basin aspects, researchers were increasingly aware of that the results land use on river water temperature; Wang et al. (2003) analyzed were unilateral if we independently studied the two aspects close the response of soil structure and nutrient dynamics to agricultural tied with, thus, the coupling research of land use change and eco- land use; Gao et al. (2004a,b) depicted the effects of the spatio- logical processes, and building a coupling model between the two temporal character of the northern climate and LUCC on regional aspects is a major trend of development. This paper presents a mod- net primary production; and Costanza et al. (2002) constructed the eling framework, TES–LUC, which couples the TESim model and PLM (Patuxent Landscape Model) model considering the reciprocity land use model (LUCC). The land use pattern depends on environ- of land use and ecological processes. mental factors including soil and Climate conditions and man-made The northern China crop-pasture band (CCPB) lies geographi- socio-economic factors, in the TES–LUC model, we considered only cally between 34.7◦N and 48.6◦N and 100.8◦E and 124.8◦E, with the former (environmental factors), thence it was a theoretical a total area of 725 527.9 km2 (Fig. 1)(Wang et al., 1999). It has a exploration. The TES–LUC model is applied to the CCPB to simu- population of approximately 60 million. Ecosystems in the region late potential changes in land use pattern, net primary production are under a typical continental monsoon climate. Annual mean and soil erosion under different decision scenarios. Results are dis- temperature is 14 ◦C in the South to 1 ◦C in the North. Annual pre- cussed in the context of land use planning and regional ecosystem cipitation decreases from approximately 580 mm in the Southeast management. to less than 200 mm in the Northwest. Vegetation patterns largely correlate with precipitation and temperature: with a small pro- 2. Model description portion of coniferous forests in the cold North and mountains: deciduous broadleaf forests in the Southeast and North: large pro- 2.1. Land use module portions of shrubs and grasses on the northwest side of the dry plateaus; and croplands distributed mostly in the middle and the Our land use model is based on the principles of the CLUE model Southeast regions. The region has been undergoing severe soil ero- (Veldkamp and Fresco, 1996; Verburg et al., 1999, 2002, 2006) sion, degradation and desertification because of inappropriate land for crop-pasture areas. Crop-pasture areas are often dominated by use and overgrazing by livestock. The rapid economic development three types of land use, crop fields, grasslands (pasture), and forests, of China over the past two decades exerts a great pressure on the whilst other types (buildings, water bodies, etc.) occupy only a small regions environments and ecosystem structure and functions. Opti- proportion. Land use in a crop-pasture region was thus grouped mal land use planning to achieve the solution of best compromise into to four types, i.e., crop fields (CROP), grasslands (GRAS), forests for both economic development and conservation of ecosystem (FORE), and others (OTHE). After initial gridding of the crop-pasture services represents a great challenge for research. It is a top pri- region into a number of discrete cells, CROP type land use was ority for both governmental policy makers and local practitioners. allocated to all grid cells meeting the following criteria: Judicious planning of land use has to be guided by comprehensive min fi (xi) ≥ 0.2 (1)
Fsite,crop + Fexpt,crop − Floss,crop >Ccrop (2)
where fi(xi) ∈ [0,1], for i =1,2,...,n, is a series of fuzzy membership functions (Chen et al., 2006) derived from the knowledge of agri- cultural and ecological experts, xi is a series of climate and soil fertility characteristics Fsite,crop is a site suitability factor statistically derived from the relationship between current land use and site n Fexpt,crop = w f x variables such as climate and topography, i=1 i i ( i) is the weighted average of the expert fuzzy membership functions, wi is the weight determined by the relative correlation between land use and xi, Floss,crop is a factor derived from past land use change data to quantify the likelihood of crop fields transferring to other land use types, thus Floss,crop characterizes the reciprocal of land use stability. Ccrop is the criteria of allocation for crop fields, a constant Fig. 1. Location of the China crop-pasture belt (CCPB). adjusted to accommodate land use demand from agricultural eco- X. Xu et al. / Ecological Modelling 220 (2009) 2503–2511 2505 nomics. Eqs. (1) and (2) require that the minimum membership probability that land use type i transfers to land use type j in the function value (which specifies the suitability) should be greater next period. ij is equal to the approximate number of sites trans- than 0.2, and that the overall suitability, i.e., suitability derived from ferred to land use type i in the later map divided by the total number site analysis plus that from experts minus the probability of loss by of sites of land use j in the earlier map. Floss,j is then calculated as transferring to other land use type, should be greater than criteria q specified by policy makers to meet the local agricultural economic demands. Floss,j = ij (6) After allocation of cells to the CROP land use type the remain- i=1,i =/ j ing grid cells were allocated to the other land use types using the following equation where q is the total number of land use types in the region. LU(r) = LTj, if max Fsite,k − Floss,k+Dk = Fsite,j − Floss,j + Dj (3) k=2,3,4 2.2. Ecosystem process simulator where LU(r) is the land use variable, r is the spatial location variable Ecosystem processes in our model were simulated using an (rth grid cell), LTj is the value of LU(r), specifying the type of land embedded model TESim which calculates ecosystem production, use. In the present study, LTj = CROP, or GRAS, or FORE or OTHE for carbon balance, soil erosion and nutrient cycling for terrestrial j = 1, 2, 3 and 4. Fsite,j and Floss,j have the same meanings as Fsite,crop ecosystems at different scales. The detailed model description of and Floss,crop, but the subscript j here indicates they are factors for TESim formulation, parameterization, validation and application to the jth land use type. Dj is a series of constants determined by socio- CCPB without land use change are detailed in previous publications economic demands for a specified land use structure. Hence land (Gao and Zhang, 1997; Gao and Yu, 1998; Gao and Reynolds, 2003; units (grid cells) will be allocated to types that have the maximum Gao et al., 2007). Mean annual NPP, annual soil erosion, SOM con- suitability and stability, adjusted by the demand. tent, and soil nitrogen are the four output variables used in the Site suitability Fsite,j was calculated using a standard logit func- present study. In particular annual NPP and soil erosion were used tion of multi-variables to show the effects of the land use model. a + m b X exp( j =1 j ) Fsite,j = (4) + a + m b X 2.3. Coupling the land use module with the ecosystem process 1 exp( j = j ) 1 simulator where X for =1,2,3,..., m is a series of site variables. In our case, these variables were population density, P (number of people/km2), The coupling processes between the land use module and site slope, ˛ (◦), site elevation, H (m), mean annual temperature, ecosystem simulation within TES–LUC was realized as an iterative MAT (◦C), cumulative daily mean temperature during the growing procedure through the exchange of data. (Figs. 2 and 3). TESim was season, TAG (◦C), mean annual precipitation, MAP (mm), precipita- run for an initial land use pattern, the output values for SOM and soil nitrogen content from TESim were then used as ecological back- tion during the growth season, MAPg (mm), and soil organic matter (%). All of these special variables were quantified from DEM (Digital ground data of the land use module. After getting the ecological Elevation Model) or long-term climate data and population data, background data, the land use module calculated the suitability of with the exception of soil organic matter, which was estimated every land use type on every land unit, by adjusting Ccrop and Dj the desired amount of crop field, forest land and grassland can be from a simulation model. Coefficients aj and bj were estimated by regressing a land use variable on all of these site variables within allocated. This completes the first round of simulation. The newly the area of application using Eq. (4). The land use variable equals 1 adjusted land use may not meet the criteria set in the first round of if a site is currently occupied by land use type j, or zero otherwise. simulation, in which case TESim is run for a second round, and land Only those coefficients that were significant were used in the land use is allocated again. This process is repeated until all conditions use module. Eq. (4) is a logistically increasing/decreasing function are met, which signals the convergence of the procedure and the iteration stops. of all X , depending on the sign of bj . The membership function was constructed according to FAO’s classification standards and agricultural ecological experts’ knowl- 3. Application to CCPB edge. These functions take the following form ⎧ −1 3.1. Data preparation and parameterization of the land use ⎨⎪ x − x 2 + i i0 ,x