Evaluation indicators for urban ecological security based on ecological network analysis

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1 Available olie at Procedia Evirometal Scieces 2 (2010) Iteratioal Society for Evirometal Iformatio Scieces 2010 Aual Coferece (ISEIS) Evaluatio idicators for urba ecological security based o ecological etwork aalysis Zhaoxue LI a, Liyu X a, * a State Key Laboratory of Water Eviromet Simulatio; School of Eviromet, Beijig ormal Uiversity, Beijig , Chia Abstract The urba ecological ifrastructure, maily cosist of urba ladscape, provides the eco-services for the developmet of society ad ecoomy. The stability of ladscape eco-system fuctio is the ecessary coditio holdig the status of urba ecological security. This article itroduces the metapopulaito capacity ito the evaluatio of ecological etwork stability, improves the calculatio of the metapopulaito capacity, ad forms a ew idicators system which combies the metapopulatio capacity with some idicator used i the ecological etwork aalysis to measure the urba ecological security. At last, idicators for urba ecological security based o ecological etwork aalysis discussed above are established for Guagzhou Published by Elsevier Ltd. Ope access uder CC BY-C-D licese. Keywords:Ecological etwork aalysis; metapopulatio capacity; Guagzhou 1. Itroductio oder cities are icreasigly expadig with social ad ecoomical developmet. Chia's urbaizatio rate is icreasig rapidly ad stood at 45.68% i 2008, accordig to the urba evirometal maagemet ad comprehesive aual report issued by the iistry of Evirometal Protectio. Expasio of city areas ad chages of lad use patter make the urba ladscape fragmeted icreasigly. Urba ecological ifrastructure, maily cosist of urba atural ladscape, is the mai provider of the eco-services for developmet of society ad ecoomy. The sharp chage of structure ad fuctio of urba ladscape has weakeed the eco-services fuctio provided by urba ecological ifrastructure, ad has threateed the urba ecological security ad sustaiable developmet. For keepig the security of urba ecological system, maagers ad scietists are always to seek for the suitable urba plaig method to regulate ad perfect the urba ladscape structure ad to protect the stability of the key ecosystem fuctio. Ecological etwork aalysis (EA) ca be used to evaluate the spatial plaig s suitability to urba ladscape eco-system, ad to optimize the spatial plaig through the sceario aalysis. This method is also suitable for the evaluatio of urba ecological security ad urba plaig. * Correspodig author. Tel.: ; fax: address: xly@bu.edu.c Published by Elsevier Ope access uder CC BY-C-D licese. doi: /j.proev

2 1394 Zhaoxue Li ad L. XU / Procedia Evirometal Scieces 2 (2010) Urbaizatio Regulate impact Impact Urba plaig keep Urba ecological security Regulate ecessary Stability of ladscape structure ad fuctio Figure1 the relatioship amog urbaizatio, urba plaig ad stability of ladscape structure ad fuctio Ecological security, proposed by the govermet of Uited States [1], does ot have uiversally accepted defiitio ow. Here, from the relatioship betwee urba ladscape ecological system ad ecological security, the urba ecological security ca be regarded as the status that the structure of the urba ladscape is itegrated ad the fuctio is stable to provide eough eco-services to support the developmet of the socio-ecoomic system ad further to maitai the urba sustaiable developmet. Ecological etworks, derived from ladscape architecture ad plaig of orth America, refer to a set of ecosystems, which liked ito a spatially coheret system through flows of orgaisms, ad iteracted with the ladscape matrix i which it is embedded. The EA is a method to aalyze, evaluate, regulate ad perfect the ecological etwork i order to hold the stability of the ladscape ecosystem fuctio. From 1990s, EA was used i regioal ad atioal scale to coserve atural resources or to maage protectio zoe [2-7]. The study cotets icluded the basis cocept of ecological etwork, the fuctio of ecological etwork, the idetificatio ad structure of ecological etwork, ad the evaluatio ad plaig of ecological etwork etc. The methods that are used i the evaluatio of ecological etworks are maily based o the ladscape ecology ad graph theory. Such as Zhag et al [8] aalyzed ecological etwork of Xiame Islad (Chia) through ladscape ecological idicators. Xiog [9] take idicators of etwork coectio ad accessibility i accordig with graph to measure the itegrity of urba eco-etwork. Adreas [10] combied graph theory ad etwork aalysis to explore ladscape or habitat coectivity. The methods based o the graph theory which simplify the complex ladscape system ito a etwork graph (digraph or udigraph) [11] is beeficial to visually measure the topology, coectivity ad complex of the ladscape etwork structure. Although, this simplicity, especially patches or habitats were abstracted odes, results to some useful iformatio lost. The method of ladscape ecology establishes the relatio betwee the ladscape structure ad fuctio, ad some of idicators could evaluate the ecological value of sigle patch ad corridor, but there is less the sythetical descriptio of the features of patches. Whe itroduced EA to urba plaig, Edward [12] thiks three pricipal aalyses i the study should be followed: (1) patch cotet aalysis, (2) corridor cotet aalysis, ad (3) etwork structure aalysis. From the situatio of the study ow, there is much emphasis put o the etwork structure aalysis. Ideed, the structure of ecological etwork i the urba area is very importat for material circulatio ad eergy flow amog fragmetized patches. But from the viewpoit of ecological security, the eco-services that support the developmet of urba socio-ecoomy is provided by the urba ecological ifrastructure, composed maily by urba atural ladscape patches, so seekig for some methods that are able to itegrate the patch ifluece ito the etwork aalysis is more valuable ad importat. Some methods ivolve metapopulaito dyamic provide ew ideas for the study. The cocept of metapopulatio was proposed by Richad Levis [13] to describe a populatio cosistig of may local populatios i which a local populatio is a populatio cosistig of idividuals. Because of its applicatio i ladscape ecology ad i coservatio biology, there are may researchers about the theory ad applicatio [14-20]. Accordig to the form of dealig with spatial relatio of metapopulatio, the models described the metapopulatio dyamic ca be divided ito three types: Spatially implicit metapopulatio model, SI; Spatially explicit metapopulatio model, SE; Spatially realistic metapopulatio model, SR. Icidece fuctio

3 Zhaoxue Li ad L. XU / Procedia Evirometal Scieces 2 (2010) model (IF), describig the spatially explicit metapopulatio, which icludes geometric iformatio of ladscape ad ca be use to directly simulate the real ladscape [21], is the most advaced model. But the IF is a liear markov model used i the sigle habitat, it is limited to be applied ito the ladscape ecological etwork. Haski ad Ovaskaie [22] tured to matrix otatio to describe the system of equatios givig the rates of chage i the probability of the sigle patch beig occupied, ad defied the leadig eigevalue of the matrix as the metapopulatio capacity of a fragmeted ladscape to measure the bearig capacity of ladscape patches for some species. Subsequetly, they discussed the global ad local assessmet of metapopulatio capacity [23]. Otso [24] explored the idividual habitat fragmet cotributio to metapopulatio persistece based o the metapopulatio capacity. Cag [25] aalyzed the iteractio of carryig capacity, populatio equilibrium, ad eviromet s maximal load. I the study about the rapid evaluatio method of metapopulatio persistece, ichael [26] improved the calculatio of metapopulatio capacity i order to apply it to highly variegated ladscapes. Although there are may researchers thik that metapopulatio capacity is suitable for the study o the ladscape ecology, there is less discussios o the ecological etworks ad i the scale of cities. So this article itroduces metapopulatio capacity ito the EA i the urba ladscape, try to improved EA ad make it applicable to evaluate the urba ecological security. At last, idicators for urba ecological security based o ecological etwork aalysis discussed above are to establish for Guagzhou city. 2. Evaluatio idicators This sectio we will firstly discuss the model applicability used i the urba ladscape ad habitats of metapopulatio (sectio2.1), the the calculatio of metapopulaito capacity ad the trasformatio will be described (sectio 2.2), last the metapopulatio capacity ad the idicator of EA will be combied to form the comprehesive idicators measurig the urba ecological security(sectio 2.3) The discussio of applicability Because there is o metapopulaito dyamic model applied i the scale of city, it is ecessary to discuss the similarity with the urba ladscape ad habitats of metapopulatio. Haski et al [27] defied a typical metapopulatio as a system satisfyig the followig four stadards: (i) a survivable iche exists i the form of scatterig patches; (ii) the largest regioal metapopulatio is faced with the risk of extictio as the smallest oe; (iii) patches are ot too separated to be recoloized; (iv) all regioal metapopulatios are ot likely to sychroize completely. (i)because of the artificial disturbace, the area of atural ladscape patches has sharply reduced i the urba ladscape, exist large patches have yet bee broke up ito several small patches coected by atural or artificial corridors. The species of urba area is survival i scatterig patches, ad deped o the corridors or other form to migrate amog the patches, seek for the optimal habitat or avoid iterferece, i order to keep the species persistece. (ii)because of the ucertaity of atural coditio ad huma activity, the chage of each patch ad coected corridors is ucertai, it could impact the capacity of the patch to the local populatio. The risk of extictio of local populatio survival i each patch is ucertai, amely the largest metapopulatio might face with the same risk of extictio as the smaller oe. (iii)for protectig the ecological flows amog the fragmeted ladscape ecosystem i the city, corridors are built up to coect each patch, these corridors could guaratee that patches are ot too separated to be recoloized. (iv) I the urba area, some patches are artificial or disturbed severely by the huma such as farmlad ad public garde, the survival coditio of each patch for some species is differet i differet period. The species had to migrate oe to aother to keep the populatio persistece accordig to resource coditio of patches. Whe there are may patches i which the resources coditio of each patch is differet i differet period, the icidece of all regioal metapopulatio sychroizig completely is very little Calculatio ad trasformatio of metapopulatio capacity The traditioal calculatio of metapopulatio capacity described by Haski ad Ovaskaie [22] is the leadig eigevalue of matrix which is a patch-by-patch matrix cosistig of elemets m ij =exp(- d ij )A i A j for i j ad m=0. Where A i is the area of path i, ij is the distace betwee patches i ad j, 1/ is the average migratio distace. I the applicatio, some researchers [26] thik w=exp(- d ij ) is the probability of successful movemet at

4 1396 Zhaoxue Li ad L. XU / Procedia Evirometal Scieces 2 (2010) distace d, ad distiguish the matrix amog patches ito good matrix ad poor matrix for a species, ad the migratio ability (refer to the movemet distace) is better i good matrix. There we will improve it with more detail iformatio. I ladscape ecology, the least-cost distace might express the relative accessibility of some path from the source to certai poit i space. So the cumulative value D R i could istead the real distace d ij. If we assume some species migratio ability (the logest distace this species ca migratio) i the ladscape is chaged with the habitat coditios. With the differetiatio with the optimum habitat icreasig, the work a species eed to sped i the process of spread will icreases, ad the species migratio ability will decrease. Accordig to the impacts to species migratio i all kids of ladscape type, we could give differet value of resistace. Table 1 The classificatio of relative resistace Relative value of resistace Impact Explai 1 o-resistace The ladscape factor is the same with the habitat 2,3 Low resistace 4,5 iddle resistace There is a little resistace, the ladscape factor is similar with the habitat, such as forest ad shrub The ladscape factor is the vegetatio form by artificial disturbace, such as Savaa ad grasslad 6,7 High resistace The zoe of artificial disturbace obviously, such as croplad 8,9 Very high resistace 10 Top resistace Urba mai highways or water which iterested species is difficult to through Urba costructed area of large, high-desity or highway or cliffs that iterested species is difficult to through ote: the impact of the matrix maily depeds o the special species attribute. At the same time, the area of path i could istead by the viable area, because the edge effect of the irregular habitat for a sigle species is always disadvatageous, we ca use roud area istead the real area i order to avoid this impact. So the elemets cotaied i the matrix ca be chaged ito m ij exp D xy R x A i A j x 1 (i j ad mij =0) (1) Where D xy is the spatial distace from the source y to some poit i space whe species passes the ladscape type i; R x is the movemet resistace of the ladscape x to some species. A i is the viable area of path i. The leadig eigevalue m is the metapopulatio capacity i the special ladscape. I metapopulatio model, the impact from other patches to iterested patch is cosidered as a idepedet process. I practice, migratio paths have the ifluece to each other i ecological etwork. But this model could ot reflect the iformatio that diversity ad cyclig amog patches are good for stability of the etwork. For example, i metapopulatio model, the impact from patch 1 ad patch 3 is the same for patch 2 i picture 1(a) ad 1(b), the etwork cyclig is overlooked, but obviously, ladscape 1(a) is more stable tha ladscape 1(b). The metapopulatio capacity could combie the structure iformatio ad biological iformatio, but could ot reflect the itegrated state of ecological etworks (a) Figure2 The impact to patch 2 of differet ladscape etwork circulatio (b)

5 Zhaoxue Li ad L. XU / Procedia Evirometal Scieces 2 (2010) The combiatio of metapopulatio capacity ad the idicator from EA I the classical EA, whose object of study is the ecological etwork based o the food web, the ecological etwork circulatio (ECI) is used to measure the itesity of circulatio paths i the etwork. Ad this idicator reflects the smooth ad diversity of the ecological process, ad the ability of material migratio, feedback ad selforgaizatio. Zag [11] has itroduced it ito the EA of ladscape to depict the circulatio of ladscape etwork. But she thought the ecological etwork circulatio ca ot depict the etwork comprehesively whe the etwork is ot the strog graph [28]. So she developed the idicator of ecological etwork coectio (ECO) to improve it. Because ECI ad ECO ca well describe the circulatio ad coectio of the ecological etwork, they could make up the isufficiet of metapopulatio capacity i the evaluatio. The ECI icrease idicates the regioal circulatio is stregtheed, the ecological diversity rise, ad the etwork is active, but some patches might become isolated. The ECO could make sure all the patches eed to coect with each other. If there are ice ECI ad ECO, patches locatio, area ad ecological flows betwee eighbours are good eough to support the key populatio developmet, the stability of ecological etwork is guarateed. So sythesize the metapopulatio capacity, ECO ad ECI, the comprehesive idicator to measure the stability of ecological etwork ca be expressed as below: m m FS ECI ECO (2) 2 Where the FS is the stability of ecological etwork; m is the largest eigevalue of the adjacet matrix depictig the etwork; is the umber of odes of the etwork; is the umber of ode i the strogly coected compoets. 3. Case study Guagzhou, capital of Guagdog Provice, is oe of Chiese mai idustrial ceters, coverig a area of 7,434 square kilometers, ad with a populatio of over 6 millios. Guagzhou stads at the cofluece of the East River, West River ad orth River, with its lad slopig from orth-east to south-west, ad a alluvial plai i the south ad south-west parts. It adjois the South Chia Sea, ad is crisscross with rivers ad streams. It has south subtropical marie climate with a aual average temperature of 21.8 degree Celsius, raifall of 1694 millimeters, ad a frost-free period of 345 days. It s abudat i agricultural ad aquatic resources. Due to the superior geographic ad climatic coditios, plat species is very rich i Guagzhou, trees species of theaceae, fagaceae ad lauraceae are domiat. The metapopulaito dyamic model simulates the coloizatio ad exictio of a sigle species, so the metapopulaito capacity get from this model is the carryig capacity to a sigle species. There the metapopulatio capacity to a sigle species will stad for the carryig capacity to the eco-system, so we should choose the typical species as the iterested species. The iterested species could be plat or aimal, whose metrapopulatio capacity ca be regarded as the idicator evaluatig the stability of urba ladscape ecological etwork. Two core priciples for choosig iterested species should be as followig: The iterested species should be located i the bottom of the food chai of eco-system. Accordig to the ecology theory, the species situated i the bottom of food chai provide the food source for the advaced species, they are the fudamet of the commuity persistece. The iterested species must be the local species, ad could represet the attribute of local biological resources. There the geological coditios is put much emphasis i metapopulaito persistece, but the coditios of climate, water etc. are igored, so we must choose the local species to avoid the other impact to the iterested species. O the basis of the curret status of biological resources i Guagzhou, ad the pricipals of the species choice, we choose the wild evergree species of Fagaceae i Guagzhou as the iterested species. The evaluated idicator system is listed below: Table 2 the evaluated idicators i Guagzhou

6 1398 Zhaoxue Li ad L. XU / Procedia Evirometal Scieces 2 (2010) Idicators Descriptio The umber of odes of the ecological etwork The umber of ode i the strogly coected compoets m ECI ECO FS etapopulatio capacity The largest eigevalue of the adjacet matrix depictig the etwork ECI m ECO m m FS ECI ECO 2 4. Coclusio ad Proposal This paper uses metapopulaito capacity to evaluate the stability of urba ladscape eco-system. The metapopulatio capacity could combie the etwork structure iformatio ad biological iformatio to measure the fuctio itegrity of the special ladscape, but, it igores the impact of the etwork cyclig. So the etwork circulatio based o the graph theory is itroduced to offset the disadvatage of metapopulatio dyamic model. The idicator of ECI ad ECO could reflect the circulatio of the whole ecological etwork. It ca weight the metapopulatio capacity to form a comprehesive idicator to measure the stability of the urba ecological etwork ad further the urba ecological security. But the idictor of metapopulaito capacity focus o a sigle species, there we use the matapopulatio capacity of a sigle species istead of the eco-system capacity of the ladscape, so the selected species should be typical ad represetative. Ad the study of multi-species metapopulaito capacity is eeded ad valuable to decrease the ucertaity of the evaluatio. The combiatio of biological idicator ad ecological etwork idicator is a iovatio of this paper, but the form of combiatio is the weight simply, it eed more research about the relatio betwee idicators. Ackowledgmet We would like to thak the fiacial support of the atioal atural Sciece Foudatio of Chia (Grat o ) ad the atioal iistry of Sciece ad Techology (Grat o. 2007BAC28B03).

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