Island protected area zoning based on ecological importance and tenacity

Ecological Indicators 112 (2020) 106139

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Island protected area zoning based on ecological importance and tenacity Yuan Chi a b c

a,b

b,⁎

, Zhiwei Zhang

b

c

, Jing Wang , Zuolun Xie , Jianhua Gao

a,⁎

T

School of Geography and Ocean Science, Nanjing University, Nanjing, Jiangsu Province 210023, PR China First Institute of Oceanography, Ministry of Natural Resources, Qingdao, Shandong Province 266061, PR China School of Geography and Tourism, Jiaying University, Meizhou, Guangdong Province 514015, PR China

ARTICLE INFO

ABSTRACT

Keywords: Island Protected area zoning Ecological importance Ecological tenacity Spatial heterogeneity Sustainable development

Island protected area zoning is highly significant for maintaining the biodiversity and achieving the island sustainable development. Ecological importance and tenacity were proposed in this study for the island protected area zoning. The ecological importance was composed of three components, namely, landscape, soil, and vegetation; the ecological tenacity was evaluated based on the ecological importance and considering three types of influences, i.e., anthropogenic, topographic, and marine influences. Two new indices, namely, ecological importance index (EII) and ecological tenacity index (ETI), were established, and remote sensing and field data were integrated to serve as the data source and realize the spatial exhibitions. Then, the island protected area zoning was conducted based on the spatial distributions of EII and ETI, and six schemes for different protection and development purposes were designed. An island chain in Dongtou Archipelago in South China was used as the study area. Results indicated that the ecological importance and tenacity showed spatial heterogeneities across islands and within the islands. The islands with higher proximities to the mainland and larger areas generally possessed lower ecological importance and tenacity. Of the six schemes, Scheme B was the recommended scheme because of its reasonable area assignments for different protected areas, the optimum compatibility with island uses, and the balance of protection and development. The demonstration of the method validated the advantages of the EII and ETI in revealing the spatial characteristics of island ecological importance and tenacity, as well as the effectiveness of the method in the island protected area zoning.

1. Introduction In recent decades, protected area zoning has became an effective tool to divide the region into different zones with different protection and development strategies and considerably contributed to the biodiversity conservation, as well as the harmonious coexistence of multipleuse activities (McNeely, 1994; Oldfield et al., 2004; Ruiz-Labourdette et al., 2010; Maksin et al., 2018). After decades of theoretical studies and practical explorations, the mode and method for protected area zoning have been continuously developed (Naughton-Treves et al., 2005; Hull et al., 2011). Specifically, the protected areas were once considered virgin areas of pristine wildlife habitats where all human impacts should be prohibited; nowadays, they are gradually designated as compound areas that balance the biodiversity conservation and other compatible human activities with limited intensities, as a result of the recognitions of the reality of the increasingly human dominated world and the necessity to guarantee the right of the basic resource access to poor people living in biodiversity hotpots (Naughton-Treves et al.,

2005; Geneletti and van Duren, 2008; Hull et al., 2011; Gonzales et al., 2003). All kinds of attributes, including but not limited to biodiversity, soil, physiography, terrain, habitat quality, landscape asset, cultural heritage, and anthropogenic disturbance, are considered, and technologies of remote sensing and geographic information system provide rapid, convenient, and accurate means for the protected area zoning (Sabatini et al, 2007; Geneletti and van Duren, 2008; Ruiz-Labourdette et al., 2010; Hull et al., 2011; Zhang et al., 2013; Vardarman et al., 2018). The current empirical researches involved different spatial scales and covered various types of terrestrial and marine ecosystems, which provided important reference for the administration and management and contributed to the sustainable development of the protected areas (Grantham et al., 2013; White et al., 2015; Lin and Li, 2016; Xu et al., 2016; Sarker et al., 2019). The protected area zoning has been applied worldwide; however, many developing areas still receive little attention. The island is one of the areas where specific protected area zoning was seldom conducted. The published paper with the terms “island” and “protected area” in the titles actually studied the

⁎ Corresponding authors at: First Institute of Oceanography, Ministry of Natural Resource, No.6, Xianxialing Road, Qingdao, Shandong Province 266061, PR China (Z. Zhang). School of Geography and Ocean Science, Nanjing University, No.163, Xianlin Road, Nanjing, Jiangsu Province 210023, PR China (J. Gao). E-mail addresses: [email protected] (Z. Zhang), [email protected] (J. Gao).

https://doi.org/10.1016/j.ecolind.2020.106139 Received 13 August 2019; Received in revised form 21 January 2020; Accepted 24 January 2020 1470-160X/ © 2020 Elsevier Ltd. All rights reserved.

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marine areas around the islands (Kamukuru et al., 2004; Thomassin et al., 2010; White et al., 2015). The island is a naturally formed land area which is encircled by the sea and higher than the sea at a high tide. The island is featured by its unique function and distinct vulnerability. For the unique function, the island is a natural storage pool for biodiversity and recognized as a “biodiversity hotspot” (Whittaker and Fernández-Palacios, 2007; Kier et al., 2009; Chi et al., 2019a). The function of biodiversity maintenance can be divided into two aspects, namely, providing habitats for biological resources and functioning as the nodes for bird migration, which indicate the permanent residence of different types of organisms and temporary stop of birds, respectively. The island accounts for only 5.3% of the global land area and occupies a disproportionate amount of the biodiversity in the world, and the isolated space provides a habitat for rare animal and plant species, such as Varanus komodoensis in Indonesian islands and Neolitsea sericea in Zhoushan Archipelago of China (Whittaker and Fernández-Palacios, 2007; Weigelt et al., 2013; Eldridge et al., 2014; Borges et al., 2018). The special location renders the island a key stop for bird migration (Liang et al., 2007). In China, most of the islands are in the coverage of the East Asia-Australia bird migration route, which is one of the world's eight largest bird migration routes, and endangered birds, such as Platalea minor, Egretta eulophotes, and Thalasseus bernsteini, are always observed on the islands (Chen et al. 2005; Chi et al., 2017a). Meanwhile, the special position and limited area render the island ecosystem distinctly vulnerable to natural and anthropogenic disturbances, i.e., the island ecosystem is easy to be damaged and hard to be recovered under the external disturbances (Eldridge et al., 2014; Chi et al., 2017b; Gil et al., 2018). Various natural disasters, including seawater intrusion, storm surge, collapse, landslide, and drought, occur and greatly affect the island ecosystem; moreover, human activities on islands are increasingly intensive and severely threaten the island ecosystem through altering the geomorphology, occupying the natural habitat, fragmenting the landscape, and generating the pollutants (China Islands Compiling Committee, 2013; Morgan and Werner, 2014; Taramelli et al., 2015; Chi et al., 2017a, 2017b, 2020; Xie et al., 2018; Gil et al., 2018). On some islands, human activity has been the dominating factor of ecological processes (Li et al., 2015; Chi et al., 2019b). Thus, the unique function of the island is remarkably vulnerable to the external disturbances, which is inevitable under the background of increasing human activities on islands. Under this background, the island protected area zoning is highly significant for maintaining the biodiversity and habitat, ensuring the reasonable demand of human activities, and thus achieving the island sustainable development. The island sustainable development denotes the protection for the natural ecosystem, the development for the social ecosystem, and the balance of the protection and development. The protection should be strict and effective because of the important function for biodiversity maintenance and the vulnerable ecosystem under different disturbances; the development should be reasonable and efficient to improve the living conditions of island residents, to bring into play the island resources of port, aquaculture, and tourism, to minimize the negative effects of human exploitations, and to reserve development space for future generations. The balance of island protection and development should be ensured to achieve an optimal solution meeting the aforementioned demands. The island protected area zoning provides a basis for the solution through dividing the island into different areas and assigning specific protection and development strategies to different areas. In the last decade, the evaluations on the island ecosystem have received increasing attention and several indices have been developed to represent the island ecosystem from different perspectives. The indices were always established to evaluate the landscape pattern of the island ecosystem (Chi et al., 2019b, 2020) or to judge the changes of the island ecosystem under one of the specific influences, including seawater intrusion (Morgan and Werner, 2014), hurricane hazard (Taramelli et al., 2015), land use (Xie et al., 2019), and tourism

activities (Kurniawan et al., 2016, 2019). Furthermore, the indices that contained multiple aspects and aimed to represent the comprehensive characteristics of the island ecosystem were also proposed; these indices involved the ecological vulnerability (Chi et al., 2017b; Ng et al., 2019), ecosystem health (Wu et al., 2018), ecological integrity (Jiang et al., 2018), ecological environment sustainability (Gao et al., 2019), and ecological footprint (Dong et al., 2019). All the aforementioned indices have been applied in different islands and good results were achieved. However, the current indices are not capable to guide the island protected area zoning, which can be attributed to the following four points: First, the aforementioned two core issues of the island ecosystem for the protected area zoning, that is, the unique function and distinct vulnerability, were not fully focused on. Second, some key elements in the island ecosystem, especially the vegetation and soil qualities, were not adequately considered in these indices. Third, many spatially homogeneous factors for the island ecosystem, including but not limited to temperature, precipitation, typhoon, population, and gross domestic product, were used to calculate the indices; yet they were not helpful for the protected area zoning. Fourth, most of the indices only measured the overall condition of the island ecosystem without representing the spatial heterogeneity within the islands, thereby failing to provide reference for the island protected area zoning. Island ecological importance and tenacity were proposed in this study to correspond to the unique function and distinct vulnerability and to provide a practical method for the island protected area zoning. The ecological importance indicates the ecological conditions that involve the unique function and quantifies the conditions to represent the importance of the island ecosystem. Landscape, soil, and vegetation constitute the components of island ecological importance, of which the landscape refers to the overall characteristics of the island surface, the soil serves as a base for the island biological community, and the vegetation represents the vitality of the island ecosystem (Chi et al., 2016, 2017a, 2017c, 2018a, 2019a, 2019b; Borges et al., 2018; Gil et al., 2018; Xie et al., 2018; Craven et al., 2019; Wilson et al., 2019). The ecological tenacity denotes the resistance to changes under the external disturbances and quantifies the resistance; it is proposed on the basis of island ecological vulnerability, which has been introduced and elaborated by the studies of Borges et al. (2014), Kurniawan et al. (2016), Chi et al. (2017b), Ng et al. (2019), Vaiciulyte et al. (2019), and Xie et al. (2019). The ecological tenacity is determined by the changes of ecological importance under different influences, including anthropogenic, topographic, and marine influences. The ecological importance and tenacity were designed to possess spatial heterogeneities across islands and within the islands; the combination of them could represent the function and vulnerability of the island and guide the island protected zoning in different schemes of protection and development. Therefore, the island ecological importance and tenacity were quantified and spatially exhibited by using two new indices, namely, ecological importance index (EII) and ecological tenacity index (ETI). Remote sensing and field data were integrated to serve as the data source. Then, six schemes for different protection and development purposes were designed based on the EII and ETI to search for the optimum scheme of island protected area zoning. A total of 10 islands in Dongtou Archipelago, a typical island group in South China, were selected as the study area. A previous study by the authors (Chi et al., 2020) revealed the various and intensive human activities and their great negative impact on the island ecosystem in the study area, which made the 10 islands ideally suitable for the study of island protected area zoning. This study aims to solve the following three questions: (1) How the island ecological importance and tenacity were identified, quantified, and spatially exhibited by integrating the components and influences of the island ecosystem? (2) How different schemes of island protected area zoning were designed based on the combination of island ecological importance and tenacity? (3) Which scheme was the optimum one to achieve the balance of island protection and development? 2

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Fig. 1. Location (left), island composition (left), sampling sites (left), and island use types (right) of the study area: Is. 1: Lingkun Island; Is. 2: Niyu Island; Is. 3: Qianmenshan Island; Is. 4: Shenmenshan Island; Is. 5: Zhuangyuan'ao Island; Is. 6: Huagang Island; Is. 7: Dasanpan Island; Is. 8: Dongtou Island; Is. 9: Shengli'ao Island; Is. 10: Banping Island. All the islands and the mainland are connected by the bridges. Is. 1 is a sandy island and the remaining nine ones are rocky islands. The island composition and use types were quoted from a previous relevant study by the authors (Chi et al., 2020).

season. On Is. 7, the real estate with high quality can be observed in the western part while rural residential areas and quarrying activities are in the eastern part. Is. 8 is the political, economic, and cultural center of Dongtou District and characterized by various exploitation types, including but not limited to urban construction, sea reclamation, farming, and tourism. Is. 9 is located to the northeast of Is. 8 and has been joined with Is. 8 by a bridge; it has also been exploited as a tourist spot. Is. 10 is at the end of the island chain with relatively low human interference, and it is mainly for fishery development. Overall, different types of human activities occur on these islands and damage the island ecosystem in different aspects (Chi et al., 2020).

2. Materials and methods 2.1. Study area and data source 2.1.1. Study area The study area is located in the estuary of the Oujiang River and bordering on the East China Sea (Fig. 1). It is featured by the coexistence of sandy and rocky islands, the linkage among the islands by bridges, and the various human activities, which render the study area typical for islands in China and thus suitable for demonstrating the method in this study (Fig. 1). The study area belongs to Dongtou District of Wenzhou City in Zhejiang Province. Since the beginning of the 21th century, human activities have been increasingly expanded and diversified due to the improvement of external traffic. At 2015, the “Dongtou District” was set to replace the former “Dongtou County” and to promote the marine economy of Wenzhou City, which indicated its indispensable position in regional development and the urgency of the island protected area zoning for conserving the island ecological functions and regulating the human activities. The sequence numbers of the islands were assigned using an ascending order along the bridges from the mainland. Is. 1 possesses the largest area and the closest distance to the mainland in the archipelago. It is an estuarine sandy island with a flat terrain, thus, it provides habitats for wetland biological resources and at the same time suffers from the seawater intrusion. The island is also an important carrier for human activities. In the western part of the island, cultivation activities are frequent because of the fertile soils and farmland covers most of the land surface; the eastern part is mainly formed by the sea reclamation and planned as areas for residence, education, and high-tech industries; besides, several aquaculture ponds can be observed in the alongshore areas of the island. Is. 2–Is. 10 are rocky islands with undulating terrain conditions. They have the unique function for biodiversity maintenance and are always considered visual landscapes, while the ecosystems are greatly influenced by natural factors. Meanwhile, human activities are also intensive and show spatial heterogeneity across islands. Is. 2 is occupied by the largest scale of quarrying area of all the 10 islands, which substantially destroys the soil and vegetation and deteriorates the visual landscape. Is. 3 and Is. 4 are uninhabited islands, yet contribute to promoting the traffic condition by serving as the nodes of the bridges connecting the islands in the archipelago. Is. 5 is exploited by the port in its northern side and the sea reclamation in its southern side; the former is an important deepwater port in Zhejiang Province while the latter provides similar functions to those on Is. 1. On Is. 6, several residential buildings have been constructed in a scatter distribution and a tourist spot exists and attracts hundreds of tourists a day in the tourist

2.1.2. Data source (1) Field investigation and sampling Field investigation and sampling were conducted in September 2018. A total of 111 sampling sites were set based on the grid method and considering the island area, topographic condition, plant community, and accessibility (Fig. 1). In detail, larger islands possessed more sampling sites; the sampling sites were set to represent the topographic condition and plant community of the surrounding areas; and the positions of the actual sampling sites were adjusted according to the accessibility. The latitude and longitude of each sampling site were measured using a GPS device. The topographic factors were measured using an electronic compass. The abundance, height, and coverage of each species in tree, shrub, and herb layers were investigated and recorded. Surface (0–20) soils were sampled, and soil factors, including moisture content (MC), salinity (Sa), total nitrogen (TN), organic matter (OM), available phosphorus (AP), and available potassium (AK), were then measured in a laboratory. (2) Remote sensing Remote sensing data were collected from SPOT6, Landsat 8, and Terra satellites for island use classification, ecological index calculation, and terrain factor extraction, respectively. Based on the SPOT 6 data in 2017 that has a high spatial resolution, the island use types were classified into 10 types and 24 sub-types using a visual interpretation method through ArcGIS 10.0 and modified through field investigation, which were described in detail in the previous study (Chi et al., 2020). The island use types include road, dock and embankment, industrial land, building land, hardened ground, quarrying area, agricultural land, water area, bare land, and vegetation area (Fig. 1). Based on the Landsat 8 data in 2017 that has 11 bands of spectra, the reflectance of each band in the study area was obtained using methods of radiometric calibration, atmospheric correction, and image clipping through ENVI 5.3 and ArcGIS 10.0. Based on the Terra data, the version two of Aster GDEM was obtained, and the spatial distribution of slope (Sl) was 3

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Fig. 2. Framework for island protected area zoning based on ecological importance and tenacity.

extracted through ArcGIS 10.0. The detailed processes can be seen in the previous study (Chi et al., 2020).

(1) Three components Landscape: The landscape considerably influences the island habitat suitability for species survival, the ecological connectivity for species flow, and the visual sense for tourism asset (Thies and Tscharntke, 1999; Zheng et al., 2018; Chi et al., 2019b). It is represented in two aspects, that is, landscape composition and configuration. The former indicates the area proportions of different landscape types; the latter

2.2. Index establishment 2.2.1. Island ecological importance The framework for island protected area zoning based on ecological importance and tenacity is shown in Fig. 2. 4

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refers to the spatial distribution and arrangement of landscape patches (Chi et al., 2019b). In this study, important landscape coverage (ILC) was adopted to represent the landscape composition using the following equation:

ILC =

(VILAi + ILAj × 0.5) TA

difference vegetation index (NDVI), which can rapidly and accurately represent the vegetation growth condition through the band calculation of remote sensing data, was selected (Xu and Zhang, 2013; Hu and Xu, 2018). The plant diversity was measured using Shannon Wiener index (H') and Pielou index (E), whose detailed calculation methods were shown in Ma and Liu (1994). Considering the low species number of woody plant and the wide distribution of herbaceous plant, the herb species data was adopted to calculate the plant diversity. Therefore, the three elements, namely, NDVI, H', and E were used in the vegetation component.

(1)

where VILAi is the area of very important landscape i; ILAi is the area of important landscape j; and TA is the total area of the evaluation unit. All the selected important landscapes should exert much more positive effects than negative ones on the island ecosystem. The reservoir (a subtype of water area) gathers and stores drinking water, which is essential to island residents (China Islands Compiling Committee, 2013; Chi et al., 2020). The alongshore bare rock (a sub-type of bare land) indicates the natural shoreline, which is an acknowledged indicator of ecological integrity in coastal areas of China, and it always appears as the featured visual landscape, which provides important tourism resources (Zheng, 2009; Fu et al., 2014). The forest (a sub-type of vegetation area) serves as an ecological shelter of the islands, and a considerable proportion of the forests are artificially planted for ecological protection with high human effort (Chi et al., 2016, 2019b). The three sub-types were considered very important landscapes. The grassland and wetland vegetation (another two sub-types of vegetation area) also contribute to the stability of the island ecosystem, yet to a lesser degree than the forest, and they always naturally grow with low human effort (Chi et al., 2020). Thus, the two sub-types were considered important landscapes. The other types and sub-types of the landscapes generate distinct negative effects or show no clear positive effects on the natural ecosystem, which has been validated by the previous study of the authors (Chi et al., 2020). Thereby, the VILAi, ILAi, and ILC were then determined. For the landscape configuration, two common landscape indices, that is, number of patches (NP) and landscape isolation index (LII), were used to represent the landscape fragmentation and connectivity, respectively (Chi et al., 2018a, 2019b; Xu et al., 2018; Lam et al., 2018). The detailed calculation methods for the two indices can be seen in the study of Chi et al. (2019b). Therefore, the three elements, namely, ILC, NP, and LII were adopted in the landscape component. Soil: The soil is a fundamental indicator of ecosystem function and potential change (Wilson et al., 2019). It provides the space for various organisms, as well as water and nutrient for plant growth (Zhou and Gong, 2007; Chi et al., 2017b). Soil BD, MC, Sa, and fertility are key factors that determine the soil quality. BD is an essential physical parameter that involves the soil porosity and gas; MC is the main water source for vegetation; Sa, which is an indicator of soil salinization in coastal areas, affects the plant community and ecosystem health; and fertility determines the available nutrient in the soil (Wang et al., 2011; Cassel et al., 2015; Chi et al., 2018b). Due to the ample rainfall and humid climate, MC was generally high in all of the sampling sites, which indicated the sufficiency of soil water in the study area, and thus MC is not considered as the element in the soil component. The other soil factors exhibited distinct spatial heterogeneities among different sampling sites, of which OM, TN, AP, and AK were integrated to measure the fertility condition using a fertility index (FI). The detailed calculation method of FI was shown in Chi et al. (2018b). Therefore, three elements, namely, BD, Sa, and FI, were used in the soil component. Vegetation: The vegetation involves fundamental matters of the island ecosystem, including biodiversity maintenance, habitat provision, freshwater conservation, wind pretention, soil fixation, and other ecological processes (Chi et al., 2016, 2019a; Borges et al., 2018). The vegetation is composed of two aspects, that is, vegetation growth condition and plant diversity. The former indicates the productivity of the community, which is important for the survival and reproduction of each member in the ecosystem; the latter refers to the species complexity of the community and considerably contributes to the ecosystem stability (Tilman et al., 2006; Chen et al., 2018a). A normalized

(2) Spatial exhibitions of the elements A size of 100 m × 100 m was used as the evaluation unit, which was created using the Fishnet tool in ArcGIS 10.0 (Chi et al., 2017a, 2017b). All of the elements need to be measured in each unit to represent their spatial distributions. Of the nine elements, ILC, NP, LII, and NDVI were obtained based on the remote sensing data, and their spatial distributions can be directly generated through the calculations in each evaluation unit using the aforementioned methods. The remaining elements, that is, BD, Sa, FI, H', and E, are site data that are obtained by filed investigation and sampling, and thus should be converted to area data by spatial simulation. The spatial simulation was conducted by combining the field and remote sensing data, which is a common approach in the ecological simulation and has been widely used in previous studies on soil and vegetation mapping (Strand et al., 2007; Asner et al., 2011; Akpa et al., 2016; Chi et al., 2019c). The Landsat 8 data is advantageous for its easy access and multiple spectra and thus provides an important data source. A cokriging method, which can achieve high simulation accuracy when the simulated object is closely related to densely sampled covariates, was used to realize the simulation (Vaughan et al., 1995; Yang et al., 2016). First, all kinds of remote sensing data, including the spectral reflectance of different bands and various ecological indices, were derived through band calculations; the detailed calculation methods can be seen in studies of Douaoui et al. (2006), Sertel et al. (2017), and Hu and Xu (2018). Second, the values of the spectral reflectance and ecological indices that correspond to the positions of the sampling sites were extracted using the Extract Values to Points tool in ArcGIS 10.0, the correlations between the remote sensing and field data were analyzed using IBM SPSS 18, and the results indicated the significant correlations of most of the field data with the remote sensing data (Table 1). Additionally, AP showed no significant correlation with any remote sensing data and thus was removed in the calculation of FI because of the failure in spatial exhibition. Third, three remote sensing factors (spectral reflectance or ecological indices) with the highest correlation coefficients were selected as the covariates for the corresponding field data; of the 111 sampling sites, 20 sites were randomly selected as validation samples, and the others were used as training samples to conduct the cokriging. Two metrics, namely, root mean squared error (RMSE) and mean absolute error (MAE), were adopted to measure the simulation accuracies by contrasting the simulated results with the measured data in the validation samples (Taghizadeh-Mehrjardi et al., 2014; Wang et al., 2017; Chi et al., 2019c). The results showed that the RMSE and MAE for the five simulated elements were generally low, which indicated the high simulation accuracies that could meet the demand of the spatial exhibitions (Table 2). Therefore, the spatial distributions of the nine elements were obtained and shown in Fig. 3. (3) Ecological importance index An EII was established by combining the three components and nine elements. Standardizations of the elements were conducted using the 95% and 5% percentiles of each element as the upper and lower limits, respectively. The elements were classified as positive and negative ones. The positive elements included ILC, FI, NDVI, H', and E; the 5

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Table 1 Correlation coefficients between field and remote sensing data. Item

BD

Sa **

B1 B2 B3 B4 B5 B6 B7 B9 B10 B11 NDVI DVI SAVI SI1 SI2 SI3 LSW IBI BSI BT10 BT11

TN **

0.372 0.370** 0.359** 0.324** 0.171 0.327** 0.351** −0.048 0.423** 0.383** −0.230* −0.070 −0.121 0.345** 0.339** 0.323** −0.270** 0.309** 0.311** 0.424** 0.384**

0.310 0.308** 0.298** 0.311** −0.168 0.128 0.221* −0.050 0.114 0.089 −0.385** −0.331** −0.354** 0.315** 0.307** 0.032 −0.164 0.293** 0.320** 0.114 0.089

OM **

AP **

−0.450 −0.452** −0.457** −0.448** −0.070 −0.376** −0.425** −0.069 −0.367** −0.321** 0.394** 0.229* 0.282** −0.458** −0.454** −0.296** 0.350** −0.440** −0.462** −0.367** −0.321**

−0.371 −0.373** −0.370** −0.360** 0.009 −0.282** −0.332** −0.006 −0.201* −0.145 0.373** 0.236* 0.281** −0.373** −0.367** −0.190* 0.285** −0.382** −0.400** −0.201* −0.145

0.115 0.104 0.092 0.070 0.077 0.065 0.053 0.093 0.059 0.058 −0.040 0.017 −0.001 0.084 0.080 0.112 −0.009 0.056 0.057 0.060 0.059

AK **

0.341 0.336** 0.295** 0.289** −0.144 0.146 0.234* 0.093 0.287** 0.231* −0.360** −0.297** −0.321** 0.311** 0.293** 0.038 −0.188* 0.317** 0.323** 0.287** 0.232*

H'

E

0.084 0.092 0.107 0.102 0.237* 0.248** 0.188* −0.044 0.136 0.188* 0.073 0.123 0.106 0.096 0.103 0.239* −0.206* 0.099 0.070 0.136 0.188*

−0.099 −0.098 −0.081 −0.083 0.189* 0.079 0.029 0.016 0.061 0.117 0.206* 0.202* 0.204* −0.093 −0.084 0.104 −0.066 −0.074 −0.109 0.061 0.117

**: P < 0.01; *: P < 0.05. BD: soil bulk density; Sa: salinity; TN: total nitrogen; OM: organic matter; AP: available phosphorus; AK: available potassium; H': Shannon-Wiener index; E: Pielou index. B1–B7 and B9–B11 refer to the spectral reflectance of bands in Landsat 8 data. NDVI: normalized difference vegetation index; DVI: difference vegetation index; SAVI: soil adjusted vegetation index; SI1: salinity index 1; SI2: salinity index 2; SI3: salinity index 3; LSW: land surface wetness; IBI: index-based built-up index; BSI: bare soil index; BT10: brightness temperature of band 10; BT11: brightness temperature of band 11.

everywhere in the study area, which was reported in the previous study of the authors (Chi et al., 2020). A natural ecosystem damaged index (NEDI) was proposed in the previous study based on island use types, size effect, utilization level, and change processes and it could accurately measure the influences of human activities on the island ecosystem (Chi et al., 2020). Thus, the NEDI was used to represent the anthropogenic influence in this study. The topographic and marine factors refer to the natural influences. The Sl involves various ecological processes and exerts influences in various aspects, including geomorphology stability, water yield, and soil quality (Koulouri and Giourga, 2007; Gao et al., 2016; Ding et al., 2017; Nabiollahi et al., 2018). Thus, the Sl was used to present the topographic influence, and the positions with higher Sl received more influences. For the marine influence, the positions nearer the sea are more easily influenced by seawater intrusion, storm surge, and sea wind, which contaminate the underground water, generate the soil sanilization, destroy the island coastline, and restrain the plant height (Moujabber et al., 2006; Fan et al., 2012; China Islands Compiling Committee, 2013; Niu et al., 2015). Distance to the shoreline (DTS) was used to represent the marine influence. Therefore, the three influences were represented by NEDI, Sl, and DTS. The NEDI itself is a calculated value that ranges from 0 to1 and can be directly used in this study. The Sl and DTS were standardized using the aforementioned methods before conducting the following step, and higher standardized Sl and DTS values indicated higher influences.

Table 2 Simulation accuracies for different elements. Item

BD (g/ cm3)

Sa (g/kg)

TN (g/kg)

OM (g/ kg)

AK (mg/ kg)

H'

E

RMSE MAE

0.234 0.154

0.362 0.273

0.375 0.306

5.519 4.131

55.927 44.155

0.396 0.328

0.063 0.047

RMSE: root mean squared error; MAE: mean absolute error. The abbreviations for BD, Sa, TN, OM, AK, H', and E are the same as for Table 1.

higher their values, the higher the ecological importance. The remaining elements were negative ones; the lower their values, the higher the ecological importance. The positive and negative elements were standardized using different methods, which were shown in study of Chi et al. (2019b). Then, the three components and EII were calculated using the following equations:

QC =

SEi × wi

(2)

EII =

QCj × wj

(3)

where QC is the quality of a component; SEi is the standardized value of element i in the component; QCj is the quality of component j; and wi and wj are the weight values of element i and component j, respectively. In this study, all of the elements and components are equally essential to the island ecological importance, thus, equal weights were assigned to the elements and components. The component qualities and EII were calculated for each evaluation unit, and their maps were created. Then, the ecological importance on different islands was analyzed.

(2) Ecological tenacity index The ecological tenacity focuses on the changes of the island ecosystem in the context of anthropogenic and natural influences. The changes of the island ecosystem can be represented by the variation of ecological importance, and the ecological tenacity is determined by the interrelation of ecological importance and influence. Four circumstances exist: (1) when the ecological importance and influence are both high, the ecological tenacity is high; (2) when the ecological importance is high and the influence is low, the ecological tenacity is intermediate; (3) when the ecological importance is low and the influence is high, the ecological tenacity is intermediate; (4) when the ecological importance and influence are both low, the ecological tenacity is low. Meanwhile, the three influences exert different influence

2.2.2. Island ecological tenacity (1) Three influences Anthropogenic, topographic, and marine factors exert practical influences on the island ecosystem. The anthropogenic influence substantially altered the island natural ecosystem in aspects of geomorphology, landscape, habitat, and pollution, and affected almost 6

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Fig. 3. Spatial distributions of all elements for the island ecological importance: The abbreviations for BD, Sa, NDVI, H', and E are the same as for Table 1. ILC: important landscape coverage; NP: number of patches; LII: landscape isolation index; FI: soil fertility index. The legends were divided using a quantile method in ascending order of values. Table 3 Partial correlation coefficients of the elements with the influences. Item AI TI MI

ILC

NP **

−0.522 0.571** −0.093**

LII **

−0.253 −0.148** 0.131**

BD **

−0.052 −0.047** 0.048**

Sa **

FI **

−0.417 0.387** 0.347**

−0.216 0.174** −0.022*

NDVI **

H' **

−0.053 −0.128** 0.158**

−0.073 0.537** −0.430**

E **

0.055 0.191** −0.149**

−0.091** 0.264** −0.023*

**: P < 0.01; *: P < 0.05. AI: anthropogenic influence; TI: topographic influence; MI: marine influence. The abbreviations for the nine elements are the same as for Table 1 and Fig. 3.

degrees on different elements of the ecological importance, and partial correlations between the elements in the ecological importance and the three influences were analyzed to identify the influence degrees. The partial correlation method rather than the correlation method was adopted because the three influences may have correlations with each other to some extent. The partial correlation results showed that all the correlations were significant, of which the negative correlations indicated the negative influences on the elements (Table 3). The elements possessing negative correlations with a type of influence were considered the selected elements for the influence, and the correlation coefficients of the elements were considered the influence degrees. The elements that had no significant negative correlations with the influences were not considered here, that is, the elements that were free from the influences couldn't represent the ecological tenacity. Thus, the ecological tenacity was calculated and an ETI was proposed. The equations are as follows:

ETI

x=

ETI = ETI

SEi × CCi × EII 1 + ETI

2 + ETI

(4)

3

(5)

where ETI-x is the ecological tenacity responding to influence × ,and ETI-1, ETI-2, and ETI-3 represent the ecological tenacities responding to anthropogenic, topographic, and marine influences, respectively; SEi and CCi are the standardized value and partial correlation coefficient of selected element i for influence × , respectively; and the SEi × CCi refers to the external influences that worsen the element i in the ecological importance. The sum of SEi × CCi indicates the sum of the influences that worsen different elements in the ecological importance, and then ETI-x was obtained by multiplying the EII by the sum of SEi × CCi. Since ETI-x and ETI did not range from 0 to 1, they were also standardized using the aforementioned method for clear and unified display. Then, ETI-x and ETI were calculated for each unit as the aforementioned EII did. 7

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Table 4 Different zones based on EII and ETI. Zone

EII

ETI

1 2 3 4 5 6 7 8 9

High High High Medium Medium Medium Low Low Low

Low Medium High Low Medium High Low Medium High

2.3. Island protected area zoning The island protected area zoning was conducted based on the EII and ETI and different schemes were proposed. First, for each of EII and ETI, high, medium, and low values were divided using a trisection method. Second, nine zones were classified according to the values of EII and ETI (Table 4). Third, core, ordinary, and non protected areas were divided, and six schemes were proposed by using different combinations of the zones (Table 5). Different schemes were designed for different protection and development strategies. Scheme A gave priority to the protection; zones with high EII or low ETI were considered core protected area, the zone with low EII and high ETI was considered non protected area, and the remaining zones were considered ordinary protected area. Schemes B–E focus on the balance of protection and development. Schemes B and C consider both the EII and ETI. In Scheme B, zones with high EII and low or medium ETI, as well as zones with low ETI and high or medium EII, were considered core protected area, zones with EII and ETI in the same level were considered ordinary protected area, and the remaining zones were considered non protected area. Scheme C assigned more zones to ordinary protected area, that is, the zones with high EII and low ETI was considered core protected area, the zone with low EII and high ETI was considered non protected area, and the remaining zones were considered ordinary protected area. Scheme D and E only consider the EII and ETI, respectively. In Scheme D, zones with high, medium, and low EII were considered core, ordinary, and non protected areas, respectively. In Scheme E, zones with low, medium, and high ETI were considered core, ordinary, and non protected areas, respectively. Scheme F took the development as the principal thing; the zone with high EII and low ETI was considered core protected area, zones with low EII or high ETI were considered non protected area, and the remaining zones were considered ordinary protected area. Then, the maps of island protected area zoning were generated, and the area proportions of different protected areas in different schemes were analyzed. The following hypotheses were proposed for this study: (1) The different components and influences for the island ecosystem could be quantified and spatially exhibited, and be integrated by two composite indices. (2) The EII and ETI showed spatial heterogeneities across different islands and across different areas within the islands, which were controlled by natural and anthropogenic factors at different scales. (3) The combination of EII and ETI served as a practical method to provide

Fig. 4. Island ecological importance and tenacity on different islands: different components for ecological importance include landscape, soil, and vegetation; different influences for ecological tenacity consist of ETI-1, ETI-2, and ETI-3, which refer to the ecological tenacities responding to anthropogenic, topographic, and marine influences, respectively. EII: ecological importance index; ETI: ecological tenacity index.

different schemes for the island protected area zoning and then to identify the optimum scheme. 3. Results 3.1. Spatial distributions of the island ecological importance The ecological importance on different islands is shown in Fig. 4. For the landscape component, Is. 4 and Is. 6 had the highest values of all the islands, showing their high important landscape coverage, low landscape fragmentation, and high connectivity. Is. 1 showed the lowest value, which revealed the poor landscape quality influenced by the large scale of farming and reclamation activities. The other islands possessed the intermediate values. For the soil component, Is. 9, Is. 10, and Is. 7 achieved the highest values, followed by Is. 6 and Is. 8, indicating their high porosity, low salinity, and high fertility in soils. Is. 3, Is. 4, Is. 2, Is. 5, and Is. 1 had low values and were in a descending order of the values, showing their bad soil quality. For the vegetation

Table 5 Schemes for island protected area zoning. Scheme Scheme Scheme Scheme Scheme Scheme Scheme

A B C D E F

Core protected area

Ordinary protected area

Non protected area

Zones 1–4 and 7 Zones 1, 2, and 4 Zone 1 Zones 1–3 Zones 1, 4, and 7 Zone 1

Zones Zones Zones Zones Zones Zones

Zone 9 Zones 6, 8, and 9 Zone 9 Zones 7–9 Zones 3, 6, and 9 Zones 3 and 6–9

5, 6, 3, 5, 2–8 4–6 2, 5, 2, 4,

and 8 and 7 and 8 and 5

8

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Fig. 5. Spatial distributions of island ecological importance: Different aspects refer to landscape, soil, and vegetation; EII indicates the ecological importance index.

biodiversity maintenance. The urbanized areas on Is. 8 had an intermediate vegetation quality, which could be attributed to the urban greening construction. The spatial distribution of EII combined the characteristics of the three components. Generally, the low EII areas were in the southeastern part of Is.1 with a continuous distribution, and they were also sporadically scattered on Is. 2 and Is. 5, as well as the remaining part of Is. 1. The intermediate EII values were observed in most areas of Is. 1, the northwestern part of Is. 2, the reclamation areas of Is. 5, and the northern part of Is. 8. The high EII values were mainly distributed in forests areas on rocky islands, revealing the good qualities of the three components and the high ecological importance of the forests. In addition, the EIIs of reclamation and non reclamation areas were 0.484 and 0.647, respectively, indicating the higher ecological importance in non reclamation areas than those in reclamation areas.

component, Is. 6 achieved the highest value, followed by Is. 8, Is. 10, Is. 7, and Is. 2. On these islands, the vegetation grew well, the species diversity was high, and the species evenness was good. Is. 4, Is. 5, Is. 3, Is. 9, and Is. 1 showed low values and were in a descending order of the values. For the EII, Is. 6 achieved the highest value of 0.788 and Is. 10, Is. 7, Is. 9, and Is. 8 possessed the values higher than 0.7, indicating the high ecological importance in the second half of the islands. Is. 4, Is. 2, Is. 3, and Is. 5 had the values lower than 0.7 and higher than 0.5, and Is. 1 exhibited the lowest value of 0.482. Is. 1 had the lowest values of all the three components and EII, indicating its bad qualities of landscape, soil, and vegetation and low ecological importance. The spatial distributions of island ecological importance are shown in Fig. 5. The landscape quality showed distinct spatial heterogeneity. The high values were mainly in the rocky islands with continuous distributions; they could also be observed in the sandy island with scattered distributions. It is noteworthy that the vegetation areas with wide distributions generally had high values. The landscape quality was low in the urbanized areas with fragmented and isolated patches, especially in the western part of Is. 1. For the soil quality, the spatial heterogeneity was not as high as the landscape quality. The eastern part of Is.1, the western parts of Is. 2 and Is. 5, and the northern part of Is. 8 showed bad soil qualities. These areas were mostly reclamation areas with low altitude. The high values were mainly observed in the northern part of Is. 7, the eastern part of Is. 8, and nearly the entire Is. 9 and Is. 10. The soil quality generally exhibited an increasing gradient from west to east within each island. The vegetation quality was very bad in the northwestern and southeastern parts of Is. 1, as well as the northwestern corner of Is. 5, because nearly no vegetation covered these areas. The forests on different islands showed high vegetation quality, showing its good growth condition and high capacities for

3.2. Spatial distributions of the island ecological tenacity The ecological tenacity on different islands is shown in Fig. 4. For the ETI-1, Is. 3, Is. 1, and Is. 7 achieved the highest three values, showing their high ecological tenacities responding to the anthropogenic influence, that is, their values of ecological importance remained high in the context of high anthropogenic influence. By contrast, Is. 9, Is. 10, and Is. 6 showed the lowest three values. Their ecological importance declined rapidly when the anthropogenic influence was in a preliminary stage. For the ETI-2, Is. 9 and Is. 6 had much higher values than the other islands, indicating their robustness under the influence of the topographic factor. Is. 8, Is. 5, Is. 3, and Is.1 exhibited low values, that is, their ecological importance responded sensitively to the topographic influence. The ETI-3 was lowest on Is. 1, revealing the high vulnerability of the sandy island to the marine 9

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Fig. 6. Spatial distributions of island ecological tenacity: ETI-1, ETI-2, and ETI-3 represent the ecological tenacities responding to anthropogenic, topographic, and marine influences, respectively; ETI refers to the ecological tenacity index.

influence. The highest three values of ETI-3 were achieved by Is. 6, Is. 10, and Is. 4. Their ecological importance kept high when facing the high marine influence. The ETI showed distinct differences across islands. Is. 6, Is. 7, Is. 2, Is. 3, Is. 10, Is. 4, Is. 8, Is. 9, Is. 5, and Is. 1 were in the descending order of the values, indicating the different ecological tenacities on different islands under the comprehensive effects of anthropogenic, topographic, and marine influences. The spatial distributions of island ecological tenacity are shown in Fig. 6. For the ETI-1, the high values were mainly observed in alongshore industrial lands in the sandy island, as well as the urbanized and reclamation areas in the rocky islands; these areas exhibited robustness under the high influences of human activities. Vegetation areas generally possessed low values of ETI-1. The ecological importance of vegetation areas was high, however, drastically declined when receiving the anthropogenic influence. The urbanized and reclamation areas showed low values of ETI-2, indicating their high sensitivity to the topographic factor. The high values of ETI-2 were distributed in vegetation areas on the rocky islands with scattered distributions. The topographic influence did not play an important role in determining the ecological importance of vegetation areas. For the ETI-3, the low values were generally in the inner areas of the islands, as well as the southeastern part of Is.1 and the northwestern parts of Is. 2 and Is. 5. The ETI3 was generally high in alongshore areas, which actually received more marine influences than the inner areas. It indicated that the spatial pattern of ecological importance in most of the study areas was not completely controlled by the marine influence. For the ETI, the developed areas, including urbanized areas, reclamation areas, and industrial regions, generally showed high values, showing their high tenacity under the comprehensive effects of the three influences. The

undeveloped areas, along with the agricultural land and wetland on Is. 1, had low values; it indicated their high sensitivity of ecological importance. Besides, the ETIs of reclamation and non reclamation areas were 0.403 and 0.516, respectively. The reclamation areas had not only lower ecological importance, but also lower ecological tenacity than the non reclamation areas. 3.3. Island protected area zoning in different schemes The six schemes for the island protected area zoning are shown in Fig. 7 and Table 6. In Scheme A, core protected area occupied the most areas and covered the vegetation area, bare land, agricultural land, and many other land use types; ordinary protected area included urbanized areas, industrial land, and other reclamation areas; and non protected area occupied only a small part of the islands. In scheme B, ordinary, non, and core protected areas were in a descending order of areas, and the area difference was not very large. In scheme C, ordinary protected area occupied about 90% of the study area, and core and non protected areas were sporadically scattered in the study area. Schemes D and E divided the three protected areas with identical area proportions, yet the spatial distributions were greatly different between the two schemes. The three protected areas showed spatial heterogeneity, which was more distinct across islands in Scheme D, however, within the islands in Scheme E. In Scheme F, non protected area occupied more than 60% of the study area, core protected area was continuously distributed in the central part of Is. 8 and sporadically scattered on the other islands, and ordinary protected area was distributed around the core protected area. Generally, Schemes A, C, and F assigned the most areas to core, ordinary, and non protected areas, respectively, and 10

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Fig. 7. Island protected area zoning in different schemes.

the value of protection; it was evaluated by combing the components of landscape, soil, and vegetation, which covered a total of nine elements and comprehensively represented the island ecological characteristics. The EII was established to identify and spatially exhibit the ecological importance and provide a basis for the ecological tenacity. The ecological tenacity referred to the urgency of protection; it was judged by distinguishing the changes of ecological importance under anthropogenic, topographic, and marine influences. The ETI was calculated based on the correlations of ecological importance with the three influences. In previous studies, island ecological vulnerability received attention and its evaluations were conducted in different areas. The island ecological tenacity possesses a connotation that corresponds to the vulnerability. They both focus on the ecosystem changes under external disturbances; the vulnerability indicates the changes while the tenacity denotes the resistance to changes. However, the tenacity is not merely a duplicate term of the vulnerability; it also contributes to affirming the merits of the island ecosystems, deepening the utilization of the ecological importance, and providing practical approaches for the island protected area zoning. The three components and the three

Table 6 Area proportions of island protected areas in different schemes (%). Scheme Scheme Scheme Scheme Scheme Scheme Scheme

A B C D E F

Core protected area

Ordinary protected area

Non protected area

57.89 25.71 5.74 32.38 31.25 5.74

37.58 41.85 89.73 33.40 33.84 29.66

4.53 32.43 4.53 34.22 34.92 64.61

Schemes B, D, and E balanced the area proportions of the three protected areas in different ways. 4. Discussion 4.1. Contributions of the island ecological importance and tenacity The ecological importance and tenacity were proposed in this study for island protected area zoning. The ecological importance indicated 11

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influences are not peculiar to the island, and can also be observed in coastal areas of the mainland. The peculiar things are that the island possesses disproportionate ecological function in such a small area, which makes the ecological importance highlighted, and that the island responds sensitively to the multiple influences, which renders the ecological tenacity extraordinarily important for the island ecosystem. Thus, though the components in the ecological importance and the influences for the ecological tenacity can also be analyzed and evaluated in the other areas, the integrations of the components and influences, the quantification of the ecological importance and tenacity, and the combination of the two new indices are special for the island protected area zoning. Two technical issues that may greatly affect the evaluation results existed in the calculations of EII and ETI. The first was the spatial exhibition of the field data using the cokriging method. The field data were point data that couldn't represent the regional characteristics, yet the remote sensing data were area data that cover the entire study area, and the remote sensing and field data were closely related to each other, which made it possible to convert the field data from point to area data. Spectral reflectance of each band and various ecological indices were adopted to adequately utilize the ecological significance of the remote sensing data and to explore their relationships with the field data. The cokriging method considered not only the spatial autocorrelation of the field data, but also the correlations between remote sensing and field data (Wu et al., 2009). The results showed the high accuracies of the simulations, which met the demand of spatial exhibition and indicated the good effectiveness of cokriging method. The second issue was the measurement of influence degrees in the calculation of ETI, which was the determinant of the accuracy of the ETI. The anthropogenic, topographic, and marine factors exerted different influences on the island ecosystem, and different elements in the ecological importance responded variously to the influences. Considering the correlations among the three influences, a partial correlation method was used to measure the influence degrees. The results showed that the influence degrees varied across influences and elements. The anthropogenic influence had negative correlations with most of the elements, indicating the dominant role of human activity in driving the changes of the island ecosystem, which was in accordance with the studies of Li et al. (2015) and Chi et al. (2019b). The partial correlation coefficient was used to represent the degree of each influence on each element, which made the influence degree explicit and comparable. The two new indices, namely, EII and ETI, were demonstrated in the study area and their advantages in revealing the spatial characteristics of island ecological importance and tenacity were confirmed, which validated the first hypothesis of this study. The needed data for the calculations of EII and ETI can be easily obtained based on commonused remote sensing data, such the data from SPOT and Landsat series satellites, as well as conventional field investigation. Besides, the calculation methods are clear and repeatable. Therefore, the two indices can be widely applied in evaluating the ecological importance and tenacity on different islands. In previous studies by the authors, three indices for evaluating the island ecosystem were established: (1) island ecological vulnerability index (IEVI), which was used to evaluate the ecological condition of the islands and their surrounding waters using an exposure-sensitivityadaptability frame (Chi et al., 2017b); (2) landscape ecological sensitivity index (LESI), which was designed to reveal the landscape pattern across different scales on islands with high landscape fragmentation (Chi et al., 2019b); (3) natural ecosystem damaged index (NEDI), which was adopted to measure the negative effects of human activities (Chi et al., 2020). The previous three indices provided a basis for the establishments of EII and ETI in this study. The IEVI introduced the concept of island ecological vulnerability, which served as the theoretical basis for the ecological tenacity. The LESI revealed the importance and sensitivity of the landscape pattern on islands, and thus the landscape quality was selected as a component in the ecological importance.

The NEDI represented the anthropogenic influence, and was directly used as an influence for the ecological tenacity. The three previous indices are not capable for guiding the island protected area because of one or more of the four points mentioned in the Introduction section. However, The EII and ETI in this study provided new insights into the island ecosystem. They could meet the aforementioned four points that the previous indices could not meet for simultaneously revealing the ecological importance and tenacity of the islands and then conducting the island protected area zoning. 4.2. Spatial heterogeneities of the island ecological importance and tenacity The island ecological importance and tenacity showed spatial heterogeneities to some extent over the study area. At the whole island scale, different islands showed different ecological importance and tenacity. Island area and proximity to the mainland are two basic factors for the island ecosystem (MacArchur and Wilson, 1963, 1967; Whittaker and Fernández-Palacios, 2007). The former determines the upper limit of biodiversity and the carrying capacity for human activities, and the latter greatly influences the species flow and the accessibility from the mainland (Weigelt et al., 2016; Whittaker et al., 2017; Chi et al., 2019a). The relationships of ecological importance and tenacity with the island area and proximity to the mainland were analyzed using scattered diagrams (Fig. 8). For the proximity, with the increase in island sequence number, all the components of ecological importance and the EII increased, of which the soil component and EII increased more distinctly; the ETI-1 decreased while the ETI-2 and ETI3 increased, and the ETI did not show clear increasing or decreasing characteristics. With the increase in island area, the components of landscape and soil, as well as the EII decreased, of which the landscape component decreased more distinctly; the ETI-1 increased whereas the ETI-2, ETI-3, and ETI decreased. Generally, the islands with higher proximities and larger areas possessed lower ecological importance and tenacity. As mentioned earlier, human activities have been the main driving factors of the island ecological changes. The higher proximities and larger island areas indicated the higher human activity intensity, thereby inducing the lower ecological importance and tenacity. At the evaluation unit scale, all of the elements contributed to the spatial heterogeneities of ecological importance and tenacity. Correlations of EII and ETI with the elements and components were analyzed using IBM SPSS 18 (Table 7). For the EII, the ILC, BD, and Sa had correlation coefficients higher than 0.6, followed by the NDVI, H', and E with correlation coefficients lower than 0.6 and higher than 0.5, indicating their large contributions to the spatial heterogeneity of EII. In the three components, the soil, vegetation, and landscape were in the descending order of correlation coefficients, yet the differences were not large. Thus, all the three components were important for the EII. For the ETI, ETI-1 and ETI-3 possessed higher correlation coefficients than ETI-2, indicating the low contribution of topographic influence to the spatial heterogeneity of ETI. Besides, the EII and ETI showed a positive correlation, which revealed that the positions with high ecological importance generally had high ecological tenacity. The aforementioned contents corresponded to the second hypothesis of the study. 4.3. Recommended scheme for the island protected zoning Land use compositions of the three protected areas in different schemes were analyzed (Table 8). The road, dock and embankment, industrial land, building land, hardened ground, and quarrying area were the use types that damaged the island ecosystem, and were considered disturbance types (DT); the agricultural land, water area, and bare land exerted negative effects to a certain degree and may generate positive effects in some occasions, and were considered neutral types (NT); and the vegetation area contributed a lot to the island ecological conservation, and was considered suitable type (ST) (Jacquelinel et al., 2008; Sajinkumar et al., 2014; Xu et al., 2015; Chi et al., 2020). For the 12

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Fig. 8. Relationships of ecological importance and tenacity with island sequence number and area: The island sequence number indicates the proximity to the mainland, and higher island sequence number denotes lower proximity to the mainland. The abbreviations for the ecological importance and tenacity are the same as for Fig. 4.

ordinary protected area. In Scheme D, the ST was mainly in core protected area, and the DT and NT were both evenly distributed in ordinary and non protected area. In Scheme E, the ST was evenly in the three protected areas, and the NT and DT were the most in core and non protected areas, respectively. In Scheme F, non protected area had the most proportions of DT, NT, and ST. Reclamation areas in the three protected areas in different schemes were analyzed (Fig. 9). The reclamation activity was aiming to expand the areas of the islands and provide more space for human activities; despite the remarkable negative effects on the marine ecosystem, it effectively solved the problem of land shortage in coastal areas (Chen et al., 2018b; Ewers Lewis et al., 2019). The reclamation areas in the study area were fundamental to the development of port construction, urbanization, and other marine economy in Dongtou District (Chi et al., 2020). Thus, its compatibility with the three protected areas was in the following order: non, ordinary, and core protected areas. In Scheme A, it was mainly in core and ordinary protected areas; in Schemes B and D, it was mainly in both ordinary and non protected areas; in Schemes C and F, it was mostly in ordinary and non protected areas, respectively; and in Scheme E, it was distributed in the three protected areas with certain proportions, and the proportion in core protected area was higher than those in ordinary and non protected areas. In summary, Schemes A and F focused on the island protection and development, respectively, and paid little attention to the other demand, which did not correspond to the goal of island sustainable development. In Scheme C, most of the study area was in ordinary

Table 7 Correlation coefficients of the EII and ETI with the elements and components. Items

EII

Items

EII

ETI

ILC NP LII BD Sa FI NDVI H' E

0.693** 0.221** 0.029** 0.637** 0.707** 0.227** 0.507** 0.526** 0.580**

Landscape Soil Vegetation ETI-1 ETI-2 ETI-3 EII ETI

0.639** 0.785** 0.751** – – – 1 0.321**

– – – 0.502** 0.350** 0.595** 0.321** 1

**

: P < 0.01. The elements refer to the standardized elements. The abbreviations for the elements, component, EII and ETI are the same as for Table 1 and Figs. 3 and 4.

DT, non, ordinary, and core protected areas were in the descending order of the compatibility, which showed the opposite characteristics for the ST; and the NT was more compatible with ordinary protected area than core and non protected areas. In Scheme A, core protected area occupied the most of ST and NT, as well as a considerable part of DT, ordinary protected area was constituted mainly by DT, and non protected area occupied only a small area. In Scheme B, core and ordinary protected areas had large and equal areas of ST; the DT and NT were mostly in non and ordinary protected areas, respectively, and both low in core protected area. In Scheme C, most of DT, NT, and ST were in 13

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0.75 2.51 0.87 0.11 0.85 3.17 0.01 3.26 0.87 0.54 2.00 1.59 0.21 0.84 3.08 0.01 0.32 3.80

4.37 7.23 0.50 1.39 4.40 6.31 0.26 11.33 0.50 2.71 5.30 4.08 1.92 4.48 5.70 0.26 2.54 9.29

0.15 0.22 0.05 0.05 0.13 0.23 0.01 0.36 0.05 0.07 0.19 0.16 0.09 0.11 0.22 0.01 0.08 0.33

0.30 1.16 0.81 0.04 0.30 1.94 0.01 1.46 0.81 0.29 1.14 0.84 0.02 0.08 2.17 0.01 0.06 2.21

7.65 5.47 0.17 5.29 5.04 2.96 0.83 12.29 0.17 2.02 7.15 4.12 6.45 5.46 1.37 0.83 7.13 5.32

3.67 2.41 0.16 0.77 3.53 1.94 0.12 5.96 0.16 0.35 1.96 3.94 3.44 1.74 1.06 0.12 1.29 4.83

6.25 5.04 0.38 0.94 6.40 4.33 0.18 11.11 0.38 1.04 3.30 7.33 5.39 3.60 2.69 0.18 1.86 9.64

30.97 9.18 0.93 16.38 17.58 7.12 4.23 35.92 0.93 24.47 9.67 6.94 10.74 14.65 15.70 4.23 15.14 21.71

protected areas, which was a compromising approach and could not reflect the function of the island protected area zoning. Schemes B, D, and E considered both the protection and development. Scheme E assigned a considerable reclamation area and NT to core protected area, and ST to non protected area; Scheme D gave the most of NT to non protected area; Scheme B assigned the most of ST to core and ordinary protected areas, the most of NT to ordinary protected area, and the most of DT to non protected area, which achieved the optimum compatibility and thus was superior to Schemes D and E. Therefore, Scheme B was considered the recommended scheme for the island protected zoning, which verified the third hypothesis of the study. Control measures for different protected areas were proposed based on the results in this study and according to the Urban master plan of Wenzhou City, which planned the Dongtou District as a base for port industry and island tourism (The People's Government of Wenzhou City, 2017). In core protected area, the strict protection measures should be implemented. In principle, new exploitations should be prohibited, especially the exploitations that occupy large areas or exert much negative effects on the island ecosystem. Specifically, the quarrying activities, which remarkably change the geomorphology, destroy the soil-vegetation system, and alter the natural landscape, as well as the factories, which emit different types of pollutants, should be completely eliminated (Chi et al., 2020). New buildings and facilities can be constructed only for the conservation purpose. Existing temporary buildings, along with other buildings with small areas and scattered distributions, could be gradually demolished and restored to vegetation areas. Existing agricultural activities should be endowed with ecological ideas. The natural shoreline and bare rock should be protected from human occupation and natural disturbances. The soil salinization should be controlled using different approaches, including improvement of water conservation facility, physical and chemical modification of soils, and plantation of salt-tolerance plants (Li et al., 2003). The vegetation areas should be improved in aspects of stand density adjustment, species composition optimization, and pest control. In ordinary protected area, the protection and development should be both considered in a harmonious mode, and the compatible exploitations can be allowed. Urban construction and industrial development should be restricted and conducted in specific areas with relatively low EII and high ETI. Eco-agriculture and eco-tourism should be promoted to balance the economic and ecological benefits of the island resources. Moreover, a list of exploitation types that were acceptable should be established on different islands based on the results of EII and ETI. In areas with extremely high EII or extremely low ETI, exploitations should not be expanded; in areas with extremely low EII, ecological restoration for damaged soils and vegetation should be conducted. Moreover, reserved areas should be assigned in this area for future generations. In non protected area, the reasonable and efficient development should be pursued. The residential areas should be organized and optimized according to the plan, and their utilization level should be promoted; the external and internal traffic conditions should be regularly maintained and further strengthened, especially the roads and bridges that connect different islands; and the green space should be reserved and constructed. All the measures aim to improve the living conditions of island residents. Meanwhile, the featured island port and tourism resources should be fully utilize to realize the high efficiency. Exploitations that may generate great negative effects, including quarrying and heavy industry should be restricted, and different kinds of pollution treatments should be conducted to minimize the negative effects of human activities on the island ecosystem. 5. Conclusions The ecological importance and tenacity were proposed for conducting the island protected area zoning in this study. The ecological importance was composed of three components, namely, landscape, soil, and vegetation, and nine elements, which comprehensively

Scheme F

Scheme E

Scheme D

Scheme C

Scheme B

3.45 3.87 0.63 0.66 3.31 3.98 0.08 7.24 0.63 0.74 2.37 4.84 2.79 2.60 2.56 0.08 1.10 6.77 Scheme A

Core protected area Ordinary protected area Non protected area Core protected area Ordinary protected area Non protected area Core protected area Ordinary protected area Non protected area Core protected area Ordinary protected area Non protected area Core protected area Ordinary protected area Non protected area Core protected area Ordinary protected area Non protected area

0.33 0.49 0.04 0.08 0.32 0.46 0.02 0.80 0.04 0.14 0.33 0.38 0.21 0.29 0.36 0.02 0.14 0.70

Industrial land Dock and embankment Road Island protected area Scheme

Table 8 Area proportions of island use types in different protected areas of each scheme (%).

Building land

Hardened ground

Quarrying area

Agricultural land

Water area

Bare land

Vegetation area

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Fig. 9. Reclamation areas in core, ordinary, and non protected areas in different schemes: CPA: core protected area; OPA: ordinary protected area; NPA: non protected area.

Declaration of Competing Interest

represented the island ecological characteristics and corresponded to the unique function. The ecological tenacity was evaluated by considering three types of influences, i.e., anthropogenic, topographic, and marine influences; it deepened the utilization of the ecological importance and corresponded to the distinct vulnerability of the island ecosystem. Two new indices, that is, EII and ETI, were established to quantify the ecological importance and tenacity, respectively. Then, the island protected area zoning was conducted based on the spatial distributions of EII and ETI, and six schemes for different protection and development purposes were designed. The demonstration in an island chain in Dongtou Archipelago validated the advantages of the EII and ETI in revealing the spatial characteristics of island ecological importance and tenacity, as well as the effectiveness of the method in the island protected area zoning. The results in the island chain in Dongtou Archipelago indicated that the ecological importance and tenacity showed spatial heterogeneities across different islands and across different areas within the islands. At the whole island scale, Is. 1 showed the lowest EII and ETI, whereas Is. 6 and Is. 3 had the highest EII and ETI, respectively; the islands with higher proximities to the mainland and larger areas generally possessed lower ecological importance and tenacity. At the evaluating unit scale, all of the landscape, soil, and vegetation components were important for the EII, and the anthropogenic and marine influences made larger contributions to the spatial heterogeneity of the ETI than the topographic influence did. Of the six schemes, Scheme B was the recommended scheme for the island protected zoning because of its reasonable area assignments for different protected areas, the optimum compatibility with island uses, and the balance of protection and development. Control measures were proposed for different protected areas to achieve the island sustainable development.

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CRediT authorship contribution statement Yuan Chi: Conceptualization, Methodology, Software, Formal analysis, Investigation, Data curation, Writing - original draft, Writing review & editing. Zhiwei Zhang: Validation, Writing - original draft, Supervision, Funding acquisition. Jing Wang: Investigation, Writing original draft. Zuolun Xie: Investigation, Writing - original draft. Jianhua Gao: Writing - review & editing, Supervision, Project administration.

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