INTRODUCTION

Recently, there has been a growing necessity for an environmental information map that can precisely show the environmental information of cities. Since Seoul made its own biotope map in 2000, about 87 cities/counties have made and are using their own biotope maps nationwide. In Seoul, after enacting an ordinance, the biotope assessment results are used in regulations for land use. They are also being used in various city plans and environmental management by stipulating it in the Enforcement Ordinance of the Natural Environment Conservation Act and the establishment guidelines for the basic plan and management plan of cities/counties. The Ministry of Environment made a guideline on how to make a biotope map and has been promoting its use. These days, the biotope maps of cities/counties are actively used in projects on the establishment of a national environmental map. Biotope maps are often used as reference data for decision making when establishing land use plans which have taken into account environmental and ecological status. The assessment on biotope in Korea can be broadly classified into an assessment on biotope types and an assessment on individual biotope. Biotope type is a generic term for biotopes which are in the target site and have similar characteristics. During the assessment on biotope types, all individual biotopes that belong to same biotope type undergo same assessment process. In order to overcome such limitations, the assessment on individual biotope, which uses the characteristics of each biotope, is conducted. Because the results are in detail and their accuracy is high, the assessment method is useful in establishing land use plans and leading development projects in an eco-friendly direction (Kim, 2012).

In Korea, the types of plant species, the occurrence of animal species, and the naturality and species diversity are used as qualitative indices for the assessment on individual biotope. In case of quantitative indices, the pavement ratio, green area ratio, appearance frequency, development period and layer composition are used. Most of the assessment indices used in Korea are related to species that compose a biotope and judgements on their naturality are made. Also, in Korea, the majority of research related to biotopes define a biotope as a habitat for certain organisms that enable the classification of a boundary based on the definition of biotope which was made by German scholars including Sukopp (1980). Therefore, assessing the characteristics of a biotope based on organisms living there lacks consideration for its value as a habitat. According to Lindenmayer & Fischer (2006), not only major organisms, but also the spatial characteristics of the habitat such as its form and area, location and diversity, changes in the metapopulation and relationships with other habitats need to be taken into account in order to assess the value of habitat. However, in regards to biotope assessment in Korea, there are not enough assessment indices on how an individual biotope functions with other biotopes in spatial context. There are indices related to areas such as the green area ratio, vegetation ratio and pavement ratio in some cases. However, there are limitations because they are used to assess the value of biotope in built-up areas, but not in green areas and open spaces (Kim, 2012).

This study tried to establish a methodology, which can assess what sort of relationship an individual biotope has with other biotopes and its functions as a habitat in spatial context; apply it to the target site; and identify the possibility of making an assessment based on biotope functions. This study also aimed at identifying the characteristics and meaning the biotope functional assessment have by conducting comparative analysis with past assessment results of individual biotope based on naturality that were carried out at the same place. For this, this study used landscape ecology of which a lot of empirical studies, which are helpful in understanding and analyzing the relationship between habitat and metapopulation in spatial context, have been made. Also, landscape indices that can deduce quantitative results were used.

MATERIALS AND METHODS

1.Study Site

1)Study Site Conditions

To inquire into the characteristics and meaning of the assessment on individual biotope, which has taken a habitat's functional aspects, comparative studies with existing assessment results are necessary. Therefore, in this study, places where assessments on individual biotope had already been made with existing methodologies were taken into consideration when selecting a study site. Seoul, Seongnam, Hanam and Siheung are places in Korea where the assessment on individual biotope was carried out. In this study, Siheung, Gyeonggi-do was chosen as the study site because there are natural forests and man-made forests of various sizes, and parks and green areas of various sizes in its new city and the vicinity of its old downtown. There are also various types of biotopes such as maritime forests, farmland and wetlands. The location of the study site is as shown in Figure 1. More than 70 % of the area of Siheung is designated as a limited development district.

However, theses days there is pressure for development due to projects related to a large industrial complex, highways and land development for this project are in progress. Accordingly, Siheung created a biotope map, which includes an assessment made on an individual biotope in 2009, and is using it for the systematic management of the city's natural environment.

2)Past Assessment on Individual Biotope of Study Site

The assessment on individual biotope, which was used to create the biotope map of Siheung in 2009, targeted only biotopes corresponding to green areas and open spaces. Three assessment indices were selected for each aspect of ecological value and spatial value. The inhabitation possibility of wild animals, the naturality and scarcity of biotope were chosen as the assessment indices for ecological value, and the area of the biotope, geographical characteristics, and the distance from a town were used as the assessment indices for spatial value. To put together the results of the assessment on the two values, a matrix technique was used to assess the value of individual biotope which was classified into grades between 1 to 5.

2.Study Method

1)Determining the Assessment Indices of Functional Aspects

The majority of assessment on biotopes carried out in Korea used assessment indices based on species composition status. Some studies included external factors such as the area of a biotope, gradient and distance for a town. However, they only paid attention to the physical characteristics of individual biotope and did not make an assessment on how it functions with other biotopes (Kim, 2012). In case of landscape ecology, which has been used as the principle of natural environment management, a study was carried out with its focus on three aspects: 1) structural aspects such as habitat size, shape, number and distribution; 2) functional aspects such as nutritional movement, seed propagation and animal movement; and 3) transitional aspects such as disturbance, climate and changes in metapopulation. Recently in landscape ecology, studies are actively underway to understand functional aspects based on study results related to habitational structures (Lee, 2001).

The purpose of this study is to establish a methodology that can evaluate an individual biotope's functional aspects as a habitat, which was not valued compared to its importance; apply the methodology to the study site; and identify what sort of characteristics assessment results have. In regards to the functional aspects of the individual biotope set in this study, an individual biotope is considered a habitat and the focus is on how an individual biotope functions with other habitats in terms of movement in energy, nutrition, animals and seeds.

For detailed assessment indices to evaluate the value of the functional aspects of individual biotope, connectivity, cohesion and diversity were selected. A lot of studies that have been conducted in Korea and abroad looked into the functional aspects of habitats by measuring the connectivity among them. A target site with high connectivity among patches can maintain various species populations that originally lived there (Brown and Kodric-Brown, 1977; Haddad and Baum, 1999). On the other hand, weak landscape connectivity may result in various negative effects and as a result, no species will inhabit the habitat (Villard and Taylor, 1994; Robinson, 1999). In particular, connectivity is often used to consider functional aspects as it enables quantitative judgements based on distance. In case of cohesion, it is an important landscape index which enables one to identify a more precise status by using not only the closest point of the approach, but also the size and circumference of the landscape as the measurement factors (Schumaker, 1996). Cohesion was selected as an assessment index to supplement the shortcomings of measuring connectivity based on the closest point of approach only. It was proved in some studies that the diversity of habitats that composed the study site was helpful in maintaining species diversity in it (Lindenmayer and Fischer, 2006). And there are many other studies that concluded the same results. Accordingly, in this study, the diversity of the individual biotope was chosen as the assessment index as the diversity of biotope is an important condition in maintaining species diversity.

2)Analysis on the Degree of Contribution

In landscape ecology, one target area, which is composed of various habitats, is regarded as the area of interest and its functional aspects are analyzed by developing landscape indices that can analyze connectivity, cohesion and the diversity of habitats within the area. With such landscape indices, the relationship among multiple biotopes in the area of interest is analyzed and one result value that represents the area is deduced. However, because a result value for each biotope is not deduced, it cannot be used in assessing each individual biotope.

Accordingly, this study tried to overcome such limitations by devising and using the concept of the degree of contribution (Figure 2). To calculate the concept of the degree of contribution, a certain area is divided based on individual biotopes; indices, in which quantified the relationship among all biotopes in the area, are deduced; and indices are deduced again after assuming a situation of which the biotope of the area of interest does not exist. It is a concept that assumes a gap between the two result values and shows how much the area of interest contributes to the functional aspects of the target area. The quantitative value of each individual biotope can be calculated using the degree of contribution. Also, individual biotopes can be assessed by interpreting them like this: the bigger the degree of contribution, the greater role the relevant biotope plays in the target area in terms of connectivity, cohesion and diversity.

3)Assessment Method for Functional Value

The results of assessment on individual biotopes in the preceding study are classified in grades of 1 to 5. To compare this with the existing study results, the results of this study were also classified into grades 1 to 5. Because the result values for the assessment indices of the functional aspects all include quantitative data, the grading criteria was established to classify individual biotopes. Relative evaluations based on the number of individual biotopes were used because of the assessment among them. Values derived from connectivity assessment, cohesion assessment and diversity assessment were classified in grades 1 to 5 at same interval based on the number of biotopes:　biotopes that make up the top 20 % were 1 Grade; the next highest 20 % were Grade 2; the next 20 % were Grade 3; the next 20 % were Grade 4; and the lowest 20% were Grade 5. It was based on the judgement that a threshold that can grade value cannot exist due to the diversity of nature and the lack of study cases conducted in Korea and abroad on a threshold that can grade a biotope's ecological value. Grades that were obtained through the analysis of connectivity, cohesion and diversity were converted into scores and put together. Then they were classified and the value of individual biotopes from functional aspects was deduced (Figure 3).

This study tried to identify the characteristics of functional aspects by comparatively analyzing existing assessment results of individual biotopes and the results deduced using the methodology established in this study. For this, The grades deduced in this study were compared with grades deduced in the assessment on individual biotopes conducted in 2009. Then, changes in the grades of all biotopes in the study site were identified and considered. Also, places with a big change in their grade were selected, and reasons for the change were closely analyzed to inquire into the strengths and limitations of this study's methodology.

4)Connectivity Assessment Method

Based on the empirical studies on connectivity among habitats and changes in populations, various indices are developed to quantify the connectivity (Turner, 1989). Most indices to quantify the connectivity are based on the distance between habitats, the number of passageways that connect those habitats and the size and shape of the patch (Baguette and Schtickzelle, 2003). It is more difficult to predict the response of a certain species based on the closest distance between neighboring habitats, which is used to quantify the connectivity, compared to a comprehensive measurement index, which has taken into account the movement capability of a species. However, it is used in many studies because it can be easily and quickly deduced and has generality (Moilanen & Nienminen, 2002).

In this study, the closest distance between neighboring habitats was used as the connectivity measurement index in order to assess the connectivity of individual biotopes. The closest distance between neighboring habitats refers to the closest distance between a certain biotope and the same type of biotope in the closest distance that exists within a certain area. The measurement criteria is based on the distance between the edge of the certain biotope and that of the closest biotope. The size of the target site was set at 1,000m from the edge of the target individual biotope. And connectivity was analyzed using the average of the closest distance between all biotopes located in the set area (Figure 4). This was based on Jedicke (1994)'s paper which set the distance at 1,000m, of which there is the possibility of the extinction of wild birds, considering whether there were obstacles due to urbanization and intensive land use.

5)Cohesion Assessment Method

Responses from species differ according to the relationship between habitats that compose the area of interest. Therefore, it is highly important to read the functional aspects of habitats that can preserve biodiversity in them (Andrén, 1996; Vos et al., 2001; Fahrig, 2001). The closest distance is a substantially important factor that has a great impact on the movement, reproduction and feeding of biospecies. However, analyzing connectivity using only the closest distance does not take into account the qualitative aspects such as the size and form of habitats. Therefore, the characteristics of the target site's landscape cannot be reflected comprehensively. To supplement such weakness, this study took into account the size and shape of biotopes and used cohesion indices that can analyze connectivity.

The cohesion indices used in this study have various strengths compared to existing relevant indices. They were devised using the area and circumference of habitats while conducting a prediction study on habitat connectivity using Schumaker (1996)'s landscape index (Figure 5). The cohesion formula is somewhat complicated. However, with a formula deduced by applying existing indices based on the relationship between circumference and area, constant results regardless of measurement unit can be obtained and with uniform scope (Schumaker, 1996). Result value deduced with the cohesion formula goes closer to 0 as the area of the habitat decreases, segmentation becomes intensified and physical connectivity decreases (Figure 6). On the other hand, cohesion becomes bigger as the patches of the same type agglomerate or assemble. The size of the target site to deduce the degree of contribution of cohesion is set at 1,000m from the edge of the target individual biotope. Then, the cohesion among biotopes within the scope was analyzed.

6)Diversity Assessment Method

Habitational diversity is an important condition in maintaining biodiversity. Many relevant studies concluded that the diversity of patches which compose a landscape is favorable in maintaining the diversity of organisms inhabiting the target site (Lindenmayer and Fischer, 2006). The most commonly used methods to identify diversity are Shannon's Diversity Index and Simpson's Diversity Index of which are used in ecology.

Shannon's Diversity Index approaches the barometer of species diversity through information theory. Shannon's Diversity Index, which is used in ecology, measuring how difficult it is to accurately assume information collected based on a function that measures the degree of uncertainty of the collected information. It inversely interprets meaning and measures diversity. In other words, it is easy to identify if a sample is randomly extracted from a community with a low species diversity. However, it is difficult to identify the species when the sample is extracted from a community with a high species diversity. The value deduced through Shannon's Diversity Index shows the information quantity of an individual and the absolute size signifies nothing. It can be used as a relative value when compared to other target sites Shannon (Shannon and Weaver, 1949; Krebs, 2008).

Simpson's Diversity Index has derived probability theory. Simpson deduced diversity indices by identifying the probability of two samples, which are randomly extracted from the community of infinite size, being the same species. In other words, the probability of the two samples being same species will go down in an area with high species diversity but will go up in an area with low species diversity (Simpson, 1949).

To analyze the diversity of landscape types, Nagendra (2002) compared and analyzed the suitability of Shannon's Diversity Index and Simpson's Diversity Index. As results, in case of Shannon's Diversity Index, it displayed high sensitivity towards rare types, whereas it was recommended to use Simpson's Diversity Index when there was a dominant species in the target site. This coincides with the preceding study results that Simpson's Diversity Index is relatively weak against species abundance and puts more emphasis on common species (O'Nell et al., 1988; Romme, 1982; Turner, 1990).

Because this study tried to identify how each biotope affects the diversity of the surrounding landscape, Shannon's Diversity Index, of which indices are deduced by sensitively reacting to the presence of rare types, was judged to be adequate to use (Figure 7). This is because when considering the value of biotopes within the target area as habitats, it will be more advantageous in maintaining species diversity in the entire target site than bitotopes with rare species.

It is 0 in case there is only one patch in the landscape when the diversity assessment on biotopes within the target site is conducted with Shannon's Diversity Index. It increases when the number of different patch types increase or area ratios among patch types become similar.

The size of the target site to deduce the degree of contribution of diversity is set at 1,000, from the edge of the target individual biotope, and the diversity among biotopes within the scope was analyzed.

RESULTS AND DISCUSSION

1.Assessment Result of Functional Aspects

1)Assessment Result of the Degree of Contribution in Connectivity

The assessment results of the degree of contribution in connectivity are as shown in Table 2. On the whole, man-made forests displayed slightly a higher degree of contribution in connectivity than natural forests. The degree of contribution is thought to be high because such type of biotopes are in a linear shape or created in urban areas and play the role of stepping stones for surrounding natural areas.

Biotopes related to man-made forests, green facilities and parks were assessed as low grades in the existing assessment frame due to their low naturality. However, when assessing the degree of each individual biotope's contribution in connectivity among habitats within the target area, a lot of individual biotopes that belong to such types are assessed as high grades. This shows the necessity of assessment from various aspects when assessing individual biotopes.

2)Assessment Result of the Degree of Contribution in Cohesion

The assessment results of the degree of contribution in cohesion are as shown in Table 3. More than 50% of biotopes related to natural forests were assessed as Grades 1 and 2, and less than 40% of those related to man-made forests were classified as Grades 1 and 2. This is because biotopes related to natural forests make up large forests in the target sites, but man-made forests exist at the edge of forests or as fragmented natural forests. 70% of biotopes related to parks and green facilities were classified as Grades 1 and 2. This result is higher than the result associated with connectivity. It also resulted from a difference between connectivity analysis, which only used distance as its assessment factor and the cohesion analysis which used area and circumference. This indicates that the weakness of connectivity analysis based on the closest distance can be supplemented with cohesion indices which use both area and circumference. However, the strong interpretation for connectivity, which only the method of using closest distance has, may be lacking when cohesion indices are used on their on. Therefore, an accurate assessment can be made when both methods are applied.

3)Assessment Result of the Degree of Contribution in Diversity

The assessment results of the degree of contribution in diversity are as shown in Table 4. While many rice paddies were classified as Grades 1 and 2, many dry fields were classified as Grades 4 and 5. Although both rice paddies and dry fields are biotopes that occur in high frequency in all target areas, their distribution patterns are different. Rice paddies, which have highly contributed to diversity, are the rare type of biotope because they are broadly distributed at the center of the target site, but do not exist in other areas. On the other hand, because dry fields are evenly distributed in various sizes in all areas of the target site, their contribution to diversity is low and many biotopes were classified as low grade.

While the degree of biotopes related to natural forests' contribution in diversity were highly rated, that of those related to man-made forests were poorly rated. This is thought to be because in case of natural forests, their rarity has highly contributed to diversity as present in large forests only, but the rarity of man-made forests is relatively low as they evenly exist in all areas of the target site.

In case of types that are related to green landscape architecture, most park types were classified as Grades 1 and 2, and most green facility types were classified as Grades 3 and 4. This is because the green facility types exist in all areas of the target site, but park types exit only in build-up areas.

4)Comprehensive Assessment Result of Functional Aspects

Table 5 shows the results of comprehensively grading the assessment results of the degree of contribution in connectivity, cohesion and diversity which was conducted to determine the functional aspects of an individual biotope. More than 70~80% of park and green facility types of biotopes and fragmented green areas were classified as Grades 1 and 2. These types were graded low in the past assessment due to their low naturality. However, when taking into account the functional aspects of a habitats' connectivity, cohesion and diversity, the result showed that artificial biotopes played important roles as habitats within the entire target site. More than 70 % of biotopes related to forests were classified above Grade 3. Also in the comprehensive assessment, the value of biotopes related to natural forests was slightly higher than that of those related to artificial forests because the former's contribution in cohesion and diversity was higher. This means that the assessment on the functional aspects of habitats does not contradict the existing assessment methods based on naturality and landscape ecology. Based on such results, a more in-depth assessment can be made through complementary assessment when the assessment on the functional aspects of habitats is used along with the assessment on the naturality of biotope components.

2.Results of Comparative Analysis with the Existing Study Results

This study identified the functional value of a biotope as a habitat that can be deduced from the landscape ecological perspective when the concept of the contribution is used by quantifying the functional aspects of habitats such as connectivity, cohesion and diversity. The results of comparing such assessments with existing study results to determine its characteristics are show in Table 6. The results of analyzing characteristics by selecting a representative case area is show in Table 8. Figure 8 shows the difference between the results of assessment on the functional aspects of individual biotopes and the existing assessment results: changes with the (+) sign mean their grades went up and those with a (-) sign means their grades went down.

If we take a look at the changes in the grades of the individual biotopes through Table 6, in terms of the number of biotopes, changes existed in 78.38 % of them and 58.59 % were changed in terms of area. On the basis of numbers, 1.07 % of biotopes displayed ±4 changes in their grades; 9.68 % ±3; 26.87 % ±2; and 40.75 % ±1. The grades of large forests, forest wetlands that are high in rarity, salt marshes and natural grasslands barely changed and maintained existing high grades. This is because the wide area of those biotopes contributed to connectivity and cohesion, and rarity also contributed to diversity. On the whole, the grades of fragmented biotopes of big forests, biotopes surrounded by built-up areas and farmland, biotopes such as park/buffer areas/landscape green areas in built-up areas and waterside green areas went up, and the increase differed according to the surrounding conditions. The value of fragmented biotopes was highly rated from the aspect of connectivity and cohesion. The naturality of artificial green areas in built-up areas was poorly rated in the existing assessment. However, the value of those areas was highly rated in this study due to the rarity of biotopes in those areas that can serve as habitats. On the whole, the grades of small biotopes located at the edge of forests and biotopes are surrounded by the same types. This is because biotopes that are located at the edge do not contribute much towards connectivity and diversity.Table 7

Case Site 1 received a low grade in terms of naturality and rarity as it is a Pinus rigida plantation. However, when evaluated by its functional aspects, all of its contributions in connectivity, cohesion and diversity were assessed Grade 1. This site, which is located at the center of a large farmland, is a highly valuable area which plays the role of a stepping stone for the target site. However, such value cannot be reflected using existing assessment methods. This is the case which clearly shows value through the method based on functional aspects which are used in this study. It also shows the limitations of a flora-oriented assessment index of the preceding studies.

Case Site 2 is a small forest area which broke away from a big forest due to urban expansion. In the existing assessment, although it is a natural forest, it overall received a low grade: its area value was assessed low due to its small area; and the influence from built-up areas was also assessed low as it is located closed to built-up areas. However, in the assessment on functional aspects, it received Grade 2 in its contribution in connectivity, Grade 3 in cohesion and Grade 2 in diversity. This is different from the results of the biotope structure assessment based on area, and it shows that a small fragmented forest in a downtown area can also play an important roles from a functional perspective.

Case Site 3 was assessed low in the existing assessment in terms of naturality, distance with built-up areas and rarity although it is an important buffer green area of the target site. However, in the assessment on functional aspects, its contribution in connectivity was rated as Grade 1, Grade 1 in cohesion and Grade 1 in diversity. Such results show that buffer green areas that are created artificially for a certain purpose can also play an important roles in improving the quality of habitats for animals and plants.

Case Site 4, a broadleaf tree plantation, is a small forest located at the edge of a big forest. It was a plantation in the existing assessment, but it was rated high in terms of naturality and rarity. This is because although it is a plantation, it is also a broadleaf forest with a well developed layer structure and wild animals. However, it was classified as Grade 4 in connectivity, Grade 3 in cohesion and Grade 5 in diversity when assessed based on its functional aspects. Most of the small forest biotopes that were located at the edge of big forests were poorly rated in terms of functional aspects compared to the existing assessment. The degree of their contribution in connectivity and cohesion was low because they were located at the edge of big forests. They also could not contribute much in diversity as there were biotopes with a similar species composition.

The assessment method suggested in this study has several limitations. In case of Case Site 4, it is located at the edge of a forest and includes a part of forest. It was downgraded from Grade 2 to Grade 4. In some cases, forests that included core areas were poorly rated. On the other hand, in the cases in which the grades of buffer green areas or fragmented green areas went up, the conditions of those areas became as good as the existing forests, resulting in the downgrading of existing forests. Such limitations can be resolved if the assessment method of this study is used together with the existing speciesoriented assessment method.

The purpose of this study was to suggest and identify the possibility of a new methodology that can assess the functional aspects of habitats. Through comparative analysis with past studies, this study identified how it was possible to assess value through quantification. Also, biotopes such as artificial forests, fragmented forests in downtown areas, and buffer/landscape green areas were found to play important roles as habitats from a functional perspective. In particular, such characteristic were judged to be highly useful in assessing biotopes in city areas.

Lopsided assessment indices cannot provide assessment results that fully reflect the value of biotopes from various aspects. The method based only on function value is also a lopsided assessment method. The results of this study should not be interpreted in a way where the assessment based on functional aspects is better than the existing assessment method. Rather, the point was that it is possible to know that we can also assess the value of habitats from a functional aspect, and although individual biotopes cannot be assessed with an existing landscape index, assessment on each biotope is possible through a concept of the degree of contribution. It is expected that more precise value can be deduced if new results can be drawn by combining results from an assessment on the naturality of biotope components, which is extensively used to this day, and the assessment on the functional aspects of habitats.