As one of the most basic and important part of wetland ecosystems, wetland spermatophyta directly or indirectly support many other organisms, including humans. Moreover, they play an essential role concerning ecological, economic and social ecosystem services. However, due to overexploitation and utilization of wetlands, the respective spermatophyta on earth are decreasing rapidly and numerous species of spermatophyta are even facing the danger of extinction (Oswald, 2007).

In recent years, scientists have to understand that all of the Earth's environmental problems fall into two broad, fundamentally different categories and the reduction of biodiversity by extinction (Dan et al., 1997). More and more countries are taking actions for biodiversity conservation, especially the Chinese government has formulated the "China Wetland Protection Action Plan" in 2000 (State Forestry Administration, P.R.China, 2000). "China Wetland Conservation Project Planning(2004-2030 year)" was adopted in 2004. The issue of wetland spermatophyta biodiversity has evoked the attention both local and international scientists.

The issues related to wetland spermatophyta diversity conservation have also arisen special attention by Chinese scholars. Quite a number of recent publications deal with this issue, focusing on species diversity of subtropical forest communities (Peng et al., 1983), the area types of Chinese genera of spermatophyta (Wu, 1991), biodiversity protection and utilization (Xie et al., 2001), plant diversity and impacts of xerophytes invasion in wetland areas close to Beijing (Ye et al., 2006), plant species diversity of wetland ecosystem in an arid and semi-arid region in northwest China (Li et al., 2007), the seed plant flora of the wetlands along the Yellow River in Lanzhou City(Liu et al., 2008), or the relationship of spermatophyte diversity between Nanyue nature reserve area and its vicinities (Liao et al., 2009) studied on.

The research selected the indicators which can describe the composition, richness, speciality, antiquity and harmfulness characters of wetland spermatophyta diversity in Hangzhou City, intended to provide a more comprehensive procedure to assess wetland spermatophyta diversity by using a multi-criteria, qualitative approach and a quantitative method.

Hangzhou's economy has grown rapidly, the conflicts between wetland spermatophyta diversity conservation and the spread of urban areas are becoming sharp. Thus, it is therefore necessary to assess the status of wetland spermatophyta diversity in Hangzhou City, which will provide making policy data for conservation and sustainable use.

1 General situation of study area

Hangzhou is located in northern Zhejiang Province, eastern China, at the southern end of the Grand Canal of China, on the plain of the mid-lower reaches of the Yangtze River(118°20′-120°37′E, 29°11′-30°34′N). Hangzhou is of subtropical monsoon climate, with distinctive four seasons and mild atmosphere and favorable geographical positions and natural conditions. Hangzhou's climate is humid subtropical, with four distinctive seasons, characterised by long, very hot, humid summers and short, cool to cold, cloudy and dry winters. The average annual temperature in Hangzhou is 16.2 ℃. Hangzhou receives an average annual rainfall of 1 450 mm.

Hangzhou wetland areas, more than a single block area of 8 hm², are 289.43×103 hm², about 17.44% of total area of Hangzhou City. The largest areas of wetland are artificial wetlands, accounting for 79.19% of the total area of wetlands, river wetlands covering 11.51% area, marine and coastal wetlands accounting for 9.11% area, lake wetlands covering 0.17% area and marsh wetlands accounting for 0.02% area.

Hangzhou forest coverage rate is 63.7%, the vegetation type is tropical evergreen broad-leaved forest, most of them are natural secondary forest and plantation, whose types are complex and the regional differences are significant. Hangzhou main soil types are red soils and yellow soils, most is acidic. The main soils related to wetlands are the coastal saline soil, alluvial soil, mountain meadow soil and paddy soil.

2 Methods 2.1 Floristic data

From 1997 to 2000, the forestry department of Zhejiang Province organized a wetland plant resources investigation in Zhejiang Province, in accordance with the unified plan drawn up by the State Forestry Administration, P. R. China. On the basis of a thorough collection and utilization of existing investigation materials, the project group followed the technical route of combining modern technology with traditional approaches, practicability with creativity, routine investigation with specialized investigation, and technical investigation with Socio-Economics. At the same time with the help of 3S integration technology, combining systematic sampling with transect and point count techniques and satellite tracking technology, a complete wetland plant resources investigation in Zhejiang Province was achieved. In 2002, the wetland plant resources investigation data of Zhejiang Province was published (Chen, 2002). This data source was used to extract and pool the wetland spermatophyta data in Hangzhou City.

2.2 Delphi method

The Delphi method is a systematic, interactive forecasting method which relies on a panel of experts (Chen et al., 2002). The research then designed and collected 30 experts' questionnaires for the assessment of wetland spermatophyta diversity of this data pool in 2009. Most of these 30 experts work for the State Forestry Administration P. R. China, the Chinese Academy of Forestry, the Academy of Forest Inventory and Planning, the Forestry Department of Zhejiang Province, the Zhejiang University, the Zhejiang Forestry College and the Forest and Water Department of Hangzhou City. Their research or activity fields all focus wetland plant management and sustainable use, and some of them attended the project of wetland plant resources investigation of Zhejiang Province. Following the experts' suggestions, the study selected the areal types of genera, the species status, the priority protection species, relict genera of glacial epoch and the injurious species as the five factors, to set up a variable layer index, which can respectively describe the composition, richness, speciality, antiquity and hazardousness characters of wetland spermatophyta diversity in Hangzhou City. Then, according to 30 experts' questionnaires, the five factors weights are calculated and the single factors are assessed qualitatively. Then, using the FCE and combining the assessment results for the single factors, the result of wetland spermatophyta diversity in Hangzhou City is assessed.

2.3 Fuzzy comprehensive evaluation method

The assessment of species diversity usually tries to consider various aspects, using different complex diversity indices. Yet, traditional mathematical methods are known as difficult to solve the problem of a comprehensive, complex, multilevel judgment, The fuzzy comprehensive evaluation method (FCE) however, can effectively fill the lack of clarity between the singular rating of indicators that are usually used and the assessment ambiguity of the experts who understand the underlying complexity of the issue concerning the final overall judgment. According to experts' suggestions, the factors of a variable layer index can be selected and the single factor can be assessed. Combining FCE with the Delphi method is simple and feasible, and can achieve a comprehensive, scientific quantitative assessment result.

The fuzzy comprehensive evaluation method is a decision finding process that under the fuzzy environment applies the fuzzy set theory, processes a comprehensive quantity evaluation on a system restrained from many uncertain factors. When a certain subject is difficult to evaluate, a complex system has to be decomposed into smaller subsystems. These smaller systems are step-by-step further decomposed into elements, and the minimum elements are weighted with respect to their estimated importance. Finally each of these smallest elements evaluated as such. Its overall contribution to the entire system quality is assumed to correspond to its singular rating and importance.

The Fuzzy comprehensive evaluation method is generally suitable to evaluate and choose subjects with incomplete information, that is to say, when the subject evaluated is not well known, this method can usually be adopted. The prerequisite is that the evaluation index of the investigated subject is decomposable (Guo, 2002).

In FCE, the remark congregation U are factor congregation V are set up:U=(U₁, U₂, …, U_m); V=(V₁, V₂, …, V_n). The single factor i is evaluated R̃₁, R̃₁=(r_i1, r_i2, …, r_im), (i=1, 2, …, n), R̃₁ is a fuzzy subset in U_m, r_ik is the factor i evaluation about membership degree in k grades, (k=1, 2, …, m).

In the formula m_ik means the assessment number for each assessment categories, n means the total of experts' questionnaires which is 30. The evaluation about n numbers of factors can be denoted by matrix R̃:

In the fuzzy comprehensive evaluation, each factor weight vector should be determined, which composes a fuzzy subsetÃ:

a_i: factor v_i is membership degree aboutÃ, which represents the evaluation ability level of single factor v_i.

After figuring out à and R̃, the fuzzy comprehensive evaluation model can calculate the assessment resultB̃.

Then B̃ is standardized, based on the principle of maximum degree of membership, the parallelism degree of max in b₁, b₂, …, b_n is the comprehensive evaluation degree.

3 Results and analysis 3.1 Areal types of genera

'The areal types of Chinese genera of spermatophyta (Wu, 1991)' has been considered as one of the most authoritative researches in China so far, and has been widely quoted in scientific papers. The analysis result of areal types of Hangzhou genera of wetland spermatophyta is relying on this publication, the results being shown in table 1.There are 13 areal types of genera of wetland spermatophyta in Hangzhou City, complying with 87% of the total types in China. This means genera of wetland spermatophyta in Hangzhou origin from a large variety of geographical elements. The main areal types of Hangzhou genera wetland spermatophyta are pantropic, north temperate and east Asia, the total percentage of these three types are 63%, which reflect the widespread character of the genera of wetland spermatophyta in Hangzhou, and deep original relationship with most parts of the world. According to 30 experts' assessment (table 3), as the single factor, the assessment result of the areal types of genera is 'very good'.

3.2 Species status

The wetland spermatophyta in Hangzhou comprise 851 species, which are 25% species in Zhejiang Province; 424 genera, which are 34% genera in Zhejiang Province; 114 families, which are 63% families in Zhejiang Province (table 2). Within the families in Hangzhou there are 95 small-scale families can be identified. According to 30 experts' assessment (table 3), as the single factor, the assessment result of the species status is 'good'.

3.3 Priority protection species

On January 1, 1997, China's first special administrative regulation to protect wild plants 'The People's Republic of China Regulation on Protection of Wild Plants' was released by the State Council of the P.R.China. As the supporting documentation of the regulation, 'the national list of wild plants under priority protection in China (first batch)' was released on August 4, 1999. This is the most authoritative list of plant protection in China. According to it, there are 7 wetland spermatophyta species under priority protection, which adds up to 64% of the 11 wetland spermatophyta species under priority protection in Zhejiang Province. Brasenia schreberi belongs to China'sⅠpriority protection grade; Trapa incisa, Zoysia sinica, Glycine soja, Fagopyrum dibotrys, Nelumbo nucifera, and Cinnamomum camphora belong to China'sⅡpriority protection grade. According to 30 experts' assessment (table 3), as the single factor, the assessment result of the priority protection species is 'neutral'.

3.4 Relict genera of glacial epoch

In wetland spermatophyta of Hangzhou City, there are some relict genera and families of the glacial epoch, such as Pinus, Salix, Pterocarya, Ulmus, Chloranthaceae, Saururaceae, Nymphaeaceae, Lardizabalaceae, and Ranunculaceae, which are valuable for research and conservation. According to 30 experts' assessment (table 3), as the single factor, the assessment result of the relict genera of glacial epoch is 'good'.

3.5 Injurious species

The State Environmental Protection Administration, P. R. China announced 'the national list of injurious adventitious plants' including 7 species; the State Forestry Administration, P. R. China announced 'the national list of injurious plants in China' including 24 species, which has been considered as the official authoritative list in China so far, and has been widely quoted in scientific papers and newspapers, radio and television. According to the two lists, the injurious wetland spermatophyta in Hangzhou comprise 47 species, which are 6% species of the total wetland spermatophyta in Hangzhou; 36 genera, which are 9% genera of the total wetland spermatophyta in Hangzhou; corresponding to 18 families, which are 16% families of the total wetland spermatophyta in Hangzhou. According to 30 experts' assessment (table 3), as the single factor, the assessment result of the injurious species is 'good'.

3.6 Factor weight vector

The assessment factor weight vectors are confirmed by the Delphi method based on 30 experts' questionnaires. These assessment factor weight vectors of the areal types of genera, the species status, the priority protection species, relict genera of glacial epoch and the injurious species are respective 0.27, 0.3, 0.19, 0.14 and 0.1.

3.7 Single factor membership degree

According to the experts' questionnaires (table 3), using formula 1, single factor membership degree of wetland spermatophyta diversity in Hangzhou can be calculated in table 4.

3.8 Calculated conclusion

According to the assessment results for single factors (table 4), the assessment of wetland spermatophyta diversity can be denoted by the formula 2:

Following the single factor membership degree, the assessment weight vector can be expressed as:

Then according to formula 3, using MATLAB software, the assessment results of wetland spermatophyta diversity in Hangzhou City can be calculated as:

Finally the second number 0.30 is chosen, which is maximum and corresponds to the assessment standard 'good', which means the assessment category of wetland spermatophyta diversity in Hangzhou City is rated as 'good'.

4 Conclusion and suggestion

The comprehensive assessment conclusion identifies the wetland spermatophyta diversity in Hangzhou City as 'good', which is corresponding to the reality. The main reasons are Hangzhou lies in the southeast coast of China, and whose natural conditions and the biological diversity are better than in other places in China. The conclusion indicates that the current wetland spermatophyta diversity in Hangzhou City is abundant and plays a very important role for ecosystem functioning, services and sustainable development.

However, the situation is not optimistic. The construction projects, such as enclosing tideland for cultivation and capital construction, result in a continuous reduction of natural wetland areas, while industrial agricultural production and urbanization aggravate the pollution in land water and shallow marine waters. The living qualities of wetland spermatophyta are dropping. So there is heavy responsibility upon people and a long way to go for wetland spermatophyta diversity in Hangzhou City.

Therefore, the key significance for the assessment of the wetland spermatophyta diversity in Hangzhou City, based on fuzzy comprehensive evaluation method is to provide scientific basis for distinguishing wetland vegetations protection zone, legitimately protecting and utilizing wetland spermatophyte in Hangzhou City. In addition, the comprehensive assessment, using qualitative and quantitative method is pioneer research, which would be useful for the next research of wetland vegetations diversity in Hangzhou City.

Because the time and funds are limited, the research only collects 30 experts' questionnaires to assess the wetland spermatophyta diversity in Hangzhou City. Due to the assessment is closely related with numerous subjects, specialties and departments, the more collecting experts' questionnaires, the objective and accuracy of the research are better.