Study on Evaluation of Timber Security in China Based on the PSR Conceptual Model

: In case of a shortage of China’s domestic timber, the research of China’s timber security has become increasingly more important. Using the pressure-state–response (PSR) conceptual model and the entropy method, the timber security of China during 1997–2017 was evaluated and analyzed to understand and master the situation of timber security in this paper. The results showed that: (1) The pressure of timber security in China during 1997–2017 was increasing in waves, with the condition of timber imports as the main factor; (2) the state of timber security in China presented a downward-then-upward tendency during 1997–2017, the main inﬂuencing factors of which were the domestic timber supply and forest resources condition; (3) responses to ensure the timber security of China almost indicated a steep rising trend, because both the timber industry technical progress index and the waste paper recovery rate improved the safety of timber in China; and (4) the changing trend of the comprehensive evaluation of timber security in China approximately agrees with that of the state evaluation, which showed that state indicators were key factors a ﬀ ecting the timber security of China. The pressures inﬂuencing the timber security of China are rising, while the state of timber security and the responses of the high-tech industry have been improving at a higher range than the pressures, which has led to an improvement of China’s timber security.


Introduction
Compared with other traditional raw materials (steel, cement, and plastic), timber is renewable and low emission, has relative low energy consumption in processing, and is widely used in construction and decoration engineering. Additionally, it is also the raw material of timber products, such as wood-based panels, furniture, paper, and paper products. With the continuous development of the economy and the continuous improvement of people's living standards, people increasingly prefer to buy green products. As the world's largest timber importer and second largest timber consumer, China has a huge demand for timber; however, China's total forest resources are relatively insufficient, with an insufficiently high quality and unbalanced forest resource structure. The proportion of youngand middle-aged forests is too high, while planted forests have a lesser proportion and are low in quality. The stock volume per hectare of planted forests is 52.76 m 3 , which is only half that of natural forests [1]. In addition, China also has a prominent structural contradiction between the domestic timber supply and demand, in that the supply of large-diameter timber is insufficient, low-end products have excess capacity, and famous and high-quality products rely mainly on imports. With the promotion of the full stop commercial logging policy on natural forests, the gap between the domestic timber supply and demand will further increase. Since the reform and opening up, the proportion concept of timber security and the PSR model, in this study, a Chinese timber security evaluation index system was built with the indicators selected from the perspectives of pressure, state, and response. Based on the time series data of 1997-2017, the entropy method and the linear weighting method were used to evaluate the level of China's timber security, analyze its changing tendency, and propose corresponding policy recommendations. The results of this study supplement and enrich the theory of timber security evaluation of the world or China, provide a scientific basis for an early warning of the world's or China's forestry industry and responding to timber security risks, and provide a decision-making reference for the formulation of sound forest resource protection policies and timber industry development policies.

Definition
This research involves the concepts of timber and timber security. In order to ensure the accuracy and scientific nature of the evaluation, the term timber in this study does not refer to logs in a narrow perspective but includes logs and their derivatives, such as sawn timber, veneer, particleboard, plywood, fiberboard, wood products, wood pulp, paper and paper products, and waste paper. The term timber security means that a country or region can obtain timber resources required for economic and social development at a reasonable price and in a sustainable, stable, and sufficient amount; and refers to a state or capacity ensuring the supply-demand balance of timber raw materials required for the healthy and sustainable development of timber-related industries, and ensuring a good ecological environment.

Evaluation Index System Construction
Drawing on the ideas of the PSR model and based on the relevant studies on resource and energy security conducted by domestic and foreign scholars, this paper covers as comprehensively as possible the situation of various aspects of timber security. Through expert consultation and the availability of index data, 14 indicators were selected from the three aspects of pressure, state, and response to build an evaluation index system of China's timber security (see Table 1). The pressure criterion (B1) includes the social pressure factor (C1), economic pressure factor (C2), resource and environment pressure factor (C3), and trade pressure factor (C4), which comprehensively reflect all aspects of the pressures facing China's timber security. The state criterion (B2) includes the resource and environment state factor (C5), supply state factor (C6), industry state factor (C7), and trade state factor (C8), which comprehensively show the current state of China's timber security. The response criterion (B3) includes the industrial technology response factor (C9), which comprehensively presents the improvement on industrial technology for the state of timber security. There is a specific indicator under the social pressure factor (C1), which is an inverse index D1-urbanization rate. D1 refers to the ratio of the urban population to the total population, which reflects the level of urbanization in a country or region. Timber is the main raw material for building and decoration. The urbanization process will promote large-scale construction of urban infrastructures and housings, which puts pressure on timber security.
There is a specific indicator under the economic pressure factor (C2), which is an inverse index D2-timber consumption per unit of Gross Domestic Product (GDP). D2 refers to the ratio of timber consumption to GDP, which is a main indicator of the level of timber consumption, reflecting the degree of timber utilization by a country's economic activities, and also reflecting changes in the economic structure and timber utilization efficiency. The greater the timber consumption per unit of GDP, the greater the pressure on China's timber security.
The resource and environment pressure factor (C3) has a specific indicator, which is an inverse index D3-population per unit of forest volume. D3 refers to the ratio of the total population to the forest volume, which partly reflects the per capita forest resources occupation, and is also the basis for determining the advantages and disadvantages of the ecological environment. The greater the population per unit of forest volume, the greater the pressure on China's timber security.
There are two specific indicators under the trade pressure factor (C4), both of which are inverse indicators D4-import concentration, and D5-inflation rate. D4, which is reflected by the Herfindahl-Hirschman index (hereinafter referred to as HHI) equal to the sum of the square of the ratio of imports from the country of import and total imports, reflects the concentration degree of import sources. A larger HHI means that the importing country of this product is relatively single and the degree of concentration is higher [21]. D5 refers to the ratio of the difference between the consumer price index (hereinafter referred to as CPI) value of the current year and the CPI value of the last year to the CPI value of the last year, which reflects the degree of inflation and the degree of currency depreciation, and partly reflects the level of timber prices. The larger the inflation rate, the lower the purchasing power of the currency.
There are three indicators under the resource and environment state factor (C5), all of which are positive indicators D6-forest coverage rate, D7-reserve-production ratio, and D8-volume per unit area. D6 is an important indicator reflecting the forest area occupation status or the richness of forest resources in a country or region. D7 refers to the ratio of the annual standing stock volume to the production volume of commercial timber, and is one of the important indicators to measure the reserves of timber resources [6]. The higher the reserve-production ratio, the longer the time available for harvesting, the longer the timber supply time, and the higher the security of the timber supply. D8 refers to the ratio of the f forest stock volume to the forest area, which is not only one of the basic indicators reflecting the total scale and level of forest resources in a country or region but also an important indicator for measuring timber production.
The supply state factor (C6) has two indicators, both of which are positive indicators: D9-proportion of timber plantation forest, and D10-proportion of mature forest of timber. D9-proportion of timber plantation forest refers to the ratio of the volume of timber plantation forests to the forest stock volume, which reflects the supply capacity of timber plantation forests. The higher the proportion of timber plantation forests, the higher the timber supply capacity, and the higher the timber security. D10-proportion of mature forest of timber refers to the ratio of the mature forest stock volume to the forest stock volume, which reflects the short-term timber supply capacity. The higher the proportion of mature forests, the more adequate the short-term timber supply, and the higher the level of timber security.
There is one indicator under the industrial state factor (C7), which is a positive indicator D11-total value of timber. D11-total value of timber refers to the sum of the values of timber processing output, the timber-based panel manufacturing, and the timber product manufacturing, which reflects the development of the timber industry. The higher the total value of timber, the better the development of the timber industry, and the higher the level of timber security. There is one indicator under the trade state factor (C8), which is an inverse indicator: D12-foreign dependence. D12-foreign dependence refers to the ratio of the sum of the import volume of logs and logs in timber products to the timber quantity supplied, which reflects the degree of dependence of a country's timber supply on foreign markets. The greater the foreign dependence, the more imported timber in China's timber consumption, the greater the dependence on imported timber, and the lower the level of Chinese timber security.
There are two indicators under the industrial technology response factor (C9), both of which are positive indicators: D13-timber industry technological progress index [22], and D14-recovery rate of recovered paper. D13-timber industry technological progress index refers to the ratio of the output of wood-based panels to the output of logs, which reflects the technological level of forestry-related industries and also reflects the utilization rate of timber. The higher the timber utilization rate, the lower the unit timber utilization, and the safer the timber. D14-recovery rate of recovered paper refers to the ratio of recovered wastepaper to paper and cardboard consumption, which reflects the level of timber saving and substitution. The higher the recovered wastepaper, the less the amount of timber utilized, and the higher the level of timber security.

Data Sources and Processing
In this study, 1997-2017 is determined as the evaluation period, and China's timber security is the evaluation object. The GDP and population data in this study were sourced from the China Statistical Yearbook; the data of forest product output, import and export trade volume, recovered wastepaper quantity, and import volume from the FAO database; the data of timber consumption from the China Forestry Development Report; the output value data of timber processing, wood-based panel manufacturing, and timber products manufacturing from the China Forestry Statistical Yearbook; the wastepaper recovery rate data from the Almanac of China Paper Industry and the website of China Technical Association of Paper Industry (http://ctapi.org.cn); the related data of forest resources from the Statistics of National Forest Resources; and the harvested commercial timber data from China Forestry Statistical Yearbook.
It should be noted that due to the change of statistical classification, there is no specific data of timber processing, timber-based panel manufacturing, and timber product manufacturing from 1997 to 1998, so the timber output value from 1997 to 1998 was calculated based on the average percentage of the total proportion of these three categories from 1999 to 2000. Since the cutting quota data is reported once every 5 years, and the amount of commercial timber harvested in each year cannot be determined, the average value was used for processing. In addition, China's forest resources inventory was conducted once every 5 years, specific values, such as forest area and stock volume, in each year could not be determined, and data were processed according to its average growth rate.

Calculation Method of the Evaluation Index Weight
Based on the above evaluation index system, the timber security level in China was evaluated, and the weight of the indicators was determined by using the entropy method. The specific steps were as follows:

Forming a Decision Matrix
Suppose that an index system consisting of m indicators is used to evaluate n objects; the eigenvalue of the i-th indicator of the j-th evaluation object is x ij , the decision matrix is formed as: X = (x ij ) m x n .

1.
Forming a standardized decision matrix In order to eliminate the influence of different index dimensions on the evaluation results, the decision matrix X is standardized to form a standardized matrix V = (v ij ) m x n . The positive indicators are standardized using Equation (1): (1) The reverse indicators are standardized using Equation (2): 2.
Calculating the characteristic proportion of the i-th evaluation object under the j-th index: 3.
Calculating the entropy value e j of the j-th index: 4.
Calculating the difference coefficient d j = 1-e j of the j-th index. If the entropy value is smaller, it indicates that the difference coefficient between the indexes is larger, and the index is more important.

5.
Determining the weight of each indicator:

Calculation Method of the Comprehensive Evaluation Value
The comprehensive evaluation value of China's timber security in each year was determined by the multi-objective linear weighting method. The following calculation formula was used: where S is the comprehensive evaluation value of China's timber security, Y i is the weight of the i-th criterion level, W ij is the weight of the j-th index of the i-th index level, and V ij is the evaluation value of the j-th index of the i-th index level (normalized value).

Evaluation Index Weight
The weight of each indicator determined by the above entropy method is shown in Table 2. The greater the weight of the indicator, the greater its impact on the evaluation results, and vice versa.
As can be seen from Table 2, among the pressure criterions, the weight of the trade pressure factor is the highest, the social pressure factor and the resource and environment pressure factor are second, and the economic pressure factor is the smallest, which indicates that the state of timber trade is the most important factor affecting China's timber security, while social pressure and resource environment pressure are also important factors. Among the state criterions, the supply state accounts for the largest weight followed by the resource and environment state factor, and the industry factor takes the smallest weight; meanwhile, that the weight of the positive indicator is much greater than that of the reverse indicator indicates that the current level of timber security in China is relatively optimistic. Among the response criterions, the weight of the technological progress indicator and the weight of the timber saving and substitution indicator are not much different, which shows that technological progress and timber saving and substitution have changed China's timber security situation.

Analysis on Evaluation Results
The pressure-state-response comprehensive evaluation values of China's timber security from 1997 to 2017 are shown in Table 3.

Analysis of the Evaluation Results of China's Timber Security Pressure
The pressure evaluation values of China's timber security from 1997 to 2017 are shown in Figure 1. As can be seen from Figure 1, the overall pressure on China's timber security shows a rising trend. As can be seen from Table 2, the urbanization rate and population per unit of forest volume had a higher weight, and thus had the biggest effect on the pressure of China's timber security. From 1997 to 2017, the continuous progress of urbanization in China led to an increasing demand for wood in China, resulting in an increased pressure on wood security. At the same time, the effect of the wood import concentration and inflation rate has led to fluctuation of the wood security pressure. China implemented a zero-tariff policy for raw sawn timber, which led to a change of China's timber import quantity and sources. In addition, increasingly more countries have formulated log export restriction policies, which have also led to the constant change of China's timber import source. The above two aspects may be the deep-seated reasons that led to the increase of the pressure level of China's timber security.

Analysis of the Evaluation Results of China's Timber Security Pressure
The pressure evaluation values of China's timber security from 1997 to 2017 are shown in Figure 1. As can be seen from Figure 1, the overall pressure on China's timber security shows a rising trend. As can be seen from Table 2, the urbanization rate and population per unit of forest volume had a higher weight, and thus had the biggest effect on the pressure of China's timber security. From 1997 to 2017, the continuous progress of urbanization in China led to an increasing demand for wood in China, resulting in an increased pressure on wood security. At the same time, the effect of the wood import concentration and inflation rate has led to fluctuation of the wood security pressure. China implemented a zero-tariff policy for raw sawn timber, which led to a change of China's timber import quantity and sources. In addition, increasingly more countries have formulated log export restriction policies, which have also led to the constant change of China's timber import source. The above two aspects may be the deep-seated reasons that led to the increase of the pressure level of China's timber security.

Analysis of China's Timber Security State
The evaluation values of China's timber security state from 1997 to 2017 are shown in Figure 2. As can be seen from Figure

Analysis of China's Timber Security State
The evaluation values of China's timber security state from 1997 to 2017 are shown in Figure 2. As can be seen from Figure

Analysis of China's Timber Security Response
The evaluation values of China's timber security response from 1997 to 2017 are shown in Figure 3. As can be seen from Figure 3

Analysis of China's Timber Security Response
The evaluation values of China's timber security response from 1997 to 2017 are shown in Figure 3. As can be seen from Figure

Analysis of the Comprehensive Evaluation of China's Timber Security
The comprehensive evaluation results of the pressure, state, and response evaluation value can be used to obtain the comprehensive evaluation value of China's timber security level. It can be seen from Figure 4

Analysis of the Comprehensive Evaluation of China's Timber Security
The comprehensive evaluation results of the pressure, state, and response evaluation value can be used to obtain the comprehensive evaluation value of China's timber security level. It can be seen from Figure 4

Analysis of the Comprehensive Evaluation of China's Timber Security
The comprehensive evaluation results of the pressure, state, and response evaluation value can be used to obtain the comprehensive evaluation value of China's timber security level. It can be seen from Figure 4 that the comprehensive evaluation value of China's timber security from 1997 to 2018 presented a downward-then-upward tendency; China's timber security level was at a relatively low level from 2002 to 2008, which is consistent with previous research conclusions. After 2008, with the continuous development of the economy and society, the continuous increase in forest coverage, the timber output value, the timber industry technology, and the timber saving and substitution, China's timber security level gradually improved, and its comprehensive evaluation value began to rise year by year. Referring to both Figures 2 and 4, it can be found that the changing trend of the comprehensive evaluation value of timber security in China approximately agrees with that of the state evaluation value, which showed that state indicators are key factors affecting the timber security of China. The continuous improvement of forest resource quality and timber supply capacity and the healthy development of the timber industry are the main factors to ensure China's timber security. Therefore, we should strengthen the cultivation of forest resources, improve the quantity and quality of forest resources, and improve the supply capacity of forest resources. comprehensive evaluation value of timber security in China approximately agrees with that of the state evaluation value, which showed that state indicators are key factors affecting the timber security of China. The continuous improvement of forest resource quality and timber supply capacity and the healthy development of the timber industry are the main factors to ensure China's timber security. Therefore, we should strengthen the cultivation of forest resources, improve the quantity and quality of forest resources, and improve the supply capacity of forest resources.

Conclusions and Discussion
In this research, based on the PSR model, and on the basis of following the principles of scientificity, globality, representativeness, comparability, and operability, a set of China's timber security evaluation index system was constructed, and China's timber security level from 1997 to 2017 was evaluated and its changing trend was analyzed by weighting the indictors objectively using the entropy method and through the multi-objective linear weighting method. The following conclusions were made: (1) During the study period, the evaluation value of China's timber security pressure increased in a wave, indicating that China's timber security pressure has been increasing, and the largest proportion of the trade indicator is the main factor causing the timber security pressure. The response evaluation value presented almost a steep rising trend, which indicates that the technology in the timber industry and timber saving and substitution have gradually been improving the state of timber security in China. Both the comprehensive evaluation value and the state calculation value of China's timber security level showed a downward-then-upward trend. In recent years, the state and response indicators have increased at a higher range than the pressure, so China's timber security level has continuously improved.

Conclusions and Discussion
In this research, based on the PSR model, and on the basis of following the principles of scientificity, globality, representativeness, comparability, and operability, a set of China's timber security evaluation index system was constructed, and China's timber security level from 1997 to 2017 was evaluated and its changing trend was analyzed by weighting the indictors objectively using the entropy method and through the multi-objective linear weighting method. The following conclusions were made: (1) During the study period, the evaluation value of China's timber security pressure increased in a wave, indicating that China's timber security pressure has been increasing, and the largest proportion of the trade indicator is the main factor causing the timber security pressure. The response evaluation value presented almost a steep rising trend, which indicates that the technology in the timber industry and timber saving and substitution have gradually been improving the state of timber security in China. Both the comprehensive evaluation value and the state calculation value of China's timber security level showed a downward-then-upward trend. In recent years, the state and response indicators have increased at a higher range than the pressure, so China's timber security level has continuously improved. (2) The trend of the comprehensive evaluation value and the state evaluation value of China's timber security situation during the study period are basically the same, indicating that the state indicators are the main factors influencing China's timber security level, and the supply capacity and industrial development of forest resources are the foundation of timber security. Based on the results of the indicator weights, the supply indicator and the resource and environment indicator occupy higher weights in the state criterion, which indicates that the state of timber security is mainly affected by the quantity, quality, and supply capacity of domestic forest resources. Therefore, we should strengthen afforestation, improve the level of forest management, and develop timber plantation to enhance the quality and supply capacity of China's forest resources and ensure China's level of timber security. (3) Based on the above analysis, the situation of China's timber security is optimistic, because this study was based on the premise that there is no restriction on timber imports. In recent years, increasingly more countries with rich forest resources, such as Gabon, Russia, and some African countries, have introduced policies to restrict or ban the export of logs. Now, more than 100 countries have issued export bans on logs. The level of China's timber security could decline if major exporting countries sharply reduce their timber exports, coupled with the implementation of comprehensive protection policies for natural forests in China. For other countries with a large consumption of timber and insufficient domestic self-sufficiency, attention should also be paid to the issue of domestic timber security. The study might provide a reference for ideas and methods. (4) Based on the conclusion, this study proposes countermeasures and suggestions to further enhance China's timber security level: Improve the quality of existing forest resources through scientific management; develop timber plantation and fast-growing high-yielding forests; strengthen the construction of reserve forest bases; accelerate the pace of forestry resource export and promote the development of overseas forest resources and cooperation of overseas timber processing; upgrade the technological level of the timber industry and enhance the timber industry's international competitiveness; vigorously expand the supply of medium and high-quality timber; promote the recovery and saving of alternative and waste timber resources; and facilitate forest certification, so as to achieve the harmony of timber production and the ecological environment's protection. (5) In this study, the entropy method was used to determine the weight, which is an objective weighting method. The entropy value was used to judge the dispersion degree of an index. The greater the dispersion degree of the index, the greater the influence of the index on the comprehensive evaluation. Based on the characteristics of the original data, the entropy method was chosen to determine the weight. However, this method of weighting only relies on the actual problem, so it also has its disadvantages, such as poor participation of decision-makers, no consideration of the subjective intention of decision-makers, and more complicated calculation methods.
Author Contributions: Q.L. wrote the manuscript. S.C. and R.Z. provided reviews and editing. All authors have read and agreed to the published version of the manuscript.
Funding: This research was funded by the Chinese National Social Science Fund, grant number 17BGL248.