Assessing forest sustainability trajectory with temporal changes in timber output and ecological reserve:the case of China

Jianwei Bai·Yang Zhao·Longyu Shi·Fengri Li

Introduction

The methodsofmulti-criteria decision analysisare increasingly popular in the field of forest sustainability assessment but the evaluation of the tradeoffs between provisioning and regulating services of forest ecosystems is rather challenging because there are too many criteria on the production of timber and non-timber forest products(Uhde et al.2015).For example,dozens of indicators on forests are commonly used in forest sustainability assessments at national and global scales(Irland 2010).In this case,there are inevitably data gaps that are hard to fill for the purpose of consistent and comparable assessment of forest sustainability across space and over time.

With the rapid development of China’s economy,the country’s forest resources are experiencing an unprecedented challenge(Dai et al.2013).In addition to providing ecological bene fits for society,forests supply raw materials for national economic development(Li et al.2006;Zhao 2013).However,the requirements for these two services are sometimes incompatible(Wu et al.2015).Forests can be divided into four modes with respect to timber output and ecological reserve(TOER):high timber output and high ecological reserve(Mode T-E);high timber output and low ecological reserve(Mode T-e);low timber output and low ecological reserve(Mode t-e);and low timber output and high ecological reserve(Mode t-E).The goal of sustainable forest development is to ensure that forests can contribute fully to economic,social,and ecological bene fits(Shen 2000).Obviously,Modes T-e,t-e,and t-E do not conform to the requirements of sustainable forest development,and only Mode T-E is ideal and should be pursued.

During the early years of China’s development,forests were almost entirely natural forests,and the standing volume per unit area was high;thus,the ecological reserve of forests was high(He et al.2007;Zhang 2006).At that time,the top priority of forestry was timber production and ecological protection was ignored.Thirty to forty years later,state-owned forests experienced a massive decline in timber resources,leading to economic losses(Zhou 2005).In the 1980s,the country decided to control timber production,but the ecological conditions of forests had already been compromised.Ecological services were reduced,and forest diseases,insect pests,and soil and water loss were becoming increasingly serious.By the end of the 1900s,Chinabegan to implementnaturalforestprotection strategies and other major projects to improve forest resource protection.This paper evaluates and discusses the current state of forest resources in China.

Materials and methods

Economic,social,and ecological bene fits of forests are integrated abstract concepts(Zhang 2013),and classi fication methods have become increasingly complex(Niu et al.2012).The quality and quantity of ecological bene fits depend on ecological conditions.For example,the ecological bene fits of mixed forests are greater than that of mono-species forests,and the ecological bene fits of forests with high standing volumes are larger than that of forests with low standing volumes.This is because the former forest types have higher ecological reserves.Social and economic bene fits are related to timber output because the timber industry is bene ficial to social employment and local economies.Ecological bene fits and timber outputs represent the contributions of forests and the status of forest resource quality can be represented as an integrated expression of these two contributions.

The ecological contribution of a forest is expressed as the average value of stand volume(V)and total area(N)of natural forests,i.e.,the ecological contribution index(En).V,which is related to canopy density and maturity of natural forests,expresses the quality of ecological contribution;N,which represents the area and effective scope of natural forests,expresses the quantity of ecological contribution.Timber contribution is expressed as the average of the total area(A)and wood yield(S)of timber land,i.e.,the timber contribution index(Wn).A and S represent the quantity and ef ficiency of timber forests,respectively.

To compare multiple factors with different dimensions,single factors were standardized.Using the stand volume of natural forests(in hectares)as an example,standardized stand volume of a natural forest was calculated as follows:

where Vminand Vmaxare the minimum and maximum values of V,respectively.The value of Vnis between-1 and 1.

Similarly,the standard values of the other three factors were calculated to obtain standardized total area(Nn)of natural forests,standardized total area(An)of timber forests,and wood yield of standardized timber forests in hectares(Sn).

Data used to calculate V,N,A,and S were obtained from forest resource inventories issued by the State Forestry Administration in 1976,1981,1988,1993,1998,2003,2008,and 2013(SFA 2014).To research the evolution of forest resources since China was founded,this research also includes data from the early days of the new nation in 1950.Annual timber yield was calculated as the average value of forest resources from two consecutive inventories.Timber yield from the early days of the new nation was determined as the average of values from 1950 to 1955,and data was obtained from relevant literature(He et al.2007;Zhang 2006).

The combinations of timber and ecological contributions can be expressed with the TOER classi fication system,which is illustrated with the four quadrants(Fig.1).The 1st quadrant represents high timber output and high ecological reserve(Mode T-E);the 2nd denotes high timber output and low ecological reserve(Mode T-e);the 3rd means low timber output and low ecological reserve(Mode t-e);and the 4th is low timber output and high ecological reserve(Mode t-E).The four corners in Fig.1 express the extreme states of these four modes:the lower left corner the absence of woodland;the upper left corner only timber production and no protection:the lower right corner only protection and no production;and the upper right corner ideal sustainable forestry development.The state of forest resources may evolve over time.Evolution towards the upper right represents positive development,whereas evolution towards the lower left represents negative development.Evolution from Mode T-e to Mode t-E or vice versa expresses transformation from one extreme to another.

Fig.1 Four classi fication modes of forest resources.A higher ecological index(x)corresponds to greater ecological bene fits of forests;a higher timber index(y)corresponds to greater timber resources and timber output

Results and analysis

Dynamic changes in ecology and timber supply

In 1950,there were 109.01 million hectares of forests in China(He et al.2007),and 95.5%were natural forests(Zhang 2006).The average stand volume was 114 m3ha-1(Zhang 2014).Although China did not apply a speci fic land classi fication system,at least 80%(87.21 m ha)of the total forest area possessed timber resources worthy of harvesting(Zhang 2008).

The stand volume of natural forests was highest in the early 1950s and lowest from 1994 to 1998.It began to rise again during the end of the 1900s.Currently,the ecological contribution of forest resources is the highest since reforms were implemented(Fig.2a).The total area of natural forests was lowest from 1977 to 1981,and highest from 2009 to 2013.The quantity of ecological contribution of forest resources is the highest(Fig.2b)and the total area of timber forests highest from 1994 to 1998 and lowest from 2004 to 2008 since the founding of the State(Fig.2c).Timber yield was lowest during the early 1950s but has improved since,although there was a recession from 1999 to 2003,and has increased rapidly over the past 10 years.The timber contribution of forest resources was recently the highest with respect to timber yield per unit area since the founding of the state(Fig.2c,d).

The ecological contribution index of forest resources has varied over time:it was positive during the early 1950s,negative from the 1970s to the end of the 1900s,and positive again after 1999(Fig.2e).Timber contribution indices displayed the opposite trend:negative during the early 1950s,almost all positive from the 1970s to the end of the last century,and negative from 1999 to 2008(Fig.2f).Both ecological and timber contribution indices were positive from 2009 to 2013,the first time since the People’s Republic of China was established in 1949.

Temporal changes in forest resources

Over more than 60 years of forestry development in China three milestones have been reached:(1)the early years of the new nation(early 1950s)represent the beginning of forestry in the country;(2)the period from 1977 to 1981 represents the beginning of reform and opening-up,as well as the beginning of the Forest Law and forest classi fication management;and,(3)the period from 1999 to 2003 represents the beginning of major forestry projects,particularly the beginning of natural forest protection projects and forest rehabilitation from slope agricultural engineering(Hu and He 2012).Therefore,this paper mainly compares temporal changes in forest resources during four time intervals:1950–1955,1977–1981,1999–2003,and 2009–2013(Table 1).The three stages between these intervals are referred to as the forest harvesting and use period,the forest regeneration and cutting period,and the sustainable forest management period,respectively(Zhang 2008).

Based on a comparison of the area of timber forests versus the stand volume of natural forests,the quality of ecological contribution greatly declined during the first period,and forestresourcesconsequently decreased(Fig.3a).Forest resources transferred from the Mode T-e to the Mode t-e during the second period but improved during the transition from the Mode t-e to the Mode t-E in the third period as the quality of ecological contributions improved and the area of timber forests decreased.

Comparing timber yields with stand volumes,forest resources again declined during the first period as the quality of ecological contributions decreased(Fig.3b).There were no substantive changes during the second period.Forest resources improved during the transition from the Mode t-e to the Mode T-E,re flecting an outstanding positive development due to improvements in ecological contribution and timber production.

Fig.2 Temporal changes of forest resources between 1950 and 2013

Table 1 Ecological and timber indices of China’s forest resources and various factors from 1950 to 2013

Fig.3 Temporal trends for individual ecological and timber indices of China’s forest resources from 1950 to 1977–1981 to 1999–2003 to 2009–2013.a x is stand volume per unit area of natural forests(Vn)and y is total area of timber forests(An);b x is stand volume per unit area of natural forests(Vn)and y is unit-area timber output of timber forests(Sn);c x is total area of natural forests(Nn)and y is total area of timber forests(An);d x is total area of natural forests(Nn)and y is unit-area timber output of timber forests(Sn)

Based on a comparison of area of timber forests versus the total area of natural forests,resources in China again declined during the first period due to the decrease in the quality of ecological contributions(Fig.3c).The reverse occurred during the second period but during the third,resources declined as timber contributions decreased.

Comparing timber yields and the total area of natural forests(Fig.3d),changes in resources were greatest during the first period,with positive development occurring during the second and ecological and timber contributions continuing to improve during the third,resulting in the ideal Mode T-E.

Based on a comparison of the timber contribution index and the ecological contribution index(Fig.4),resources decreased during the first period,shifting from Mode t-E to Mode t-e,as ecological contributions declined and timber contribution ef ficiency increased.During the second and third periods,ecological and timber contributions improved,resulting in the transition to Mode t-E and finally to Mode T-E,representing sustainable development.

Conclusions and prospects

Forest resources in China greatly declined during the early 1950s(harvesting period),but improved during the forest tending and cutting periods.Even greater improvement has occurred since the beginning of the current century(the start of the sustainable forest management period),and the goalofsustainable managementisbeing gradually achieved.

Fig.4 Temporal trends of combinations of ecological and timber indices for China’s forest resources from 1950 to 1977–1981 to 1999–2003 to 2009–2013

To ensure the continuation and strengthening of sustainable forest development,current ecological conditions and timber yields of forests should be maintained.Based on the four factors discussed in this paper,the area of timber forests is relatively low and should be increased.With the increase in natural forest protection and improvements in the construction and management of fast-growing and high-yield plantations,forest resources in China will achieve sustainable development with a better balance between ecological reserves and timber supplies which will be reached and maintained in the long-term and should not be altered easily by new forest policies.

Various methods and indices for assessing the quality of forest resources exist.The four-mode TOER evaluation method is a simple but effective approach for characterizing the overall quality and quantity of forest resources.The framework introduced in this paper focuses on data that is usually available to construct indices that are comparable across regions and countries.At this time in world development,the ability to monitor progress towards forest sustainability in a way that can be adopted by countries with consistent data resources for index construction represents a positive step towards a general approach of forest sustainability assessment.

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