Linhai Jiang?Wei Zhao?Bernard J.Lewis?Yawei Wei?Limin Dai

Abstract Carbon sinks constitute an important element within the complex phenomenon of global climate change,and forest ecosystems are important global carbon sinks.The Natural Forest Protection Program(NFPP)is an ecological program in China that was established after catastrophic flooding in the country in 1998.The goals of the NFPP are to curb the deterioration of the ecological environment,strengthen the protection and restoration of habitat to increase biodiversity,and rehabilitate natural forests to support sustainable development in forest regions.This study looked at changes in carbon sequestration in a forested area of northeast China after the inception of the NFPP.The program divides China’s natural forests into three classes—commercial and two types of noneconomic forests—that are subject to management regimes prescribing varying levels of timber harvest,afforestation,and reforestation.During the 18-year period from 1998 to 2015,the total amount of carbon sequestration increased at an average annual rate of 0.04 MT C.This trend reflects a transformation of forest management practices after implementation of the NFPP that resulted in prohibited and/or restricted logging and tighter regulation of allowable harvest levels for specific areas.In documenting this trend,guidelines for more effective implementation of forestry programs such as the NFPP in other countries in the future are also suggested.

Keywords Natural Forest Protection Program(NFPP)·Carbon sequestration·San Chazi Forestry Bureau·China forestry

Introduction

Climate change stimulated by emissions of CO2and other greenhouse gases has become a major global issue.As the largest carbon pool in the world’s terrestrial ecosystems,forests offer opportunities to mitigate climate change by serving as carbon sinks(Li 2004;Wing field et al.2015).Forests play an important role in regional and global C cycles.Quantitative estimation of components of forest C budgets and their spatial and temporal distributions is both of scientific and political importance(Fang et al.2015).Forest systems cover more than 41 million km2of the Earth’s surface area.Globally,forest vegetation and soils contain approximately 1146 MT C (1 MT=106Mg=1012g)(Dixon et al.1994).In China,the largest developing country in the world,policies of forest exploitation and monoculture plantation during the past half century have led to disastrous consequences,including degradation of forests and landscapes,loss of biodiversity,unacceptable levels of soil erosion,and catastrophic flooding(Zhang et al.2000).China’s government has recognized the severity and urgency of the problem.A series of stringent forestry policies have been adopted to afforest and rehabilitate degraded forest lands and address other environmental concerns and timber shortages(Pascal et al.2010).The first of these major shifts in policy occurred in 1998 after the country’s worst flooding in the 20th century along the Yangzi River,when China adopted the Natural Forest Protection Program(NFPP),which was implemented in 17 provinces(including autonomous regions and municipalities).The goals of the NFPP are to curtail excessive logging to protect natural forest resources,to increase afforestation,and to implement other measures to improve the ecological environment(Wei et al.2014).

Adopting a sustainable development perspective linking ecological functions and modern forest utilization,the NFPP divides the nation’s forests into 3 classes:key noneconomic forests(KNEF),generic non-economic forests(GNEF)and commercial forests(COMF).

The goal of KNEF is the conservation of native biodiversity and ecosystem processes and functions.No logging activity is permitted in forests with this classification.Logging is permitted in GNEF,as long as it is in keeping with the preservation of native biodiversity.Ecosystem management practices are often designed to mimic patterns created by natural disturbances(Kuuluvainen 2002;Bergeron et al.2004;Bouchard and Kneeshaw 2007).The use of partial cutting in GNEF does help to support the nation’s timber supply.The main purpose of COMF forests is to serve as the primary source for the nation’s domestic timber supply and in the process maintain the economic viability of the forestry sector.

To achieve productivity gains,various types of traditional silvicultural practices,such as thinning and vegetation management,have been employed(Duinker et al.2010).Genetically improved native tree species and fastgrowing hybrids have also been planted.Care is taken to select strains that will not interfere with the functioning or species composition of the rest of the forest through nonnative invasion or hybridization.Although each class of forests has its particular set of management objectives,all are encompassed by the overall goal of increasing the ecological and economic sustainability of China’s forests.

On an overall basis,effective forest development policies have been the most important contributor to the trend of increasing forest biomass in China over the past two decades(Zhang and Liang 2014).In particular,since the NFPP was adopted in 1998,it has led to reductions in the production of commercial timber from a previously excessive to a sustainable level,incorporating viable management and protection practices,constructing public benefit forests,and employing surplus labor.

Previous studies have documented the role of forest ecosystems as carbon sinks(Liu et al.2000;Fang and Wang 2001;Pan et al.2004;Litton et al.2007;Luyssaert et al.2008).In light of such an important function,it is worthwhile to examine how forests in China have performed as carbon sinks since the inception of the NFPP in 1998.Two important questions in this regard are:How have the various forest management strategies affected carbon sequestration?How might the provision of forest ecosystem services in China be further enhanced under the auspices of the NFPP?In what follows we address these important concerns regarding the efficacy of the NFPP with respect to carbon sequestration.

Materials and methods

Study area and forest characteristics

The study area is located in Jilin Province(126°17′–127°08′E,42°07′–42°48′N)near the North Korean border in northeast China(Fig.1a)on lands administered by the San Chazi Forestry Bureau.It is close to Jing Yu Forestry Bureau,Wan Gou Forestry Bureau,and so on(Fig.1b).Average elevation is 560 masl.The climate is north temperate continental monsoon characterized by long winters,with a frost-free period of about 140 days.Average annual rainfall is approximately 910 mm.GNEF and COMF covered more than 75%of all forest land in the study area.Major forest types in the study area include coniferous mixed forest(CMF),coniferous and broad-leaved mixed forest(CBF),broadleaved mixed forest(BMF),larch forest(LF),and birch forest(BF).

Due to the strict regulation of harvesting in natural forests,by the end of 2015 the forest area and forest stocking volume administered by the San Chazi Forestry Bureau had increased significantly from levels estimated in 1998.Plantation area and standing timber volume both decreased over the same time period(Fig.2).The forest land base increased from 201.37 to 207.48 thousand ha;while forest stocking increased from 23.17 to 24.74 million m3.Forest coverage in the study area increased from 87.2%in 1998 to 92.9%in 2015.

The proportions of both mature and over-mature natural forest increased over the 18-year study period(Fig.3),and the unit volume increased simultaneously.

Field design

Fig.1 a Forest coverage of China in 2013.b The location of the San Chazi Forestry Bureau and its surrounding Forestry Bureau

Fig.2 Forest area and stocking volume in the study area in 1998 and 2015

The San Chazi Forestry Bureau manages seven forest farms,all of which are comprised of the three representative forest classes described above,viz.,KNEF,GNEF and COMF.Five fixed plots of dimension 400 m2(20×20 m)have been sampled for each forest class in the seven forest farms since 1998,resulting in a total of 105 study plots.All forest types(CMF,CBF,BMF,LF and BF)have been sampled for the three forest classes.Each type was divided into natural forest and plantation,and four stand age classes were delineated according to the predominant tree species and other information(i.e.,forest maps,forest management,and logging history)provided by the San Chazi Forestry Bureau(Table 1).

Tree biomass within each plot was estimated annually in August from 1999 to 2016.All trees(standing and fallen)with a diameter at breast height(DBH)of≥5 cm in each plot were identified as to species,measured for height and DBH,and assigned status as living or dead.Individual treebiomass(above and below-ground)was estimated using species-specific allometric equations developed by Han(1994)for the Changbai Mountain area of northeast China.

Fig.3 Age structure of natural forests in the study area in 1998 and 2015

Table 1 Category by different forest type and age group(unit:year)

Method for data analysis

There are many regional methods for assessing carbon levels that are utilized in major Chinese ecological engineering programs(Zheng et al.2016).In this study per tree biomass and volume were estimated using the forest growth allometric equation for Changbai Mountain(Chen and Zhu 1989),as well as the local forest volume table for Jilin Province.The estimates were then transformed to biomass density and volume density according to the forest plot scale and volume as well as the established regression equations for the biomass(Y)and volume(V)of the main tree types in the study area using Eq.(1):

whereYandVare the biomass density(Mg ha-1)and volume density(m3ha-1),respectively,and a and b are parameters.Tree biomass C storage was calculated as the product of biomass multiplied by the carbon conversion coefficient,0.5(Brown and Lugo 1984).

To estimate total carbon sequestration and subtotal amounts by stand age-class,species,functional areas,and management regimes/practices,Eq.(1)and coefficients(Table 2)were utilized in combination with the annual forest inventory data from the San Chazi Forestry Bureau.

Results

Total amount of carbon sequestration

After the San Chazi Forestry Bureau adopted the NFPP in 1998,the total amount of carbon sequestration increased from 10.71 MT C in 1998 to 11.43 MT C in 2015,with an average annual increase of 0.04 MT C.BMF and CBF forest types together accounted for more than 80%of the total, with BMF accounting for the maximum(7.45–7.62 MT C),followed by CBF(2.05–2.13 MT C).These were followed by LF(0.40–0.44 MT C),CMF(0.32–0.332 MT C)and BF(0.108–0.125 MT C).

Carbon sequestration by the three classes of forests

GNEF displayed the highest level of carbon sequestration from 1998 to 2015,followed by COMF and KNEF.Carbon sequestration rose continuously only for KNEF,from 2.4802 MT C in 1998 to 2.6492 MT C in 2015,for a totalincrease of 0.1690 MT C.GNEF displayed a fluctuating sequestration trend with a slight overall increase of approximately 4.7 MT C.COMF showed a downward trend,with a decrease of 0.1901 MT C from 1998 to 2015(Fig.4).This part is an important source of total increment amount of carbon sequestration.

Table 2 Parameters of the biomass-volume models for dominant species

Carbon sequestration by management regimes

Afforestation and reforestation

China has afforested and reforested large areas over the past several decades(Carle et al.2002;Wang et al.2007).This reflects an essential part of the NFPP management prescription.By afforestation we refer to the establishment of a forest or stand of trees in an area in which there was previously no forest;while reforestation is the natural or intentional restocking of existing forests and woodlands that have been depleted,usually through deforestation.Since 1998,the area of afforestation in the study area totaled 44.24 thousand ha,with a cumulative carbon sequestration of 1.63 MT C,which is much greater than the total increment(0.68 MT C)of the study area’s carbon sequestration.

Logging and reducing timber yield

Prior to 1998,excessive logging and failure to replant neglected cultivated areas left the exploitable forest reserves in the study area almost exhausted.A substantial decrease in the area of natural forests was accompanied by disruption of stand structure and degradation of overall forest quality and functions(Yu et al.2011).NFPP restrictions require that the timber yield from the study area be adjusted to accommodate cessation of logging of natural forests,that consumption of timber be controlled,and that harvest levels be restricted to assigned quotas.This has resulted in the bulk of logging being conducted in plantations in GNEF and COMF.At the same time,the national plans under NFPP required that timber yield be reduced by 9000–40,000 m3annually.Under these circumstances,a large volume of timber is still harvested each year.Total forest stocking volume of logging was 3.32 million m3in the study area from 1998 to 2015.The carbon loss originating from logging was 1.53 MT C,a major direct contribution to the total carbon sequestration loss.However,this loss of carbon loss is basically equivalent to the total increment gained from afforestation and reforestation,thus showing that logging can be compensated for by afforestation and reforestation.

Fig.4 Changes of carbon sequestration in three classes

Quantification of carbon sequestration by stand age

Mature forests accounted for the largest percentage of carbon sequestration(46.82%)in the study area from 1998 to 2015,followed by mid-aged forests(37.45%),young forests(11.72%)and over-mature forests(4.01%).

Young forests displayed a decreasing trend over time in terms of percentage of overall carbon sequestration.Sequestration in mid-aged forests changed significantly,both increasing and decreasing at different points throughout the 18-year period.Mature forests were characterized by a mixed trend(increase/decrease/stable),as were mid-aged forests(increase/decrease/increase/decrease).Over-mature forests showed little change in carbon sequestration.

Discussion

Variation in carbon sequestration following adoption of the NFPP

Since the NFPP was initiated in 1998,the forest land base,coverage and stocking volume in the study area have all increased.As a result,the total amount of carbon sequestration in the study area has increased.

Carbon sequestration increased steadily in KNEF,the cumulative increment in this class being equivalent to the total increase for all forest classes in the entire study area.Carbon sequestration in GNEF showed small fluctuations,but increased overall over the study period.Sequestration in COMF declined due to logging,but the cumulative increment from the GNEF offset sequestration loss from the COMF.All of the above suggests that the NFPP appears to be a new and truly sustainable forest management program for effectively protecting natural forests by conserving forest structures and functions,soils,and biodiversity.

At the same time,we found some protected areas of KNEF which,while reducing the likelihood of deforestation to some degree,often did so with limited effectiveness due to a lack of sophistication in forest management measures employed,particularly with respect to the basic characteristics of natural forests.In the future,we need to determine the structure and composition of the ‘‘natural’’forest as well as the intensity,extent,and periodicity of the major natural disturbances that affect this forest,rather than only protecting or selectively logging while ignoring the forest’s natural ecology(Ganzlin et al.2016;Ren et al.2015).The rates of survival and preservation of natural forests could be increased by enhancing planning and management of plantations and strengthening the application of silvicultural techniques in the management of young forests.Slower deforestation combined with an increase in afforestation and other management measures to improve forest ecosystem productivity,would in turn conserve or sequester significant quantities of carbon.Without the aforementioned enhancements in our knowledge of natural forest characteristics and application of effective management techniques,natural forests will continue to suffer major disturbances,and their capacity for self-regulation and resisting natural disasters will continue to decline(Booth et al.2015;Cabrera et al.2016).

Effects of different management regimes and practices on changes in carbon sequestration

Since the adoption of the NFPP in 1998,the relationship of different forest management regimes employed in the study area to the amount of carbon sequestration generated there may be summarized as follows.Although carbon loss from logging and from reducing the wood yield was related to the establishment of new plantations,the amount of carbon sequestration from new plantations exceeded sequestration losses due to logging.If the NFPP had not been implemented and the forestry bureau had not reduced the amount of cutting,carbon losses from logging would have been much greater and could even have constituted a carbon source in some years.

The rate of China’s use of improved varieties of seeds in planting is only 51%compared to that of 80%in developed countries(SFA 2010).Long-term practices that are already in place have proven that rehabilitating degraded forest land is a complex engineering undertaking involving socioeconomic policies, administrative and institutional arrangements,laws and regulations,and a variety of silvicultural techniques(Zhou and Chokkalingam 2010).While these matters are undoubtedly enormous challenges for afforestation and reforestation,they clearly have significant effects on carbon sequestration.

From 2000 to 2012,the global loss of forests reached 2.3 million square kilometers, while the gain was 0.8 million square kilometers(Hansen et al.2013).China is the largest developing country in the world,and changes in the status of Chinese forests significantly impact both domestic ecosystems and the global environment.Since 2015 a new logging ban in natural forests has been in place as part of the continuation of the NFPP.All commercial logging is prohibited on NFPP lands in northeast China and Inner Mongolia,which is undoubtedly beneficial to carbon sequestration.Plans for sustainable afforestation and forest protection programs by the Chinese government could also enhance forest biomass carbon sinks in the future(Shi et al.2011;Sun et al.2015).

Although afforestation and reforestation have become vitally important,proper management of under-aged forests can also result in marked gains in biomass carbon sequestration(Liu et al.2016;Sun et al.2016).Increasingly improved varieties should be planted,since genetically modified trees often grow more aggressively than natural trees.Together these practices may more effectively help produce and maintain mature,old,and unevenaged forests within the range of natural variability.

Another important ingredient to successful implementation of a program such as the NFPP merits attention here.When sample plots were surveyed for study area,local residents occasionally harvested young trees protected by the program for fuelwood.Experience has shown that the success of this or any forestry program will be greatly influenced by its national,local and personal economic costs and benefits and that the success of sustainable management of natural resources over the long run depends on the support of local people(Macura et al.2011).To the greatest extent possible,opportunities for income and employment should be provided to firms and individuals affected by forest restrictions.This is part of the larger task of local governments to help improve skills and widen employment opportunities for residents to enrich their lives while assuring the sustainability of programs for forest protection and restoration.

Effects of tree age and species on carbon sequestration

Forest stand age and species are important parameters in carbon density studies(Guan et al.2015).This is confirmed in the results of this study.Carbon sequestration varied significantly from 1998 to 2015 based on tree age and species.This phenomenon occurs largely due to differences in forest management practices,which contribute to different growth rates in trees of the same species and age.For example,we found if the forest is tended in GNEF,it will grow more than 20%faster in KNEF.Active management improves stand health conditions and the quality of trees,adjusts the structure of forest types and species,and improves the accumulation and productivity per unit area of forest,all of which contribute to the economic,ecological and social benefits of forests.Such management under the NFPP has had a great effect on carbon sequestration in the study area.

At the same time,results from other studies suggest that these differences in biomass carbon storage are probably related to stand age and species(Goodale et al.2002;Keith et al.2009).The average global temperate forest biomass C has been reported to be 114.7 Mg C ha-1(Pregitzer and Euskirchen 2004).In the temperate forests of the American Pacific Northwest,biomass carbon storage was found to be 506–627 Mg C ha-1(Smithwick et al.2002);while in coniferous and broadleaved mixed forests of northeastern China it has been found to range from 182.7 to 191 Mg C ha-1(Zhu et al.2010;Zhou et al.2011).From these estimates of biomass carbon storage of different temperate forests,it is evident that tree species are also important factors for carbon storage.

In addition to the above,other measures can be taken to enhance forest productivity in order to increase biomass carbon storage in the ecological setting encompassed by the study area.First,attention should be given to rehabilitating the productivity of secondary forests to correspond to the level of natural forests.Such an undertaking has great potential for enhancing carbon sequestration(Bongers et al.2015).Mature and near-mature stands in natural forests require more intensive protection designed to enhance their contributions to species’gene pools.With respect to natural forests,the scientific basis and technological sophistication of tree species breeding must be improved,including a focus on better understanding the mechanisms that maintain the heterogeneity of genomes in a way that facilitates determining the contribution of the processes that affect diversity(Legendre et al.2009).This is a matter of cardinal significance for carbon sequestration under the NFPP.

Secondly,regarding the protection and restoration of China’s natural forests,since the initiation of the NFPP there remains a pressing need for both stricter enforcement of laws and regulations that protect natural forests as well as strengthening ongoing research on factors that influence tree growth under different management regimes(Herrmann and Torri 2009;Tang et al.2010).

Finally,local forestry bureaus need to devote more attention to the quality of afforestation and reforestation activities as opposed to the scale of ambitious projects.The NFPP has a significant potential for enhancing carbon sequestration in plantation forests under its domain(Zhou et al.2014).The area of afforestation and reforestation in the study area since the NFPP began has risen to 44.24 thousand hm2,with a corresponding carbon sequestration of 1.63 MT C.While local forestry bureaus are applying basic silvicultural principles towards enhancing the survival rate of planted trees,equal attention must be paid to tending young and middle-aged stands as part of the afforestation and reforestation processes.This will help achieve the full potential of forests for contributing to carbon sequestration.

Conclusion

This study represents an early step in understanding the size and distribution of the carbon pool in forests encompassed by the NFPP.We found that carbon sequestration in the study area continued to increase after the program was implemented.The 0.169 MT C cumulative increase in the KNEF is equivalent to the total cumulative increase(0.1797 MT C).This reveals that most of the total cumulative increase in the NFPP came from the KNEF.In this class of forests,however,the activities allowed can actually discourage effective forest management.Implementing the necessary tending measures would be beneficial to forest growth as well as increase the amount of carbon sequestration.

At the same time,a series of new effective measures has been implemented with effective results,including dividing forest classes,reducing the amount of timber harvesting,and afforestation and reforestation.Both forest area and stocking have increased,indicating a positive trend of long-term forest recovery along with substantial positive effects on carbon sequestration.The increase carbon sequestration from afforestation and reforestation(1.63 MT C)has offset carbon lost by logging and reducing the total wood yield (1.53 MT C).All forestry programs, not only in China but worldwide,should devote more attention to these activities in the future.