Strong Seedlings of Improved Varieties and High-efficiency Cultivation of Artificial Forests Promotes the Early Realization of "Carbon Neutrality"

Menghong HU, Jiying LI, Man SUN

Abstract China is striving to achieve "carbon dioxide peaking" in 2030 and "carbon neutrality" in 2060. In addition to optimizing and upgrading the industrial structure and increasing industrial emission reduction， afforestation is an important way to increase forest carbon sinks and achieve carbon dioxide peaking and carbon neutrality. Improved seedlings are significantly better than general seedlings in terms of afforestation adaptability， growth and stress resistance. The use of improved varieties for afforestation can improve the quality of afforestation from the source. Although the growth cycle of economical tree species is short， and the carbon storage does not increase after directional cultivation， they significantly improve the quality and yield， and indirectly reduce carbon emissions compared with ordinary seedlings. Therefore， in agricultural and forestry production， the transformation and utilization efficiency of improved varieties should be improved and the planting structure should be optimized to improve the quality and efficiency and significantly improve the yield and carbon storage， and the management of plantations should be strengthened to help achieve the goal of "carbon neutrality" as soon as possible. This paper analyzed the current situation of improved varieties and plantation management in China， and put forward corresponding countermeasures.

Key words Improved seedlings; Afforestation; Afforestation quality; Plantation management; Carbon neutrality

Received： March 7， 2022  Accepted： May 8， 2022

Supported by Tianshui Science and Technology Support Program Project （2020-NCK-2106）; Gansu Forestry and grassland science and technology plan project （Project No.2020kj034）; Central Finance National Forest Seed Base Seed Breeding Subsidy Project.

Menghong HU （1965-）， male， P. R. China， senior engineer， devoted to research about seed orchard management and seed cultivation.

*Corresponding author.

Carbon neutrality means that enterprises， groups or individuals measure the total amount of greenhouse gas emissions directly or indirectly generated within a certain period of time， and offset their own carbon dioxide emissions through afforestation， energy saving and emission reduction， and achieve "zero emission" of carbon dioxide. Carbon dioxide peaking refers to the steady decline of carbon emissions after entering the plateau period. That is， carbon dioxide emissions "break even". Any human activity may cause carbon emissions， ranging from industry， construction， transportation， etc.， to peoples daily life and behavior. Preliminary statistics show that in 2020， Chinas coal， oil， and natural gas CO2 emissions will be about 7.2 billion， 1.6 billion， and 600 million t， with a total of 9.4 billion t. It is estimated that the CO2 released by burning 1 L of fuel in a car engine into the atmosphere is 2.5 kg， the average indirect emission of CO2 for one year of computer use is 10.5 kg， and the amount of CO2 emitted by a plane transporting 1 t of fruit for the flight mileage of 10 000 km is 3.2 t. On September 22， 2020， the Chinese government proposed at the 75th United Nations General Assembly： "China will increase our nationally determined contributions， adopt more powerful policies and measures， and strive to peak CO2 emissions by 2030 and achieve carbon neutrality by 2060"[1].

The time from carbon dioxide peaking to carbon neutrality in China is only 30 years， far less than the 50-70-year transition period of developed economies such as the European Union. We have a limited amount of time and a heavy task to accomplish. The realization of the carbon neutrality goal is closely related to each of us. Therefore， on the one hand， we must carry out supply-side reforms， optimize， adjust and upgrade the industrial structure， eliminate outdated production capacity， improve the technological content and develop green and low-carbon industries， change the traditional way of life， and advocate green and low-carbon travel. For example， walking up and down the stairs can reduce carbon emissions by 0.218 kg per floor; turning on an air conditioner for one hour less can reduce carbon emissions by 0.621 kg; and using one ton of water less can reduce carbon emissions by 0.194 kg. In addition， multiple measures should be taken at the same time. Compared with industrial emission reduction， forest carbon sinks are more cost-effective[2]， and have multiple benefits. They are both carbon sinks and carbon sources[3]， and play a key role in reducing carbon budget balance[4-7]. Forest carbon sinks serve as an important strategy for countries around the world to deal with climate change[8-10]. Afforestation is an important way to increase forest carbon sinks and achieve carbon dioxide peaking and carbon neutrality[11-15]. The Chinese government also clearly put forward the forestry development goal to deal with climate change in our commitment to voluntary emission reduction："By 2030， Chinas forest stock volume will increase by 6 billion m3 compared with 2005". From this， it can be deduced that Chinas forestry development goal to address climate change is to achieve at least 18.46 billion m3 of forest stock by 2030. At present， the data from the 9th forest resource inventory in China shows that the national forest accumulation is 17.56 billion m3， which still has a certain gap with the expected forest development goals[8，15]. Due to the low utilization rate of improved species， single tree species， low afforestation quality， and soil fertility decline in early plantations in China[16-18]， the carbon sequestration in forestry is far less than expected. At present， the existing carbon storage of forest vegetation is only 44.3% of the potential storage， and the development potential is huge[9-10]. Improving quality and efficiency is the main task of forest carbon sink construction， and the key to improving forest carbon sink construction is to improve seedlings[14，19-21]. Therefore， in the future， it is necessary to increase the breeding and utilization rate of improved varieties， accurately improve the quality of afforestation， and fully tap the carbon sequestration potential of forest vegetation， so as to accelerate the early realization of the carbon dioxide peaking and carbon neutrality goals.

Present Situation of the Use of Improved Varieties and the Management of Plantations in China

Improved varieties of forest trees are the carrier of excellent genetic genes. They are artificially bred with stable genetic gain and superior to general seedlings in terms of growth， adaptability and stress resistance. They are basic and strategic resources for the development of forestry productivity[19]， as well as an irreplaceable guarantee and support for improving the quality of afforestation， promoting the healthy， stable and sustainable high-quality development of plantations and improving carbon sequestration capacity. It does not matter whether they are used for national reserve forests， urban and rural greening， or economic forests and industrial raw material forests， improved seedlings can provide greater benefits than ordinary seedlings in terms of afforestation quality， yield and quality， and improved varieties are the basis for improving the quality of forest carbon sinks[20]. According to the introduction by the head of the Forestry Seedling Department of the State Forestry and Grassland Administration at the Nanjing International Forest and Seed Garden Conference in 2019： "The utilization rate of improved varieties of afforestation tree species in China has increased to 65%， and the utilization rate of improved varieties of some commercial and economic forest tree species has reached 70%"[16]. Compared with developed forestry countries in the world， the utilization rate of improved afforestation varieties in China is relatively low， and the supply and demand of improved varieties are extremely unbalanced[18-19]. Some seedlings without genetic improvement are still the main body of afforestation[22-25]， and the tree species structure and planting structure are unreasonable. Coniferous tree species are more used and planted into forests， and fine broad-leaved native tree species are less used in afforestation， and the management level is not high， resulting in low quality of afforestation， poor growth of some artificial forests， low quality and low efficiency， and serious damage by pests and diseases. Moreover， these problems cause soil fertility decline， forest vegetation degradation， and carbon sequestration decline， which seriously restricts the modernization of Chinas ecological forestry[14，16-21，26-28]. Therefore， it is necessary to adjust the tree species structure for afforestation and planting structure， adapt trees to suitable sites， increase the efficiency of breeding and transformation and utilization of improved varieties， pay special attention to the breeding and utilization of improved varieties of broad-leaved native tree species， and optimize the selection of strong seedlings of fine varieties， so as to improve the quality of afforestation and greening from the source and strengthen the management level. Continuously improving the quality of afforestation and management level， promoting the high-quality development of plantations， establishing a healthy， stable， efficient and sustainable forest ecosystem， continuously optimizing the structure and function of plantations and improving carbon sequestration capacity is the only way to achieve "carbon dioxide peaking" and "carbon neutrality" at an early date and to a beautiful China[14].

Comparison of Afforestation and Carbon Sequestration between Improved Seedlings and General Seedlings

Planting trees and vigorously creating artificial forests is considered to be the most important measure to improve forest coverage， and it plays an important role in evaluating the contribution of forests to terrestrial carbon sinks[5]. Plantations are one of the most effective and ecologically effective carbon sink-increasing ways to absorb CO2 and slow climate warming， which plays an irreplaceable role in safeguarding and supporting global climate change[11-13，29-31]. According to relevant data， trees can absorb 1.83 t of CO2 and release 1.62 t of O2 for every 1 m3 of tree growth. From a global perspective， if 400 million hm2 of fast-growing short-rotation plantation forests can be planted in the world， about 6 billion t of CO2 can be fixed in one year[12， 29]. The structure of the ninth national forest resources inventory shows that China has 79.542 8 million hm2 of planted forests， and 1/4 of the global greening comes from China， which is the country with the largest area of  planted forests in the world[15]. The growth rate of carbon storage in plantation forests in China is higher than that in natural forests， and the average annual increase of carbon storage is 5.05% in plantation forests and 0.85% in natural forests[9]. However， the forest accumulation per unit area in China is 78.17 m3/hm2， which is far lower than the global average forest accumulation per unit area of 131 m3/hm2， and the average growth per unit area of 4.73 m3/hm2[33]. There are many factors affecting plantation carbon storage， including tree species， forest age， stand type， forest quality， site conditions， climate and other ecological and human factors[11-13]. Therefore， under the circumstance of limited afforestation area in China， to achieve the goals of "carbon dioxide peaking" and "carbon neutrality" as soon as possible， the only way is to carry out the selection and breeding of good varieties and strong seedlings and improve the efficiency of conversion and utilization of good varieties and the level of plantation management. For afforestation， we must establish the concept that "forests are species-oriented， and species are based on quality first"[16]， adjust the structure of tree species， adapt trees to suitable locations， and select tree species with excellent adaptability， growth， stress resistance and carbon sequestration， so as to improve the quality of afforestation from the source. Meanwhile， it is necessary to manage based on classification and strengthen the management level of plantations[17，35] to give full play to the potential of forest land， and continuously improve the growth and carbon storage of plantations， which is the key to protecting biodiversity， building a beautiful China， and achieving "carbon dioxide peaking" and "carbon neutrality" as soon as possible.

Comparison between afforestation with improved varieties and with common seedlings

The calculation methods of carbon storage mainly include the biomass method， stand volume method， biomass inventory method， micro-meteorology method， box method， model simulation method and stable isotope method， etc.， but the biomass method is currently the most widely used， direct and accurate method[36]， in which the forest biomass is predicted from the biomass of a single tree， and then the forest carbon storage is calculated. The expression compatible with the biomass of a single tree and the stock volume is generally m=f（D，H）[37-42]. It can be seen that the size of biomass mainly depends on the growth of tree height （H） and diameter at breast height （D）， that is， the size of carbon storage is closely related to the growth of tree height and diameter at breast height.

The quality and management level of plantations determine the development of the potential of the forest land， which in turn determines the growth of plantations， and the biomass determines the amount of carbon sequestration. Therefore， using strong seedlings of good varieties can increase the biomass and carbon sequestration of plantations from the source. We took the improved variety "Erbaiyang" in Gansu Province and the Pinus tabuliformis bred by Xiaolongshan Forest Branch in Gansu Province as examples to illustrate the contribution of afforestation with improved varieties and general seedlings to biomass and carbon sequestration. "Erbaiyang" （Wuwei No.2， No.5， No.10， Jiuquan No.22） are 54 Erbaiyang trees selected by the comprehensive forestry service center of Wuwei City， Gansu Province in 1982 from the census of the provinces tree species resources. After progeny determination， 18 indicators were observed and counted， and 10 optimal clones were screened out. The average tree height was 6.98% higher than the control， and the average DBH was 12.07% higher than the control， and the genetic gain of each indicator was 25.58%. Using the BLUP breeding value estimation method， the Xiaolongshan Forestry Institute of Gansu Province selected 24 excellent families of P. tabulaeformis with a genetic gain of 18.63%， and on the basis of pedigree selection， 61 excellent individual plants were selected from the pedigree with an actual genetic gain of 40.19%[42]. It can be seen that using improved tree species for afforestation has significantly higher increments such as afforestation survival rate， tree height， diameter at breast height， and stock volume than afforestation using general seedling， resulting in greatly improved quality of afforestation and significant genetic gains of individual tree height， DBH and stand volume. The increase of single tree height， DBH， and stock volume means that the gains of single tree and stand biomass and carbon storage are significantly improved， and the carbon sequestration effect of afforestation using fine varieties is significantly higher than that of afforestation using general seedlings.

Analysis on the effects of economic forests of improved variety

Economic forests have a short growth cycle， and the carbon sequestration increases during the growth period. Generally， directional cultivation is carried out after 5 to 6 years， and the growth is very slow. After entering the stable and fruiting period， the carbon sequestration will not increase rapidly， and there is only a short-term carbon sequestration capacity[41，43]. However， the direct or indirect carbon consumption in later management is higher than that of general economic forests. Gansus excellent variety "Zaosu pear variety" and Sichuan pepper "Qinan No.1 variety" were taken as examples.

Compared with common varieties， the Zaosu pear variety （No.S6201051495014） bred by Linxia Prefecture Forestry and Seedling Management Station in Gansu Province has a single fruit weight increased from 200-250 to 250-350 g， a maximum fruit weight increased from 480 to 700 g， and sugar content from 13% to 13.1%-14.0%， and the yield and quality of Zaosu pear are higher than those of other varieties. Another example is Qinan No.1 （Zanthoxylum bungeanum variety， No.S6201051495015）， a new variant of the Dahongpao Zanthoxylum bungeanum series， which is a new excellent short-branched variety selected by Qinan County， Gansu Province. It has the characteristics of early maturity， high yield， high quality， stable characters， strong stress resistance， easy picking and wide range of suitable growth. According to typical measurements： eight-year-old single plant yields 15.61 kg of fresh peppers， and the yield  is 13 112.4 kg/hm2 （calculated based on 840 plants）. The values are， respectively， 6.71 and 5 636.4 kg/hm2 higher than the Dahongpao with the same site conditions at the same age， which can produce 8.9 kg of fresh peppers per plant and 7 476 kg/hm2[42]. It has a significant yield-increasing effect. Although the growth cycle of economic forests is short， and the carbon sequestration increases during the growth period and will not increase rapidly after entering the stable and fruiting period， improved varieties also have a certain carbon sequestration capacity themselves in the stable and fruiting period， and indirectly reduces carbon emissions. If common varieties are used to achieve the same yield， management costs will increase， and the increased input of pesticides and fertilizers pollutes the environment and becomes a point source of pollution to soil and water[23]， while the production and transportation of pesticides and fertilizers produces carbon emissions.

From the above analysis， it can be seen that the improved seedlings are much larger than the general seedlings in terms of growth， yield and quality. Therefore， the use of improved varieties in agricultural and forestry production， on the one hand， improves the yield and quality of agricultural and forestry production， increases carbon sequestration， and on the other hand， reduces the use of pesticides and fertilizers， which indirectly reduces carbon emissions. It is estimated that a medium-sized plant can absorb about 6 kg of CO2 per year. The use of improved varieties in agricultural and forestry production has significant benefits of increasing carbon sequestration and reducing carbon emissions. Therefore， the selection， promotion and application of improved varieties should be accelerated in agricultural and forestry production. It is an effective measure to achieve the goals of "carbon dioxide peaking" and "carbon neutrality" as soon as possible.

Future Measures

With the demand for seedlings from land greening， China has initially formed a market-oriented seedling production and supply system with the national forest tree improved variety bases as the backbone and non-bases as the supplement， with the effective combination of national macro-control and the independent adjustment of each province， and all forms of ownership growing side by side， presenting a pattern of common development of state-owned economy， collective economy and individual economy[16，19，44-45]. However， Chinas seedling industry is extremely unbalanced and uneven. In order to improve the quality of Chinas seedlings and the efficiency of transformation and utilization of improved varieties， the production and utilization of improved varieties should be improved from the following aspects in the future to meet the societys demand for improved varieties.

Give full play to the main role of state-owned improved variety bases

In order to improve the yield and supply capacity of improved variety bases， China implemented central financial subsidies to improved variety bases of forest trees in 2010. Since the implementation of the subsidy for fine varieties， it has achieved remarkable results， effectively improving the production and supply capacity of improved variety bases， and the yield and quality of seeds and cuttings of improved varieties have been continuously improved. According to statistics， China has established 294 national key forest tree improved variety bases， providing 160 million t of improved seeds and 21 billion scions of improved varieties for forestry construction[16]， which greatly meet the demand for improved varieties by land greening. However， Chinas improved variety bases are relatively simple in tree species， and have a small number of improved species and a large number of coniferous tree species. In particular， there are few excellent native tree species suitable for local afforestation. The planting structure is unreasonable， and the proportion of coniferous trees is large， resulting in poor ability to resist natural disasters. In the future， with the support of the central governments subsidy funds for improved varieties， the research on the selection and breeding of improved varieties will be increased and the yield of improved varieties will be increased， with particular attention paid to the research on the selection and breeding of fine broad-leaved native tree species. We should select and breed excellent local tree species with fast growth and high carbon sequestration to meet the needs of ecological forestry construction for afforestation with improved tree species. Reasonable and scientific selection of tree species for afforestation should be carried out， and they should be planted in right places， so as to improve tree species structure. Strong seedlings of improved varieties should be selected to improve the quality of afforestation， establish a healthy， stable and efficient forest ecosystem and enhance its carbon sequestration capacity.

Provide policy and technical support for seedling management cooperatives （households）

The demand for forest tree seedlings in China has shown a trend of diversification. The seedling industry has developed in the direction of regionalization， marketization and industrialization. Meanwhile， it has shown a trend of socialization， and the production scale has expanded rapidly[19，44-45]. Chinas seedling planting and operating households （cooperatives） provide a large number of seedlings for the national forestry construction， which greatly meet the needs of land greening for seedlings and support national forestry ecological construction， and also increase income. The number of people engaged in the seedling industry is also increasing.  However， the phenomenon of following the trend in China is serious among seedling growers， which has led to chaos in the seedling market， imbalance of supply and demand， oversupply of easy-to-cultivate seedlings， and shortage of rare tree species， famous seedlings and unique native tree seedlings. For example， Castanea mollissima with high economic value and medicinal and edible Potentilla glabra Lodd. var. mandshurica （Maxim.） are widely distributed in the Longnan Mountains.

The operation of seedling farmers is relatively scattered， lacks scale， and has a low technical content. Seedling farmers lack the awareness of improved seedlings， as well as seedling raising techniques and pest control techniques. At present， seedling planting and operating households （cooperatives） purchase seeds randomly， mainly from the market or by themselves， lacking the awareness of improved seeds. The government should make overall planning， guide seedling growers to raise seedlings according to the afforestation plan， increase policy orientation， and avoid loss of financial and material resources and unnecessary waste due to blindly following the trend. The competent department should actively organize technical training， technical guidance， and publicity of knowledge about improved seeds， reward and compensate farmers （cooperatives） who raise seedlings of improved varieties， give policy support and preferential funding， and encourage seedling planting and operating households （cooperatives） to use improved seeds to raise seedlings.

While giving full play to the main role of the bases for fine varieties， the selection and breeding of fine varieties should give full play to and mobilize social forces as a supplement to make concerted efforts to carry out extensive selection and breeding of fine varieties.

Give full play to the effect of demonstration and promotion of improved varieties

In the promotion and application of improved varieties， we should exert the leading role and the demonstration and promotion effect of the bases for improved varieties. With the support of the subsidy program for improved varieties from the central government， we can give full play to the leading role of improved variety bases， intensify the selection and breeding of high-quality varieties， especially the research on improved variety breeding of native tree species， cultivate more fine native tree species suitable for local areas， and carry out demonstration and promotion. In the planning and selection of tree species for afforestation， local governments should implement order seedling production， Internet+smart forestry， with seedling growers （cooperatives）， so as to overcome the blindness of seedling breeding. It will make common people recognize and be willing to accept the use of improved varieties， and enable seedling farmers （cooperatives） to obtain real and visible income-increasing benefits. We should fully mobilize the enthusiasm of seedling planting and management （cooperative） households to raise seedling of improved varieties.

Establish and improve the supervision and inspection mechanism of improved variety afforestation

We should establish and improve the seedling supervision and inspection mechanism， improve the efficiency of conversion and utilization of improved varieties， adjust the tree species structure and political structure， and rationally optimize the planting configuration structure， so as to give full play to the potential of afforestation land. Under the circumstance of limited afforestation land in China， scientific planning and suitable trees should be used to give full play to the potential of forest land and increase carbon storage.

Forestry authorities and afforestation units must strictly implement the Seed Law in the production and operation of seedlings， and establish a sound file management system for the production and operation of seedlings to enable tracing the source.

Plantation Management Strategy

Plantation forests are an important part of global forest resources and play an important role in safeguarding timber production， environmental improvement， landscape construction and climate change mitigation. Although China is the country with the largest area of planted forests， the planted forests have problems such as poor quality， unreasonable structure， low productivity， weak ecological functions， and decline in ecological stability and carbon storage[17，46]. Therefore， in addition to strengthening the utilization rate of improved varieties and improving the quality of afforestation from the source， the management level of plantations should be strengthened， and classified management should be carried out to turn from the single-target management that pursues wood production to the multi-target management that improves the quality and efficiency of ecosystem services. And based on absorbing and learning from the concepts， experience and practical achievements of international plantation management， the transformation of low-quality and low-yield forests can be carried out to continuously improve the level of plantation management at multiple levels and multiple scales. According to estimates， the forest carbon storage will increase by 4.30% to 6.86% with the forest management level increasing 5%， and by 9.89% to 12.47% with an increase of 10%， by 15.48% to 18.09% with an increase of 15%， and by 20.96% to 21.07% with an increase of 20%[10]. In the face of the continuous increase in the area of plantation in China being seriously restricted by the suitable development space and the actual and potential impact of climate change， plantation management should adopt the high-efficiency cultivation technology to increase volume and efficiency and promote high-quality development of plantations， so as to help achieve the goal of "carbon neutrality" as soon as possible.

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