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Journal of Resources and Ecology >

2023 , Vol. 14 >Issue 5: 903 - 913

DOI: https://doi.org/10.5814/j.issn.1674-764x.2023.05.002

Ecosystem and Ecological Function

Ecological Function Service Value and Quantity of Fruit-tree Economic Forests in the Semi-arid Loess Hilly and Gully Region of Central Gansu—A Case Study of the Hulu River Basin

  • WANG Fu ,
  • HE Qian ,
  • HAN Fen ,
  • ZHANG He ,
  • ZHAO Qiang ,
  • SHA Xiaoyan
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  • Pingliang Institute of Soil and Water Conservation, Pingliang, Gansu 744000, China

WANG Fu, E-mail:

Received date: 2022-10-19

  Accepted date: 2023-03-06

  Online published: 2023-08-02

Supported by

The Gansu Provincial Water Science Experimental Research and Technology Extension Project(22GSLK044)

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Abstract

The compensatory effect and deep impact of the fruit tree economic forest on water and soil conservation ecology in a semi-arid region are investigated by exploring the ecological service value and ecological functions of the fruit tree economic forest, and further by analyzing its functional effects on reducing water and soil loss, conserving water and soil, conserving the water source, improving environmental quality and maintaining biodiversity. This analysis provides a theoretical basis and support for coordinating the relationship between economic and social development, ecological protection, agriculture and forestry in the semi-arid area of the Loess Plateau; promoting the systematic management of mountain, water, forest, farmland, lake grass and sand; and promoting the ecological protection and high-quality development of the whole Hulu River Basin. According to the Standards for Evaluation of Forest Ecosystem Service Function (GB/T38582-2020), the forestry industry standard of the People’s Republic of China, the current market method, shadow price method, opportunity cost method, Swedish Carbon Tax law and other methods were adopted. The main functions of the fruit-tree economic forest ecosystem and its eco-economic value in the Hulu River Basin in Pingliang City were quantitatively analyzed, and the existing measured data from domestic ecological stations were combined with quantitative analysis and qualitative evaluation. The calculations included the ecological service values of the fruit tree economic forest ecosystem in water conservation, soil conservation, carbon sequestration, oxygen production, nutrient accumulation, environment purification and biodiversity protection, and the dynamic change characteristics of the ecological function quantity corresponding to its value were systematically analyzed. (1) In the four developmental stages of the fruiting economic forest in the Hulu River Basin in Pingliang City, the ecological function service value showed an increasing trend. Among the stages, the total value contribution of the first stage (2005-2009) is 1.299×1010 yuan; the second stage (2010-2013) is 2.497×1010 yuan; the third stage (2014-2017) is 2.662×1010 yuan; and total value contribution of the fourth stage (2018-2020) is 2.774×1010 yuan. (2) In the composition of the ecological functional service value of the fruit tree economic forest, the value of water conservation is the highest, accounting for the largest proportion at 32.97% of the total value of ecosystem services. Therefore, it plays an important role in regulating the hydrological balance of the basin in the arid and semi-arid region of the Loess Plateau. The function value of the purifying environment is relatively small, accounting for only 0.19% of the total value, followed by the function value of species conservation, accounting for 5.42%. In order of service value, the ecological function values of water conservation, oxygen release, carbon sequestration, nutrient accumulation, soil conservation, fertility maintenance, species conservation and environment purification accounted for 32.97%, 25.94%, 11.63%, 11.34%, 6.37%, 6.14%, 5.42% and 0.19% of the total value, respectively. The conclusions of this study are basically consistent with other domestic studies. Compared with the annual output value of fruit trees in the same period, the total value of ecological services was 2.42 times of the annual output value of the fruit. Therefore, the fruit tree economic forest not only provides a large amount of fresh fruit products and creates tremendous economic and social benefits for the people, but it also provides a major increase in ecological service value, and the contribution of local GEP is greater than that of GDP. (3) After accounting, the water conservation amount of the fruit tree economic forest (2005-2020) in the Hulu River Basin in Pingliang City was 2.586×109 m3, with 2.135×109 t of soil fixation, 2.264×105 t of fertilizer retention, 9.568×106 t of carbon fixation, 2.562×107 t of oxygen production, 9.278×105 t of nutrient accumulation, and 1.137×105 t of environmental purification function (and within that function, the amount of sulfur dioxide absorbed is 94656.02 t, the amount of fluoride absorbed is 1793.82 t, the amount of nitrogen oxide absorbed is 6406.50 t, and the amount of dust fall is 10794.95 t), and the amount of negative ions provided is 1.564×1025, which greatly regulates and improves the ecological environmental quality of the region.

Key words： semi-arid loess hilly and gully region in central Gansu; fruit tree economic forest; ecological function service value; ecological function quantity

Cite this article

WANG Fu , HE Qian , HAN Fen , ZHANG He , ZHAO Qiang , SHA Xiaoyan . Ecological Function Service Value and Quantity of Fruit-tree Economic Forests in the Semi-arid Loess Hilly and Gully Region of Central Gansu—A Case Study of the Hulu River Basin[J]. Journal of Resources and Ecology, 2023 , 14(5) : 903 -913 . DOI: 10.5814/j.issn.1674-764x.2023.05.002

1 Introduction

In recent years, ecosystem service value assessment has become one of the hot spots in ecosystem research. Remarkable achievements have been made, which are helping people to increasingly realize the extreme importance of maintaining the benign cycle and sustainable development of ecosystems (Wang and Lu, 2009). Based on the theories and methods of foreign countries, many scholars in China have carried out research on the evaluation of different types of ecosystem services from different perspectives and fields (Yu et al., 2007; Feng and Chen, 2009; Liu et al., 2011; Wang et al., 2012). In a nutshell, ecosystem service value assessment basically has two technical routes. One is the research on regional-scale ecosystem service value assessment, from different levels at different scales, such as on a global, national, provincial or city scale, and such research will generally scale the comprehensive systematic analysis and evaluation of the ecological subsystem. On the other hand, starting from a single ecosystem, such as farmland, forest, wetland ecosystem, water body, grassland, etc., more in-depth and detailed research can be carried out. However, the research on a single forest ecosystem mainly focuses on the ecological service value mining of large-scale natural forests and ecological forests, and the research on economic forests is relatively rare. However, there are no reports on the ecological service function of economic forests of fruit trees planted artificially under specific climatic conditions in the range of medium to small scales. This research gap may be mainly caused by the different land use patterns of fruit-tree economic forests.
At the same time, most of the current studies on the value of ecosystem services are focused on the simple mining of service value, but lack the mining of the ecological function quantity corresponding to the value of the ecosystem services. It is easy to transfer people’s understanding to the economic value while ignoring the significance and role of the ecological functions. Generally speaking, the fruit tree economic forest is an artificial forest planted on agricultural land, which is an important part of many agricultural systems, and it is mainly used for the production of fresh fruit products. Its primary attribute is that of the agricultural field, and its main role is to adjust the agricultural industrial structure, develop the rural economy and increase farmers' income. People have long ignored the planting of the fruit economic forest at a certain period, as it still has a stable stand structure of plantation attributes. Therefore, they have also overlooked the huge hidden economic value of the fruit forest ecological service, ignored the large amount of ecological function generated by the economic forest fruit trees, and the quantity of ecological function for the loess plateau region coverage is generally low. However, there is no doubt about its ecological significance. Especially in the arid and semi-arid ecologically fragile areas of the Loess Plateau, by excavating the ecological function service value of the fruit tree economic forest and analyzing the large ecological function quantity corresponding to its service value, the compensatory function and deep impact of the ecological aspect of soil and water conservation are analyzed in this study. This analysis is of great significance and necessary for coordinating the relationships between economic development and ecological protection, agriculture and forestry, and human and nature in the arid and semi-arid areas of the Loess Plateau.

2 Regional overview

The Hulu River Basin in Pingliang City is located in the west of Pingliang City, in the central part of Gansu Province. Its geographical coordinates are 35°00'36"-35°45'00"N and 105°20'24"-106°24'00"E. It is about 102.36 km long from east to west and 81.68 km wide from north to south, with a total area of 3701.67 km2. The river basin is under the jurisdiction of Zhuanglang County and Jingning County. It is located in the central region of the Northwest Loess Plateau, and belongs to the loess hilly and gully region of central Gansu. The gully density is 1.5-2 km km-2, the annual average precipitation is 484.7 mm, the annual average evaporation is 880.7 mm, the average annual runoff depth was 50.0 mm and the average annual evapotranspiration was 196.47 mm during the growth period of the stand (from April to October), and the drought index is 1.83. It belongs to the semi-arid continental climate in the middle temperate zone of central Gansu. The main type of soil is yellow soil with a deep soil layer that is 10-50 m thick, with a heavy or medium soil texture. The vegetation type is warm temperate semi-arid forest grassland transition zone, and the natural forest distribution is sparse. In recent years, the total area of forestland in the whole basin has reached 121435.83 ha and the forest coverage rate has reached 32.81% as a result of measures such as closing the mountains for afforestation and artificial afforestation. With the optimization and adjustment of the regional rural industrial structure, the fruit-tree economic forest developed rapidly and the planting scale continued to expand, mainly using high-quality red Fuji apple (Malus pumila Mill) as the planting variety. According to a recent survey (Jingning County Statistics Bureau, 2012-2020; Zhuanglang County Statistics Bureau, 2012-2020), the area of fruit-tree economic forest planted in the Hulu River Basin in Pingliang City reached 107768.26 ha by the end of 2020, accounting for 29.00% of the total land area, while the existing fruit area of 84961.33 ha accounted for 22.86% of the total land area, and the annual output reached 1.346 million tons, with the annual output value reaching 4.711 billion yuan①. The development of fruiting economic forest in the Hulu River Basin in Pingliang City went through four stages, as shown in Table 1. 1) In the first stage (2005-2009), as the basic development period, the planting scale of fruit-tree economic forest increased from 18849.42 ha to 39054.02 ha, the annual fruit yield increased from 148000 t to 302400 t, and the annual output value increased from 221 million yuan to 1.055 billion yuan, an increase of 4.77 fold. 2) In the second stage (2010-2013), as the period of continuous growth, the planting scale of the economic forest of fruit trees increased from 39054.02 ha in 2009 to 79414.64 ha in 2013, and the annual fruit yield increased from 428200 t to 506600 t. The annual output value increased from 1.4971 billion yuan to 2.108 billion yuan, an increase of 1.41 fold. 3) In the third stage (2014-2017), the planting scale of the fruit tree economic forest decreased from 91623.77 ha to 80816 ha, but the annual fruit production increased from 630500 t to 903100 t, and the annual output value increased from 2.203 billion yuan to 3.161 billion yuan, an increase of 1.43 fold. 4) In the fourth stage (2018-2020), the planting scale of the fruit tree economic forest increased rapidly from 80816 ha in 2017 to 107768.26 ha, and reached a maximum value of 111120.09 ha in 2019. The annual fruit yield increased from 937600 t to 1.346 million t. The annual output value increased from 3.282 billion yuan to 4.711 billion yuan, an increase of 1.44 fold.
Table 1 Survey of the economic forest development of fruit trees in the Hulu River Basin in Pingliang City
Year Planting area
(ha)		 Percentage of planting area in the total land area of the basin (%) Fruit area
(ha)		 Percentage of fruit area in the total land area of the basin (%) Annual production (104 t) Annual output value (108 yuan)
2005 18849.42 5.07 9322.52 2.51 14.80 2.21
2006 22777.74 6.13 11263.6 3.03 17.86 2.65
2007 25442.18 6.85 12579.5 3.38 21.52 3.46
2008 34327.78 9.24 16974.4 4.57 26.90 5.02
2009 39054.02 10.51 19144.6 5.15 30.24 10.55
2010 54886.72 14.77 27131.72 7.30 42.82 14.97
2011 65082.87 17.51 32161.31 8.65 50.66 17.76
2012 70669.13 19.01 34903.30 9.39 57.08 20.23
2013 79414.64 21.37 39216.50 10.55 60.08 21.08
2014 91623.77 24.65 45174.60 12.15 63.05 22.03
2015 79690.91 21.44 46008.00 12.38 69.28 24.24
2016 77692.98 20.90 47260.80 12.72 76.61 26.72
2017 80816.00 21.74 52330.00 14.08 90.31 31.61
2018 108533.32 29.20 77500.00 20.85 93.76 32.82
2019 111120.09 29.90 82293.40 22.14 129.15 45.20
2020 107768.26 29.00 84961.33 22.86 134.60 47.11

① The relevant data of fruit tree economic forest and soil and water conservation forest are from the Statistical Bulletin of National Economic and Social Development of Jingning County, Zhuanglang County, 2005-2020

3 Data sources

The following data sources were consulted for the relevant years. 1) Various government reports were consulted. 2) Statistical Yearbooks for 2005-2020 were obtained. 3) The price parameters were obtained from social public data released by national authorities. For example, the SO2 emission charge (yuan kg‒1) is 1.2 yuan kg‒1 in the “Collection Standard and Calculation Method of Pollutant Discharge Fee” of the National Development and Reform Commission. The dust removal and cleaning fee shall be charged according to the air pollutant emission standard of a coal-fired furnace, 0.56 yuan kg‒1. The price of oxygen is the average price of oxygen on the website of the Ministry of Health of the People’s Republic of China, which is 1000 yuan t‒1. The current market price of domestic water is 6.0 yuan t‒1. According to the Ministry of Agriculture “China Agricultural Information Network”, the current market prices for diammonium phosphate, potassium chloride, and organic matter are 2400 yuan t‒1, 2200 yuan t‒1, and 320 yuan t‒1, respectively. 4) The parameters related to ecological function were obtained from the measured data of the relevant forest ecological stations in China and related literature references (Gao, 2014). 5) The soil erosion modulus was obtained from the updated data of the latest Planning of Soil and Water Conservation of Pingliang City. According to the contour map of the soil erosion modulus, the intermediate values were selected to avoid calculating values of soil conservation and fertilizer conservation that were too high or too low. 6) The annual net productivity of the stand was determined by the average annual net growth of a single plant at 12 years of age using the typical survey method. 7) The carbon sequestration value was calculated by Sweden’s carbon tax law, which is generally used internationally and most commonly in China. Diversity conservation index grade determination was calculated as follows. The Shannon-Wiener index level was selected for determining the biodiversity conservation index level. This index is consistent with its ecological function, considering that the Hulu River Basin is the national key ecological functional area, the loess hilly gully ecological functional area of soil and water conservation in Longdong, and the provincial key ecological functional area of restricted development but not belonging to the national Nature Reserve.. In this study, the fruit tree economic forest was selected as grade 5 (2≤index< 3) and water conservation forest as grade 4 (3≤index<4), and their corresponding values were calculated as 10000 yuan ha‒1 yr‒1 and 20000 yuan ha‒1 yr‒1, respectively. The negative ion concentration values refer to the observed values of Li et al. (4645 cm‒3) in the woodland of the Loess Plateau in the north of the Qinling Mountains in Shaanxi Province (Li et al., 2008).

4 Research methods and calculation process

According to the Code for Evaluation of Forest Ecosystem Service Function (GB/T 38582-2020), the forestry industry standard of the People’s Republic of China, the comprehensive application of ecology, economic theories and the principles of soil and water conservation, this study used the current market method, shadow price method, opportunity cost method, Swedish carbon tax law and other methods, The main functions and ecological and economic values of the fruit tree economic forest ecosystem in the region were quantitatively analyzed, and the existing measured data of relevant ecological stations in China were combined with the quantitative analysis and qualitative assessment. The ecological service value of the fruit tree economic forest ecosystem in Hulu River Basin in Pingliang City was calculated in terms of water conservation, soil conservation, carbon sequestration, oxygen production, nutrient accumulation, environmental purification and biodiversity protection. Then the characteristics of dynamic changes in the ecological function quantity corresponding to its value were systematically analyzed.

4.1 Conservation of water sources

The water source conservation function mainly refers to the regulating effect of the ecosystem on atmospheric precipitation. According to the characteristics of monitoring and evaluation, it can be divided into two indexes: regulating water quantity index and purifying water quality index.

4.1.1 Adjusting the water value

The water value of ecosystem regulation was determined according to the storage cost of reservoir engineering (shadow engineering method), and its formula is:
Uadjust =10×Creservoir ×A× (P-E-C)
where Uadjust is the value of the annual adjusted water quantity, yuan yr‒1; Creservoir is the storage capacity cost of a reservoir, yuan m‒3; P is the annual precipitation outside the forest, mm; E is the annual evapotranspiration of the stand, mm; A is the stand area, ha; and C is the surface runoff, mm.

4.1.2 Value of purified water quality

The annual purified water quality value of the ecosystem was calculated by the average price of residential water in Pingliang City, and the formula is:
UWater quality =10×Kwater ×A× (P-E-C)
where Uwater quality is the annual purifying water quality value, yuan yr‒1; Kwater is the average price of residential water, yuan m‒3; A is the stand area, ha; P is the annual precipitation outside the forest, mm; E is the annual evapotranspiration of the stand, mm; and C is the surface runoff, mm.

4.2 Soil conservation

4.2.1 Maintaining soil values

The value of soil conservation can be calculated according to the water storage cost method and the method of reducing siltation and sediment. The formula is:
USoil conservation= A×CStorage capacity ×(X2 ‒ X1) /ρ
where Usoil preservation is the annual soil consolidation value, yuan yr‒1; X1 is the annual erosion modulus of woodland soil, t ha‒1 yr‒1; X2 is the annual erosion modulus of unforested soil, t ha‒1 yr‒1; ρ is the average density of sediment, t m‒3; and A is the stand area, ha.

4.2.2 Maintaining fertility value

The value of reducing soil fertility loss can be written as:
Ufertilizer =A×(X2-X1) ×(N×Cl/Rl+P×C1/R2+×K×C2/R3+M×C3)/100
where Ufertilizer is the annual protection value of fertilizer, yuan yr‒1; N, P and K are the average contents of soil nitrogen, phosphorus and potassium, respectively, %; M is the average content of soil organic matter, %; R1 is the nitrogen content of diammonium phosphate, %; R2 is the phosphorus content of diammonium phosphate, %; R3 is the potassium content of potassium chloride, %; C1, C2 and C3 are the average prices of diammonium phosphate, potassium chloride and organic matter, respectively, yuan t‒1; and A is the stand area, ha.

4.3 Carbon fixation and oxygen production

4.3.1 Carbon sequestration value

According to the chemical equation of photosynthesis, each l g of dry matter accumulated by forest vegetation can fix 1.63 g of CO2 and release 1.19 g of O2, and the proportion of carbon in CO2 is 27.27%. Therefore, the formula for calculating the carbon sequestration value of forest vegetation and soil is:
Ucarbon =A×Ccarbon ×(0.4445×Byears +Fsoil carbon)
where Ucarbon is the annual carbon sequestration value of the stand, yuan yr‒1; Byears is the annual net productivity of the stand, t ha‒1 yr‒1; Ccarbon is the carbon sequestration price, yuan t‒1; coefficient 0.4445 is the product of 1.63 and 27.27%; Fsoil carbon is the annual carbon sequestration of forest soil per unit area, t ha‒1 yr‒1; and A is the stand area, ha.

4.3.2 Oxygen release value

The formula for calculating the value of oxygen release is:
Uoxygen =1.19×A×Coxygen ×Byears
where Uoxygen is the annual oxygen production value of the stand, yuan yr‒1; Byears is the annual net productivity of the stand, t ha‒1 yr‒1; Coxygen is the price of oxygen, yuan t‒1; and A is the stand area, ha.

4.4 Nutrient accumulation

Forest vegetation continuously absorbs nitrogen, phosphorus, potassium and other nutrients from the surrounding environment during its growth process, and they are stored in various organs. In this study, only the accumulation index of forest nutrients (nitrogen, phosphorus, potassium) was selected to reflect this function. Its formula is:
Unutrient=A×Byears×(Nnutrient×C1/Rl+Pnutrient×C1/R2+Knutrient×C2/R3)
where Unutrition is the annual nutrient accumulation value of the stand, yuan yr‒1; Nnutrition, Pnutrition and Knutrition are the nitrogen, phosphorus and potassium contents of forest trees, respectively, %; R1 is the nitrogen content of diammonium phosphate, %; R2 is the phosphorus content of diammonium phosphate, %; R3 is the potassium content of potassium chloride, %; C1 and C2 are the prices of diammonium phosphate and potassium chloride respectively, yuan t‒1; and A is the stand area, ha.

4.5 Cleaning the environment

The shadow price method was adopted to calculate the value of the purified environment based on forest area and the ability of forest trees to reduce toxic and harmful substances, dust, noise and radiation in the environment.

4.5.1 Absorption value of sulfur dioxide

The annual total value of sulfur dioxide absorbed by forest (Usulfur dioxide, yuan yr‒1) can be written as:
Usulfur dioxide =Ksulfur dioxide ×Qsulfur dioxide ×A
where Ksulfur dioxide is the treatment cost of sulfur dioxide, yuan kg‒1; Qsulfur dioxide is the annual absorption of sulfur dioxide per unit area of forest, kg ha‒1 yr‒1; and A is the stand area, ha.

4.5.2 Value of fluoride absorption

The annual total value of fluoride absorbed by forest (Ufluoride, yuan yr‒1) can be written as:
Ufluoride =Kfluoride ×Qfluoride ×A
where K fluoride is the treatment cost of fluoride, yuan kg‒1; Qfluoride is the annual fluoride absorption of forest per unit area, kg ha‒1 yr‒1; and A is the stand area, ha.

4.5.3 Value of absorbed nitrogen oxides

The annual total value of nitrogen oxides absorbed by the forest (Unitrogen oxides, yuan yr‒1) can be written as:
Unitrogen oxide =Knitrogen oxide ×Qnitrogen oxide ×A
where Knitrogen oxide is nitrogen oxide treatment cost, yuan kg‒1; Qnitrogen oxide is the annual nitrogen oxide absorption of forest per unit area, kg ha‒1 yr‒1; and A is the stand area, ha.

4.5.4 Value of blocking dust removal

The annual blocking dust removal value of forest vegetation (Udust retention, yuan yr‒1) can be written as:
Udust retention =Kdust retention ×Qdust retention ×A
where Kdust retention is dust removal cost, yuan kg‒1; Qdust retention is the annual dust retention of forest per unit area, kg ha‒1 yr‒1; and A is the stand area, ha.

4.5.5 Negative ion value

The negative ion value provided by the stand year (Unegative ion, yuan yr‒1) can be written as:
Unegative ion =5.256×1015×A×H×Knegative ion ×Qnegative ion ×L
where Knegative ion is the production cost of anions, yuan anion‒1; Qnegative ion is the stand negative ion concentration, anions cm‒3; L is the retention time of negative ions, min; H is the stand height, m; and A is the stand area, ha.

4.6 Biodiversity conservation

Biodiversity refers to the ecological complex formed by living things and their environment as well as the sum of various ecological processes related to it. It is the basis for the survival and sustainable development of human society. The annual biological species conservation value of the forest ecosystem (Uspecies conservation, yuan yr‒1) can be written as:
Uspecies conservation =Sspecies conservation ×A
where Sspecies conservation is the annual conservation value of biological species resources per unit area, yuan ha‒1 yr‒1; and A is the stand area, ha.

5 Results and analysis

5.1 Analysis of the ecological service value and functional quantity of the fruit tree economic forest in Hulu River Basin

5.1.1 Dynamic changes of the total value of ecological services of the fruit tree economic forest and individual values of different service functions

According to the calculations, the total value of ecological services of the fruit tree economic forest in the whole Hulu River Basin and the dynamic values of ecological services in different service functions, such as water conservation, soil conservation, carbon sequestration, oxygen production, nutrient accumulation, biodiversity protection and environment purification, are shown in Tables 2 and 3. The dynamic changes of the service value of each ecological function are shown in Figs. 1 and 2.
Table 2 Changes in ecosystem service value of the fruit-tree economic forest in different years (2005‒2020) (Unit: 104 yuan)
Year Total value of ecological
function		 Conserve water value Annual fixed soil value Annual fertilizer preservation value Annual carbon sequestration value Annual oxygen production value Stand annual nutrient accumulation value Species
conservation value
2005 174316.97 57478.37 11096.26 10705.65 20269.43 45220.51 19761.63 9424.71
2006 210645.56 69457.16 13408.78 12936.77 24493.69 54644.71 23880.05 11388.87
2007 235285.95 77581.96 14977.28 14450.05 27358.85 61036.81 26673.44 12721.09
2008 317458.81 104677.21 20208.05 19496.69 36913.84 82353.72 35989.05 17163.89
2009 361166.46 119089.14 22990.29 22180.99 41996.13 93692.16 40944.01 19527.01
2010 507585.20 167368.49 32310.67 31173.27 59021.58 131675.44 57542.93 27443.36
2011 601877.85 198460.06 38312.93 36964.25 69985.85 156136.41 68232.51 32541.44
2012 653538.86 215494.49 41601.45 40137.00 75992.95 169538.07 74089.12 35334.57
2013 734416.19 242162.56 46749.75 45104.07 85397.30 190518.90 83257.86 39707.32
2014 847324.62 279392.39 53937.01 52038.32 98526.20 219809.09 96057.84 45811.89
2015 593628.41 99662.32 46912.38 45260.98 85694.38 191181.68 83547.50 39845.46
2016 594035.61 112453.73 45736.24 44126.24 83545.94 186388.57 81452.88 38846.49
2017 626997.84 126057.85 47574.70 45899.98 86904.23 193880.82 84727.04 40408.00
2018 877176.24 204429.74 63891.31 61642.21 116709.62 260375.78 113785.72 54266.66
2019 900320.45 211539.79 65414.09 63111.39 119491.26 266581.54 116497.68 55560.05
2020 996626.75 328622.50 63440.94 61207.69 115886.92 258540.37 112983.64 53884.13
Fig. 1 Dynamic changes in ecosystem service value of the fruit tree economic forest in different years (2005-2020)
Table 3 Dynamic changes in the environmental purification functional value of the fruit tree economic forest ecosystem in different years (2005-2020) (Unit: 104 yuan)
Year Total value of environmental purification function Value of absorption of sulfur dioxide Value of absorption of fluoride Value of absorption of nitrogen oxide Value of blocking dust Value of providing negative ions
2005 289.68 200.52 2.19 7.13 10.67 69.17
2006 350.05 242.31 2.64 8.61 12.90 83.59
2007 390.99 270.65 2.95 9.62 14.40 93.37
2008 527.55 365.18 3.98 12.98 19.44 125.98
2009 600.18 415.46 4.53 14.76 22.11 143.32
2010 843.49 583.88 6.36 20.75 31.07 201.43
2011 1000.19 692.35 7.54 24.60 36.85 238.84
2012 1086.04 751.78 8.19 26.71 40.01 259.34
2013 1220.44 844.81 9.21 30.02 44.96 291.44
2014 1408.07 974.69 10.62 34.63 51.87 336.24
2015 1224.68 847.75 9.24 30.12 45.12 292.45
2016 1193.98 826.50 9.01 29.37 43.99 285.12
2017 1241.97 859.72 9.37 30.55 45.75 296.58
2018 1667.93 1154.58 12.58 41.03 61.45 398.30
2019 1707.69 1182.10 12.88 42.00 62.91 407.79
2020 1656.17 1146.44 12.49 40.74 61.01 395.49
Fig. 2 Dynamic changes of the environmental purification functional value of the fruit tree economic forest ecosystem in different years (2005-2020)
The data show that the value of water conservation was the highest and accounted for the largest proportion in the ecological service value of the fruit tree economic forest, accounting for 32.97% of the total value of ecosystem services. Thus, it plays an important role in regulating the hydrological balance of the watershed in the arid and semi-arid areas of the Loess Plateau. The value of purifying atmospheric environment function is relatively small, accounting for only 0.19% of the total value. The order of service values is as follows: the ecological function values of water conservation, oxygen release, carbon sequestration, nutrient accumulation, soil conservation, fertility maintenance, species conservation and environmental purification accounted for 32.97%, 25.94%, 11.63%, 11.34%, 6.37%, 6.14%, 5.42% and 0.19% of the total value, respectively. The conclusion of this analysis is basically consistent with other domestic studies. Compared with the annual output value of the economic forest of fruit trees in the same period, the total value of ecological services was 2.42 times the annual output value of fruits in the same period. Therefore, the fruit tree economic forest not only provides a large amount of fresh fruit products and creates tremendous economic and social benefits for the people, but it also contributes a large increase in ecological service value, and the contribution of local GEP is greater than the contribution of GDP.

5.1.2 Dynamic coupling analysis of the ecological service value of the fruit tree economic forest in different stages and its development

Regression analysis shows that there was a significant linear correlation between the ecological service value of fruit tree economic forest V (104 yuan) and the planting area of the fruit tree economic forest A (ha). The linear regression equation is as follows:
V = 10.562×A-207.707 (R = 0.98, R2=1.000, Adj R2=1.000)
The accumulation of ecological service value in different development stages of the fruit tree economic forest shows that both total service value and the individual service values of different service functions are synchronized with the development stages of the fruit tree economic forest, which has a high degree of dynamic coupling characteristics. The changes in the characteristics of dynamic coupling are shown in Figs. 3, 4 and 5. At the same time, the regression equation shows that every 1 ha increase or decrease of fruit tree economic forest in this area will bring about 105600 yuan of ecological service value change. The data of the mutation points in Table 4 and Figs. 3, 4 and 5 (peak accumulation at the end of each developmental stage) indicate that the ecological service values of the fruit tree economic forest in the four development stages show increasing trends of continuous accumulation. Among the four stages, the total value contribution of the first stage (2005-2009) is 1.299×1010 yuan; the second stage (2010-2013) is 2.497×1010 yuan; the third stage (2014-2017) is 2.662×1010 yuan; and the total value contribution of the fourth stage (2018-2020) is 2.774×1010 yuan.
Fig. 3 Dynamic changes in the development stages of the fruit economic forest in Hulu River Basin
Fig. 4 The total value of ecological function services and the phased changes of the individual service function values
Fig. 5 The function values of purifying atmospheric environment change dynamically among the different stages
Table 4 Ecological service value accumulation in the different stages of fruit tree economic forest development in Hulu River Basin
Development stage 2005‒2009 2010‒2013 2014‒2017 2018‒2020
Development area (ha) 140451.14 270053.36 329823.66 327421.67
Accumulated value of ecological services (104 yuan) 1298873.74 2497418.09 2661986.48 2774123.44

5.2 Ecological function output of the fruit tree economic forest in the Hulu River Basin in Pingliang City

The quantity of an ecological function is the embodiment of the ecological service ability and specific function of the fruit tree economic forest. The greater the value of an ecological service, the stronger the corresponding ecological service function, and vice versa. The main ecological functions of the fruit tree economic forest in the semi-arid loess hilly region are as follows: 1) Maintaining the balance of the regional hydrological cycle by intercepting runoff and conserving water by the tree canopy; 2) Reducing soil and water loss, conserving water and soil resources, and reducing soil fertility loss through soil consolidation; 3) Absorbing CO2 and releasing O2 through photosynthesis to promote the accumulation of nutrients; 4) By absorbing SO2, NO, fluoride, dust, etc., the contents of particulate matter and toxic and harmful substances in the air are reduced, and the concentration of PM2.5 is reduced, greatly improving the regional environmental quality. At the same time, the environment can be effectively purified by the release of a large number of negative oxygen ions, which is beneficial to human health. 5) In the semi-arid loess hilly and gully region, due to the coverage of a certain scale of fruit tree economic forest, the spatial pattern of regional land use has been changed, and the continuity and extension of the limited forest and grass vegetation have been greatly enhanced, which is conducive to the conservation and propagation of species in the region, as well as the maintenance and enhancement of biodiversity in the region, and the harmonious coexistence between man and nature. The accounting results of these functions are shown in Table 5. The amount of water conservation of the fruit tree economic forest (2005-2020) in the Hulu River Basin in Pingliang City is 25.8753×108 m3. Soil fixation is 21.3550×108 t, fertilizer retention is 22.64×104 t, carbon fixation is 9.5682×106 t, oxygen production is 25.6157×106 t, nutrient accumulation is 9.278×105 t, the environmental purification function is 11.3651×104 t (in which the amount of sulfur dioxide absorbed is 94656.02 t, the amount of fluoride absorbed is 1793.82 t, the amount of nitrogen oxide absorbed is 6406.50 t, and the amount of dust fall is 10794.95 t), and the amount of negative ions provided is 15.641×1024. All of these greatly regulate and improve the ecological environmental quality of the region.
Table 5 Total accumulation of the various ecological service functions of the fruit tree economic forest in Hulu River Basin in Pingliang City (2005-2020)
Region Conserve the total water supply (108 m3) Maintain total soil (108 t) Protect fertilizer amount (104 t) Total carbon sequestration (106 t) Oxygen generation (106 t) Total accumulation of nutrients (105 t) Environmental Purification Service Provide the total amount of negative ions (1024)
Total absorption of sulfur dioxide (104 t) Total absorption of fluoride (102 t) Total absorption of nitrogen oxides (103 t) Amount of dust (103 t)
Jinning 18.4831 15.5170 16.4480 6.9525 18.6129 6.7413 6.8779 13.0343 4.6551 7.8438 11.365
Zhuanglang 7.3923 5.8380 6.1883 2.6158 7.0028 2.5363 2.5877 4.9039 1.7514 2.9511 4.276
The whole basin 25.8753 21.3550 22.6363 9.5682 25.6157 9.2776 9.4656 17.9382 6.4065 10.7950 15.641

5.3 Comparative analysis of ecological function quantities of the fruit tree economic forest and the water and soil conservation forest in the same period

The three main indexes of water conservation, soil conservation and fertility conservation of the soil and water conservation forest and the fruit economic forest were compared and analyzed for each year during 2012-2020, as shown in Table 6. The results show three main trends for the conservation of water, soil, and soil fertility. 1) Water conservation sources: From 2012 to 2020, the cumulative total of water conservation sources in the soil and water conservation forest was 635183.0 ten thousand m3, and that in fruit tree economic forest was 586968.6 ten thousand m3, for a difference of 48214.1 ten thousand m3. Thus, the value for the fruit tree economic forest was less than the soil and water conservation forest. 2) Soil conservation: The total amount of soil conservation in the soil and water conservation forest was 145607.4 Ten thousand tons, and that in the fruit tree economic forest was 161465.8 Ten thousand tons, for a difference of 15858.4 Ten thousand tons. Again, the fruit tree economic forest had a higher value than the soil and water conservation forest. 3) Soil fertility conservation: The total amount of soil fertility conservation accumulated by the soil and water conservation forest was 154343.8 t, and the total amount of soil fertility conservation accumulated by the fruit tree economic forest was 171153.8 t, for a difference of 16809.97 t. Therefore, the fruit tree economic forest was higher than the soil and water conservation forest. There is no significant difference between the two forest types in terms of unit area. These data show that the fruit tree economic forest also has the ecological service function of the ecological public welfare forest.
Table 6 Comparisons of the main ecological function services between the soil and water conservation forest and the fruiting economic forest
Year Area (ha) Annual water
conservation (104 m3)		 Annual soil retention (104 t) Annual maintenance fertilizer consumption (t)
Soil and water conservation forest Fruit-bearing economic forest Soil and water conservation forest Fruit-bearing economic forest Soil and water conservation forest Fruit-bearing economic forest Soil and water conservation forest Fruit-bearing economic forest
2012 17236.80 70669.13 15038.4 51380.0 3447.4 14133.8 3654.2 14981.9
2013 72860.00 79414.64 63567.4 57738.4 14572.0 15882.9 15446.3 16835.9
2014 77080.00 91623.77 67249.2 66615.1 15416.0 18324.8 16341.0 19424.2
2015 81250.00 79690.91 70887.4 57939.3 16250.0 15938.2 17225.0 16894.5
2016 84380.00 77692.98 73618.2 56486.7 16876.0 15538.6 17888.6 16470.9
2017 88630.00 80816.00 77326.1 58757.3 17726.0 16163.2 18789.6 17133.0
2018 97380.00 108533.32 84960.2 78909.2 19476.0 21706.7 20644.6 23009.1
2019 102700.00 111120.09 89601.6 80789.9 20540.0 22224.0 21772.4 23557.5
2020 106520.00 107768.26 92934.4 78352.9 21304.0 21553.7 22582.2 22846.9
Total 728036.80 807329.10 635183.0 586968.6 145607.4 161465.8 154343.8 171153.8

6 Conclusions

(1) Among the components of ecological service value of the fruit tree economic forest, the value of water conservation is the highest, accounting for the largest proportion, at 32.97% of the total value of ecosystem services. Therefore, it plays an important role in regulating the hydrological balance of the basin in the arid and semi-arid region of the Loess Plateau. The function value of the purifying environment is relatively small, accounting for only 0.19% of the total value, followed by the function value of species conservation, accounting for 5.42%. In order of service value, the ecological function values of water conservation, oxygen release, carbon sequestration, nutrient accumulation, soil conservation, fertility maintenance, species conservation and environment purification accounted for 32.97%, 25.94%, 11.63%, 11.34%, 6.37%, 6.14%, 5.42% and 0.19% of the total value, respectively. The conclusions of this study are basically consistent with those of other domestic studies. Compared with the annual output value of fruit trees in the same period, the total value of ecological services was 2.42 times the annual output value of fruit. Clearly, the fruit tree economic forest not only provides a large amount of fresh fruit products and creates tremendous economic and social benefits for the people, but it also provides a large increase in ecological service value, and the contribution of local GEP is greater than that of GDP.
(2) The total service value of the fruit tree economic forest and the individual service values of the different service functions are synchronized with the development stages of the fruit tree economic forest, which has a high degree of dynamic coupling characteristics. At the same time, the regression equation shows that every 1 ha increase or decrease in the fruit economic forest in this region will bring about a change of 105600 yuan in ecological service value.
(3) The fruit tree economic forest also has the ecological service function of the ecological public welfare forest. A comparative analysis with the soil and water conservation forest in the same period in this region found that there is no significant difference between the fruit tree economic forest and the soil and water conservation forest with respect to the three main ecological functions of water conservation, soil conservation and soil fertility conservation. Due to the extreme importance of forest vegetation to the ecology of the arid and semi-arid fragile area of Loess Plateau and the prevention and control of soil and water loss, it is necessary to consider the ecological public welfare impact that would be caused by the adjustment of the fruit tree economic forest in this region when adjusting the industrial structure.

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