Ecological Service Function Evaluation Of Artificial Forests With Different Configuration Patterns In Yan’an Suburb

Assessment of urban forest ecosystem services plays a critical role in promoting urban sustainability.Different tree species and forest layout affect the provision of ecosystem services.To clarify the characteristics and differences of forest ecosystem services in different forest configurations in Yan’an city and provide a basis for the healthy development of urban forests,this study investigated and analyzed the production of materials,carbon sequestration and oxygen release,soil physicochemical properties,plant nutrient elements,and biodiversity of eight different forest configurations in Yan’an city.The physical and value quantities of six service functions,namely water conservation,soil conservation,carbon sequestration,nutrient accumulation,air purification,and biodiversity protection,were estimated for each configuration on a per unit area basis,and differences in ecosystem services were evaluated.Furthermore,the total physical and value quantities of Yan’an city’s forest ecosystem services were calculated after optimizing the forest layout and tree species configuration,aiming to provide reference for the sustainable and high-quality development of Yan’an city’s forests.The main conclusions are as follows:（1）Through field investigations of eight different configurations of artificial forests in the outskirts of Yan’an City,it was shown that mixed configurations had higher forest biomass than pure forests.Among them,the biomass accumulation of the Robinia pseudoacacia and Lonicera maackii Maxim mixed configuration was the highest,with a vegetation nitrogen accumulation of 56.15-159.41 kg·hm^-2·a^-1,vegetation phosphorus accumulation of 9.51-20.97kg·hm^-2·a^-1,and vegetation potassium accumulation of 43.81-86.31 kg·hm^-2·a^-1.The Robinia pseudoacacia,Robinia pseudoacacia and Lonicera maackii Maxim configuration and the Platycladus orientalis and Quercus mongolica mixed configuration had better nutrient accumulation effects.In the soil depth range of 0-60 cm,the content ranges of soil total nitrogen,total phosphorus,total potassium,and organic matter were 1.52-2.69g/kg,3.54-3.11g/kg,53.87-64.97g/kg,and 11.79-29.92g/kg,respectively.The Platycladus orientalis and Quercus mongolica mixed configuration and the Robinia pseudoacacia and Lonicera maackii Maxim configuration performed best in soil nutrient accumulation.（2）The water conservation capacity of different forest stand configurations ranges from1637.3 to 1165.8 m^-3·hm^-2·a^-1,with the Robinia pseudoacacia and Pinus tabulaeformis mixed configuration having the highest physical water conservation capacity.The annual reduction in nitrogen loss for different configuration modes ranges from 5.56 to 9.81 kg·hm^-2·a^-1,while the annual reduction in phosphorus loss ranges from 11.40 to 13.34 kg·hm^-2·a^-1 and the annual reduction in potassium loss ranges from 205.4 to 244.37 kg·hm^-2·a^-1.The annual reduction in organic matter loss ranges from 42.97 to 108.19 k kg·hm^-2·a^-1.The Platycladus orientalis and Quercus mongolica configuration and the Robinia pseudoacacia and Lonicera maackii Maxim configuration have a stronger ability to reduce soil nutrient loss.The vegetation carbon fixation of different configuration modes ranges from 0.57 to 3.54 t·hm^-2·a^-1,and the annual oxygen release ranges from 1.53 to 9.47 t·hm^-2·a^-1.Compared to pure forests,the mixed forest configurations all have higher levels of carbon fixation and oxygen release.The Shannon-Wiener index of the ecosystem ranges from 2.66 to 4.06,and the Simpson index ranges from0.718 to 0.922.With the exception of the Platycladus orientalis and Hippophae rhamnoides configuration,the biodiversity of forest stands in different configurations is higher than that of pure forests.The negative oxygen ions provided by different configurations range from 1.22to 2.19×10¹⁸ ions·hm^-2·a^-1,with the Platycladus orientalis and Populus davidiana configuration having the strongest ability to provide negative oxygen ions.The amount of sulfur dioxide absorbed by different configurations ranges from 144.05 to 288.05 kg·hm^-2·a^-1,the amount of fluoride absorbed ranges from 4.2 to 16.40 kg·hm^-2·a^-1,and the amount of nitrogen oxides absorbed ranges from 0.79 to 5.43 kg·hm^-2·a^-1,all of which show that mixed forest configurations perform better than pure forests.（3）In the suburbs of Yan’an city,the total ecological service value per unit area under different configuration modes ranged from 45663 to 88962.3 yuan·hm^-2·a^-1.The ecological service values of different configuration modes ranked from high to low as follows:Robinia pseudoacacia and Lonicera maackii Maxim configuration mode(88962.3 yuan·hm^-2·a^-1)>Robinia pseudoacacia and Pinus tabulaeformis mixed configuration mode(77190.9 yuan·hm^-2·a^-1)>Robinia pseudoacacia pure forest(72826.7 yuan·hm^-2·a^-1)>Platycladus orientalis and Robinia pseudoacacia configuration mode（60916.9 yuan·hm-2·a-1）>Platycladus orientalis and Quercus mongolica configuration mode(57737.6 yuan·hm^-2·a^-1)>Platycladus orientalis and Populus davidiana configuration mode(57163.9 yuan·hm^-2·a^-1)>Platycladus orientalis pure forest(53030.5 yuan·hm^-2·a^-1)>Platycladus orientalis and Hippophae rhamnoides configuration(45663.4 yuan·hm^-2·a^-1).Except for the Platycladus orientalis and Hippophae rhamnoides configuration mode,the ecological service value of other configuration modes is higher than that of the pure forest.（4）Based on the characteristics of different forest configurations in Yan’an suburban areas,layout optimization was carried out on the premise of suitable site and tree species selection.After the promotion of configuration optimization,the total value of ecosystem services provided by 8 different forest configurations was 3,430.77 million yuan per year,with the following order:Robinia pseudoacacia and Pinus tabulaeformis configuration（73,447.2million yuan per year）>Platycladus orientalis and Robinia pseudoacacia configuration（68,999.0 million yuan per year）>Platycladus orientalis and Quercus mongolica configuration（64,608.2 million yuan per year）>Platycladus orientalis and Hippophae rhamnoides configuration（62,755.7 million yuan per year）>Robinia pseudoacacia pure forest（39,916.6 million yuan per year）>Platycladus orientalis pure forest（15,510.7 million yuan per year）>Platycladus orientalis and Populus davidiana configuration（11,438.1 million yuan per year）>Robinia pseudoacacia and Lonicera maackii Maxim（9,848.9 million yuan per year）.The different ecosystem services values of 8 forest configurations in Yan’an suburban areas were presented as follows:water conservation value（144,106.5 million yuan per year）>biodiversity conservation value（109,267.7 million yuan per year）>carbon sequestration and oxygen release value（45,947.8 million yuan per year）>soil conservation value（24,371.0 million yuan per year）>nutrient accumulation value（15,510.2 million yuan per year）>air purification value（3,874.2 million yuan per year）.（5）Water conservation and biodiversity conservation were the main ecological service functions of different allocation patterns in suburban Yan’an,and the ecological service value per unit area was highest in robinia pseudoacacia,honeysuckle Lonicera.Different allocation patterns can effectively enhance forest ecosystem service function.