| Mu Us Sandy Land is one of the four sandy lands in China.Its ecological environment is relatively fragile,and the ecological disasters,such as desertification,occure frequently.In order to control desertification,artificial vegetation construction had been widely used in this area as the main technical means and measures.After more than 40 years of management,a large area of artificial shrubbery of Salix psammophila,Hedysarum leave and Caragana intermedia has been formed in Mu Us Sandy Land,and the application practice of different replanting modes was also carried out for the "wind erosion breach" in the process of vegetation restoration.However,there is still a lack of systematic research and evaluation on these restoration measures and replanting modes.Therefore,in this study we took the artificial shrubbery of S.psammophila and H.leave in Mu Us Sandy Land as the study object,from the perspectives of stand age and micro-topography,analyzed the community characteristics changes and succession direction in the process of vegetation restoration,and constructed the assessment index system of ecosystem services for sandy land vegetation restoration.In this paper,the characteristics of ecosystem services changes in the artificial shrubs during the vegetation restoration process were analyzed too,and we evaluated different stages of vegetation restoration and different planting modes in the "wind erosion breach" occured in the process of vegetation restoration.Finally,the trade-off and synergistic relationship of ecosystem services were discussed.This study not only enriches the research on ecosystem services based on statistical methods,but also aims to provide a scientific basis for guiding restoration vegetation and optimal regulation and control of degradation restoration in sandy areas of China,as well as providing a reference for the formulation of win-win policies for regional development and ecological protection.The results are as follows:(1)With the increase of afforestation time,the populations of S.psammophila and H.laeve were degraded and their important values also decreased to 0.8475 and0.4994 respectively after 34 and 38 years of afforestation,indicating that both communities were undergoing positive succession in the direction of Artemisia ordosica community with H.laeve community having much faster speed.At the late stage of community succession,perennial grasses appeared in the herb layer,and the community tended to be more stable.With the increase of afforestation time,the index value of community characteristics increased,but the growth rate of aerial seeding of H.laeve was slower than that of S.psammophila afforestation.The microtopography analysis showed that with the decrease of slope position the individual sizes of H.laeve decreased obviously with the highest population vitality being found in inter-dune lowland,followed by the windward slope and the leeward slope.The leeward slope was faster in the succession process.In addition,aboveground biomass per unit area,total nitrogen and soil water content were higher in inter-dune lowlands,while aboveground biomass per unit area and available potassium were higher in middle-slope of windward slope,and wind erosion was greatest on up-slope of leeward slope.(2)Taking biodiversity,carbon fixation regulation,soil fertility regulation,water conservation and windbreak and sand fixation as the criteria layer,the assessment index system of ecosystem services for vegetation restoration in Mu Us Sandy Land was constructed.The weight of windbreak and sand fixation was the largest(0.42),followed by biodiversity(0.25)and water conservation(0.17).(3)Ecosystem services change index(ESCI)analysis showed that with the increase of afforestation time,most of ecosystem services of S.psammophila and H.laeve shrubs showed an obvious state of gain.The increases of biodiversity and carbon sequestration regulation were the fastest at the initial stage of afforestation,and the growth rate of S.psammophila shrubs was higher than that of H.laeve shrubs.The soil fertility regulation increased most obviously in the middle stage of afforestation,and the water conservation did not decrease in the early afforestation stage of S.psammophila shrubs but slightly decreased in the H.laeve shrubs.Both S.psammophila and H.laeve shrubs had significant effect on windbreak and sand fixation in the early stage of afforestation,and could provide stable windbreak and sand fixation function after 23 and 14 years of afforestation,respectively.In addition,we divided each stage of S.psammophila and H.laeve shrubs into four types of ecosystem service clusters: i.the type of lacking vegetation services,ii.the type of water and soil conservation,iii.the type of plant soil conservation,and iv.multifunctional type.ESCI analysis of microtopography showed that the regulation of carbon sequestration and soil fertility were in a state of gain in the middle-slope compared with the up-slope.Compared with the middle-slope,water conservation and windbreak and sand fixation showed a gain state in down-slope;the inter-dune lowland showed obvious gain state for all the services compared with the down-slope.In addition,compared with the windward slope and leeward slope,the inter-dune lowland showed obvious gain state.In leeward slope,compared with windward slope,water conservation and windbreak and sand fixation were in a state of gain,while other services reduced.(4)With the increase of afforestation time,the evaluation score of ecosystem services of both S.psammophila and H.laeve shrubs increased,and were respectively similar to that of A.ordosica community after 8 and 30 years of afforestation.The microtopography results showed that the highest score of ecosystem services was obtained in the inter-dune lowland,and then followed by middle-slope,and up and down-slope,and the windward slope was superior to the leeward slope.The evaluation results of different replanting modes in "wind erosion breach" showed that the carbon fixation ability,soil fertility regulation and windbreak and sand fixation of S.psammophila sand barrier were the best,and the biodiversity of the Amorpha fruticosa community was the highest,while all the services of Pinus sylvestris var.mongolica community were the lowest.The score of ecosystem services of the A.fruticosa community was only slightly lower than that of S.psammophila sand barrier,which can be continued to be popularized.Compared with the P.sylvestris var.mongolica,the local S.psammophila was more worthy of promotion in Mu Us Sandy Land and the shrub construction is more suitable for this area.(5)There was a synergistic relationship between soil fertility regulation and water conservation in bare sandy land,and the relative benefits of soil fertility regulation in the trade-off were based on the loss of biodiversity.A.ordosica community had a synergistic relationship among carbon sequestration regulation,soil fertility regulation and water conservation.Windbreak and sand fixation and biodiversity had reached relative saturation,and neither of them benefit in the trade-off.With the increase of shrub bery age,there had always been a synergistic relationship between soil fertility regulation and water conservation in S.psammophila shrubs,but the relationship between various services was still dominated by trade-off with the carbon sequestration regulation not being benefits in the trade-off and the benefit of biodiversity begining to increase as the synergy appearing.With the increase of afforestation time,the synergistic relationship in H.laeve shrubs increased slightly,but the relationship between services was still dominated by the trade-off with a basically same law of windbreak and sand fixation not being benefits while water conservation being relatively benefits as the trade-off degree and competition decreasing.In terms of microtopography,the most synergistic relationship was found in the down-slope,followed by the middle-slope,up-slop and inter-dune lowalnd.However,windbreak and sand fixation were not relative benefits with the decline of slope position on the whole.The trade-off and synergistic relationship of different slope directions were similar,but the trade-off degree of leeward slope was higher and more obvious,and the competition was more intense.In addition,there was a high correlation between the indexes of biodiversity in S.psammophila community,soil fertility regulation too.In H.laeve community,all the diversity indices were significantly positively correlated with biomass per unit area,soil organic matter,available phosphorus and soil water content,while all indexes were negatively correlated with the height of wind erosion piles.It was found that H.laeve shrubs could be replaced into A.ordosica community faster than S.psammophila shrubs,but the speed of improving the community ecological benefits by aerial seeding of H.laeve was slower than that of S.psammophila afforestation.At the initial stage of S.psammophila and H.laeve afforestation,biodiversity,carbon sequestration regulation and windbreak and sand fixation were all in the state of gain,but did not use up too much soil water content.While at the middle stage of afforestation,soil fertility regulation was in the state of gain,and S.psammophila and H.leave community could provide stable windbreak and sand fixation function after 23 and 14 years of afforestation,respectively.Microtopography had an important effect on community succession and ecosystem services,so in the process of optimizing tending the specific restoration measures of different slope should be carried out according to the functional needs.On the whole,artificial promotion of vegetation restoration in Mu Us Sandy Land was successful,but more consideration should be given to native tree species when selecting species in the future. |
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