| In order to explore the spatial scale effect,key driving factors,and tradeoff/cooperative relationships of the mountain forest ecosystem function across scales,the Haodifang Forestry Station of Mount Taiyue in Shanxi Province was selected as the study area to calculate and evaluate the main ecological functions(MEF)at different scales.Five representative forest types,i.e.Pinus tabulaeformis forest(PF),Larix principis-rupprechtii forest(LF),Betula platyphylla forest(BF),Coniferous and broad-leaved mixed forest(MF)and shrub wood(SW)have been selected as the research object at the ecosystem scale.The fuzzy matter-element method,evaluation methods based on biomass and species diversity index were selected to estimate the MEF.And the critical factors affecting them were screened by redundancy analysis(RDA).The spatial distribution of the MEF in the study area was simulated by In VEST ecological service function evaluation model at the landscape scale.And the contribution rate of the main drivers to their spatial differences was explained by the generalized additive model(GAMs).Finally,we constructed a hypothetical scenario to optimize the landscape pattern on the basis of identifying the trade-offs between different scales.The results showed that:(1)The layers of carbon sequestration(CS)of two coniferous forests(i.e.PF and LF)showed that the carbon storage was increasing obviously with the stand age at the ecosystem scale.The average value of their total carbon storage(221.9 Mg ha-1)was more than MF(198.5 Mg ha-1),followed by BF(143.9 Mg ha-1),and SW had the lowest value(100.4 Mg ha-1).It is indicated that the carbon storage gradually accumulates with the time of vegetation restoration.Plantations and natural forest protection have significant effects on forest carbon storage.However,water conservation(WC)and biodiversity conservation(BC)were the dominant functions of MF.With the diversification of stand structure,i.e.the transition from BF to MF,the dominant function became more prominent.Maximum water holding capacity of litter of MF was 0.48,2.21 and 0.05 times higher than that of LF,PF,and BF,respectively.The corresponding proportion for non-capillary porosity in the soil was 0.14,0.42 and 0.36.The efficiency of MF was also verified by the sort result of the fuzzy matter element model(pHi=0.71).The Shannon diversity index of shrub and herb layer in MF was 1.91 and 3.06,which was 24.8%and 23.3%higher than that of the average value of coniferous forests,and 51.6%and 18.1%higher than SW,respectively.It is indicated that there are trade-offs between functions of CS and WC,BC under different forest types.(2)Water conservation function was mainly affected by forest types,litter storage as well as the steady infiltration rate of soil at the ecosystem scale.The cumulative variance of the stand density,aspect and age could explain 90.8%variance of the maximum water holding capacity of litter and soil saturated water content.The corresponding ratio of 90.4%of CS could be explained by stand age and understory light radiation.The ratio of 87.5%of BC was explained by leaf area index,understory light radiation and aspect.(3)The landscape pattern of the study area has obvious grain effect,and the first scale domain of each landscape type appears near 5～10 m.The simulation results of In VEST showed that the actual evapotranspiration(AET),water yield,water conservation,carbon storage and biodiversity were affected by terrain factors,especially by elevation and slope.Due to the change of water and heat condition caused by topography and vegetation factors,the AET in the whole area varied from 200.8 to 604.8 mm.The distribution pattern of the amount of WC showed that the north was high and south was low.The WC capacity of LF had the highest value of 3.2×107 m3,while SW had the lowest of 3.5×106 m3.However,MF had the maximum depth of WC(150.7 mm)and smallest soil loss amount(0.32 t·ha-1·a-1).The mature LF and MF had the highest value of carbon density(286.6 Mg ha-1)and biodiversity conservation index(0.96),respectively.The spatial pattern of soil organic carbon has a significant and aggregated spatial autocorrelation,with a correlation distance of about 1.2 km.(4)The spatial heterogeneity of the amount of WC was mainly restricted by precipitation,evapotranspiration,vegetation types,saturated hydraulic conductivity,and elevation at the landscape scale.Correspondingly,CS was restricted by vegetation types,altitude and slope;BC was significalty affected by elevation,slope and distance to the threat source.Topographic factors and normalized difference vegetation index(NDVI)could explain 30.3%,39.2%,and 42.5%of the spatial variability of function values of WC,CS,and BC,respectively.(5)Tradeoff analysis show that there is a significant synergistic relationship between WC,CS and BC at the landscape scale,which has a difference with that at ecosystem scale,representing a scale dependent.The vegetation cover of the landscape was optimized aiming at improving the weak ecological function area.The results show that the average amounts of most MEF have been improved,but there is a significant difference in the magnitude of the increase.The potential value of water conservation increases 45.8%compared with the present value,while the carbon storage increases by only 1.36%.The research results can provide scientific basis for landscape pattern optimization and forest structure adjustment in North China.It also has important significance for guiding the formulation of vegetation restoration strategy and optimizing the regional ecological function. |
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