Assessment And Spatial Patterns Of Forest Water Conservation Capacity In Beijing-Tianjin-Hebei Region Based On The Meta-Analysis Method

Water conservation capacity is one of the most important ecosystem services of forest.Understanding the heterogeneity and influencing factors of forest water conservation capacity can contribute to the functional area construction of water conservation,the vegetation restoration and forest ecosystem protection in Beijing-Tianjin-Hebei Region.Based on 193 relevant literatures published from 1980to 2017,we extracted water conversation parameters and their influencing factors throughout Beijing-Tianjin-Hebei Region via a meta-analysis approach and obtained1366 effective records of canopy(203 records),litter layer(686 records)and soil layer(477 records).First,we used Pearson correlation method to analysis influence factors of water conservation capacity.Then the path analysis was used to explore the significant factors affecting the canopy interception capacity,litter maximum water-holding capacity and soil water storage capacity.Finally,we through Assignment method and InVEST model to simulation differentiation characteristics of water conservation capacity on spatial scale.The main conclusions are as follows:(1)The mixed forest had the highest water conservation capacity of vegetation types in Beijing-Tianjin-Hebei Region,followed by the broad-leaf forest,the coniferous forest and the shrub forest.The soil layer had the largest water conservation capacity regardless of forest type,followed by the canopy and litter layer.(2)The heterogeneity of water conservation capacity under different environmental gradients in the study area was obvious.The canopy interception decreased with the increase of altitude,increased with the increase of diameter at breast height(DBH),leaf area index,maximum daily precipitation and evapotranspiration.The maximum water holding capacity of litter kept the same growth trend with vegetation index,altitude and litter storage,first increased and then decreased with forest age.The soil effective water capacity increased with the increase of non-capillary porosity and precipitation,decreased with the increase of capillary porosity and forest age.(3)The influencing factors of water conservation capacity in different forest layers were different.There was a significant positive correlation between canopy interception and maximum daily precipitation,evapotranspiration,leaf area index,forest age,DBH and slope,had a significant negative correlation with the annual sunshine hours,latitude and altitude.The correlation between the maximum water holding capacity of litter and litter storage was very high,and the correlation coefficient of litter in semi decomposed state was greater than non-decomposed state.The correlation between soil effective water holding capacity and non-capillary porosity and soil thickness was significant.(4)The results of path analysis show that the main influencing factors of canopy interception capacity(R~2=0.49)were leaf area index and maximum daily precipitation,and the influencing coefficients were 0.34 and 0.30 respectively.However,the accumulation of litters in the semi-decomposed layer(with a coefficient of 0.51)was the most important for the litter maximum water-holding capacity(R~2=0.51).Non-capillary porosity and soil thickness had relative high contributions to the soil water storage capacity(R~2=0.61),and the influencing coefficients were 0.60 and 0.38respectively.(5)Climate conditions and forest growth may be the main reasons for the spatial differentiation of water conservation in Beijing-Tianjin-Hebei Region,the water conservation capacity of Yanshan Mountain in the north was higher than that of Taihang Mountain in the west of Hebei Province.In climate differentiation,the trend of water conservation capacity was consistent with precipitation and sunshine hours,but opposite to temperature and evapotranspiration.In terrain differentiation,the water conservation capacity of shady slope was higher than that of sunny slope.In watershed differentiation,Luanhe River Basin had the strongest water conservation capacity,while Haihe River Basin had the weaker water conservation capacity.In vegetation differentiation,the mixed forest had the highest water conservation capacity,followed by the broad-leaf forest,the coniferous forest and the shrub forest.In soil differentiation,gray brown soil,brown soil,brown soil and mountain meadow soil had strong water conservation capacity.In administrative differentiation,Beijing has the largest water conservation capacity,and Hebei Province has the largest total water conservation capacity.The comprehensive analysis of forest water conservation capacity in the study area by meta-analysis method overcame the limitation of space-time scale of sample plot experiment,and ensured the authenticity of data,which provided strong support for mechanism interpretation.Our study can provide validation at the site scale for results from simulation based on the water balance model or from remote sensing,and also can provide a scientific basis of data and methods for further researches on the effects of global change on water conservation.