| In the southwest karst region,under the background of large-scale ecological management project,the vegetation coverage is significantly improved.The treatment objects are mainly concentrated in the relatively deep depressions and foothills of the soil layer,while the typical natural restoration slope is still in the early stage of succession because of the bad soil water environment and limited by water deficit.How to improve the soil water environment of sloping land and enhance its water conservation function is an important prerequisite for vegetation restoration and reconstruction in karst sloping land.This study takes the typical natural restoration slope in the Riverside Karst ecosystem observation Research Station of the Chinese Academy of Sciences as the research object,distinguishes the upper and lower slope,and carries out a series of artificial induction work,such as vegetation community optimization,soil improvement and so on.Through the monitoring and analysis of rainfall,penetrating rain and soil water content during the experimental period,The difference of primary vegetation in penetrating rain,the benefit of removal experiment on rainfall penetration rate,the dynamic change of soil moisture and its response to rainfall,and the benefit of soil improvement on upper slope were quantified.The feasibility of artificial induction measures in lifting the water environment of slope was evaluated,and the possible ways to promote the positive succession of vegetation community in the target area were discussed in order to provide theoretical basis and practical experience for regional vegetation restoration and reconstruction.The main conclusions are as follows:(1)In terms of penetrating rain,from the level of rainfall classification: the comparison of different types of vegetation canopy,that is,the comparison of penetrating rain in the control area and the restoration area,when the rainfall of < 20 mm,the average value of penetrating rain of the former is about 21% higher than that of the latter,while the rainfall of > 20 mm is about 21% higher than that of the latter.The value is about 30%.On the whole,the penetrating rainfall rate increases with the increase of rainfall level.The penetrating rainfall rate of 0～5mm rainfall is 7.6% higher than that of the latter.When rainfall is more than 30 mm,the increase can reach 15.9%.The comparison of similar vegetation canopy,that is,the comparison of penetrating rain between the optimized area and the control area,the average value of penetrating rain and the increase of penetrating rainfall rate gradually decreased with the increase of rainfall level.When 0～5mm rained,the average value and penetration rate of penetrating rain in the former were 30.8% and 7.6% higher than those in the latter,respectively.When the rainfall was 20～30mm,this value decreased to 12.97% and 8.44%,respectively.When the rainfall was greater than 30 mm,there was no difference between the two.Generally speaking,the artificial induction measures have the most obvious effect on small rainfall,but for heavy rain or rainstorm,the optimization effect is weak.when the rainfall level is greater than 30 mm,the optimization measures have no obvious effect.(2)In the aspect of soil water content,the difference of soil water content in other areas was significant except that there was no significant difference in soil water content between baffle treatment area and restoration area.Through the further analysis of the "black box" effect,it is concluded that the "black box" effect in the untreated area(reference)is negative and the size is-5.4% during the observation period.After stripping off the "black box" effect,the cumulative effects of environmental factors in the baffle treatment area,the baffle-water retaining agent combination treatment area and the restoration area(specific vegetation)were all positive,and the sizes were 32.2%,17.3% and 30.6%,respectively.From the quantitative results,for the soil moisture on the upper slope,the cumulative effect of vegetation cover and the layout of baffle is positive and large,indicating that the effect is obvious,while the cumulative effect of the combined treatment area of baffle and water-retaining agent is almost half of that of the first two.The second is the effect,and the reason is likely to be caused by the characteristics of the water-retaining agent itself.It can be expected that the comprehensive means of soil moisture enhancement on the uphill position: suitable vegetation cover,the layout of baffles can create a relatively considerable water environment.(3)The correlation between rainfall dynamics and soil water content dynamics was analyzed by time series.The results showed that there was no significant autocorrelation in rainfall series(the correlation coefficients corresponding to lag time fell within 2 times standard deviation),but there was obvious autocorrelation in soil water content,and the autocorrelation coefficients were the highest when the first lag time was 4 days.And then it keeps decreasing.The correlation domains of the optimized area,the control area,the recovery area and the untreated area were 2.5,3,3 and 3 lag distances,respectively,while the end lag time distances were concentrated in the range of 4-5,4.6,4.4,5 and 4.8,respectively.That is to say,the peaks and valleys on the precipitation map were reproduced on the soil water content after 4.6,4.4,5 and 4.8 lag intervals.(4)Through the monitoring and analysis of two types of soil water content in the vertical space of the typical "alveolar" section on the upper slope,It is concluded that the vegetation adaptation to the "alveolar" niche can be used: the plants with shallow roots can make full use of the water content of the 0～40cm soil layer in the alveolar,and the water retention capacity of the soil and stone layer is stable and has strong resistance to variability in rainy season or dry season.However,the vegetation should be mainly water-saving and the density is not easy to be too large,after all,the water base is not large;The depth of 40～60cm is a mixed water utilization area,which should be dominated by soil and rock layer water and supplemented by rock layer water.At the same time,the root system of this layer is beneficial to maintain its own stability,especially in the slope with the requirements of wind resistance and lodging resistance,which is of great significance.Beyond the depth of 60 cm,the water content in weathered rock strata is rich in both dry season and rainy season,which is suitable for the utilization of high-grade vegetation,such as deep root burial and high water consumption.At the same time,the phenomenon of "cluster" of upslope vegetation,that is,the growth of relatively high-grade plants,was observed.Combined with the characteristics of "alveolar" water environment,it is considered that the two may be related and need to be further explored.(5)From the point of view of the time node of about four months in the target area of "plant probe"(suitable seedlings in the later stage of succession),the preliminary evaluation is as follows:(1).In terms of survival rate,Qinggang(evergreen)currently has a high mortality rate of about 60%.The reasons behind the high mortality rate are analyzed: Quercus variabilis is sensitive to drought,poor rewatering recovery,and gives priority to the development of root strategy;The survival rate of other seedlings(>90%)was considerable.(2).In terms of growth,the monitoring of the growth of the constructive tree(deciduous leaves)showed that the plant had good adaptation and good growth.However,the growth indexes of the seedlings in the other mixed groups did not change much and needed to be further monitored for a long time. |
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