Effects Of Vegetation Patterns On Typical Slopes In Loess Hilly Areas On Soil Properties And Plant Communities

The loess hilly region is one of the most seriously eroded areas in China and even in the world.With the implementation of the project of grain for green,vegetation restores naturally,and the mosaic pattern of vegetation-bare land gradually forms on the slope.The vegetation pattern affects the hydrological and erosion processes on the slope.However,the formation and maintenance mechanism of vegetation pattern in the erosion environment is lack of in-depth researches.And the impact of patchy pattern on slope ecological process especially needs to be further studied.Therefore,exploring the influence of slope vegetation pattern on soil properties and plant communities can provide theoretical basis for further understanding of the development law of slope vegetation and the evaluation of soil and water conservation benefits.Our goal is to fully understand the impact of slope vegetation pattern on soil and plant communities.In this paper,the sample plots are set up from southeast to northwest along the precipitation gradient,and obtain the distribution of vegetation-bare patches by taking pictures on typical slope,to calculate the slope landscape pattern index.The sampling of vegetation patch and bare patch on typical slope was selected.The physical and chemical properties of soil under different patches were analyzed.The survey method is the sample method.The species diversity characteristics of community and different patches were analyzed.The relationship between vegetation pattern index and soil and community diversity was comprehensively revealed.The main results are as follows:(1)The characteristics of vegetation patches were studied from the characteristics of patch quantity,shape,dispersal index and aggregation degree.The results showed that the vegetation patch density(PD)and fractal dimension of plaques(FRAC MN)increased with the decrease of precipitation.However,the percentage of vegetation patches(PLAND)was decreasing.At the same time,community characteristics of dominant species play an important role in patch pattern.The Sophora viciifolia community was relatively concentrated,while the Bothriochloa ischaemum community was relatively dispersed.(2)Community type and patch characteristics affect soil properties.The soil bulk density of vegetation patches was smaller than that of bare patches.The ones that reach a significant level are 0-5c.The stable aggregate content of different communities is as follows:the community of Bothriochloa ischaemum<Artemisia sacrorum<Sophora viciifolia.The highest proportion was found in large aggregates(diameter of>2mm).The contents of soil organic carbon,available P,total nitrogen,and available N in vegetation patches are larger than those in bare plots except for individual plots.Among them,SOC in vegetation patches of 0-10 cm reached a significant level.SOC and total nitrogen showed a decreasing trend with precipitation reduction on the gradient.While nitrate nitrogen increased first and then decreased,and ammonium nitrogen decreased first and then increased.(3)The total number of species in this study is 65 on the ground,and the total number of species found in the seedling bank is 81.At the same time,vegetation patch species were abundant.But there was little difference between vegetation patch species diversity index and bare patch species diversity index.? to ? precipitation reduction gradient under the Simpson dominance index and Shannon wiener diversity index with lower rainfall fluctuation change,no significant decline.With the decrease of precipitation,the Cody index of the latter increased to a certain extent,which reflected that the species composition of different patches increased with the increase of drought.The species composition,density and diversity of the seedlings were generally>patches,and the species density decreased with the decrease of precipitation.(4)The analysis of the relationship between the vegetation pattern index and the physical and chemical properties of the soil found that:There was a positive correlation between water stable aggregates and vegetation patch aggregation index.There was a significant correlation with the patch near-circle index CIRCLE MN.The aggregation of plaques and the near-round feature are conducive to the formation of aggregates.There was a positive correlation between available nitrogen and the degree of aggregation of vegetation patches.And available P,TN,SOC and partition index were positively correlated.The relationship between vegetation pattern index and species diversity was found that the correlation between species richness index and MESH,CLUMPY and FRAC_MN was the most significant.It means that the vegetation patch is more complex.The Margalef richness index and Pielou evenness index of the species with more densely clustered plaques tended to decrease.The evenness index decreased significantly,and more plants were planted which were more suitable for the harsh environment.In conclusion,with the decrease of precipitation,the vegetation patches become more fragmented,the proportion of vegetation patches decreases,the degree of aggregation decreases,and the soil stability and nutrients tend to decrease.Soil stability and nutrient content tended to decrease,but the correlation was not significant.There was no obvious change between plaque characteristics and species diversity.