Effects Of Introduced Native Species On Community Characteristics Of Natural

Introduction is an effective way to promote vegetation restoration and ecosystem stability.To study the typical native species of the loess hilly region,such as HippopHae rhamnoides L,Caragana korshinskii,SopHora viciifolia,and Platycladus orientalisSopHora viciifolia to study the different modes of introduction(HippopHae rhamnoides L,Caragana korshinskii,Platycladus orientalis,Platycladus orientalis-SopHora viciifolia.The characteristics of the communities recovered from the reclaimed farmland,the differences in soil pHysical and chemical properties,the interactions between the vegetation and the soil,and the effects of introduction on the characteristics of the natural shrub community were revealed,providing a theoretical basis for ecological restoration measures.The following conclusions were reached:(1)After introducing native species such as Hippophae rhamnoides,Caragana korshinskii,and Platycladus orientalis in the Bothriochloa ischaemum community,the newly formed Hippophae rhamnoides,Caragana korshinskii,and Platycladus orientalis community have the following changes compared to the original community after 16 years:Introduction changes the spatial structure of the plant community.Introduced to the Hippophae rhamnoides,Caragana korshinskii,Platycladus orientalis formed after the introduction of species as the dominant species of the community.Compared with the Bothriochloa ischaemum community,arborvitae communities in the arbor layer increased Platycladus orientalis species;shrub Hippophae rhamnoides community and Caragana korshinskii community increased the density of introduced species,and the Platycladus orientalis community had no shrubs;the Hippophae rhamnoides community in the herb layer reduced the important value of 25% and increase the species of Heteropappus altaicus,the population of Caragana korshinskii significantly reduced the important value of Bothriochloa ischaemum by 89.58%,increased the density of Artemisia gmelinii by 252.8%,and increased the species of Heteropappus altaicus and Leymus secalinus.The introduction of shrubs(Hippophae rhamnoides,Caragana korshinskii)treatment had no significant effect on the total coverage.Platycladus orientalis significantly reduced the total coverage of 52.62%;the arborvitae introduced 42.53% coverage of Platycladus orientalis;the introduction of Hippophae rhamnoides and Caragana korshinskii coverage in the shrub layer increased.50.48% and 36.51% of the Platycladus orientalis community had no shrubs;the coverage of seabuckthorn,Caragana korshinskii and Platycladus orientalis in herb layer decreased by 49.23%,34.69% and 56.1%,respectively.After introduction of Hippophae rhamnoides and Caragana korshinskii,the Simpson diversity increased by 162.5 and 115.62%,Shannon-Wiener diversity increased by 164.1% and 42.65%,Pielou evenness increased by 178.13% and 84.38%,and Platycladus orientalis significantly reduced the Margalef abundance of Platycladus orientalis communities.54.12%.In terms of renewal,Hippophae rhamnoides had a hump-type distribution at the individual diameter and no other shrubs in the community.The community will maintain a community dominated by Hippophae rhamnoides for a long time.The open skylight is beneficial to the growth of undergrowth species and promotes the emergence of arbor and shrub seedlings;The grades are descending,with many small trails,but the Caraganakorshinskii species decline,and the Caragana korshinskii trees or arbors need to be replanted to promote positive succession.The Platycladus orientalis has a hump type,and the community has a few herbs,no other species,and the community is seriously degraded.The change of soil properties had no significant effect on the bulk density and Ph of the shrub community(Hippophae rhamnoides,Caragana korshinskii).pH was alkaline,and organic carbon,total nitrogen,and oxidizable organic carbon all showed a decrease with increasing depth,and there was a phenomenon of surface aggregation.There was no significant effect on total phosphorus levels and treatments.Rapid phosphorus(9.34%,38.61%)and nitrate nitrogen(44.9%,55.1%)all increased.The average organic carbon content of Hippophae rhamnoides community and Caragana korshinskii community was 14.84% and 2.7% higher than that of Bothriochloa ischaemumcommunity,and the average of total nitrogen was 10% and 2.12% higher than that of Bothriochloa ischaemum community,and the average oxidizable organic carbon was 47.82% higher than that of Bothriochloa ischaemum community.19.57%.The introduction of Platycladus orientalis had no significant effect on bulk density and Ph,but pH was alkaline.Organic carbon,total nitrogen,and readily oxidizable organic carbon all decreased with depth.Average reduction in organic carbon(43.17%),total nitrogen(55.32%),total phosphorus(36.54%),easily oxidized organic carbon(22.22%),available phosphorus(36.58%),nitrate nitrogen(63.26%),ammonium nitrogen(17.5%).The chemical properties of the soil were lower than those of the Bothriochloa ischaemum community.The above results indicate that the introduced shrubs(Hippophae rhamnoides,Caragana korshinskii.)are developing towards the shrub community and increase soil organic carbon,total nitrogen,available phosphorus,and nitrate nitrogen.However,artificial measures are needed to improve forest conditions and promote recovery.In the Hippophae rhamnoides communities,the opening of the Hippophae rhamnoides can promote the growth of seedlings under the forest,and the replantation of Caragana korshinskii community may promote succession.The introduction of Platycladus orientalis caused the degradation of the community and it is not suitable for direct introduction of Platycladus orientalis in the Bothriochloa ischaemum community.(2)After introduction of Platycladus orientalis in Sophora viciifolia community,after 16 years,the newly formed Platycladus orientalis-Sophora viciifolia community and the Sophora viciifolia community have the following changes:The change of community composition showed that the plant density(16.51%)and coverage(16.45%)in the shrub layer decreased after the introduction of Platycladus orientalis in natural Sophora viciifolia community.Plant density of willow;In addition,introduction of Platycladus orientalis reduced herbaceous plant species(33.33%)and coverage(56.43%).In general,the introduction of Platycladus orientalis increased the Shannon-Wiener index of the herbaceous layer and decreased the Margalef richness index of the community and herb layers.Compared with the natural Platycladus orientalis,the Platycladus orientalis-Sophora viciifolia community was introduced in the tree layer of Platycladus orientalis The number was relatively low(50%),but the numbers of Pyrus betulifolia(83.33%)and Robinia pseudoacacia(100%)were higher;the number of shrubs in the shrub layer was relatively high(95%);the herbaceous layer species(45.45%)and cover The degree(75.28%)is relatively low,and the species richness index and diversity index are also relatively low.There was no species of Platycladus orientalis in the natural Sophora viciifolia community,and the individual size distribution of Sophora viciifolia showed a decline type.The individual diameter distributions of Platycladus orientalis and Sophora viciifolia in the introduced Platycladus orientalis and Sophora viciifolia community were both shown as Decline type,but the normal reproduction and renewal of Platycladus orientalis and thorns may be related to the relatively high densities of arbor and shrub vegetation in the community and the low survival rate of seedlings in these two species.Soil physical and chemical properties.After introduction of Platycladus orientalis,the soil physical properties(bulk weight,pH)were not significantly affected,and pH was alkaline.The organic carbon,total nitrogen,and easily oxidizable organic carbon decreased in chemical properties as the soil depth increased,and there was a polycondensation phenomenon,which significantly reduced the available phosphorus(39.28%)and nitrate nitrogen(57.14%),to total phosphorus and ammonium nitrogen.The effect is not significant.Compared with natural Platycladus orientalis communities,organic carbon 0-20 cm decreased by 21.14%,total nitrogen 0-20 cm decreased by 23.8%,and other indicators had no significant difference.The results showed that the introduction of Platycladus orientalis significantly changed species composition and structure of Sophora viciifolia communities and accelerated the positive succession of communities.Moderate tending(reducing the densities of Sophora viciifolia and Periploca sepium in the community)may further accelerate the succession rate of Sophora davidii community to Platycladus orientalis communities.(3)The dominant factor affecting the gray scale of the soil is organic carbon.It indicates that vegetation restoration in the loess hilly region is closely related to organic carbon.Soil total nitrogen and oxidizable organic carbon are also important factors affecting vegetation recovery.(4)Introduction of Hippophae rhamnoides and Caragana korshinskii in the community of Bothriochloa ischaemum can effectively increase the diversity of plant community and form a stable community.It can also increase soil organic carbon,total nitrogen,easily oxidized organic carbon,available phosphorus and nitrate nitrogen,and effectively improve soil quality.However,there are problems with the update and manual measures are needed to promote positive succession.Introduction of Hippophae rhamnoides and Caragana korshinskii in the community of Bothriochloa ischaemum can promoted community succession from the herb stage to the shrub stage.There was no sign of shrub stage to tree stage.The community structure of Platycladus orientalis is single,the community is seriously degraded,and the soil quality is significantly decreased.It is not suitable to introduce the plant directly on the farmland.The introduction of Platycladus orientalis in Sophora viciifolia community can optimize the community structure and form a similar community structure with natural Platycladus orientalis.The shrub density in the updated area is relatively high,limiting the arborvitae renewal and requiring selective cutting to accelerate the arborvitae renewal.The soil physical and chemical properties of surface organic carbon,total nitrogen,readily oxidized organic carbon,available phosphorus,nitrate-nitrogen were reduced,but the community feedback the soil by reducing the number of species to maintain community stability.Introduction of Platycladus orientalis in Sophora viciifolia community can promote the mid-late succession tolate succession.