Study On Development Of Goat Track Landscape And Succession Of Plant Community In Semi-arid Hilly Region Of Loess Plateau

Grazing disturbance has an important impact on the grassland ecosystem.During the grazing process,landscape diversity has been increased on a spatial scale due to the free feeding and stamping of livestock.The landscape composed of small paths and plant patches trampled by livestock,named of track landscape,is widely distributed in the semi-arid area of the Loess Plateau in China.In this study,the goat track landscape in the semi-arid hilly area of the Loess Plateau was taken as the research object.The three grasslands?G₀,G₁,and G₂?were selected as the study area,and ploughed to remove the original goat pasture.Grassland without goats was used as a control?G₀?.The plants in G₀ and G₁ were picked out,and the plants in G₂were retained.The field observation was carried out for 6 years by using photogrammetry and remote-sensing technology.The experiment quantitatively depicts the formation and dynamic changes of the goat track network through track density and vertices,and comparatively analyzes the characteristics of plant communities and species diversity in the study area,and then discusses development and evolution process of the goat track landscape.The results of the study are as follows:1.During the formation of the goat track network,the dominant species at various stages have been continuously replaced with the development of track.The plant communities in the G₀,G₁ and G₂ plots had 14 families,21 genera and 24species,and the proportion of Compositae?35.71%?and Gramineae?28.57%?were greater than that of other families.The disturbance of grazing has a significant effect on the composition and structure of plant communities.Compared with G₀,the plant richness and diversity index of G₁ and G₂ increased,but the plant density and cover decreased due to feeding and trampling of goats.2.The goat track network consists of track and vertices,and the track road turns or crosses are vertices.A few parallel track appeared one month after tilling,which did not penetrate the entire plot.Four months later,parallel track penetrated the entire plot and formed bifurcations.Half a year later,parallel tracks were evenly distributed and formed a main road for goats to walk,and connecting track roads appeared between parallel track roads,and the connectivity of the track network was enhanced.Throughout the process,the first-degree vertices gradually decreased,the second-degree vertices first increased and then decreased,the third-degree vertices gradually increased,and the fourth-degree vertices finally disappeared.The density of the track was positively correlated with the total number of vertices,so the connectivity of the track network was enhanced.3.The formation of the track network has a close relationship with the plant community.Before tilling,the track density of the G₁ and G₂ plots were 24.88%and20.84%respectively,the first-degree vertices distribution frequency were 0,the second-degree vertices distribution frequency were 37.28%and 33.94%,the third-degree vertices distribution frequency were 57.40%and 60%,the distribution frequency of the fourth-degree vertices were the lowest.In the 6th year after ploughing?2019?,the track network has not yet returned to its original state.The track density of G₁ and G₂ were 20.27%and 19.38%respectively,the first-degree vertices distribution frequency were 0,the second-degree vertices distribution frequency were51.20%and 43.82%,the third-degree vertices distribution frequency were 48.80%and 56.18%respectively,the fourth-degree vertices distribution frequency was also 0.During the same recovery time,more edible plants appeared in G₂,which increased the trampling frequency and residence time of goats.The formation speed of the track network was faster and closer to the original track network.4.Goats are the main driving force of goat track landscape.After ploughing,there was no track in the plot without goats.For the plot with goats,it would become a main track within six months,and interact with the surrounding plant communities to form plant patches,that is,track landscape.