| Grassland ecosystem is an important part of the terrestrial ecosystem and the survival of pastoralists in pastoral areas.With the intensification of human activities,the continuous extension and expansion of roads have caused the direct and indirect degradation of grasslands to become more and more serious.In addition,the various impacts of roads on the ecological environment have a certain lag in time,which is often overlooked by people.Therefore,it is urgent to clarify the change of grassland road and its impact mechanism on vegetation ecology,so as to provide scientific basis for road planning and ecosystem stability in pastoral areas.For this reason,this paper selects Nalenbaolagsumu in Abaga banner as a typical research area,and extracts the roads in 2009 and 2017,and uses GIS spatial analysis technology,This paper analyzes the temporal and spatial distribution and change characteristics of grassland roads from the perspectives of time,space,density and orientation,and probes into the influence of natural factors such as altitude,slope and water system,and social factors such as policies,settlements and road construction on the development of grassland roads;Based on NDVI and NPP data of vegetation obtained by Landsat TM / ETM and MODIS and grassland vegetation sample data obtained by field survey and visit,the vegetation change characteristics of the study area in 2009-2017 are comprehensively reflected.By overlaying road data,the impact mechanism of road expansion on vegetation degradation is further revealed.The main conclusions are as follows:(1)The roads in Narenburgrasumu of Abaga banner are mainly class III,followed by class II,and class I is the least.In 2009 and 2017,the proportion of class III roads in total road length exceeded 90%;In the two periods,except for the first level road,the total length of the second level road and the third level road increased,and the road density in the northern region increased significantly.From the road distribution direction,the ellipse center of the road distribution direction moved 25.95 m to the west,1298.94 m to the North,and the long axis and the short axis of the ellipse were enlarged,with the rotation angle enlarged by 1.53 degrees;From the change of the spatial distribution of the roads between the upper and lower levels,the distance between the center of the first level road and the second level road increases,and the distance between the center of gravity of the second level road and the third level road decreases,indicating that the second level road mainly expands outside the first level road,and the third level road is mainly densified near the second level road;from the change of the location of the road and the residential area,the increase and expansion of the residential area have a great impact on the location and quantity of the road Influence;From the perspective of the road changes in the typical herdsman grassland,the road expansion of the three typical herdsman grassland close to the second level road is obvious,while the road expansion of the typical herdsman grassland close to the first level road is not obvious.(2)To some extent,the spatial distribution of the road is affected by natural factors such as altitude,slope and other geomorphic factors.More than 70% of the roads in the study area are distributed below the elevation of 1300m;in 2009,the road density increased with the elevation,but not significantly,while in 2017,the road density was positively correlated with the elevation,and the change of the road density increased with the elevation from 2009 to 2017;the distribution of the traffic road density at each slope level showed that the road density increased with the slope The characteristics of increase,but not significant correlation,and the range of slope is very small;the increase value of traffic road density of the low-lying valley bottom in this area increases with the buffer distance from the seasonal Valley to a certain extent.(3)In the study area,nearly half of the normalized vegetation index(NDVI)spatial area shows a downward trend,and the reduced area is mainly distributed in the north central part of Narensumu;the absolute value of NDVI change decreases with the increase of the distance from the road,indicating that the change of NDVI near the road is large,the vegetation is greatly affected,and the degradation is obvious.The farther away from the road,the smaller the change of NDVI is In the study,80% of the vegetation biomass in the NPP space decreased,and the absolute value of NPP change decreased with the distance from the road within 100 m,the farther away from the road,the smaller the impact on the vegetation biomass,the smaller the impact may be on the road beyond 100 m.(4)Based on the comparison and analysis of vegetation samples in and near the herdsman grassland,from the perspective of the impact on the grassland habitat,the Jaccard index of the grassland plant samples and roadside plant samples in the five herdsman networks are mostly lower than 0.45,indicating that the destruction of roadside vegetation habitat is more serious;from the perspective of the impact on the plant composition structure,roadside plant structure is simpler than that in the network;from the perspective of the impact on vegetation In terms of the impact of material quantity structure,the number of species on the roadside is far less than that in the network;in terms of the impact on the difference of life structure of plant community,the life structure of plant community in the roadside quadrat outside the network is a unique one,while the life type of plant community in the fence is relatively more balanced.On the whole,the species,diversity index and life structure balance of plant communities in roadside quadrat are all low,which indicates that road expansion has a great impact on the stability of vegetation ecosystem on both sides of the road. |
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